Key Figures

  • 126 articles in high-impact journals
  • 80+% joint publications
  • 5+ hot & very important papers
  • 1 editor's pick
  • 14 cover pages
  • 115+ press releases & highlights
  • 1530+ citations
  • 11+ average impact factor

Phototuning Selectively Hole and Electron Transport in Optically Switchable Ambipolar Transistors

W. Rekab, T. Leydecker, L. Hou, H. Chen, M. Kirkus, C. Cendra, M. Herder, S. Hecht, A. Salleo, I. McCulloch, E. Orgiu, P. Samorì

Adv. Funct. Mater., 2020, 30, 1908944. Link to article and accepted manuscript (open access).

One of the grand challenges in organic electronics is to develop multicomponent materials wherein each component imparts a different and independently addressable property to the hybrid system. In this way, the combination of the pristine properties of each component is not only preserved but also combined with unprecedented properties emerging from the mutual interaction between the components. Here for the first time, that tri‐component materials comprised of an ambipolar diketopyrrolopyrrole‐based semiconducting polymer combined with two different photochromic diarylethene molecules possessing ad hoc energy levels can be used to develop organic field‐effect transistors, in which the transport of both, holes and electrons, can be photo‐modulated. A fully reversible light‐switching process is demonstrated, with a light‐controlled 100‐fold modulation of p‐type charge transport and a tenfold modulation of n‐type charge transport. These findings pave the way for photo‐tunable inverters and ultimately for completely re‐addressable high‐performance circuits comprising optical storage units and ambipolar field‐effect transistors.

A Bacterial Photosynthetic Enzymatic Unit Modulating Organic Transistors with Light

M. Di Lauro, S. la Gatta, C. A. Bortolotti, V. Beni, V. Parkula, S. Drakopoulou, M. Giordani, M. Berto, F. Milano, T. Cramer, M. Murgia, A. Agostiano, G. M. Farinola, M. Trotta, F. Biscarini

Adv. Electron. Mater., 2020, 6, 1900888. Link to article.

The photochemical core of every photosynthetic apparatus is the reaction center, a transmembrane enzyme that converts photons into charge‐separated states across the biological membrane with an almost unitary quantum yield. A light‐responsive organic transistor architecture, which converts light into electrical current by exploiting the efficiency of this biological machinery, is presented. Proper surface tailoring enables the integration of the bacterial reaction center as photoactive element in organic transistors, allowing the transduction of its photogenerated voltage into photomodulation of the output current up to two orders of magnitude. This device architecture, termed light‐responsive electrolyte‐gated organic transistor, is the prototype of a new generation of low‐power hybrid bio‐optoelectronic organic devices.



The Role of Morphology in Optically Switchable Transistors Based on a Photochromic Molecule/p‐Type Polymer Semiconductor Blend

M. Carroli, D. T. Duong, E. Buchaca-Domingo, A. Liscio, K. Börjesson, M. Herder, V. Palermo, S. Hecht, N. Stingelin, A. Salleo, E. Orgiu, P. Samorì

Adv. Funct. Mater., 2020, 30, 1907507. Link to article and accepted manuscript (open access).

The correlation between morphology and optoelectronic performance in organic thin‐film transistors based on blends of photochromic diarylethenes (DAE) and poly(3‐hexylthiophene) (P3HT) is investigated by varying molecular weight (Mw = 20–100 kDa) and regioregularity of the conjugated polymer as well as the temperature of thermal annealing (rt‐160 °C) in thin films. Semicrystalline architectures of P3HT/DAE blends comprise crystalline domains, ensuring efficient charge transport, and less aggregated regions, where DAEs are located as a result of their spontaneous expulsion from the crystalline domains during the self‐assembly. The best compromise between field‐effect mobility (μ) and switching capabilities is observed in blends containing P3HT with Mw = 50 kDa, exhibiting μ as high as 1 × 10−3 cm2 V−1 s−1 combined with a >50% photoswitching ratio. Higher or lower Mw than 50 kDa are found to be detrimental for field‐effect mobility and to lead to reduced device current switchability. The microstructure of the regioregular P3HT blend is found to be sensitive to the thermal annealing temperature, with an increase in μ and a decrease in current modulation being observed as a response to the light‐stimulus likely due to an increased P3HT‐DAE segregation, partially hindering DAE photoisomerization. The findings demonstrate the paramount importance of fine tuning the structure and morphology of bicomponent films for leveraging the multifunctional nature of optoelectronic devices.

Stepwise Lateral Extension of Phenyl‐Substituted Linear Polyphenylenes

I. C.‐Y. Hou, A. Narita, K. Müllen

Macromol. Chem. Phys., 2020, 221, 1900374. Link to article (open access). COVER PAGE.

Polyphenylenes (PPs) are unique polymers showing high mechanical strength and chemical stability, and having potential applications, for example, in proton transfer and gas‐separation membranes. Moreover, phenyl‐substituted linear PPs can serve as precursors for bottom‐up syntheses of graphene nanoribbons (GNRs), a new class of nanoscale carbon materials that appear promising for nanoelectronics. Notably, lateral extensions of linear PPs with appropriate “branched” phenyl substituents, that is, avoiding spatial overlap of benzene rings in their projections into a plane, can lead to wider GNRs with modulated electronic and optical properties. GNRs with widths up to ≈2 nm are obtained, but synthetic methods to further expand PPs laterally so as to achieve even wider GNRs have not yet been developed. Here, phenyl‐substituted linear PPs bearing two ethynyl groups at “outer” positions in each repeating unit, together with 3,4‐diphenylcyclopentadienones bearing a trimethylsilyl‐protected ethynyl group are used for stepwise lateral extension of the PPs, based on a sequence of Diels–Alder cycloadditions and deprotections. Each successive reaction step is corroborated by 1H NMR and IR spectroscopy, as well as gel permeation chromatography, providing a new pathway toward branched polyphenylenes with linear‐PP‐backbones that can potentially serve as precursors of wider GNRs with tunable electronic bandgaps.

Determination and evaluation of the nonadditivity in wetting of molecularly heterogeneous surfaces

Z. Luo, A. Murello, D. M. Wilkins, F. Kovacik, J. Kohlbrecher, A. Radulescu, H. I. Okur, Q. K. Ong, S. Roke, M. Ceriotti, F. Stellacci

Proc. Natl. Acad. Sci. U.S.A., 2019, 116, 25516–25523. Link to article (open access).

The interface between water and folded proteins is very complex. Proteins have “patchy” solvent-accessible areas composed of domains of varying hydrophobicity. The textbook understanding is that these domains contribute additively to interfacial properties (Cassie’s equation, CE). An ever-growing number of modeling papers question the validity of CE at molecular length scales, but there is no conclusive experiment to support this and no proposed new theoretical framework. Here, we study the wetting of model compounds with patchy surfaces differing solely in patchiness but not in composition. Were CE to be correct, these materials would have had the same solid–liquid work of adhesion (WSL) and time-averaged structure of interfacial water. We find considerable differences in WSL, and sum-frequency generation measurements of the interfacial water structure show distinctively different spectral features. Molecular-dynamics simulations of water on patchy surfaces capture the observed behaviors and point toward significant nonadditivity in water density and average orientation. They show that a description of the molecular arrangement on the surface is needed to predict its wetting properties. We propose a predictive model that considers, for every molecule, the contributions of its first-nearest neighbors as a descriptor to determine the wetting properties of the surface. The model is validated by measurements of WSL in multiple solvents, where large differences are observed for solvents whose effective diameter is smaller than ∼6 Å. The experiments and theoretical model proposed here provide a starting point to develop a comprehensive understanding of complex biological interfaces as well as for the engineering of synthetic ones.

Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene: Efficient Synthesis via Photochemical Cyclodehydroiodination, Optoelectronic Properties, and Single-Molecule Spectroscopy

Q. Chen, S. Thoms, S. Stöttinger, D. Schollmeyer, K. Müllen, A. Narita, T. Basché

J. Am. Chem. Soc., 2019, 141, 16439–16449. Link to article (open access).

Dibenzo[hi,st]ovalene (DBOV), as a new nanographene, has demonstrated promising optical properties, such as red emission with a high fluorescence quantum yield of 79% and stimulated emission, as well as high thermal stability and photostability, which indicated its promise as a light-emitting and optical gain material. However, the previous synthetic routes required at least 12 steps. This obstructed access to different derivatives, e.g., to obtain crystals suitable for X-ray diffraction analysis and to tune the optoelectronic properties. Here, we report an efficient synthetic pathway to DBOV based on a sequential iodination-benzannulation of bi(naphthylphenyl)diyne, followed by photochemical cyclodehydroiodination (PCDHI). This protocol included a fused bischrysene as a key intermediate and furnished scalable amounts of meso-substituted DBOV derivatives with different substituents. DBOV with 2,6-dimethylphenyl groups could be used for single-crystal X-ray analysis, revealing the precise structure of the DBOV core. The optoelectronic properties of the DBOV derivatives were investigated by UV–vis absorption and fluorescence spectroscopy, cyclic voltammetry, and density functional theory calculations. Single-molecule spectroscopy at room and low temperatures provided novel insights into the photophysics of DBOV embedded in a polymer film. As a result of weak coupling of the optical transitions to the matrix, single-molecule emission spectra at 4.5 K showed narrow vibronic lines. The fluorescence autocorrelation function covering 9 orders of magnitude in time displayed high contrast photon antibunching and bunching, from which the fluorescence decay rate and the triplet population and depopulation rates could be retrieved. Remarkably, the intersystem crossing rate into the triplet state decreased by more than an order of magnitude at low temperature, demonstrating that temperature can be a crucial parameter to boost single photon emission of an aromatic hydrocarbon.

Unraveling the Complexity of Amyloid Polymorphism Using Gold Nanoparticles and Cryo-EM

U. Cendrowska, P. J. Silva, N. Ait-Bouziad, M. Müller, Z. P. Guven, S. Vieweg, A. Chiki, L. Radamaker, S. Thangaraj, M. Fändrich, F. Tavanti, M. C. Menziani, A. Alexander-Katz, F. Stellacci, H. Lashuel

bioRxiv, 2019. Link to article (open access).

The misfolding and self-assembly of proteins into β-sheet-rich amyloid fibrils of various structures and morphologies is a hallmark of several neurodegenerative and systemic diseases. Increasing evidence suggests that amyloid polymorphism gives rise to different strains of amyloids with distinct toxicity and pathology-spreading properties. Validating this hypothesis is challenging due to a lack of tools and methods that allow for the direct characterization of amyloid polymorphism in hydrated and complex biological samples. Here, we report on the use of 11-mercapto-1-undecanesulfonate-coated gold nanoparticles (NPs) to label the edges of synthetic, recombinant and native amyloid fibrils to assess amyloid morphological polymorphism using cryogenic transmission electron microscopy (cryo TEM). The fibrils studied were derived from amyloid proteins involved in disorders of the central nervous system (amyloid-β, tau, α-synuclein) and in systemic amyloidosis (a fragment of an immunoglobulin light chain). The labeling efficiency enabled imaging and characterization of amyloid fibrils of different morphologies under hydrated conditions using cryo TEM. These NPs allowed for the visualization of morphological features that are not directly observed using standard imaging techniques, including TEM with use of the negative stain or cryo TEM imaging. We also demonstrate the use of these NPs to label native paired helical filaments (PHFs) from the postmortem brain of an Alzheimer's disease patient, as well as amyloid fibrils extracted from the heart tissue of a patient suffering from systemic amyloid light-chain (AL) amyloidosis. Analysis of the cryo TEM images of amyloids decorated with NPs shows exceptional homogeneity across the fibrils derived from human tissue in comparison to fibrils aggregated in vitro. The use of these NPs enabled us to gain novel insight into the structural features that distinguish amyloid fibrils formed in vivo from those formed in cell-free in vitro systems. Our findings demonstrate that these NPs represent a potent tool for rapid imaging and profiling of amyloid morphological polymorphism in different types of samples, including those derived from complex biological aggregates found in human tissue and animal models of amyloid diseases. This study should not only facilitate the profiling and characterization of amyloids for structural studies by cryo TEM but also pave the way to elucidate the structural basis of amyloid strains and toxicity and possibly the correlation between the pathological and clinical heterogeneity of amyloid diseases.

3D hybrid networks of gold nanoparticles: mechanoresponsive electrical humidity sensors with on-demand performances

M. A. Squillaci, M.-A. Stoeckel, P. Samorì

Nanoscale, 2019, 11, 19319–19326. Link to article and accepted manuscript (open access).

We have engineered macroscopic 3D porous networks of gold nanoparticles (AuNPs) chemically interconnected by di-thiolated ethylene glycol oligomers. The formation of such superstructures has been followed by means of UV-Vis spectroscopy by monitoring the aggregation-dependent plasmonic band of such nanomaterials. The controlled chemical tethering of the AuNPs with di-thiolated linkers possessing a well-defined contour length rules the interparticle distance. The use of ad-hoc linkers ensures charge transport via direct tunneling and the hygroscopic nature of the ethylene glycol backbone allows interaction with moisture. Upon interaction with water molecules from the atmosphere, our 3D networks undergo swelling reducing the tunnelling current passing through the system. By exploiting such a behavior, we have devised a new approach for the fabrication of electrical resistive humidity sensors. For the first time we have also introduced a new strategy to fabricate stable and robust devices by covalently attaching our 3D networks to gold electrodes. Devices comprising both 4 (TEG) or 6 (HEG) ethylene glycol repetitive units combined with AuNPs exhibited (i) unprecedentedly high response speed (∼26 ms), (ii) short recovery time (∼250 ms) in the absence of any hysteresis effect, and (iii) a linear response to humidity changes characterized by a highest sensitivity of 51 kΩ per RH(%) for HEG- and 500 Ω per RH(%) for TEG-based devices. The employed green solution processing in water and the extreme robustness of our 3D networks make them interesting candidates for the fabrication of sensors which can operate under extreme conditions and for countless cycles.

Single-Step Synthesis of Dual Phase Bright Blue-Green Emitting Lead Halide Perovskite Nanocrystal Thin Films

H. Bhatia, J. A. Steele, C. Martin, M. Keshavarz, G. Solis-Fernandez, H. Yuan, G. Fleury, H. Huang, I. Dovgaliuk, D. Chernyshov, J. Hendrix, M. B. J. Roeffaers, J. Hofkens, E. Debroye

Chem. Mater., 2019, 31, 6824–6832. Link to article.

Metal trihalide perovskites are rapidly redefining the landscape of solid-state semiconductors utilized as an active medium in photovoltaics and in light generation. Within this materials space, organic–inorganic hybrid formamidinium lead bromide (FAPbBr3) has arisen as a promising candidate for efferent light emitting devices, due to its capacity for sharp and bright green light emissions (530 nm). Herein we have applied a facile single-step ligand-mediated method for phase-controlled synthesis of FAPbBr3 cube- and rod-shaped nanocrystals (NCs), starting from different ratios of precursor agents. Examining their structural and optoelectronic properties—using a combination of synchrotron X-ray diffraction, X-ray spectroscopy, scanning electron microscopy, and steady-state and time-resolved photoluminescence (PL)—we reveal the two NC types to fundamentally differ. While the cube-shaped NCs exhibit properties aligning with those of bulk FAPbBr3, the nanorods exhibit a two-phase microstructure and the coexistence of both a typical cubic perovskite structure alongside the formation of a new low-symmetry monoclinic phase (P2/m). Further, the two-phase nanorods display a bright dual PL emission (peaks centered near 490 and 530 nm) and complex luminescence dynamics, properties characteristic of quasi-2D perovskites. The two phase nanorod generation can be assigned to the proton exchange in the presence of excess of FA+ during the synthesis.

Modulating the Charge Transport in 2D Semiconductors via Energy‐Level Phototuning

H. Qiu, Y. Zhao, Z. Liu, M. Herder, S. Hecht, P. Samorì

Adv. Mater., 2019, 31, 1903402. Link to article and accepted manuscript (open access).

The controlled functionalization of semiconducting 2D materials (2DMs) with photoresponsive molecules enables the generation of novel hybrid structures as active components for the fabrication of high‐performance multifunctional field‐effect transistors (FETs) and memories. This study reports the realization of optically switchable FETs by decorating the surface of the semiconducting 2DMs such as WSe2 and black phosphorus with suitably designed diarylethene (DAE) molecules to modulate their electron and hole transport, respectively, without sacrificing their pristine electrical performance. The efficient and reversible photochemical isomerization of the DAEs between the open and the closed isomer, featuring different energy levels, makes it possible to generate photoswitchable charge trapping levels, resulting in the tuning of charge transport through the 2DMs by alternating illumination with UV and visible light. The device reveals excellent data‐retention capacity combined with multiple and well‐distinguished accessible current levels, paving the way for its use as an active element in multilevel memories.

2D hybrid networks of gold nanoparticles: mechanoresponsive optical humidity sensors

M. A. Squillaci, X. Zhong, L. Peyruchat, C. Genet, T. W. Ebbesen, P. Samorì

Nanoscale, 2019, 11, 19315–19318. Link to article and accepted manuscript (open access).

Plasmonic coupling is a fascinating phenomenon occurring between neighboring metal nanostructures. We report a straightforward approach to study such process macroscopically by fabricating 2D networks of gold nanoparticles, interconnected with responsive hygroscopic organic linkers. By controlling the humidity we tune the interparticle distance to reversibly trigger plasmonic coupling collectively over several millimeters.





Photomodulation of Two-Dimensional Self-Assembly of Azobenzene–Hexa-peri-hexabenzocoronene–Azobenzene Triads

I. C.-Y. Hou, V. Diez-Cabanes, A. Galanti, M. Valášek, M. Mayor, J. Cornil, A. Narita, P. Samorì, K. Müllen

Chem. Mater., 2019, 31, 6979–6985. Link to article (open access).

Achieving exquisite control over self-assembly of functional polycyclic aromatic hydrocarbons (PAH) and nanographene (NG) is essential for their exploitation as active elements in (nano)technological applications. In the framework of our effort to leverage their functional complexity, we designed and synthesized two hexa-peri-hexabenzocoronene (HBC) triads, pAHA and oAHA, decorated with two light-responsive azobenzene moieties at the pseudo-para and ortho positions, respectively. Their photoisomerization in solution is demonstrated by UV–vis absorption. 1H NMR measurements of oAHA suggested 23% of Z-form can be obtained at a photostationary state with UV irradiation (366 nm). Scanning tunneling microscopy imaging revealed that the self-assembly of pAHA and oAHA at the solid–liquid interface between highly oriented pyrolytic graphite (HOPG) and their solution in 1,2,4-trichlorobenzene can be modulated upon light irradiation. This is in contrast to our previous work using HBC bearing a single azobenzene moiety, which did not show such photomodulation of the self-assembled structure. Upon E-Z isomerization both pAHA and oAHA displayed an increased packing density on the surface of graphite. Moreover, pAHA revealed a change of self-assembled pattern from an oblique unit cell to a dimer row rectangular crystal lattice whereas the assembly of oAHA retained a dimer row structure before and after light irradiation, yet with a modification of the inter-row molecular orientation. Molecular mechanics/molecular dynamics simulations validated the self-assembly patterns of pAHA and oAHA, comprising azobenzenes in their Z-forms. These results pave the way toward use of suitably functionalized large PAHs, as well as NGs, to develop photoswitchable devices.

A New Class of Rigid Multi(azobenzene) Switches Featuring Electronic Decoupling: Unravelling the Isomerization in Individual Photochromes

A. Galanti, J. Santoro, R. Mannancherry, Q. Duez, V. Diez-Cabanes, M. Valášek, J. De Winter, J. Cornil, P. Gerbaux, M. Mayor, P. Samorì

J. Am. Chem. Soc., 2019, 141, 9273−9283. Link to article and accepted manuscript (open access).

We report a novel class of star-shaped multiazobenzene photoswitches comprising individual photochromes connected to a central trisubstituted 1,3,5-benzene core. The unique design of such C3-symmetric molecules, consisting of conformationally rigid and pseudoplanar scaffolds, made it possible to explore the role of electronic decoupling in the isomerization of the individual azobenzene units. The design of our tris-, bis-, and mono(azobenzene) compounds limits the π-conjugation between the switches belonging to the same molecule, thus enabling the efficient and independent isomerization of each photochrome. An in-depth experimental insight by making use of different complementary techniques such as UV–vis absorption spectroscopy, high performance liquid chromatography, and advanced mass spectrometry methods as ion mobility revealed an almost complete absence of electronic delocalization. Such evidence was further supported by both experimental (electrochemistry, kinetical analysis) and theoretical (DFT calculations) analyses. The electronic decoupling provided by this molecular design guarantees a remarkably efficient photoswitching of all azobenzenes, as evidenced by their photoisomerization quantum yields, as well as by the Z-rich UV photostationary states. Ion mobility mass spectrometry was exploited for the first time to study multiphotochromic compounds revealing the occurrence of a large molecular shape change in such rigid star-shaped azobenzene derivatives. In view of their high structural rigidity and efficient isomerization, our multiazobenzene photoswitches can be used as key components for the fabrication of complex stimuli-responsive porous materials.

Reversible switching of the Au(111) work function by near infrared irradiation with a bistable SAM based on a radical donor–acceptor dyad

V. Diez-Cabanes, A. Gómez, M. Souto, N. González-Pato, J. Cornil, J. Veciana, I. Ratera

J. Mater. Chem. C, 2019, 7, 7418–7426. Link to article (open access).

We describe the modification of the work function (WF) of Au(111) upon deposition of self-assembled monolayers (SAMs) with two donor–acceptor (D–A) systems, one based on a ferrocene-polychlorotriphenylmethyl radical (Fc–PTM) dyad and another on its non-radical dyad analogue. Kelvin Probe Force Microscopy (KPFM) has been used to measure the changes in the Contact Potential Difference (CPD) between the tip and the SAM under application of a cycling sweep of direct current (DC) voltage bias. These measurements showed that both SAMs exhibit a hysteretic behaviour in their WF changes. Interestingly, the hysteresis loop of the radical SAM is notably reduced when irradiated with NIR light, which we attribute to the bistable nature of this SAM in which neutral radical dyad molecules are excited into a zwitterionic state following a light driven intramolecular charge transfer (ICT) from the Fc unit to the PTM radical unit. Consequently, under NIR irradiation the WF hysteresis is almost quenched and the WF value of the functionalized gold surface is significantly shifted by +250 mV recovering their original values when the irradiation is suppressed. Remarkable is the large WF shift attained, one of the highest values reported in the literature, and the unprecedented fact that it is achieved under irradiation in the IR region due to an intramolecular electronic reorganization. In contrast, the WF value and the WF hysteresis of the non-radical SAM does not change upon NIR irradiation since this SAM does not display bistability.

Functionalization of 2D Materials with Photosensitive Molecules: From Light‐Responsive Hybrid Systems to Multifunctional Devices

Y. Zhao, S. Ippolito, P. Samorì

Adv. Opt. Mater., 2019, 7, 1900286. Link to article and accepted manuscript (open access). COVER PAGE.

2D materials possess exceptional physical and chemical properties that render them appealing components for numerous potential applications in (opto)electronics, energy storage, sensing, and biomedicine. However, such unique properties are hardly tunable or modifiable. The functionalization of 2D crystals with molecules constitutes a powerful strategy to adjust and modulate their properties, by also imparting them new functions. In this framework, the combination of 2D materials with photosensitive molecules is a viable route for harnessing their light‐responsive nature. The latter takes full advantage of the extremely high sensitivity of 2D materials to subtle changes in the local environment and the capacity of photosensitive molecules to modify their intrinsic properties when exposed to electromagnetic fields. The hybrid molecule–2D materials can preserve the unique optical and electrical properties of 2D layers and can exhibit additional light‐tunable features. In this Progress Report, the protocols that can be pursued for the 2D material functionalization and switching mechanisms in photosensitive systems are reviewed, followed by an in‐depth discussion on their tunable optical properties and their exploitation when integrated in novel photoswitchable electronic devices. The opportunities and associated challenges to be tackled for the development of unprecedented and high‐performance light‐responsive devices are discussed.

Tracking Structural Phase Transitions in Lead‐Halide Perovskites by Means of Thermal Expansion

M. Keshavarz, M. Ottesen, S. Wiedmann, M. Wharmby, R. Küchler, H. Yuan, E. Debroye, J. A. Steele, J. Martens, N. E. Hussey, M. Bremholm, M. B. J. Roeffaers, J. Hofkens

Adv. Mater., 2019, 31, 1900521. Link to article.

The extraordinary properties of lead‐halide perovskite materials have spurred intense research, as they have a realistic perspective to play an important role in future photovoltaic devices. It is known that these materials undergo a number of structural phase transitions as a function of temperature that markedly alter their optical and electronic properties. The precise phase transition temperature and exact crystal structure in each phase, however, are controversially discussed in the literature. The linear thermal expansion of single crystals of APbX3 (A = methylammonium (MA), formamidinium (FA); X = I, Br) below room temperature is measured using a high‐resolution capacitive dilatometer to determine the phase transition temperatures. For δ‐FAPbI3, two wide regions of negative thermal expansion below 173 and 54 K, and a cascade of sharp transitions for FAPbBr3 that have not previously been reported are uncovered. Their respective crystal phases are identified via powder X‐ray diffraction. Moreover, it is demonstrated that transport under steady‐state illumination is considerably altered at the structural phase transition in the MA compounds. The results provide advanced insights into the evolution of the crystal structure with decreasing temperature that are essential to interpret the growing interest in investigating the electronic, optical, and photonic properties of lead‐halide perovskite materials.

Switching the Electronic Properties of ZnO Surfaces with Negative T‐Type Photochromic Pyridyl‐dihydropyrene Layers and Impact of Fermi Level Pinning

Q. Wang, G. Ligorio, R. Schlesinger, V. Diez‐Cabanes, D. Cornil, Y. Garmshausen, S. Hecht, J. Cornil, E. J. W. List‐Kratochvil, N. Koch

Adv. Mater. Interfaces, 2019, 6, 1900211. Link to article.

Remote control of the electronic energy levels by external stimuli such as light will enable optoelectronic devices with improved or additional functionalities. Here, it is demonstrated that the electronic properties of ZnO interfaced with negative T‐type photoswitches, that is, pyridyl‐dihydropyrene (Py‐DHP), can indeed be photomodulated. The process of forward switching of Py‐DHP with green light from an isomer with a low energy gap to an isomer with a wider one is followed by a thermally activated backward transfer. Using photoemission spectroscopy and density functional theory modeling, it is shown that Py‐DHP ring closure/opening reactions result in a reversible shift of frontier occupied molecular levels by 0.7 eV with respect to the Fermi level. Notably, in both molecular configurations, the energy level alignment at ZnO/Py‐DHP interfaces is governed by a Fermi level pinning at the lowest unoccupied molecular level. Moreover, upon switching, an increase in the ionization energy for Py‐DHP multilayers compared to that of a monolayer is observed. This is attributed to a different preferred molecular orientation in monolayer versus multilayers. The results show that a dynamic tuning of the energy level alignment at inorganic/organic interfaces by external stimuli is feasible and will aid the development of photoprogrammable optoelectronic devices.

Unconventional Nanofabrication for Supramolecular Electronics

Y. Yao, L. Zhang, E. Orgiu, P. Samorì

Adv. Mater., 2019, 31, 1900599. Link to article and accepted manuscript (open access).

The scientific effort toward achieving a full control over the correlation between structure and function in organic and polymer electronics has prompted the use of supramolecular interactions to drive the formation of highly ordered functional assemblies, which have been integrated into real devices. In the resulting field of supramolecular electronics, self‐assembly of organic semiconducting materials constitutes a powerful tool to generate low‐dimensional and crystalline functional architectures. These include 1D nanostructures (nanoribbons, nanotubes, and nanowires) and 2D molecular crystals with tuneable and unique optical, electronic, and mechanical properties. Optimizing the (opto)electronic properties of organic semiconducting materials is imperative to harness such supramolecular structures as active components for supramolecular electronics. However, their integration in real devices currently represents a significant challenge to the advancement of (opto)electronics. Here, an overview of the unconventional nanofabrication techniques and device configurations to enable supramolecular electronics to become a real technology is provided. A particular focus is put on how single and multiple supramolecular fibers and gels as well as supramolecularly engineered 2D materials can be integrated into novel vertical or horizontal junctions to realize flexible and high‐density multifunctional transistors, photodetectors, and memristors, exhibiting a set of new properties and excelling in their performances.

Two-dimensional self-assembly and electrical properties of the donor-acceptor tetrathiafulvalene-polychlorotriphenylmethyl radical on graphite substrates

J. Guasch, N. Crivillers, M. Souto, I. Ratera, C. Rovira, P. Samorì, J. Veciana

J. Appl. Phys., 2019, 125, 142909. Link to article and accepted manuscript (open access). Selected as Editor's Pick.

The electron donor-acceptor tetrathiafulvalene-polychlorotriphenylmethyl (PTM) radical dyad, which shows a strong interplay between intra- and intermolecular charge transfer processes in solution, has been deposited by drop-casting on highly oriented pyrolytic graphite substrates, and its self-assembled structure has been investigated. Conducting atomic force microscopy revealed that the presence of a PTM radical in the molecules enhances the electrical conduction by almost two orders of magnitude and that this enhancement occurs in spite of the poor molecular orientation control achieved with drop-casting. Moreover, the study also reveals that the presence of a tetrathiafulvalene subunit in the deposited molecules can result in slightly asymmetric I-V curves.

A Universal Approach toward Light-Responsive Two-Dimensional Electronics: Chemically Tailored Hybrid van der Waals Heterostructures

Y. Zhao, S. Bertolazzi, P. Samorì

ACS Nano, 2019, 13, 4814–4825. Link to article and accepted manuscript (open access). Highlighted in Nature Nanotechnology.

Stimuli-responsive hybrid van der Waals heterostructures (vdWHs), composed of organic molecular switches superimposed on inorganic 2D materials (2DMs), can combine the outstanding physical properties of the latter components with the virtually infinite variety of tunable functionality of molecules, thereby offering an efficient protocol for the development of high-performance multifunctional materials and devices. The use of light as a remote control to modulate the properties of semiconducting 2DMs when interfaced with photochromic molecules suffers from both the limitation associated with the persistent photoconductivity characterizing the 2DMs and the finite thermal stability of the photochromic molecule in its different states. Here, we have devised a universal approach toward the fabrication of optically switchable electronic devices comprising a few nanometers thick azobenzene (AZO) layer physisorbed on 2D semiconductors supported on a trap-free polymer dielectric. The joint effect of the improved 2D/dielectric interface, the molecule’s light-modulated dipolar doping, and the high thermal stability of cis-AZO offers the highest control over the reversible and efficient charge carrier tuning in 2D semiconductors with a preserved high performance in 2D field-effect transistors, as quantified in terms of carrier mobility and Ion/Ioff ratio. The device has the potential to operate as an optical memory with four current levels and long retention time (>15 h). Furthermore, by using a CMOS-compatible micropatterning process, the photoswitchable resistor–diode transition has been achieved on hybrid lateral heterojunction devices. Our approach is of general applicability toward the generation of high-performance hybrid vdWHs for the emergence of functional and responsive devices.

EGOFET Gated by a Molecular Electronic Switch: A Single‐Device Memory Cell

V. Parkula, M. S. Maglione, S. Casalini, Q. Zhang, P. Greco, C. A. Bortolotti, C. Rovira, M. Mas-Torrent, F. Biscarini

Adv. Electron. Mater., 2019, 5, 1800875. Link to article.

Electrolyte‐gated organic field‐effect transistors (EGOFETs) exploit the transduction of interfacial phenomena, such as biorecognition or redox processes, into detectable changes of electrical response. Here, it is shown that, beyond sensing applications, EGOFETs may act effectively as memory devices, through the functionalization of the gate electrode with a self‐assembly monolayer comprising a switching molecule undergoing a large and persistent change of dipole moment, upon application of a small (0.6 V) programming potential. This first example of a switchable EGOFET device with memory retention is based on a tetrathiafulvalene derivative self‐assembled on gold and an aqueous buffer as electrolyte in a microfluidic assembly. Changes of the self‐assembled monolayer redox state lead to variations of the gate electrochemical potential and, as a consequence, the EGOFET's threshold voltage undergoes reversible shifts larger than 100 mV. The distinctive electrical readout upon different redox states opens the possibility of writing and erasing information, thus making the transistor behave as a single memory cell.

A robust, modular approach to produce graphene–MOx multilayer foams as electrodes for Li-ion batteries

Z. Y. Xia, M. Christian, C. Arbizzani, V. Morandi, M. Gazzano, V. Quintano, A. Kovtun, V. Palermo

Nanoscale, 2019, 11, 5265–5273. Link to article (open access).

Major breakthroughs in batteries would require the development of new composite electrode materials, with a precisely controlled nanoscale architecture. However, composites used for energy storage are typically a disordered bulk mixture of different materials, or simple coatings of one material onto another. We demonstrate here a new technique to create complex hierarchical electrodes made of multilayers of vertically aligned nanowalls of hematite (Fe2O3) alternated with horizontal spacers of reduced graphene oxide (RGO), all deposited on a 3D, conductive graphene foam. The RGO nanosheets act as porous spacers, current collectors and protection against delamination of the hematite. The multilayer composite, formed by up to 7 different layers, can be used with no further processing as an anode in Li-ion batteries, with a specific capacity of up to 1175 μA h cm−2 and a capacity retention of 84% after 1000 cycles. Our coating strategy gives improved cyclability and rate capacity compared to conventional bulk materials. Our production method is ideally suited to assemble an arbitrary number of organic–inorganic materials in an arbitrary number of layers.

Regioselective Hydrogenation of a 60-Carbon Nanographene Molecule toward a Circumbiphenyl Core

X. Yao, X.-Y. Wang, C. Simpson, G. M. Paternò, M. Guizzardi, M. Wagner, G. Cerullo, F. Scotognella, M. D. Watson, A. Narita, K. Müllen

J. Am. Chem. Soc., 2019, 141, 4230–4234. Link to article (open access).

Regioselective peripheral hydrogenation of a nanographene molecule with 60 contiguous sp2 carbons provides unprecedented access to peralkylated circumbiphenyl (1). Conversion to the circumbiphenyl core structure was unambiguously validated by MALDI-TOF mass spectrometry, NMR, FT-IR, and Raman spectroscopy. UV–vis absorption spectra and DFT calculations demonstrated the significant change of the optoelectronic properties upon peripheral hydrogenation. Stimulated emission from 1, observed via ultrafast transient absorption measurements, indicates potential as an optical gain material.

Regioselective Bromination and Functionalization of Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene with Zigzag Edges

Q. Chen, D. Wang, M. Baumgarten, D. Schollmeyer, K. Müllen, A. Narita

Chem. Asian J., 2019, 14, 1703–1707. Link to article.

Dibenzo[hi,st]ovalene (DBOV) is a nanographene with a combination of zigzag and armchair edges, consisting of 38 sp2 carbons. Excellent optical properties with strong red emission have been demonstrated. Here we report the regioselective bromination of DBOV bearing two mesityl groups (DBOV‐Mes) by treatment with N‐bromosuccinimide (NBS) under mild conditions. The dibrominated DBOV was further subjected to transition‐metal‐catalyzed cross‐coupling reactions, that is, Suzuki and Sonogashira coupling, demonstrating the edge‐decoration of DBOV with different functional groups. Notably, DBOVs arylated at the bay regions showed intense red emission and enhanced fluorescence quantum yields of up to 0.97. Amphoteric reduction and oxidation behavior were observed by cyclic voltammetry (CV) measurements. Chemical oxidation to stable radical cation species was also demonstrated, followed by reduction back to their neutral species.

Optically switchable organic light-emitting transistors

L. Hou, X. Zhang, G. F. Cotella, G. Carnicella, M. Herder, B. M. Schmidt, M. Pätzel, S. Hecht, F. Cacialli, P. Samorì

Nat. Nanotechnol., 2019, 14, 347–353. Link to article. Link to accepted manuscript (open access). UNISTRA, ISISFRC, LabEx CSC, HU Berlin, Adlershof and IRIS Adlershof press releases. Highlighted in Nature and Nature Research Device & Materials Engineering Community.

Organic light-emitting transistors are pivotal components for emerging opto- and nanoelectronics applications, such as logic circuitries and smart displays. Within this technology sector, the integration of multiple functionalities in a single electronic device remains the key challenge. Here we show optically switchable organic light-emitting transistors fabricated through a judicious combination of light-emitting semiconductors and photochromic molecules. Irradiation of the solution-processed films at selected wavelengths enables the efficient and reversible tuning of charge transport and electroluminescence simultaneously, with a high degree of modulation (on/off ratios up to 500) in the three primary colours. Different emitting patterns can be written and erased through a non-invasive and mask-free process, on a length scale of a few micrometres in a single device, thereby rendering this technology potentially promising for optically gated highly integrated full-colour displays and active optical memory.



A tool box to ascertain the nature of doping and photoresponse in single-walled carbon nanotubes

A. Santidrián, J. M. González-Domínguez, V. Diez-Cabanes, J. Hernández-Ferrer, W. K. Maser, A. M. Benito, A. Anśon-Casaos, J. Cornil, T. Da Ros, M. Kalbáč

Phys. Chem. Chem. Phys., 2019, 21, 4063–4071. Link to article (open access).

The effect of doping on the electronic properties in bulk single-walled carbon nanotube (SWCNT) samples is studied for the first time using a new in situ Raman spectroelectrochemical method, and further verified by DFT calculations and photoresponse. We use p-/n-doped SWCNTs prepared by diazonium reactions as a versatile chemical strategy to control the SWCNT behavior. The measured and calculated data testify an acceptor effect of 4-aminobenzenesulfonic acid (p-doping), and a donor effect (n-doping) in the case of benzyl alcohol. In addition, pristine and covalently functionalized SWCNTs were used for the preparation of photoactive film electrodes. The photocathodic current in the photoelectrochemical cell is consistently modulated by the doping group. These results validate the in situ Raman spectroelectrochemistry as a unique tool box for predicting the electronic properties of functionalized SWCNTs in the form of thin films and their operational functionality in thin film devices for future optoelectronic applications.

Dynamically Switching the Electronic and Electrostatic Properties of Indium–Tin Oxide Electrodes with Photochromic Monolayers: Toward Photoswitchable Optoelectronic Devices

Q. Wang, V. Diez-Cabanes, S. Dell’Elce, A. Liscio, B. Kobin, H. Li, J.-L. Brédas, S. Hecht, V. Palermo, E. J. W. List-Kratochvil, J. Cornil, N. Koch, G. Ligorio

ACS Appl. Nano Mater., 2019, 2, 1102–1110. Link to article and accepted manuscript (open access).

The chemical modification of electrodes with organic materials is a common approach to tuning the electronic and electrostatic landscapes between interlayers in optoelectronic devices, thus facilitating charge injection at the electrode/semiconductor interfaces and improving their performance. The use of photochromic molecules for surface modification allows a dynamic control of the electronic and electrostatic properties of the electrode and thereby enables additional functionalities in such devices. Here, we show that the electronic properties of a transparent indium–tin oxide (ITO) electrode are reversibly and dynamically modified by depositing organic photochromic switches (diarylethenes) in the form of self-assembled monolayers (SAMs). By combining a range of surface characterization and density functional theory calculations, we present a detailed picture of the SAM binding to ITO, the packing density of molecules, their orientation, and work function modification of the ITO surface due to SAM deposition. Upon illumination with UV and green light, we observe a reversible shift of the frontier occupied levels by 0.7 eV and concomitantly a reversible work function change of ca. 60 meV. Our results prove the viability of dynamic switching of the electronic properties of the electrode with external light stimuli upon modification with a monolayer of photochromic molecules, which could be used to fabricate ITO-based photoswitchable optoelectronic devices.

Controlling Ambipolar Transport and Voltage Inversion in Solution-Processed Thin-Film Devices through Polymer Blending

T. Leydecker, M. A. Squillaci, F. Liscio, E. Orgiu, and P. Samorì

Chem. Mater., 2019, 31, 6491–6498. Link to article and accepted manuscript (open access).

Ambipolar semiconductors are attracting a great interest as building blocks for photovoltaics and logic applications. Field-effect transistors built on solution-processable ambipolar materials hold strong promise for the engineering of large-area low-cost logic circuits with a reduced number of devices components. Such devices still suffer from a number of obstacles including the challenging processing, the low Ion/Ioff, the unbalanced mobility, and the low gain in complementary metal–oxide–semiconductor (CMOS)-like circuits. Here, we demonstrate that the simple approach of blending commercially available n- and p-type polymers such as P(NDI2OD-T2), P3HT, PCD-TPT, PDVT-8, and IIDDT-C3 can yield high-performing ambipolar field-effect transistors with balanced mobilities and Ion/Ioff > 107. Each single component was studied separately and upon blending by means of electrical characterization, ambient ultraviolet photoelectron spectroscopy, atomic force microscopy, and grazing incidence wide angle X-ray scattering to unravel the correlation between the morphology/structure of the semiconducting films and their functions. Blends of n- and p-type semiconductors were used to fabricate CMOS-like inverter circuits with state-of-the-art gains over 160 in the case of P(NDI2OD-T2) blended with PDVT-8. Significantly, our blending approach was successful in producing semiconducting films with balanced mobilities for each of the four tested semiconductor blends, although the films displayed different structural and morphological features. Our strategy, which relies on establishing a correlation between ambipolar performances, film morphology, molecular structure, and blending ratio, is extremely efficient and versatile; thus it could be applied to a wide range of polymers or solution processable small molecules.

Pump–Push–Probe for Ultrafast All‐Optical Switching: The Case of a Nanographene Molecule

G. M. Paternò, L. Moretti, A. J. Barker, Q. Chen, K. Müllen, A. Narita, G. Cerullo, F. Scotognella, G. Lanzani

Adv. Funct. Mater., 2019, 29, 1805249. Link to article and accepted manuscript (open access).

In the last two decades, the three‐beam pump–push–probe (PPP) technique has become a well‐established tool for investigating the multidimensional configurational space of a molecule, as it permits disclosure of precious information about the multiple and often complex deactivation pathways of the excited molecule. From the spectroscopic point of view, such a tool has revealed details about the efficiency of charge pair generation and conformational relaxation in π‐conjugated molecules and macromolecules. In addition, PPP is effectively utilized for modulating the gain signal in conjugated materials by taking advantage of the spectral overlap between stimulated emission and charge absorption in those systems. However, the relatively low stability of conjugated polymers under intense photoexcitation is a crucial limitation for their real employment in plastic optical fibers (POFs) and for signal control applications. Herein, the role of PPP for achieving ultrafast all‐optical switching in π‐conjugated systems is highlighted. Furthermore, new experimental data on optical switching of a newly synthesized nanographene molecule, namely dibenzo[hi,st]ovalene (DBOV), is reported. The superior environmental and photostability of DBOV and, in general, of graphene nanostructures can represent a great advantage for their effective applications in POFs and information and communications technology.

Accurate chemical analysis of oxygenated graphene-based materials using X-ray photoelectron spectroscopy

A. Kovtun, D. Jones, S. Dell’Elce, E. Treossi, A. Liscio, V. Palermo

Carbon, 2019, 143, 268–275. Link to article and accepted manuscript (open access).

A simple, fast and general protocol for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data provides accurate estimations of chemical species in graphene and related materials (GRMs). XPS data are commonly used to estimate the quality of and defects in graphene and graphene oxide (GO), by comparing carbon and oxygen 1s XPS peaks, obtaining an O/C ratio. This approach, however, cannot be used in the presence of extraneous oxygen contamination.

The protocol, based on quantitative line-shape analysis of C 1s signals, uses asymmetric pseudo-Voigt line-shapes (APV), in contrast to Gaussian-based approaches conventionally used in fitting XPS spectra, thus allowing better accuracy in quantifying C 1s contributions from graphitic carbon (sp2), defects (sp3 carbon), carbons bonded to hydroxyl and epoxy groups, and from carbonyl and carboxyl groups. The APV protocol was evaluated on GRMs with O/C ratios ranging from 0.02 to 0.30 with film thicknesses from monolayers to bulk-like (>30 nm) layers and also applied to previously published data, showing better results compared to those from conventional XPS fitting protocols.

Based uniquely on C 1s data, the APV protocol can quantify O/C ratio and the presence of specific functional groups in GRMs even on SiOx, substrates, or in samples containing water.

Highly sensitive amperometric sensor for morphine detection based on electrochemically exfoliated graphene oxide. Application in screening tests of urine samples

G. Maccaferri, F. Terzi, Z. Xia, F. Vulcano, A. Liscio, V. Palermo, C. Zanardi

Sens. Actuators B Chem., 2019, 281, 739–745. Link to article and accepted manuscript (open access).

Graphene oxide modified screen-printed electrodes have been tested as amperometric sensors for morphine determination. The results demonstrate that the arising of electrocatalytic processes ascribable to the graphene coating, combined with the use of a suitable cleaning procedure, allow the sensor to achieve higher sensitivity (2.61 nA ppb−1) and lower limit of detection (2.5 ppb) with respect to those reported in the literature for similar devices.

Due to very low detection limit found, the device is suitable to detect the presence of morphine in urine samples after a very simple and rapid pre-treatment of the matrix, allowing the removal of interfering species affecting the voltammetric responses. Tests performed in synthetic urine samples demonstrate that the presence of the electrocatalytic coating is mandatory in resolving the peak due to morphine oxidation in respect to uric acid. The sensor proposed is, thus, suitable to detect this drug even at concentration values below the cut-off levels defined by European and American regulations. These results allow us to propose the sensor for screening tests in portable devices, to be applied in systematic controls of drug abuses, e.g. in drivers and in men at work.

Effect of the Molecular Polarizability of SAMs on the Work Function Modification of Gold: Closed‐ versus Open‐Shell Donor–Acceptor SAMs

V. Diez‐Cabanes, D. C. Morales, M. Souto, M. Paradinas, F. Delchiaro, A. Painelli, C. Ocal, D. Cornil, J. Cornil, J. Veciana, I. Ratera

Adv. Mater. Technol., 2019, 4, 1800152. Link to article. Link to accepted manuscript (open access).

Charge injection barriers at metal/organic interfaces can be tuned by modifying the work function of metallic electrodes using self‐assembled monolayers (SAMs) of polar molecules. An interesting example of polar molecules is offered by donor–acceptor (D–A) dyads based on ferrocene (Fc) as electron‐donor unit and either a polychlorotriphenylmethyl radical or a polychlorotriphenylmethane as electron‐acceptor units, connected by a π‐conjugated vinylene bridge. The D–A radical exhibits high chemical and thermal stability and presents different electronic, optical, and magnetic properties with respect to the closed‐shell form. The magnitude of the shift in the charge injection barriers for these two D–A systems is estimated by means of surface potential measurements performed by Kelvin probe force microscopy. The experimental data are compared with density functional theory calculations, which evidence the importance of the molecular dipole moments and polarizabilities to understand the experimental values. In order to achieve high work function shifts of metals upon SAM formation, the molecules forming the SAM have to exhibit both a high permanent dipole moment and a low polarizability along the direction normal to the substrate. In presence of polarizable molecules, the work function shifts can be enhanced by reducing the intermolecular interactions; by using mixed SAMs with active molecules embedded into a passive matrix.

Indium Tin Oxide–Based Fully Spray‐Coated Inverted Solar Cells with Nontoxic Solvents: The Role of Buffer Layer Interface on Low‐Bandgap Photoactive Layer Performance

G. Polino, S. Dell’Elce, A. Liscio, L. La Notte, G. Cardone, A. Di Carlo, F. Brunetti

Energy Technol., 2019, 7, 1800627. Link to article.

In bulk heterojunction solar cells, the morphology of the interfaces between the photoactive layer (PAL) and charge transporting layers during the deposition process plays a key role in achieving high‐efficiency devices. Herein, an inverted fully spray‐coated solar cell fabricated on an indium tin oxide (ITO)‐glass substrate is presented. It is demonstrated that a spray‐coated double electron transporting layer composed of zinc oxide (ZnO) nanoparticles coated with polyethylenimine ethoxylated (PEIE) improves the morphology of the spray‐coated active layer on top of the spray‐coated cathode. Moreover, focusing on the hole transporting layer and anode, the performance obtained using a commercial poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) blend is compared with a high‐conductive anhydrous PEDOT:PSS (A‐PEDOT) mixed with a commercial PEDOT:PSS (CPP‐105D) as transporting layer. By optimizing the spray deposition of all the layers, a fully scalable spray process is used to produce polymer solar cells with ITO/ZnO/PEIE/poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b’]dithiophene‐2,6‐diyl] [3‐fluoro‐2‐ [(2‐ethylhexyl)carbonyl] thieno[3,4‐b]thiophenediyl]] (PTB7): [6,6]‐phenyl‐C70‐butyric‐acid‐methyl‐ester (PC70BM)/CPP:A‐PEDOT structure, achieving a power conversion efficiency (PCE) of 3.6%. Such result is significant if compared to a spray‐coated structure with evaporated anode (MoO3‐Ag). In this case (ITO/ZnO/PEIE/PTB7:PCBM/MoO3‐Ag), a power conversion efficiency of 5.5% is obtained.

3D to 2D reorganization of silver–thiol nanostructures, triggered by solvent vapor annealing

S. Dell’Elce, F. Liscio, A. Kovtun, S. Allegri, O. M. Roscioni, C. Albonetti, G. De Luca, H. W. Amenitsch, N. Demitri, L. Giorgini, V. Morandi, F. Stellacci, A. Liscio, V. Palermo

Nanoscale, 2018, 10, 23018–23026. Link to article (open access).

Metal–organic composites are of great interest for a wide range of applications. The control of their structure remains a challenge, one of the problems being a complex interplay of covalent and supramolecular interactions. This paper describes the self-assembly, thermal stability and phase transitions of ordered structures of silver atoms and thiol molecules spanning from the molecular to the mesoscopic scale. Building blocks of molecularly defined clusters formed from 44 silver atoms, each particle coated by a monolayer of 30 thiol ligands, are used as ideal building blocks. By changing solvent and temperature it is possible to tune the self-assembled 3D crystals of pristine nanoparticles or, conversely, 2D layered structures, with alternated stacks of Ag atoms and thiol monolayers. The study investigates morphological, chemical and structural stability of these materials between 25 and 300 °C in situ and ex situ at the nanoscale by combining optical and electronic spectroscopic and scattering techniques, scanning probe microscopies and density-functional theory (DFT) calculations. The proposed wet-chemistry approach is relatively cheap, easy to implement, and scalable, allowing the fabricated materials with tuned properties using the same building blocks.

Electronic Decoupling in C3-Symmetrical Light-Responsive Tris(Azobenzene) Scaffolds: Self-Assembly and Multiphotochromism

A. Galanti, V. Diez-Cabanes, J. Santoro, M. Valášek, A. Minoia, M. Mayor, J. Cornil, P. Samorì

J. Am. Chem. Soc., 2018, 140, 16062–16070. Link to article and accepted manuscript (open access).

We report the synthesis of a novel C3-symmetrical multiphotochromic molecule bearing three azobenzene units at positions 1, 3, 5 of the central phenyl ring. The unique geometrical design of such a rigid scaffold enables the electronic decoupling of the azobenzene moieties to guarantee their simultaneous isomerization. Photoswitching of all azobenzenes in solution was demonstrated by means of UV–vis absorption spectroscopy and high performance liquid chromatography (HPLC) analysis. Scanning tunneling microscopy investigations at the solid–liquid interface, corroborated by molecular modeling, made it possible to unravel the dynamic self-assembly of such systems into ordered supramolecular architectures, by visualizing and identifying the patterns resulting from three different isomers, thereby demonstrating that the multiphotochromism is retained when the molecules are confined in two dimensions.

Amorphous CaCO3: Influence of the Formation Time on Its Degree of Hydration and Stability

H. Du, M. Steinacher, C. Borca, T. Huthwelker, A. Murello, F. Stellacci, E. Amstad

J. Am. Chem. Soc., 2018, 140, 14289–14299. Link to article (open access). COVER PAGE.

Calcium carbonate (CaCO3) is one of the most abundant biominerals that is prevalent in rocks and often used as a structural material in marine animals. Many of these natural CaCO3-based materials display excellent mechanical properties that are difficult to reproduce by man-made counterparts. This difficulty arises from the incomplete understanding of the influence of processing conditions on the structure and composition of CaCO3. To gain a better understanding of the evolution of the structure and composition of amorphous CaCO3 (ACC) particles during early stages, we introduce a new, organic solvent-free method that quenches this process with a high temporal resolution. We produce ACC particles inside small airborne drops that are formed with a microfluidic spray-dryer. These drops dry within 100 ms to 10 s and thereby arrest the formation of CaCO3 particles on that time scale. Using the microfluidic spray-dryer, we demonstrate that the amount of mobile water contained in ACC particles increases with increasing formation time and hence with increasing particle size. As a result of the higher concentration of mobile water, larger particles are less stable against temperature-induced solid-state crystallization and electron beam-induced decomposition than smaller counterparts. The amount of mobile water contained in ACC can be substantially reduced, and hence their kinetic stability against solid-state transformations increased, if certain organic additives, such as poly(acrylic acid) (PAA), are incorporated. These insights might open up new opportunities to fabricate biomimetic CaCO3-based materials with tunable structures and hence with properties that can be adapted to the needs of specific applications.

Influence of the donor unit on the rectification ratio in tunnel junctions based on donor–acceptor SAMs using PTM units as acceptors

M. Souto, V. Díez-Cabanes, L. Yuan, A. R. Kyvik, I. Ratera, C. A. Nijhuis, J. Cornil, J. Veciana

Phys. Chem. Chem. Phys., 2018, 20, 25638–25647. Link to article and accepted manuscript (open access).

Dyads formed by an electron donor unit (D) covalently linked to an electron acceptor (A) by an organic bridge are promising materials as molecular rectifiers. Very recently, we have reported the charge transport measurements across self-assembled monolayers (SAMs) of two D–A systems consisting of the ferrocene (Fc) electron-donor linked to a polychlorotriphenylmethane (PTM) electron-acceptor in its non-radical (SAM 1) and radical (SAM 2) forms. Interestingly, we observed that the non-radical SAM 1 showed rectification behavior of 2 orders of magnitude higher than its radical analogue dyad 2. In order to study the influence of the donor unit on the transport properties, we report herein the synthesis and characterization of two new D–A SAMs in which the electron-donor Fc unit is replaced by a tetrathiafulvalene (TTF) moiety linked to the PTM unit in its non-radical (SAM 3) and radical (SAM 4) forms. The observed decrease in the rectification ratio and increased current density for TTF-PTM based SAMs 3 and 4 in comparison to Fc-PTM based SAMs 1 and 2 are explained, supported by theoretical calculations, by significant changes in the electronic and supramolecular structures.

Photophysical Pathways in Highly Sensitive Cs2AgBiBr6 Double‐Perovskite Single‐Crystal X‐Ray Detectors

J. A. Steele, W. Pan, C. Martin, M. Keshavarz, E. Debroye, H. Yuan, S. Banerjee, E. Fron, D. Jonckheere, C. Woong Kim, W. Baekelant, G. Niu, J. Tang, J. Vanacken, M. Van der Auweraer, J. Hofkens, M. B. J. Roeffaers

Adv. Mater., 2018, 30, 1804450. Link to article and accepted manuscript (open access). COVER PAGE.

The sensitive detection of X‐rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for detection. Among metal halide perovskites, the double‐perovskite Cs2AgBiBr6 system has emerged as a promising candidate for the detection of X‐rays, capable of high X‐ray stability and sensitivity (105 μC Gy−1 cm−2). Herein, the important photophysical pathways in single‐crystal Cs2AgBiBr6 are detailed at both room (RT) and liquid‐nitrogen (LN2T) temperatures, with emphasis made toward understanding the carrier dynamics that influence X‐ray sensitivity. This study draws upon several optical probes and an RT excitation model is developed which is far from optimal, being plagued by a large trap density and fast free‐carrier recombination pathways. Substantially improved operating conditions are revealed at 77 K, with a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. The temperature dependence of a single‐crystal Cs2AgBiBr6 X‐ray detecting device is characterized and a strong and monotonic enhancement to the X‐ray sensitivity upon cooling is demonstrated, moving from 316 μC Gy−1 cm−2 at RT to 988 μC Gy−1 cm−2 near LN2T. It is concluded that even modest cooling—via a Peltier device—will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.

Biomimetic graphene for enhanced interaction with the external membrane of astrocytes

M. Durso, A. I. Borrachero-Conejo, C. Bettini, E. Treossi, A. Scidà, E. Saracino, M. Gazzano, M. Christian, V. Morandi, G. Tuci, G. Giambastiani, L. Ottaviano, F. Perrozzi, V. Benfenati, M. Melucci, V. Palermo

J. Mater. Chem. B, 2018, 6, 5335–5342. Link to article (open access). COVER PAGE.

Graphene and graphene substrates display huge potential as material interfaces for devices and biomedical tools targeting the modulation or recovery of brain functionality. However, to be considered reliable neural interfaces, graphene-derived substrates should properly interact with astrocytes, favoring their growth and avoiding adverse gliotic reactions. Indeed, astrocytes are the most abundant cells in the human brain and they have a crucial physiological role to maintain its homeostasis and modulate synaptic transmission. In this work, we describe a new strategy based on the chemical modification of graphene oxide (GO) with a synthetic phospholipid (PL) to improve interaction of GO with brain astroglial cells. The PL moieties were grafted on GO sheets through polymeric brushes obtained by atom-transfer radical-polymerization (ATRP) between acryloyl-modified PL and GO nanosheets modified with a bromide initiator. The adhesion of primary rat cortical astrocytes on GO–PL substrates increased by about three times with respect to that on glass substrates coated with standard adhesion agents (i.e. poly-D-lysine, PDL) as well as with respect to that on non-functionalized GO. Moreover, we show that astrocytes seeded on GO–PL did not display significant gliotic reactivity, indicating that the material interface did not cause a detrimental inflammatory reaction when interacting with astroglial cells. Our results indicate that the reported biomimetic approach could be applied to neural prosthesis to improve cell colonization and avoid glial scar formation in brain implants. Additionally, improved adhesion could be extremely relevant in devices targeting neural cell sensing/modulation of physiological activity.

Collective molecular switching in hybrid superlattices for light-modulated two-dimensional electronics

M. Gobbi, S. Bonacchi, J. X. Lian, A. Vercouter, S. Bertolazzi, B. Zyska, M. Timpel, R. Tatti, Y. Olivier, S. Hecht, M. V. Nardi, D. Beljonne, E. Orgiu, P. Samorì

Nat. Commun., 2018, 9, 2661. Link to article (open access). UNISTRA, ISIS, FRC, Adlershof, IRIS Adlershof, Research in Germany and Graphene Flagship press releases.

Molecular switches enable the fabrication of multifunctional devices in which an electrical output can be modulated by external stimuli. The working mechanism of these devices is often hard to prove, since the molecular switching events are only indirectly confirmed through electrical characterization, without real-space visualization. Here, we show how photochromic molecules self-assembled on graphene and MoS2 generate atomically precise superlattices in which a light-induced structural reorganization enables precise control over local charge carrier density in high-performance devices. By combining different experimental and theoretical approaches, we achieve exquisite control over events taking place from the molecular level to the device scale. Unique device functionalities are demonstrated, including the use of spatially confined light irradiation to define reversible lateral heterojunctions between areas possessing different doping levels. Molecular assembly and light-induced doping are analogous for graphene and MoS2, demonstrating the generality of our approach to optically manipulate the electrical output of multi-responsive hybrid devices.

Synthesis of Triply Fused Porphyrin-Nanographene Conjugates

Q. Chen, L. Brambilla, L. Daukiya, K. S. Mali, S. De Feyter, M. Tommasini, K. Müllen, A. Narita

Angew. Chem. Int. Ed., 2018, 57, 11233–11237. Link to article and accepted manuscript (open access).

Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor‐made precursors based on benzo[m]tetraphene‐substituted porphyrins. The chemical structures were validated by a combination of high‐resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HR MALDI‐TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV‐vis‐near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red‐shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π‐conjugated systems.

Controlling the Functional Properties of Oligothiophene Crystalline Nano/Microfibers via Tailoring of the Self-Assembling Molecular Precursors

F. Di Maria, M. Zangoli, M. Gazzano, E. Fabiano, D. Gentili, A. Zanelli, A. Fermi, G. Bergamini, D. Bonifazi, A. Perinot, M. Caironi, R. Mazzaro, V. Morandi, G. Gigli, A. Liscio, G. Barbarella

Adv. Funct. Mater., 2018, 28, 1801946. Link to article.

Oligothiophenes are π‐conjugated semiconducting and fluorescent molecules whose self‐assembly properties are widely investigated for application in organic electronics, optoelectronics, biophotonics, and sensing. Here an approach to the preparation of crystalline oligothiophene nano/microfibers is reported based on the use of a “sulfur overrich” quaterthiophene building block, T4S4–, containing in its covalent network all the information needed to promote the directional, π–π stacking‐driven, self‐assembly of Y‐T4S4‐Y oligomers into fibers with hierarchical supramolecular arrangement from nano‐ to microscale. It is shown that when Y varies from unsubstituted thiophene to thiophene substituted with electron‐withdrawing groups, a wide redistribution of the molecular electronic charge takes place without substantially affecting the aggregation modalities of the oligomer. In this way, a structurally comparable series of fibers is obtained having progressively varying optical properties, redox potentials, photoconductivity, and type of prevailing charge carriers (from p‐ to n‐type). With the aid of density functional theory (DFT) calculations, combined with powder X‐ray diffraction data, a model accounting for the growth of the fibers from molecular to nano‐ and microscale is proposed.

Design of Perchlorotriphenylmethyl (PTM) Radical-Based Compounds for Optoelectronic Applications: The Role of Orbital Delocalization

V. Diez-Cabanes, G. Seber, C. Franco, F. Bejarano, N. Crivillers, M. Mas-Torrent, J. Veciana, C. Rovira, J. Cornil

ChemPhysChem, 2018, 19, 2572–2578. Link to article and accepted manuscript (open access).

Perchlorotriphenylmethyl (PTM) radical‐based compounds are widely exploited as molecular switching units. However, their application in optoelectronics is limited by the fact that they exhibit intense absorption bands only in a narrow range of the UV region around 385 nm. Recent experimental works have reported new PTM based compounds which present a broad absorption in the visible region although the origin of this behavior is not fully explained. In this context, Time‐Dependent Density Functional Theory (TD‐DFT) calculations have been performed to rationalize the optical properties of these compounds. Moreover, a new compound based on PTM disubstituted with bistriazene units has been synthetized and characterized to complete the set of available experimental data on related compounds. The results point to the delocalization of the Highest Occupied Molecular Orbital (HOMO) of the substituents along the PTM core as the origin of the new high absorption bands in the visible region. As a consequence, the absorption of the PTM‐based compounds can be tuned via the choice of the nature of the donor substituent, type of connection, and number of substituents.

Dynamic Photoswitching of Electron Energy Levels at Hybrid ZnO/Organic Photochromic Molecule Junctions

Q. Wang, G. Ligorio, V. Diez-Cabanes, D. Cornil, B. Kobin, J. Hildebrandt, M. V. Nardi, M. Timpel, S. Hecht, J. Cornil, E. J. W. List-Kratochvil, N. Koch

Adv. Funct. Mater., 2018, 28, 1800716. Link to article and accepted manuscript (open access).

The functionality of interfaces in hybrid inorganic/organic (opto)electronic devices is determined by the alignment of the respective frontier energy levels at both sides of the heterojunctions. Controlling the interface electronic landscape is a key element for achieving favourable level alignment for energy and charge transfer processes. Here, it is shown that the electronic properties of polar ZnO surfaces can be reversibly modified using organic photochromic switches. By employing a range of surface characterization techniques combined with density functional theory calculations, it is demonstrated that self‐assembled monolayers (SAMs) of photochromic phosphonic acid diarylethenes (PA‐DAEs) can be employed to reversibly change the electronic properties of polar ZnO/SAM structures by light stimuli. The highest occupied molecular orbital level of PA‐DAE is raised by 0.7 eV and the lowest unoccupied one lowered by 0.9 eV, respectively, upon illumination by ultraviolet light and the levels shift back to their original position upon illumination by green light. The results thus provide a pathway to tailor hybrid interface electronic properties in a dynamic manner upon simple light illumination, which can be exploited to reversibly tune the electrical properties of photoswitchable (opto)electronic devices.

Self-Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting Crystals

L. Zhang, N. Pasthukova, Y. Yao, X. Zhong, E. Pavlica, G. Bratina, E. Orgiu, P. Samorì

Adv. Mater., 2018, 30, 1801181. Link to article and accepted manuscript (open access). COVER PAGE.

Self‐standing nanostructures are of fundamental interest in materials science and nanoscience and are widely used in (opto‐)electronic and photonic devices as well as in micro‐electromechanical systems. To date, large‐area and self‐standing nanoelectrode arrays assembled on flexible substrates have not been reported. Here the fabrication of a hollow nanomesh scaffold on glass and plastic substrates with a large surface area over 1 mm2 and ultralow leakage current density (≈1–10 pA mm−2 @ 2 V) across the empty scaffold is demonstrated. Thanks to the continuous sub‐micrometer space formed in between the nanomesh and the bottom electrode, highly crystalline and dendritic domains of 6,13‐bis(triisopropylsilylethinyl)pentacene growing within the hollow cavity can be observed. The high degree of order at the supramolecular level leads to efficient charge and exciton transport; the photovoltaic detector supported on flexible polyethylene terephthalate substrates exhibits an ultrafast photoresponse time as short as 8 ns and a signal‐to‐noise ratio approaching 105. Such a hollow scaffold holds great potential as a novel device architecture toward flexible (opto‐)electronic applications based on self‐assembled micro/nanocrystals.

Sensitive Assays by Nucleophile-Induced Rearrangement of Photoactivated Diarylethenes

S. Fredrich, A. Bonasera, V. Valderrey, S. Hecht

J. Am. Chem. Soc., 2018, 140, 6432–6440. Link to article and accepted manuscript (open access).

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure–reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes’ intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalytic cycle, leading to an amplified decoloration process. This additional catalytic pathway allows us to enhance the sensitivity of our method and successfully discriminate between amines and thiols. Moreover, probes that exhibit strong analyte-induced fluorescence modulation have been designed to further decrease the detection limit by using a more sensitive read-out. The optimized DAE probes are promising molecular components for future programmable sensing materials and devices.

Direct Photolithography on Molecular Crystals for High Performance Organic Optoelectronic Devices

Y. Yao, L. Zhang, T. Leydecker, P. Samorì

J. Am. Chem. Soc., 2018, 140, 6984–6990. Link to article and accepted manuscript (open access). COVER PAGE. UNISTRA, CNRS Alsace, ISIS, FRC and Tchapp press releases.

Organic crystals are generated via the bottom-up self-assembly of molecular building blocks which are held together through weak noncovalent interactions. Although they revealed extraordinary charge transport characteristics, their labile nature represents a major drawback toward their integration in optoelectronic devices when the use of sophisticated patterning techniques is required. Here we have devised a radically new method to enable the use of photolithography directly on molecular crystals, with a spatial resolution below 300 nm, thereby allowing the precise wiring up of multiple crystals on demand. Two archetypal organic crystals, i.e., p-type 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (Dph-BTBT) nanoflakes and n-type N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) nanowires, have been exploited as active materials to realize high-performance top-contact organic field-effect transistors (OFETs), inverter and p–n heterojunction photovoltaic devices supported on plastic substrate. The compatibility of our direct photolithography technique with organic molecular crystals is key for exploiting the full potential of organic electronics for sophisticated large-area devices and logic circuitries, thus paving the way toward novel applications in plastic (opto)electronics.

Electrochemically driven host–guest interactions on patterned donor/acceptor self-assembled monolayers

M. S. Maglione, J. Casado-Montenegro, E.-C. Fritz, N. Crivillers, B. J. Ravoo, C. Rovira, M. Mas-Torrent

Chem. Commun., 2018, 54, 3038–3041. Link to article and accepted manuscript (open access). ICMAB-CSIC press release.

Here, on ITO//Au patterned substrates SAMs of ferrocene (Fc) on the Au regions and of anthraquinone (AQ) on the ITO areas are prepared, exhibiting three stable redox states. Furthermore, by selectively oxidizing or reducing the Fc or AQ units, respectively, the surface properties are locally modified. As a proof-of-concept, such a confinement of the properties is exploited to locally form host–guest complexes with β-cyclodextrin on specific surface regions depending on the applied voltage.


Role of the Open-Shell Character on the Pressure‐Induced Conductivity of an Organic Donor–Acceptor Radical Dyad

M. Souto, M. C. Gullo, H. Cui, N. Casati, F. Montisci, H. O. Jeschke, R. Valentí, I. Ratera, C. Rovira, J. Veciana

Chem. Eur. J., 2018, 24, 5500–5505. Link to article and accepted manuscript (open access).

Single‐component conductors based on neutral organic radicals have received a lot of attention due to the possibility that the unpaired electron can serve as a charge carrier without the need of a previous doping process. Although most of these systems are based on delocalized planar radicals, we present here a nonplanar and spin localized radical based on a tetrathiafulvalene (TTF) moiety, linked to a perchlorotriphenylmethyl (PTM) radical by a conjugated bridge, which exhibits a semiconducting behavior upon application of high pressure. The synthesis, electronic properties, and crystal structure of this neutral radical TTF‐Ph‐PTM derivative (1) are reported and implications of its crystalline structure on its electrical properties are discussed. On the other hand, the non‐radical derivative (2), which is isostructural with the radical 1, shows an insulating behavior at all measured pressures. The different electronic structures of these two isostructural systems have a direct influence on the conducting properties, as demonstrated by band structure DFT calculations.

Imaging Heterogeneously Distributed Photo‐Active Traps in Perovskite Single Crystals

H. Yuan, E. Debroye, E. Bladt, G. Lu, M. Keshavarz, K. P. F. Janssen, M. B. J. Roeffaers, S. Bals, E. H. Sargent, J. Hofkens

Adv. Mater., 2018, 30, 1705494. Link to article and accepted manuscript (open access).

Organic–inorganic halide perovskites (OIHPs) have demonstrated outstanding energy conversion efficiency in solar cells and light‐emitting devices. In spite of intensive developments in both materials and devices, electronic traps and defects that significantly affect their device properties remain under‐investigated. Particularly, it remains challenging to identify and to resolve traps individually at the nanoscopic scale. Here, photo‐active traps (PATs) are mapped over OIHP nanocrystal morphology of different crystallinity by means of correlative optical differential super‐resolution localization microscopy (Δ‐SRLM) and electron microscopy. Stochastic and monolithic photoluminescence intermittency due to individual PATs is observed on monocrystalline and polycrystalline OIHP nanocrystals. Δ‐SRLM reveals a heterogeneous PAT distribution across nanocrystals and determines the PAT density to be 1.3 × 1014 and 8 × 1013 cm−3 for polycrystalline and for monocrystalline nanocrystals, respectively. The higher PAT density in polycrystalline nanocrystals is likely related to an increased defect density. Moreover, monocrystalline nanocrystals that are prepared in an oxygen‐ and moisture‐free environment show a similar PAT density as that prepared at ambient conditions, excluding oxygen or moisture as chief causes of PATs. Hence, it is concluded that the PATs come from inherent structural defects in the material, which suggests that the PAT density can be reduced by improving crystalline quality of the material.

Application of graphene-based flexible antennas in consumer electronic devices

A. Scidà, S. Haque, E. Treossi, A. Robinson, S. Smerzi, S. Ravesi, S. Borini, V. Palermo

Mater. Today, 2018, 21, 223–230. Link to article (open access). COVER PAGE.

We describe the fabrication and characterization of Near-Field Communication (NFC) devices based on highly flexible, carbon-based antennas composed of stacked graphene multilayers. This material features a high value of conductivity (4.20 * 105 S/m) comparable to monocrystalline graphite, but is much more flexible and processable. We first studied the replacement of metal with carbon antennas using computer modeling, to select the best design. Then we manufactured several devices to be used according to the communication protocol ISO/IEC 15693. The inductance of the G-paper antennas was tested before and after hundreds of thousands of bending cycles at bending radii of 45 and 90 mm. During bending the self-resonance frequency and inductance peak showed minimal variation and the resistance at 1 MHz changed from 33.09 Ω to 34.18 Ω, outperforming standard, commercial metallic antennas. The devices were successfully tested by exchanging data with a smartphone and other commercial NFC readers, matching the performance of standard, commercial metallic antennas. The graphene antennas could be deposited on different standard polymeric substrates or on textiles. Smart cards, flexible NFC tags and wearable NFC bracelets were prepared in this way to be used in electronic keys, business cards and other typical NFC applications.

Energy Level Alignment at Interfaces Between Au (111) and Thiolated Oligophenylenes of Increasing Chain Size: Theoretical Evidence of Pinning Effects

V. Diez-Cabanes, S. Rodriguez Gonzalez, S. Osella, D. Cornil, C. Van Dyck, J. Cornil

Adv. Theory Simul., 2018, 1, 1700020. Link to article and accepted manuscript (open access).

We present a detailed theoretical characterization of the energetic alignment between the HOMO level of a series of thiolated oligophenylenes of increasing chain size, and the Fermi level of gold electrodes, using density functional theory (DFT) calculations for molecular self-assembled monolayers (SAMs) chemisorbed on an Au (111) surface, and the nonequilibrium Green's function (NEGF) formalism coupled to DFT for single molecule junctions. The additional role of the dynamic electronic polarization effects neglected in standard DFT calculations is also discussed. Interestingly, whereas the HOMO energy varies significantly among the unsubstituted oligomers in the gas phase, their alignment with respect to the Fermi level of the electrode is almost insensitive to chain size upon chemisorption, thus pointing to a strong pinning effect. The energy at which the HOMO is pinned strongly depends on the degree of interfacial hybridization, and hence on the contact geometry, as well as on the degree of surface coverage although a different mechanism enters into play.



Photoconversion of Far‐Red Organic Dyes: Implications for Multicolor Super‐Resolution Imaging

L. Dirix, K. Kennes, E. Fron, Z. Debyser, M. van der Auweraer, J. Hofkens, S. Rocha

ChemPhotoChem, 2018, 2, 433–441. Link to article and accepted manuscript (open access).

Localization‐based super‐resolution microscopy has become an indispensable tool in biology to study features smaller than the diffraction limit of light. In a multicolor approach, adequate spectral separation of the different photoswitchable probes is required. A far‐red emitting dye is often one of the labels of choice. However, irradiation with high laser intensity can induce photo‐conversion of some of the most frequently used fluorophores. Herein we show that upon intense irradiation with a 561 nm laser line, far‐red organic dyes photoconvert to blue‐shifted emissive species. In the case of Alexa Fluor 647, the most commonly used fluorescent label in super‐resolution microscopy, this derivative is created over time in an intramolecular, irreversible photoinduced chemical reaction. The dynamics of this reaction are altered by the presence of reducing agents. Importantly, the blue‐shifted derivatives emit in the spectral range of the red fluorescent proteins (e. g. PAmCherry and converted mEos3.2), severely implicating multicolor super‐resolution imaging.

Bulk Heterojunction Solar Cells: The Role of Alkyl Side Chain on Nanoscale Morphology of Sulfur Over-rich Regioregular Polythiophene/Fullerene Blends

E. Salatelli, M. Marinelli, M. Lanzi, A. Zanelli, S. Dell’Elce, A. Liscio, M. Gazzano, F. Di Maria

J. Phys. Chem. C, 2018, 122, 4156–4164. Link to article and accepted manuscript (open access).

Regioregular HH-TT poly(3,3′-thioalkylbithiophene)s-bearing branched or linear alkyl side-chain substituents (PT2SR) have been synthesized and characterized to investigate their behavior, when used as electron-donor components in blend with a fullerene derivative [[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)] as an electron acceptor, in air-processed photovoltaic solar cells with bulk heterojunction architecture. The optoelectronic characteristics, energy gap, nanoscale morphology, and crystallinity of the blends (PT2SR/PCBM) were examined by ultraviolet–visible spectroscopy, cyclic voltammetry, Kelvin probe force microscopy (KPFM), and X-ray diffraction (XRD). We demonstrate that thioalkyl substituents are able to influence the PCBM self-assembly and the morphology of the polymeric film, important parameters to maximize the efficiency of the solar cell. In particular, the presence of chemical branching in the side chain of the sulfur over-rich polythiophene backbone favors the formation of PCBM clusters, of size of about 100 ± 30 nm, as confirmed by XRD and KPFM measurements. This facilitates the intermixing between donor and acceptor materials at the nanoscale level, determining an increase in the device performance.

Graphene-Pyrene Nanocomposites Obtained Using Azide Chemistry

Z. Xia, R. Kabe, A. Liscio, A. Kovtun, E. Treossi, X. Feng, V. Palermo

J. Nanosci. Nanotechnol., 2018, 18, 1290–1295. Link to article.

In this study we describe a simple and fast procedure for the covalent functionalization of pristine graphene with a pyrene-terminated alkylazide, transformed in a highly reactive radical by thermal activation. The functionalized graphene sheets showed enhanced dispersibility in organic solvents compared to the pristine ones, thus enhancing their solution processability and compatibility with solvents or polymers. The relative improvement of solubility estimated from the absorption spectra was ≈60% in CHCl3 and ≈1200% in THF. The obtained materials were characterized by optical absorption spectroscopy, photoemission spectroscopy, infrared spectroscopy and X-rays photoelectron spectroscopy. The presence of the pyrene photoemitting chromophore in the grafting unit allowed to monitor the successful grafting and to confirm the effectiveness of the alkylazide to improve graphene solubility even when present in small amounts on the graphene surface.

Polystyrene nanoparticle-templated hollow titania nanosphere monolayers as ordered scaffolds

V. Robbiano, G. M. Paternò, G. F. Cotella, T. Fiore, M. Dianetti, M. Scopelliti, F. Brunetti, B. Pignataro, F. Cacialli

J. Mater. Chem. C, 2018, 6, 2502–2508. Link to article (open access).

We report a novel multi-step method for the preparation of ordered mesoporous titania scaffolds and show an illustrative example of their application to solar cells. The method is based on (monolayer) colloidal nanosphere lithography that makes use of polystyrene nanoparticles organised at a water–air interface and subsequently transferred onto a solid substrate. A titania precursor solution (titanium(IV) isopropoxide in ethanol) is then drop-cast onto the monolayer and left to “incubate” overnight. Surprisingly, instead of the expected inverse monolayer-structure, a subsequent calcination step of the precursor yields an ordered monolayer of hollow titania nanospheres with a wall thickness of ∼30–50 nm, and a slightly larger diameter than that of the starting spheres. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterization of such scaffolds confirm that they consist of nanocrystalline anatase titania, and that any polystyrene/carbon residues in the scaffolds are below the XPS detection level. As an illustrative application we prepared perovskite solar cells incorporating the templated-nanoparticle scaffolds displaying a respectable power conversion efficiency of ∼9%, twice as large as that of our unoptimized “reference” cells (i.e. incorporating conventional mesoporous or compact titania scaffolds), thereby also demonstrating that the process is relatively robust with respect to optimization of the process parameters.

Fluid Mixing for Low-Power ‘Digital Microfluidics’ Using Electroactive Molecular Monolayers

M. S. Maglione, S. Casalini, S. Georgakopoulos, M. Barbalinardo, V. Parkula, N. Crivillers, C. Rovira, P. Greco, M. Mas-Torrent

Small, 2018, 14, 1703344. Link to article and accepted manuscript (open access). ICMAB-CSIC press release.

A switchable electrode, which relies on an indium-tin oxide conductive substrate coated with a self-assembled monolayer terminated with an anthraquinone group (AQ), is reported as an electrowetting system. AQ electrochemical features confer the capability of yielding a significant modulation of surface wettability as high as 26° when its redox state is switched. Hence, an array of planar electrodes for droplets actuation is fabricated and integrated in a microfluidic device to perform mixing and dispensing on sub-nanoliter scale. Vehiculation of cells across microfluidic compartments is made possible by taking full advantage of surface electrowetting in culture medium.



Self-Assembly of Functionalized Oligothiophene into Hygroscopic Fibers: Fabrication of Highly Sensitive and Fast Humidity Sensors

M. A. Squillaci, A. Cipriani, M. Melucci, M. Zambianchi, G. Caminati, P. Samorì

Adv. Electron. Mater., 2018, 4, 1700382. Link to article and accepted manuscript (open access).

A new symmetric oligothiophene exposing tetraethylene glycol (TEG)‐based side‐chains is designed and synthesized. This molecule is found to self‐assemble in solution forming supramolecular fibers, via π–π stacking between the conjugated oligothiophene backbones, which are phase segregated on the sub‐nanometer scale from the TEG side‐groups. The delocalization of the charges through the oligothiophene π–π stack ensures efficient charge transport while the hygroscopic shell, decorating the surface of the fibrillar structures, determines a certain affinity for polar molecules. Upon exposure to humidity, under environmental conditions, such supramolecular architectures are capable of reversibly absorbing and desorbing water molecules. Absorption of water molecules, due to increased environmental humidity, causes a fast and reproducible increase of the electrical current through the fibers by a factor 100 from 15% to 90% relative humidity, as measured in 2‐terminal devices. Such process is extremely fast, taking place in less than 45 ms. The humidity‐responsive characteristics of the presented oligothiophene‐based fibers can be exploited for the facile fabrication of high‐performances and solution‐processable electrical resistive humidity sensors.

Light- and Temperature-Modulated Magneto-Transport in Organic–Inorganic Lead Halide Perovskites

M. Keshavarz, S. Wiedmann, H. Yuan, E. Debroye, M. Roeffaers, J. Hofkens

ACS Energy Lett., 2018, 3, 39–45. Link to article and accepted manuscript (open access).

The optoelectronic properties and charge carrier dynamics in hybrid organic–inorganic perovskites under steady-state illumination are the key elements for understanding their high efficiency. We present temperature-dependent Hall and photoconductivity measurements down to a temperature of 4.2 K on single crystals of MAPbI3 and MAPbBr3 in magnetic fields up to 30 T and observed different transport regimes. For temperatures down to 25 K, charge transport is dominated by acoustic phonon scattering as inferred from the temperature dependence of both zero and high-field resistance. Below 25 K, transport is determined by thermally activated hopping of charge carriers reflected in a diverging zero-field resistance and a strong decrease in the carrier’s mobility and concentration. Our findings demonstrate the importance of performing experiments at low temperature to unravel the fundamental charge carrier dynamics and stimulate the need for a comprehensive theoretical model for perovskite-based devices.

Fluorescence Commutation and Surface Photopatterning with Porphyrin Tetradithienylethene Switches

T. Biellmann, A. Galanti, J. Boixel, J. A. Wytko, V. Guerchais, P. Samorì, J. Weiss

Chem. Eur. J., 2018, 24, 1631–1639. Link to article and accepted manuscript (open access).

Four tetradithienylethene (DTE) substituted porphyrins, the free base 1H2, and three metal derivatives (1Zn, 1Co, 1Ni), were synthesized and studied. These dyads, for which the DTE units are connected to the porphyrin's meso positions via a meta-phenyl spacer, exhibit reversible photochromic properties in all cases, with conversion to the photostationary state (PSS) up to 88 %, as confirmed by absorption and NMR spectroscopies. Compounds 1H2 and 1Zn are fluorescent in solution and display a red emission. Upon irradiation with UV light to trigger the closing of the DTEs, the fluorescence of both the free base and zinc porphyrin was very efficiently quenched in solution. The reversible, photo-switching of luminescence was retained in a tetra-DTE free-base porphyrin-doped polystyrene film, for which photo-patterning was demonstrated by confocal scanning microscopy. The tunable fluorescent properties of this multi-DTE framework render this compound of interest as a photo-rewritable fluorescent ink.

Diels–Alder polymerization: a versatile synthetic method toward functional polyphenylenes, ladder polymers and graphene nanoribbons

I. C.-Y. Hou, Y. Hu, A. Narita, K. Müllen

Polym. J., 2018, 50, 3–20. Link to article and accepted manuscript (open access).

The Diels–Alder reaction has been widely used in synthetic organic chemistry since its discovery in 1928. The catalyst-free nature, functional group tolerance and high efficiency of the Diels–Alder reaction also make it promising for the fabrication of functional polymeric materials. In particular, a large variety of functional polyphenylenes (polymer structures mainly consisting of phenylenes) and ladder polymers (double-stranded polymers with periodic linkages connecting the strands) have been obtained by this method, offering potential applications such as polymer electrolyte membranes and gas separation. More recently, tailor-made polyphenylenes prepared by Diels–Alder polymerization have been used as precursors of structurally well-defined graphene nanoribbons (ribbon-shaped nanometer-wide graphene segments) with different widths, exhibiting long lengths (>600 nm) and tunable electronic bandgaps. This article provides a comprehensive review of the use of Diels–Alder polymerization to build functional polyphenylenes, ladder polymers and graphene nanoribbons.

Edge Functionalization of Structurally Defined Graphene Nanoribbons for Modulating the Self-Assembled Structures

A. Keerthi, B. Radha, D. Rizzo, H. Lu, V. Diez Cabanes, I. C.-Y. Hou, D. Beljonne, J. Cornil, C. Casiraghi, M. Baumgarten, K. Müllen, A. Narita

J. Am. Chem. Soc., 2017, 139, 16454–16457. Link to article (open access).

Edge functionalization of bottom-up synthesized graphene nanoribbons (GNRs) with anthraquinone and naphthalene/perylene monoimide units has been achieved through a Suzuki coupling of polyphenylene precursors bearing bromo groups, prior to the intramolecular oxidative cyclo-dehydrogenation. High efficiency of the substitution has been validated by MALDI-TOF MS analysis of the functionalized precursors and FT-IR, Raman, and XPS analyses of the resulting GNRs. Moreover, AFM measurements demonstrated the modulation of the self-assembling behavior of the edge-functionalized GNRs, revealing that GNR-PMI formed an intriguing rectangular network. This result suggests the possibility of programming the supramolecular architecture of GNRs by tuning the functional units.

Carbon-Rich Monolayers on ITO as Highly Sensitive Platforms for Detecting Polycyclic Aromatic Hydrocarbons in Water: The Case of Pyrene

J. Muñoz, N. Crivillers, M. Mas-Torrent

Chem. Eur. J., 2017, 23, 15289–15293. Link to article and accepted manuscript (open access). ICMAB-CSIC press release.

The determination of polycyclic aromatic hydrocarbons (PAHs) in water at low levels is a current challenge given their great impact on the health and safety of the public. Here, a novel pyrene-based self-assembled monolayer (SAM) platform is exploited as an electrochemical sensing recognition device. Interestingly, the formation of π–π sandwich complexes between PAHs and the recognition element switches the surface electron transfer capability. The unique supramolecular interaction between identical aromatic molecules provides a highly sensitive and selective sensor for pyrene in the order of part per trillion. Accordingly, and using pyrene as a proof-of-concept, this work presents the basis for an “at-point-of-use” impedimetric sensor focused on a highly sensitive carbon-rich SAM for PAHs determination in water at ultra-trace levels.


Light-Induced Contraction/Expansion of 1D Photoswitchable Metallopolymer Monitored at the Solid–Liquid Interface

M. El Garah, E. Borré, A. Ciesielski, A. Dianat, R. Gutierrez, G. Cuniberti, S. Bellemin-Laponnaz, M. Mauro, P. Samorì

Small, 2017, 13, 1701790. Link to article and accepted manuscript (open access).

The use of a bottom-up approach to the fabrication of nanopatterned functional surfaces, which are capable to respond to external stimuli, is of great current interest. Herein, the preparation of light-responsive, linear supramolecular metallopolymers constituted by the ideally infinite repetition of a ditopic ligand bearing an azoaryl moiety and Co(II) coordination nodes is described. The supramolecular polymerization process is followed by optical spectroscopy in dimethylformamide solution. Noteworthy, a submolecularly resolved scanning tunneling microscopy (STM) study of the in situ reversible trans-to-cis photoisomerization of a photoswitchable metallopolymer that self-assembles into 2D crystalline patterns onto a highly oriented pyrolytic graphite surface is achieved for the first time. The STM analysis of the nanopatterned surfaces is corroborated by modeling the physisorbed species onto a graphene slab before and after irradiation by means of density functional theory calculation. Significantly, switching of the monolayers consisting of supramolecular Co(II) metallopolymer bearing trans-azoaryl units to a novel pattern based on cis isomers can be triggered by UV light and reversed back to the trans conformer by using visible light, thereby restoring the trans-based supramolecular 2D packing. These findings represent a step forward toward the design and preparation of photoresponsive “smart” surfaces organized with an atomic precision.

Supramolecular Self-Assembly in a Sub-micrometer Electrodic Cavity: Fabrication of Heat-Reversible π-Gel Memristor

L. Zhang, S. Li, M. A. Squillaci, X. Zhong, Y. Yao, E. Orgiu, P. Samorì

J. Am. Chem. Soc., 2017, 139, 14406–14411. Link to article and accepted manuscript (open access). COVER PAGE. CNRS, CNRS Alsace, ISIS, LabEx CSC and SCF press releases.

The use of biomimetic approaches toward the production of nonsolid yet functional architectures holds potential for the emergence of novel device concepts. Gels, in particular those obtained via self-assembly of π-conjugated molecules, are dynamic materials possessing unique (opto)electronic properties. Their adaptive nature imparts unprecedented responsivity to various stimuli. Hitherto, a viable device platform to electrically probe in situ a sol–gel transition is still lacking. Here we describe the fabrication of a sub-micrometer electrodic cavity, which enables low-voltage electrical operation of π-gels. Thanks to the in situ supramolecular self-assembly of the π-gelator occurring within the cavity, we conceived a novel gel-based memristor whose sol–gel transition is reversible and can be controlled via heating and dc bias. This work opens perspectives toward the fabrication of a novel generation of nonsolid multiresponsive devices.

Tetrathiafulvalene–Polychlorotriphenylmethyl Dyads: Influence of Bridge and Open-Shell Characteristics on Linear and Nonlinear Optical Properties

M. Souto, J. Calbo, I. Ratera, E. Ortí, J. Veciana

Chem. Eur. J., 2017, 23, 11067–11075. Link to article and accepted manuscript (open access).

Three conjugated donor-π-acceptor radical systems (1 a1 c) were prepared by bridging a tetrathiafulvalene (TTF) electron-donor unit to a polychlorotriphenylmethyl (PTM) electron-acceptor radical through vinylene units of different lengths. The dependence of the intramolecular charge transfer on the length of the conjugated bridge has been analyzed by different electrochemical and spectroscopic techniques. Linear optical properties and the second-order nonlinear optical (NLO) response of these derivatives have been computed by comparing systems 1 a1 c with the non-radical analogues (2 a2 c). Interestingly, an enhanced NLO response is predicted for dyads 1 a1 c with PTM in the radical form and for compounds with longer vinylene bridges. Calculations confirm the active role the bridge plays for electronic communication between the donor TTF and the acceptor PTM units.

Reversible, Fast, and Wide-Range Oxygen Sensor Based on Nanostructured Organometal Halide Perovskite

M.-A. Stoeckel, M. Gobbi, S. Bonacchi, F. Liscio, L. Ferlauto, E. Orgiu, P. Samorì

Adv. Mater., 2017, 29, 1702469. Link to article and accepted manuscript (open access). COVER PAGE. CNRS, CNRS Alsace, ISIS, LabEx CSC and SCF press releases.

Nanostructured materials characterized by high surface–volume ratio hold the promise to constitute the active materials for next-generation sensors. Solution-processed hybrid organohalide perovskites, which have been extensively used in the last few years for optoelectronic applications, are characterized by a self-assembled nanostructured morphology, which makes them an ideal candidate for gas sensing. Hitherto, detailed studies of the dependence of their electrical characteristics on the environmental atmosphere have not been performed, and even the effect of a ubiquitous gas such as O2 has been widely overlooked. Here, the electrical response of organohalide perovskites to oxygen is studied. Surprisingly, a colossal increase (3000-fold) in the resistance of perovskite-based lateral devices is found when measured in a full oxygen atmosphere, which is ascribed to a trap healing mechanism originating from an O2-mediated iodine vacancies filling. A variation as small as 70 ppm in the oxygen concentration can be detected. The effect is fast (<400 ms) and fully reversible, making organohalide perovskites ideal active materials for oxygen sensing. The effect of oxygen on the electrical characteristics of organohalide perovskites must be taken into deep consideration for the design and optimization of any other perovskite-based (opto-) electronic device working in ambient conditions.

Asymmetric Injection in Organic Transistors via Direct SAM Functionalization of Source and Drain Electrodes

T. Mosciatti, P. Greco, T. Leydecker, M. Eredia, F. Biscarini, P. Samorì

ACS Omega20172, 3502–3508. Link to article (open access).

The fabrication of organic optoelectronic devices integrating asymmetric electrodes enables optimal charge injection/extraction at each individual metal/semiconductor interface. This is key for applications in devices such as solar cells, light-emitting transistors, photodetectors, inverters, and sensors. Here, we describe a new method for the asymmetric functionalization of gold electrodes with different thiolated molecules as a viable route to obtain two electrodes with drastically different work function values. The process involves an ad hoc design of electrode geometry and the use of a polymeric mask to protect one electrode during the first functionalization step. Photoelectron yield ambient spectroscopy and X-ray photoelectron spectrometry were used to characterize the energetic properties and the composition of the asymmetrically functionalized electrodes. Finally, we used poly(3-hexylthiophene)-based organic thin-film transistors to show that the asymmetric electronic response stems from the different electronic structures of the functionalized electrodes.

Photoswitchable Micro-Supercapacitor Based on a Diarylethene-Graphene Composite Film

Z. Liu, H. I. Wang, A. Narita, Q. Chen, Z. Mics, D. Turchinovich, M. Kläui, M. Bonn, K. Müllen

J. Am. Chem. Soc.2017139, 9443–9446. Link to article (open access).

Stimuli-responsive micro-supercapacitors (MSCs) controlled by external stimuli can enable a wide range of applications for future on-chip energy storage. Here, we report on a photoswitchable MSC based on a diarylethene-graphene composite film. The microdevice delivers an outstanding and reversible capacitance modulation of up to 20%, demonstrating a prototype photoswitchable MSC. Terahertz spectroscopy indicates that the photoswitching of the capacitance is enabled by the reversible tuning of interfacial charge injection into diarylethene molecular orbitals, as a consequence of charge transfer at the diarylethene–graphene interface upon light modulation.

Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities

J. Wudarczyk, G. V. Papamokos, T. Marszalek, T. Nevolianis, D. Schollmeyer, W. Pisula, G. Floudas, M. Baumgarten, K. Müllen

ACS Appl. Mater. Interfaces, 2017, 9, 20527–20535. Link to article and accepted manuscript (open access).

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor–acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (2D-WAXS), and thin films (GiWAXS). Combining these results, we found a switching of dielectric permittivity of the 4,7-alkylthienyl-substituted dicyanobenzothiadiazole at the transition from the liquid crystalline to the isotropic phase with values capable of competing with the best known rodlike liquid crystals. 

Graphene oxide doped polysulfone membrane adsorbers for the removal of organic contaminants from water

M. Zambianchi, M. Durso, A. Liscio, E. Treossi, C. Bettini, M. L. Capobianco, A. Aluigi, A. Kovtun, G. Ruani, F. Corticelli, M. Brucale, V. Palermo, M. L. Navacchia, M. Melucci

Chem. Eng. J., 2017, 326, 130–140. Link to article.

This work explored polysulfone (PS) – graphene oxide (GO) based porous membranes (PS-GO) as adsorber of seven selected organic contaminants of emerging concern (EOCs) including pharmaceuticals, personal care products, a dye and a surfactant from water. PS-GO was prepared by phase inversion method starting from a PS and GO mixture (5% w/w of GO). The porous PS-GO membranes showed asymmetric and highly porous micrometer sized pores on membrane top (diameter ≈20 μm) and bottom (diameter ≈2–5 μm) surfaces and tens of microns length finger like pores in the section. Nanomechanical mapping reveals patches of a stiffer material with Young modules comprised in the range 15–25 GPa, not present in PS pure membranes that are compatible with the presence of GO flakes on the membrane surfaces. PS-GO was immersed in EOCs spiked tap water and the adsorbance efficiency at different contact times and pH evaluated by HPLC analysis. Ofloxacin (OFLOX), benzophenone-3 (BP-3), rhodamine b (Rh), diclofenac (DCF) and triton X-100 (TRX) were removed with efficiency higher than 90% after 4 h treatments. Regeneration of PS-GO and reuse possibilities were demonstrated by washing with ethanol. The adsorption efficiencies toward OFLOX, Rh, DCF and carbamazepine (CBZ) were significantly higher than those of pure PS membrane. Moreover, PS-GO outperformed a commercial granular activated carbon (GAC) at low contact times and compared well at longer contact time for OFLOX, Rh, BP-3 and TRX suggesting the suitability of the newly introduced material for drinking water treatment.

High yield production of graphene-Fe2O3 nano-composites via electrochemical intercalation of nitromethane and iron chloride, and their application in lithium storage

Z. Y. Xia, C. Arbizzani, L. Ortolani, V. Morandi, V. Bellani, G. Giambastiani, M. Gazzano, V. Palermo

FlatChem, 2017, 3, 8–15. Link to article and accepted manuscript (open access).

We demonstrate a facile, scalable and tunable method to produce a composite material based on graphene multilayers and Fe2O3, combining the good conductivity and 2D layered structure of the former and the lithium storage capacity of the latter. The composite was obtained directly from bulk graphite, exploiting the fast electrochemical intercalation of tetrachloroferrate (III) anions (FeCl4) and nitromethane molecules between the graphene sheets. Then, irradiation with microwaves triggered the simultaneous exfoliation of graphite and its functionalization with Fe2O3 nanocrystals, produced by the thermal hydrolysis of the FeCl4. This process was monitored in real time using thermal gravimetry and mass spectrometry. X-rays diffraction, Raman spectroscopy, scanning electron and transmission microscopies confirmed the final structure of the composite formed by conductive 2D nanosheets coated by Fe2O3 crystals, featuring both high crystallinity and nanometric size. The composite could be used directly as an anode in Li-ion batteries, demonstrating the viability of this approach for high yield and scalable production of graphene/metal oxide composites.

Redox-Induced Gating of the Exchange Interactions in a Single Organic Diradical

R. Gaudenzi, J. de Bruijckere, D. Reta, I. d. P. R. Moreira, C. Rovira, J. Veciana, H. S. J. van der Zant, E. Burzurí

ACS Nano, 201711, 5879–5883. Link to article (open access).

Embedding a magnetic electroactive molecule in a three-terminal junction allows for the fast and local electric field control of magnetic properties desirable in spintronic devices and quantum gates. Here, we provide an example of this control through the reversible and stable charging of a single all-organic neutral diradical molecule. By means of inelastic electron tunnel spectroscopy we show that the added electron occupies a molecular orbital distinct from those containing the two radical electrons, forming a spin system with three antiferromagnetically coupled spins. Changing the redox state of the molecule therefore switches on and off a parallel exchange path between the two radical spins through the added electron. This electrically controlled gating of the intramolecular magnetic interactions constitutes an essential ingredient of a single-molecule quantum gate.

Synthesis of Dibenzo[hi,st]ovalene and Its Amplified Spontaneous Emission in a Polystyrene Matrix

G. M. Paternò, Q. Chen, X.-Y. Wang, J. Liu, S. G. Motti, A. Petrozza, X. Feng, G. Lanzani, K. Müllen, A. Narita, F. Scotognella

Angew. Chem. Int. Ed., 2017, 56, 6753–6757. Link to article and accepted manuscript (open access).

A large number of graphene molecules, or large polycyclic aromatic hydrocarbons (PAHs), have been synthesized and display various optoelectronic properties. Nevertheless, their potential for application in photonics has remained largely unexplored. Herein, we describe the synthesis of a highly luminescent and stable graphene molecule, namely a substituted dibenzo[hi,st]ovalene (DBO 1), with zigzag edges and elucidate its promising optical-gain properties by means of ultrafast transient absorption spectroscopy. Upon incorporation of DBO into an inert polystyrene matrix, amplified stimulated emission can be observed with a relatively low power threshold (ca. 60 μJ cm−2), thus highlighting its high potential for lasing applications.

“Supertrap” at Work: Extremely Efficient Nonradiative Recombination Channels in MAPbI3 Perovskites Revealed by Luminescence Super-Resolution Imaging and Spectroscopy

A. Merdasa, Y. Tian, R. Camacho, A. Dobrovolsky, E. Debroye, E. L. Unger, J. Hofkens, V. Sundström, I. G. Scheblykin

ACS Nano, 201711, 5391–5404. Link to article and accepted manuscript (open access).

Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI3) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI3 occurs by the activation/passivation of a “supertrap” which presumably is a donor–acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (1012–1015 cm–3), is much more efficient than via all other defect states present in the material at higher concentrations (1016–1018cm–3). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI3 crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.

Systematic study of the correlation between surface chemistry, conductivity and electrocatalytic properties of graphene oxide nanosheets

G. Maccaferri, C. Zanardi, Z. Y. Xia, A. Kovtun, A. Liscio, F. Terzi, V. Palermo, R. Seeber

Carbon, 2017, 120, 165–175. Link to article and accepted manuscript (open access).

A main advantage of graphene oxide (GO) over other materials is the high tunability of its surface functional groups and of its electric conductivity. However, the complex chemical composition of GO renders difficult to unravel the correlation between structural and electric properties. Here, we use a combination of electron spectroscopy and electrochemistry to correlate the surface chemistry of GO to its electrical conductivity and electrocatalytic properties with respect to two molecules of high biological interest: β-nicotinamide adenine dinucleotide (NADH) and vitamin C. We demonstrate that the electrocatalytic properties of the material are due to hydroxyl, carbonyl and carboxyl groups residues that, even if already present on pristine GO, become electroactive only upon GO reduction.

The results of this study demonstrate the advantages in the use of GO in amperometric biosensing and in enzymatic biofuel cells: it allows the oxidation of the target molecules at low potential values, with a sensitivity >15 times higher with respect to standard, carbon-based electrode materials.

Finally, we demonstrate that the right amount of chemical groups to achieve such high performance can be obtained also by direct electrochemical exfoliation of bulk graphite, without passing through GO production, thus rendering this approach suitable for cheap, large-scale applications.

Improving the electrical performance of solution processed oligothiophene thin-film transistors via structural similarity blending

T. Leydecker, L. Favaretto, D. T. Duong, G. Zappalà, K. Börjesson, A. Licciardello, A. Salleo, M. Melucci, E. Orgiu, P. Samorì

J. Mater. Chem. C, 2017, 5, 5048–5054. Link to article and accepted manuscript (open access).

Here we show that the blending of structurally similar oligothiophene molecules is an effective approach to improve the field-effect mobility and Ion/Ioff as compared to single component based transistors. The effect of addition of each component is studied extensively using a wide array of methods such as X-ray diffraction, ToF-SIMS, and ambient UPS correlated with the electrical characterization. 


Generation of Low-Dimensional Architectures through the Self-Assembly of Pyromellitic Diimide Derivatives

C. Musumeci, M. Wałęsa-Chorab, A. Gorczyński, G. Markiewicz, A. Bogucki, R. Świetlik, Z. Hnatejko, W. Jankowski, M. Hoffmann, E. Orgiu, A. R. Stefankiewicz, V. Patroniak, A. Ciesielski, P. Samorì

ACS Omega, 2017, 2, 1672–1678. Link to article (open access).

Small π-conjugated molecules can be designed and synthesized to undergo controlled self-assembly forming low-dimensional architectures, with programmed order at the supramolecular level. Such order is of paramount importance because it defines the property of the obtained material. Here, we have focused our attention to four pyromellitic diimide derivatives exposing different types of side chains. The joint effect of different noncovalent interactions including π–π stacking, H-bonding, and van der Waals forces on the four derivatives yielded different self-assembled architectures. Atomic force microscopy studies, corroborated with infrared and nuclear magnetic resonance spectroscopic measurements, provided complementary multiscale insight into these assemblies.

Photoisomerisation and light-induced morphological switching of a polyoxometalate–azobenzene hybrid

G. Markiewicz, D. Pakulski, A. Galanti, V. Patroniak, A. Ciesielski, A. R. Stefankiewicz, P. Samorì

Chem. Commun.201753, 7278–7281. Link to article and accepted manuscript (open access).

The functionalization of a spherical Keplerate-type polyoxometalate {Mo72V30} with a cationic azobenzene surfactant has been achieved through ionic self-assembly. The photoisomerisation reaction of this complex, which emerges in a light-triggered aggregation–disaggregation process, has been followed by 1H NMR spectroscopy, dynamic light scattering, absorption spectroscopy and scanning electron microscopy analyses.


Direct covalent grafting of an organic radical core on gold and silver

M. R. Ajayakumar, I. Alcón, S. T. Bromley, J. Veciana, C. Rovira, M. Mas-Torrent

RSC Adv., 2017, 7, 20076–20083. Link to article (open access).

The functionalisation of surfaces with organic radicals, such as perchlorotriphenylmethyl (PTM) radicals or tris(2,4,6-trichloro-phenyl)methyl (TTM) radicals, is appealing for the development of molecular spintronic devices. Conventionally, organic radicals are chemisorbed to metal substrates by using long alkyl or aromatic spacers resulting in a weak spin–electron coupling between the radical and the substrate. To circumvent this problem, here we have employed a new design strategy for the fabrication of radical self-assembled monolayers (r-SAMs). This newly designed radical–anchor (R–A) molecule, a TTM based radical disulfide (1), can be easily synthesized and it was here characterized by electron spin resonance (ESR), cyclic voltammetry (CV) and superconducting quantum interference device magnetometry (SQUID). We have succeeded in fabricating TTM based r-SAMs by using thiolate bonds (Au–S and Ag–S) where the TTM cores are only one-atom distance from the metal surface for the first time. The resultant robust 1/Au and 1/Ag r-SAMs were well characterized, and the electrochemical and the magnetic properties were unambiguously confirmed, proving the persistence of the molecular spin. 

Estimation of π–π Electronic Couplings from Current Measurements

J. Trasobares, J. Rech, T. Jonckheere, T. Martin, O. Aleveque, E. Levillain, V. Diez-Cabanes, Y. Olivier, J. Cornil, J. P. Nys, R. Sivakumarasamy, K. Smaali, P. Leclere, A. Fujiwara, D. Théron, D. Vuillaume, N. Clément

Nano Lett., 2017, 17, 3215–3224. Link to article and accepted manuscript (open access).

The π–π interactions between organic molecules are among the most important parameters for optimizing the transport and optical properties of organic transistors, light-emitting diodes, and (bio-) molecular devices. Despite substantial theoretical progress, direct experimental measurement of the π–π electronic coupling energy parameter t has remained an old challenge due to molecular structural variability and the large number of parameters that affect the charge transport. Here, we propose a study of π–π interactions from electrochemical and current measurements on a large array of ferrocene-thiolated gold nanocrystals. We confirm the theoretical prediction that t can be assessed from a statistical analysis of current histograms. The extracted value of t ≈35 meV is in the expected range based on our density functional theory analysis. Furthermore, the t distribution is not necessarily Gaussian and could be used as an ultrasensitive technique to assess intermolecular distance fluctuation at the subangström level. The present work establishes a direct bridge between quantum chemistry, electrochemistry, organic electronics, and mesoscopic physics, all of which were used to discuss results and perspectives in a quantitative manner.

Rheological and physical characterization of PEDOT:PSS/graphene oxide nanocomposites for perovskite solar cells

A. Giuri, S. Masi, S. Colella, A. Listorti, A. Rizzo, A. Kovtun, S. Dell’Elce, A. Liscio, C. E. Corcione

Polym. Eng. Sci., 2017, 57, 546–552. Link to article and accepted manuscript (open access).

In this work, the influence of graphene oxide (GO) doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin nanocomposite on an indium–tin-oxide (ITO) anode, as hole transport layer (HTL) in perovskite solar cells, was investigated. Different concentrations of GO were added into the PEDOT:PSS in order to enhance its conductivity. In particular, the influence of GO content on the rheological and thermal properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GO nanocomposites was initially examined. The GO filler was prepared by using modified Hummers method and dispersed into PEDOT:PSS in different quantity (ranging from 0.05 to 0.25%wt/wt). The obtained nanocomposite solutions were analyzed by rheological characterizations in order to evaluate the influence of the GO filler on the viscosity of the PEDOT:PSS matrix. The wettability of solutions was evaluated by Contact Angle (CA) measurements. The quality of GO dispersion into the polymer matrix was studied using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thermal characterizations (DSC and TGA) were, finally, applied on nanocomposite films in order to evaluate thermal stability of the films as well as to indirectly comprehend the GO influence on PEDOT:PSS-water links.

Tuning the Rectification Ratio by Changing the Electronic Nature (Open-Shell and Closed-Shell) in Donor–Acceptor Self-Assembled Monolayers

M. Souto, L. Yuan, D. C. Morales, L. Jiang, I. Ratera, C. A. Nijhuis, J. Veciana

J. Am. Chem. Soc., 2017, 139, 4262–4265. Link to article and accepted manuscript (open access). ICMAB-CSIC and NANOMOL press releases.

This Communication describes the mechanism of charge transport across self-assembled monolayers (SAMs) of two donor–acceptor systems consisting of a polychlorotriphenylmethyl (PTM) electron-acceptor moiety linked to an electron-donor ferrocene (Fc) unit supported by ultraflat template-stripped Au and contacted by a eutectic alloy of gallium and indium top contacts. The electronic and supramolecular structures of these SAMs were well characterized. The PTM unit can be switched between the nonradical and radical forms, which influences the rectification behavior of the junction. Junctions with nonradical units rectify currents via the highest occupied molecular orbital (HOMO) with a rectification ratio R = 99, but junctions with radical units have a new accessible state, a single-unoccupied molecular orbital (SUMO), which turns rectification off and drops R to 6.

Study of the EZ stilbene isomerisation in perchlorotriphenyl-methane (PTM) derivatives

F. Bejarano, I. Alcon, N. Crivillers, M. Mas-Torrent, S. T. Bromley, J. Veciana, C. Rovira

RSC Adv., 2017, 7, 15278–15283. Link to article (open access).

The EZ isomerisation of two perchlorotriphenylmethane derivatives containing stilbene units has been investigated, both thermally and photochemically. The irreversibility of the EZ isomerisation in both compounds is experimentally demonstrated and supported by density functional calculations.





Electronic Properties of Optically Switchable Photochromic Diarylethene Molecules at the Interface with Organic Semiconductors

Q. Wang, J. Frisch, M. Herder, S. Hecht, N. Koch

ChemPhysChem, 2017, 18, 722–727. Link to article and accepted manuscript (open access). COVER PAGE. Cover Profile. Selected as a Very Important Paper.

Light-switching-induced changes in the electronic properties of photochromic diarylethene, i.e., 1,2-bis(2-methyl-5-p-tolylthiophen-3-yl)cyclopent-1-ene (DAE1), thin films at interfaces to a gold electrode and two polymer semiconductors are investigated by direct and inverse photoelectron spectroscopy. The photoisomerization is achieved by in situ irradiation of ultraviolet and visible light. Efficient and reversible switching between the open and closed isomers of DAE1 is evidenced at all interfaces, with profound impact on the energy-level alignment. The frontier occupied level of DAE1 changes by 0.8 eV with respect to the Au Fermi level upon switching. Corresponding sizable changes in the electron and transport level offsets between the two polymers and DAE1 in its open and closed form are determined. This gives rise to fundamentally different functionality of these interfaces in terms of charge transport. Our study proves the viability of light-controlled energy-level manipulation at various interfaces in photoswitchable opto-electronic devices.

Poly(3-hexylthiophene) Nanoparticles Containing Thiophene-S,S-dioxide: Tuning of Dimensions, Optical and Redox Properties, and Charge Separation under Illumination

F. Di Maria, A. Zanelli, A. Liscio, A. Kovtun, E. Salatelli, R. Mazzaro, V. Morandi, G. Bergamini, A. Shaffer, S. Rozen

ACS Nano, 2017, 11, 1991–1999. Link to article and accepted manuscript (open access).

We describe the preparation of poly(3-hexylthiophene-S,S-dioxide) nanoparticles using Rozen’s reagent, HOF·CH3CN, either on poly(3-hexylthiophene) (P3HT) or on preformed P3HT nanoparticles (P3HT-NPs). In the latter case, core–shell nanoparticles (P3HT@PTDO-NPs) are formed, as confirmed by X-ray photoelectron spectroscopy measurements, indicating the presence of oxygen on the outer shell. The different preparation modalities lead to a fine-tuning of the chemical–physical properties of the nanoparticles. We show that absorption and photoluminescence features, electrochemical properties, size, and stability of colloidal solutions can be finely modulated by controlling the amount of oxygen present. Atomic force microscopy measurements on the nanoparticles obtained by a nanoprecipitation method from preoxidized P3HT (PTDO-NPs) display spherical morphology and dimensions down to 5 nm. Finally, Kelvin probe measurements show that the coexistence of p- and n-type charge carriers in all types of oxygenated nanoparticles makes them capable of generating and separating charge under illumination. Furthermore, in core–shell nanoparticles, the nanosegregation of the two materials, in different regions of the nanoparticles, allows a more efficient charge separation.

Evolution of the size and shape of 2D nanosheets during ultrasonic fragmentation

A. Liscio, K. Kouroupis-Agalou, X. Diez Betriu, A. Kovtun, E. Treossi, N. M. Pugno, G. De Luca, L. Giorgini, V. Palermo

2D Mater., 2017, 4, 025017. Link to article and accepted manuscript (open access). Highlighted in Advanced Science News.

2-dimensional (2D) nanosheets such as graphene, graphene oxide, boron nitride or transition metal dichalcogenides can be produced on a large scale by exfoliation techniques. The lateral shape of these 2D materials is typically considered random and irregular, and their average size is often estimated using techniques characterized by strong approximations or poor statistical significance. Here we measure in a quantitative, objective way the size and shape of 2D monoatomic nanosheets using a combination of optical, electronic and scanning probe techniques. We measure, one by one, the size and shape of thousands of sheets of graphene oxide as they undergo a standard ultrasonication treatment. Using automatic image processing and statistical modelling we identify two different fragmentation processes in 2D at the nanoscale, related to two populations of nanosheets described by gamma and exponential size distributions respectively. The two populations of sheets coexist during the fragmentation process, each one retaining its average size and shape. Our results explain the size reduction commonly observed in nanosheets upon sonication as an effect of changes in the respective weights of the two populations of nanosheets present in the material.

High, Anisotropic, and Substrate-Independent Mobility in Polymer Field-Effect Transistors Based on Preassembled Semiconducting Nanofibrils

S. Bonacchi, M. Gobbi, L. Ferlauto, M.-A. Stoeckel, F. Liscio, S. Milita, E. Orgiu, P. Samorì

ACS Nano, 2017, 11, 2000–2007. Link to article and accepted manuscript (open access). CNRS, CNRS Alsace, FRC and SCF press releases.

Achieving nanoscale control over the crystalline structure and morphology of electroactive polymer films and the possibility to transfer them onto any solid substrate are important tasks for the fabrication of high-performance organic/polymeric field-effect transistors (FETs). In this work, we demonstrate that ultrathin active layers preassembled at the water/air interface can possess high, anisotropic, and substrate-independent mobility in polymer FETs. By exploiting a modified approach to the Langmuir–Schaeffer technique, we self-assemble conjugated polymers in fibrillar structures possessing controlled thickness, nanoscale structure, and morphology; these highly ordered nanofibrils can be transferred unaltered onto any arbitrary substrate. We show that FETs based on these films possess high and anisotropic hole mobility approaching 1 cm2 V–1 s–1 along the nanofibrils, being over 1 order of magnitude beyond the state-of-the-art for Langmuir–Schaefer polymer FETs. Significantly, we demonstrate that the FET performances are independent of the chemical nature and dielectric permittivity of the substrate, overcoming a critical limit in the field of polymer FETs. Our method allows the fabrication of ultrathin films for low-cost, high-performance, transparent, and flexible devices supported on any dielectric substrate.

Fast-Response Photonic Device Based on Organic-Crystal Heterojunctions Assembled into a Vertical-Yet-Open Asymmetric Architecture

L. Zhang, E. Pavlica, X. Zhong, F. Liscio, S. Li, G. Bratina, E. Orgiu, P. Samorì

Adv. Mater., 2017, 29, 1605760. Link to article and accepted manuscript (open access).

Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis(triisopropylsilylethynyl) pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light.








A four-state capacitance molecular switch based on a redox active tetrathiafulvalene self-assembled monolayer

E. Marchante, M. S. Maglione, N. Crivillers, C. Rovira, M. Mas-Torrent

RSC Adv., 2017, 7, 5636–5641. Link to article (open access).

An electroactive tetrathiafulvalene (TTF) self-assembled monolayer (SAM) on gold has been prepared and fully characterised by electrochemical impedance spectroscopy. Transfer rates of the same order were found for the two redox processes. Remarkably, the TTF SAM was successfully exploited as a 4-state electrochemical switch using the capacitance of the SAM as output signal.




Light-Controlled Reversible Modulation of Frontier Molecular Orbital Energy Levels in Trifluoromethylated Diarylethenes

M. Herder, F. Eisenreich, A. Bonasera, A. Grafl, L. Grubert, M. Pätzel, J. Schwarz, S. Hecht

Chem. Eur. J., 2017, 23, 3743–3754. Link to article and accepted manuscript (open access). Selected as a Hot Paper.

Among bistable photochromic molecules, diarylethenes (DAEs) possess the distinct feature that upon photoisomerization they undergo a large modulation of their π-electronic system, accompanied by a marked shift of the HOMO/LUMO energies and hence oxidation/reduction potentials. The electronic modulation can be utilized to remote-control charge- as well as energy-transfer processes and it can be transduced to functional entities adjacent to the DAE core, thereby regulating their properties. In order to exploit such photoswitchable systems it is important to precisely adjust the absolute position of their HOMO and LUMO levels and to maximize the extent of the photoinduced shifts of these energy levels. Here, we present a comprehensive study detailing how variation of the substitution pattern of DAE compounds, in particular using strongly electron-accepting and chemically stable trifluoromethyl groups either in the periphery or at the reactive carbon atoms, allows for the precise tuning of frontier molecular orbital levels over a broad energy range and the generation of photoinduced shifts of more than 1 eV. Furthermore, the effect of different DAE architectures on the transduction of these shifts to an adjacent functional group is discussed. Whereas substitution in the periphery of the DAE motif has only minor implications on the photochemistry, trifluoromethylation at the reactive carbon atoms strongly disturbs the isomerization efficiency. However, this can be overcome by using a nonsymmetrical substitution pattern or by combination with donor groups, rendering the resulting photoswitches attractive candidates for the construction of remote-controlled functional systems.

Facile Morphology-Controlled Synthesis of Organolead Iodide Perovskite Nanocrystals Using Binary Capping Agents

E. Debroye, H. Yuan, E. Bladt, W. Baekelant, M. Van der Auweraer, J. Hofkens, S. Bals, M. B. J. Roeffaers

ChemNanoMat, 2017, 3, 223–227. Link to article (open access).

Controlling the morphology of organolead halide perovskite crystals is crucial to a fundamental understanding of the materials and to tune their properties for device applications. Here, we report a facile solution-based method for morphology-controlled synthesis of rod-like and plate-like organolead halide perovskite nanocrystals using binary capping agents. The morphology control is likely due to an interplay between surface binding kinetics of the two capping agents at different crystal facets. By high-resolution scanning transmission electron microscopy, we show that the obtained nanocrystals are monocrystalline. Moreover, long photoluminescence decay times of the nanocrystals indicate long charge diffusion lengths and low trap/defect densities. Our results pave the way for large-scale solution synthesis of organolead halide perovskite nanocrystals with controlled morphology for future device applications.



Light-Activated Sensitive Probes for Amine Detection

V. Valderrey, A. Bonasera, S. Fredrich, S. Hecht

Angew. Chem. Int. Ed.2017, 56, 1914–1918. Link to article and accepted manuscript (open access).

Our new, simple, and accurate colorimetric method is based on diarylethenes (DAEs) for the rapid detection of a wide range of primary and secondary amines. The probes consist of aldehyde- or ketone-substituted diarylethenes, which undergo an amine-induced decoloration reaction, selectively to give the ring-closed isomer. Thus, these probes can be activated at the desired moment by light irradiation, with a sensitivity that allows the detection of amines at concentrations as low as 10−6 M in solution. In addition, the practical immobilization of DAEs on paper makes it possible to detect biogenic amines, such as cadaverine, in the gas phase above a threshold of 12 ppbv within 30 seconds.


Covalent Modification of Highly Ordered Pyrolytic Graphite with a Stable Organic Free Radical by Using Diazonium Chemistry

G. Seber, A. V. Rudnev, A. Droghetti, I. Rungger, J. Veciana, M. Mas-Torrent, C. Rovira, N. Crivillers

Chem. Eur. J., 201723, 1415–1421. Link to article and accepted manuscript (open access). ICMAB-CSIC press release.

A novel, persistent, electrochemically active perchlorinated triphenylmethyl (PTM) radical with a diazonium functionality has been covalently attached to highly ordered pyrolytic graphite (HOPG) by electrografting in a single-step process. Electrochemical scanning tunneling microscopy (EC-STM) and Raman spectroscopy measurements revealed that PTM molecules had a higher tendency to covalently react at the HOPG step edges. The cross-section profiles from EC-STM images showed that there was current enhancement at the functionalized areas, which could be explained by redox-mediated electron tunneling through surface-confined redox-active molecules. Cyclic voltammetry clearly demonstrated that the intrinsic properties of the organic radical were preserved upon grafting and DFT calculations also revealed that the magnetic character of the PTM radical was preserved.

TTF–PTM dyads: from switched molecular self assembly in solution to radical conductors in solid state

M. Souto, C. Rovira, I. Ratera, J. Veciana

CrystEngComm, 2017, 19, 197–206. Link to article and accepted manuscript (open access). COVER PAGEICMAB-CSIC and NANOMOL press releases.

Organic donor–acceptor (D–A) systems formed by the electron-donor tetrathiafulvalene (TTF) linked to the electron-acceptor perchlorotriphenylmethyl (PTM) radical through different π-conjugated bridges exhibit interesting physical properties such as bistability in solution or conductivity in solid state. Understanding the interplay between intra- and intermolecular charge transfer processes in solution is of high interest in order to rationalize the self-assembling ability and conducting properties of such dyads in solid state. In this Highlight we examine the self-assembling properties of different TTF–π–PTM radical dyads that have potential applications as molecular switches or conductors in the field of molecular electronics.

Field-Controlled Charge Separation in a Conductive Matrix at the Single-Molecule Level: Toward Controlling Single-Molecule Fluorescence Intermittency

K. Kennes, P. Dedecker, J. A. Hutchison, E. Fron, H. Uji-i, J. Hofkens, M. Van der Auweraer

ACS Omega, 2016, 1, 1383–1392. Link to article (open access).

The fluorescence intermittency or “blinking” of single molecules of ATTO647N (ATTO) in the conductive matrix polyvinylcarbazole (PVK) is described in the presence of an external applied electric field. It is shown that due to the energy distribution of the highest occupied molecular orbital (HOMO) level of PVK, which is energetically close to the HOMO of ATTO, sporadic electron transfer occurs. As a result, the on/off dynamics of blinking can be influenced by the electric field. This field will, depending on the respective position and orientation of the dye/polymer system with respect to those of the electrodes, either enhance or suppress electron transfer from PVK to ATTO as well as the back electron transfer from reduced ATTO to PVK. After the charge-transfer step, the applied field will pull the hole in PVK away from the dye, increasing the overall time the dye resides in a dark state.

Synthesis and Characterization of Ethylenedithio-MPTTF-PTM Radical Dyad as a Potential Neutral Radical Conductor

M. Souto, D. Bendixen, M. Jensen, V. Díez-Cabanes, J. Cornil, J. O. Jeppesen, I. Ratera, C. Rovira, J. Veciana

Magnetochemistry, 2016, 2, 46. Link to article (open access).

During the last years there has been a high interest in the development of new purely-organic single-component conductors. Very recently, we have reported a new neutral radical conductor based on the perchlorotriphenylmethyl (PTM) radical moiety linked to a monopyrrolo-tetrathiafulvalene (MPTTF) unit by a π-conjugated bridge (1) that behaves as a semiconductor under high pressure. With the aim of developing a new material with improved conducting properties, we have designed and synthesized the radical dyad 2 which was functionalized with an ethylenedithio (EDT) group in order to improve the intermolecular interactions of the tetrathiafulvalene (TTF) subunits. The physical properties of the new radical dyad 2 were studied in detail in solution to further analyze its electronic structure.

Understanding the Influence of the Electronic Structure on the Crystal Structure of a TTF-PTM Radical Dyad

S. Vela, M. Souto, I. Ratera, C. Rovira, J. Veciana

J. Phys. Chem. A, 2016120, 10297–10303. Link to article and accepted manuscript (open access).

The understanding of the crystal structure of organic compounds, and its relationship to their physical properties, have become essential to design new advanced molecular materials. In this context, we present a computational study devoted to rationalize the different crystal packing displayed by two closely related organic systems based on the TTF-PTM dyad (TTF = tetrathiafulvalene, PTM = polychlorotriphenylmethane) with almost the same molecular structure but a different electronic one. The radical species (1), with an enhanced electronic donor–acceptor character, exhibits a herringbone packing, whereas the nonradical protonated analogue (2) is organized forming dimers. The stability of the possible polymorphs is analyzed in terms of the cohesion energy of the unit cell, intermolecular interactions between pairs, and molecular flexibility of the dyad molecules. It is observed that the higher electron delocalization in radical compound 1 has a direct influence on the geometry of the molecule, which seems to dictate its preferential crystal structure.

Modifying the Size of Ultrasound-Induced Liquid-Phase Exfoliated Graphene: from Nanosheets to Nanodots

A. Ciesielski, S. Haar, A. Aliprandi, M. El Garah, G. Tregnago, G. F. Cotella, M. El Gemayel, F. Richard, H. Sun, F. Cacialli, F. Bonaccorso, P. Samorì

ACS Nano, 201610, 10768–10777. Link to article and accepted manuscript (open access).

Ultrasound-induced liquid-phase exfoliation (UILPE) is an established method to produce single- (SLG) and few-layer (FLG) graphene nanosheets starting from graphite as a precursor. In this paper we investigate the effect of the ultrasonication power in the UILPE process carried out in either N-methyl-2-pyrrolidone (NMP) or ortho-dichlorobenzene (o-DCB). Our experimental results reveal that while the SLGs/FLGs concentration of the NMP dispersions is independent of the power of the ultrasonic bath during the UILPE process, in o-DCB it decreases as the ultrasonication power increases. Moreover, the ultrasonication power has a strong influence on the lateral size of the exfoliated SLGs/FLGs nanosheets in o-DCB. In particular, when UILPE is carried out at ∼600 W, we obtain dispersions composed of graphene nanosheets with a lateral size of 180 nm, whereas at higher power (∼1000 W) we produce graphene nanodots (GNDs) with an average diameter of ∼17 nm. The latter nanostructures exhibit a strong and almost excitation-independent photoluminescence emission in the UV/deep-blue region of the electromagnetic spectrum arising from the GNDs’ intrinsic states and a less intense (and strongly excitation wavelength dependent) emission in the green/red region attributed to defect states. Notably, we also observe visible emission with near-infrared excitation at 850 and 900 nm, a fingerprint of the presence of up-conversion processes. Overall, our results highlight the crucial importance of the solvent choice for the UILPE process, which under controlled experimental conditions allows the fine-tuning of the morphological properties, such as lateral size and thickness, of the graphene nanosheets toward the realization of luminescent GNDs.

A redox-active radical as an effective nanoelectronic component: stability and electrochemical tunnelling spectroscopy in ionic liquids

A. V. Rudnev, C. Franco, N. Crivillers, G. Seber, A. Droghetti, I. Rungger, I. V. Pobelov, J. Veciana, M. Mas-Torrent, C. Rovira

Phys. Chem. Chem. Phys., 2016, 18, 27733–27737. Link to article (open access).

A redox-active persistent perchlorotriphenylmethyl (PTM) radical chemically linked to gold exhibits stable electrochemical activity in ionic liquids. Electrochemical tunnelling spectroscopy in this medium demonstrates that the PTM radical shows a highly effective redox-mediated current enhancement, demonstrating its applicability as an active nanometer-scale electronic component.



Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface Traps

H. Yuan, E. Debroye, G. Caliandro, K. P. F. Janssen, J. van Loon, C. E. A. Kirschhock, J. A. Martens, J. Hofkens, M. B. J. Roeffaers

ACS Omega, 2016, 1, 148–159. Link to article (open access).

Photoluminescence (PL) of organometal halide perovskite materials reflects the charge dynamics inside of the material and thus contains important information for understanding the electro-optical properties of the material. Interpretation of PL blinking of methylammonium lead iodide (MAPbI3) nanostructures observed on polycrystalline samples remains puzzling owing to their intrinsic disordered nature. Here, we report a novel method for the synthesis of high-quality single-crystal MAPbI3 nanorods and demonstrate a single-crystal study on MAPbI3 PL blinking. At low excitation power densities, two-state blinking was found on individual nanorods with dimensions of several hundred nanometers. A super-resolution localization study on the blinking of individual nanorods showed that single crystals of several hundred nanometers emit and blink as a whole, without showing changes in the localization center over the crystal. Moreover, both the blinking ON and OFF times showed power-law distributions, indicating trapping–detrapping processes. This is further supported by the PL decay times of the individual nanorods, which were found to correlate with the ON/OFF states. Furthermore, a strong environmental dependence of the nanorod PL blinking was revealed by comparing the measurements in vacuum, nitrogen, and air, implying that traps locate close to crystal surfaces. We explain our observations by proposing surface charge traps that are likely related to under-coordinated lead ions and methylammonium vacancies to result in the PL blinking observed here.

Chemical control over the energy-level alignment in a two-terminal junction

L. Yuan, C. Franco, N. Crivillers, M. Mas-Torrent, L. Cao, C. S. S. Sangeeth, C. Rovira, J. Veciana, C. A. Nijhuis

Nat. Commun., 20167, 12066. Link to article (open access). ICMAB-CSIC and NANOMOL press releases.

The energy-level alignment of molecular transistors can be controlled by external gating to move molecular orbitals with respect to the Fermi levels of the source and drain electrodes. Two-terminal molecular tunnelling junctions, however, lack a gate electrode and suffer from Fermi-level pinning, making it difficult to control the energy-level alignment of the system. Here we report an enhancement of 2 orders of magnitude of the tunnelling current in a two-terminal junction via chemical molecular orbital control, changing chemically the molecular component between a stable radical and its non-radical form without altering the supramolecular structure of the junction. Our findings demonstrate that the energy-level alignment in self-assembled monolayer-based junctions can be regulated by purely chemical modifications, which seems an attractive alternative to control the electrical properties of two-terminal junctions.



Hexa-peri-hexabenzocoronene with Different Acceptor Units for Tuning Optoelectronic Properties

A. Keerthi, I. C.-Y. Hou, T. Marszalek, W. Pisula, M. Baumgarten, A. Narita

Chem. Asian J., 2016, 11, 2710–2714. Link to article and accepted manuscript (open access).

Hexa-peri-hexabenzocoronene (HBC)-based donor–acceptor dyads were synthesized with three different acceptor units, through two pathways: 1) “pre-functionalization” of monobromo-substituted hexaphenylbenzene prior to the cyclodehydrogenation; and 2) “post-functionalization” of monobromo-substituted HBC after the cyclodehydrogenation. The HBC–acceptor dyads demonstrated varying degrees of intramolecular charge-transfer interactions, depending on the attached acceptor units, which allowed tuning of their photophysical and optoelectronic properties, including the energy gaps. The two synthetic pathways described here can be complementary and potentially be applied for the synthesis of nanographene–acceptor dyads with larger aromatic cores, including one-dimensionally extended graphene nanoribbons.

A nanomesh scaffold for supramolecular nanowire optoelectronic devices

L. Zhang, X. Zhong, E. Pavlica, S. Li, A. Klekachev, G. Bratina, T. W. Ebbesen, E. Orgiu, P. Samorì

Nat. Nanotechnol., 2016, 11, 900–906. Link to article and accepted manuscript (open access). CNRS, CNRS Alsace, SCF, ISISFRC, LabEx CSCChemistryViews and IEEE Spectrum press releases. Highlighted in Nature NanotechnologyScience, L’Actualité Chimique and CNRS Alsace Activity Report 2016.

Supramolecular organic nanowires are ideal nanostructures for optoelectronics because they exhibit both efficient exciton generation as a result of their high absorption coefficient and remarkable light sensitivity due to the low number of grain boundaries and high surface-to-volume ratio. To harvest photocurrent directly from supramolecular nanowires it is necessary to wire them up with nanoelectrodes that possess different work functions. However, devising strategies that can connect multiple nanowires at the same time has been challenging. Here, we report a general approach to simultaneously integrate hundreds of supramolecular nanowires of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) in a hexagonal nanomesh scaffold with asymmetric nanoelectrodes. Optimized PTCDI-C8 nanowire photovoltaic devices exhibit a signal-to-noise ratio approaching 107, a photoresponse time as fast as 10 ns and an external quantum efficiency >55%. This nanomesh scaffold can also be used to investigate the fundamental mechanism of photoelectrical conversion in other low-dimensional semiconducting nanostructures.

Flexible non-volatile optical memory thin-film transistor device with over 256 distinct levels based on an organic bicomponent blend

T. Leydecker, M. Herder, E. Pavlica, G. Bratina, S. Hecht, E. Orgiu, P. Samorì

Nat. Nanotechnol., 2016, 11, 769–775. Link to article and accepted manuscript (open access). CNRS, CNRS Alsace, SCFISIS, FRCIRIS AdlershofNanowerkResearch in GermanyChemistryViewsIEEE Spectrum and press releases. Highlighted in Le FigaroNature Photonics, C&EN, CNRS Activity Report 2016 (available in English and French) and CNRS Alsace Activity Report 2016.

Organic nanomaterials are attracting a great deal of interest for use in flexible electronic applications such as logic circuits, displays and solar cells. These technologies have already demonstrated good performances, but flexible organic memories are yet to deliver on all their promise in terms of volatility, operational voltage, write/erase speed, as well as the number of distinct attainable levels. Here, we report a multilevel non-volatile flexible optical memory thin-film transistor based on a blend of a reference polymer semiconductor, namely poly(3-hexylthiophene), and a photochromic diarylethene, switched with ultraviolet and green light irradiation. A three-terminal device featuring over 256 (8 bit storage) distinct current levels was fabricated, the memory states of which could be switched with 3 ns laser pulses. We also report robustness over 70 write–erase cycles and non-volatility exceeding 500 days. The device was implemented on a flexible polyethylene terephthalate substrate, validating the concept for integration into wearable electronics and smart nanodevices.

Electrochemical Functionalization of Graphene at the Nanoscale with Self-Assembling Diazonium Salts

Z. Xia, F. Leonardi, M. Gobbi, Y. Liu, V. Bellani, A. Liscio, A. Kovtun, R. Li, X. Feng, E. Orgiu, P. Samorì, E. Treossi, V. Palermo

ACS Nano, 201610, 7125–7134. Link to article and accepted manuscript (open access).

We describe a fast and versatile method to functionalize high-quality graphene with organic molecules by exploiting the synergistic effect of supramolecular and covalent chemistry. With this goal, we designed and synthesized molecules comprising a long aliphatic chain and an aryl diazonium salt. Thanks to the long chain, these molecules physisorb from solution onto CVD graphene or bulk graphite, self-assembling in an ordered monolayer. The sample is successively transferred into an aqueous electrolyte, to block any reorganization or desorption of the monolayer. An electrochemical impulse is used to transform the diazonium group into a radical capable of grafting covalently to the substrate and transforming the physisorption into a covalent chemisorption. During covalent grafting in water, the molecules retain the ordered packing formed upon self-assembly. Our two-step approach is characterized by the independent control over the processes of immobilization of molecules on the substrate and their covalent tethering, enabling fast (t < 10 s) covalent functionalization of graphene. This strategy is highly versatile and works with many carbon-based materials including graphene deposited on silicon, plastic, and quartz as well as highly oriented pyrolytic graphite.

Pressure-Induced Conductivity in a Neutral Nonplanar Spin-Localized Radical

M. Souto, H. Cui, M. Peña-Álvarez, V. G. Baonza, H. O. Jeschke, M. Tomic, R. Valentí, D. Blasi, I. Ratera, C. Rovira, J. Veciana

J. Am. Chem. Soc., 2016, 138, 11517–11525. Link to article and accepted manuscript (open access). ICMAB-CSIC and NANOMOL press releases.

There is a growing interest in the development of single-component molecular conductors based on neutral organic radicals that are mainly formed by delocalized planar radicals, such as phenalenyl or thiazolyl radicals. However, there are no examples of systems based on nonplanar and spin-localized C-centered radicals exhibiting electrical conductivity due to their large Coulomb energy (U) repulsion and narrow electronic bandwidth (W) that give rise to a Mott insulator behavior. Here we present a new type of nonplanar neutral radical conductor attained by linking a tetrathiafulvalene (TTF) donor unit to a neutral polychlorotriphenylmethyl radical (PTM) with the important feature that the TTF unit enhances the overlap between the radical molecules as a consequence of short intermolecular S···S interactions. This system becomes semiconducting upon the application of high pressure thanks to increased electronic bandwidth and charge reorganization opening the way to develop a new family of neutral radical conductors.

Tuning the energetics and tailoring the optical properties of silver clusters confined in zeolites

O. Fenwick, E. Coutiño-Gonzalez, D. Grandjean, W. Baekelant, F. Richard, S. Bonacchi, D. De Vos, P. Lievens, M. Roeffaers, J. Hofkens, P. Samorì

Nat. Mater., 2016, 15, 1017–1022. Link to article and accepted manuscript (open access). CNRS, CNRS Alsace, SCFISIS, FRCQMUL, Phys.orgNANOR&DECN, AlphaGalileo, EurekAlert!NanowerkScienceDailyMaterials Today, KU Leuven, ECNEurekAlert!, NanowerkScienceDaily, Electronics WeeklyAzoOptics, EC and Madri+d press releases. Highlighted in Nature Materials.

The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal–host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the clusters optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure–property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging.

Light-Modulation of the Charge Injection in a Polymer Thin-Film Transistor by Functionalizing the Electrodes with Bistable Photochromic Self-Assembled Monolayers

T. Mosciatti, M. G. del Rosso, M. Herder, J. Frisch, N. Koch, S. Hecht, E. Orgiu, P. Samorì

Adv. Mater., 201628, 6606–6611. Link to article and accepted manuscript (open access).

High fatigue resistance, bistability, and drastic property changes among isomers allow efficient modulation of the current output of organic thin-film transistors (OTFTs) to be obtained by a photogating of the charge-injection mechanism.

Direct Patterning of Organic Functional Polymers through Conventional Photolithography and Noninvasive Cross-Link Agents

M. A. Squillaci, F. Qiu, A. Aliprandi, F. Zhang, X. Feng, P. Samorì

Adv. Mater., 2016, 28, 5249–5254. Link to article and accepted manuscript (open access).

A new technique for direct patterning of functional organic polymers using commercial photolithography setups with a minimal loss of the materials' performances is reported. This result is achieved through novel cross-link agents made by boron- and fluorine-containing heterocycles that can react between themselves upon UV- and white-light exposure.








Design, synthesis, chemical stability, packing, cyclic voltammetry, ionisation potential, and charge transport of [1]benzothieno[3,2-b][1]benzothiophene derivatives

C. Ruzié, J. Karpinska, A. Laurent, L. Sanguinet, S. Hunter, T. D. Anthopoulos, V. Lemaur, J. Cornil, A. R. Kennedy, O. Fenwick, P. Samorì, G. Schweicher, B. Chattopadhyay, Y. H. Geerts

J. Mater. Chem. C, 2016, 4, 4863–4879. Link to article and accepted manuscript (open access). Selected as a Hot Paper.

Five new molecular semiconductors that differ from dioctylbenzothienobenzothiophene, by the introduction of ether or thioether side chains, have been synthesized and obtained in good yields. Their availability in sufficient quantities has allowed investigation of their electrochemical behaviour in solution and their electronic properties in solid state. Both ether and thioether compounds oxidise rather easily in solution, but nevertheless, they exhibit rather high ionisation potentials. This is a consequence of their crystal structure. Dioctylthioetherbenzothienobenzothiophene is rather sensitive to oxidation and degrades easily in close to ambient conditions. Dioctyletherbenzothienobenzothiophene is more stable. Its charge carrier mobility remains however rather moderate, on the order of 0.5 cm2 V−1 s−1, whereas that of dioctylbenzothienobenzothiophene reached 4 cm2 V−1 s−1, in the same conditions. The difference is explained by intrinsic factors as shown by a theoretical modelling. 

A surface confined yttrium(III) bis-phthalocyaninato complex: a colourful switch controlled by electrons

I. Alcón, M. Gonidec, M. R. Ajayakumar, M. Mas-Torrent, J. Veciana

Chem. Sci., 20167, 4940–4944. Link to article (open access). ICMAB-CSIC press release.

SAMs of a Y(III) double-decker complex on ITO have been prepared and their electrical and optical properties explored, exhibiting three accessible stable redox states with characteristic absorption bands in the visible spectra, corresponding to three complementary colors (i.e., green, blue and red). These absorption bands are exploited as output signals of this robust ternary electrochemical switch, behaving hence as an electrochromic molecular-based device.

Donor/Acceptor Mixed Self-Assembled Monolayers for Realising a Multi-Redox-State Surface

J. Casado-Montenegro, E. Marchante, N. Crivillers, C. Rovira, M. Mas-Torrent

ChemPhysChem, 2016, 17, 1810–1814. Link to article and accepted manuscript (open access).

Mixed molecular self-assembled monolayers (SAMs) on gold, based on two types of electroactive molecules, that is, electron-donor (ferrocene) and electron-acceptor (anthraquinone) molecules, are prepared as an approach to realise surfaces exhibiting multiple accessible redox states. The SAMs are investigated in different electrolyte media. The nature of these media has a strong impact on the types of redox processes that take place and on the redox potentials. Under optimised conditions, surfaces with three redox states are achieved. Such states are accessible in a relatively narrow potential window in which the SAMs on gold are stable. This communication elucidates the key challenges in fabricating bicomponent SAMs as electrochemical switches.

Coupling carbon nanomaterials with photochromic molecules for the generation of optically responsive materials

X. Zhang, L. Hou, P. Samorì

Nat. Commun., 2016, 7, 11118. Link to article (open access). CNRSCNRS Alsace, SCFFRC and LabEx CSC press releases. Highlighted in the CNRS Alsace Activity Report 2016.

Multifunctional carbon-based nanomaterials offer routes towards the realization of smart and high-performing (opto)electronic (nano)devices, sensors and logic gates. Meanwhile photochromic molecules exhibit reversible transformation between two forms, induced by the absorption of electromagnetic radiation. By combining carbon-based nanomaterials with photochromic molecules, one can achieve reversible changes in geometrical structure, electronic properties and nanoscale mechanics triggering by light. This thus enables a reversible modulation of numerous physical and chemical properties of the carbon-based nanomaterials towards the fabrication of cognitive devices. This review examines the state of the art with respect to these responsive materials, and seeks to identify future directions for investigation.




High-Performance Phototransistors Based on PDIF-CN2 Solution-Processed Single Fiber and Multifiber Assembly

W. Rekab, M.-A. Stoeckel, M. El Gemayel, M. Gobbi, E. Orgiu, P. Samorì

ACS Appl. Mater. Interfaces, 20168, 9829–9838. Link to article and accepted manuscript (open access).

Here we describe the fabrication of organic phototransistors based on either single or multifibers integrated in three-terminal devices. These self-assembled fibers have been produced by solvent-induced precipitation of an air stable and solution-processable perylene di-imide derivative, i.e., PDIF-CN2. The optoelectronic properties of these devices were compared to devices incorporating more disordered spin-coated PDIF-CN2 thin-films. The single-fiber devices revealed significantly higher field-effect mobilities, compared to multifiber and thin-films, exceeding 2 cm2 V–1 s–1. Such an efficient charge transport is the result of strong intermolecular coupling between closely packed PDIF-CN2 molecules and of a low density of structural defects. The improved crystallinity allows efficient collection of photogenerated Frenkel excitons, which results in the highest reported responsivity (R) for single-fiber PDI-based phototransistors, and photosensitivity (P) exceeding 2 × 103 AW–1, and 5 × 103, respectively. These findings provide unambiguous evidence for the key role played by the high degree of order at the supramolecular level to leverage the material’s properties toward the fabrication of light-sensitive organic field-effect transistors combining a good operational stability, high responsivity and photosensitivity. Our results show also that the air-stability performances are superior in devices where highly crystalline supramolecularly engineered architectures serve as the active layer.

Adding Four Extra K-Regions to Hexa-peri-hexabenzocoronene

T. Dumslaff, B. Yang, A. Maghsoumi, G. Velpula, K. S. Mali, C. Castiglioni, S. De Feyter, M. Tommasini, A. Narita, X. Feng, K. Müllen

J. Am. Chem. Soc., 2016138, 4726–4729. Link to article and accepted manuscript (open access).

A multistep synthesis of hexa-peri-hexabenzocoronene (HBC) with four additional K-regions was developed through a precursor based on two benzotetraphene units bridged with p-phenylene, featuring preinstalled zigzag moieties. Characterization by laser desorption/ionization time-of-flight mass spectrometry, Raman and IR spectroscopy, and scanning tunneling microscopy unambiguously validated the successful formation of this novel zigzag edge-rich HBC derivative. STM imaging of its monolayers revealed large-area, defect-free adlayers. The optical properties of the modified HBC were investigated by UV/visible absorption spectroscopy.

Optical Input/Electrical Output Memory Elements based on a Liquid Crystalline Azobenzene Polymer

T. Mosciatti, S. Bonacchi, M. Gobbi, L. Ferlauto, F. Liscio, L. Giorgini, E. Orgiu, P. Samorì

ACS Appl. Mater. Interfaces, 20168, 6563–6569. Link to article and accepted manuscript (open access).

Responsive polymer materials can change their properties when subjected to external stimuli. In this work, thin films of thermotropic poly(metha)acrylate/azobenzene polymers are explored as active layer in light-programmable, electrically readable memories. The memory effect is based on the reversible modifications of the film morphology induced by the photoisomerization of azobenzene mesogenic groups. When the film is in the liquid crystalline phase, the transcis isomerization induces a major surface reorganization on the mesoscopic scale that is characterized by a reduction in the effective thickness of the film. The film conductivity is measured in vertical two-terminal devices in which the polymer is sandwiched between a Au contact and a liquid compliant E-GaIn drop. We demonstrate that the transcis isomerization is accompanied by a reversible 100-fold change in the film conductance. In this way, the device can be set in a high- or low-resistance state by light irradiation at different wavelengths. This result paves the way toward the potential use of poly(metha)acrylate/azobenzene polymer films as active layer for optical input/electrical output memory elements.

Exchange Coupling Inversion in a High-Spin Organic Triradical Molecule

R. Gaudenzi, E. Burzurí, D. Reta, I. de P. R. Moreira, S. T. Bromley, C. Rovira, J. Veciana, H. S. J. van der Zant

Nano Lett., 2016, 16, 2066–2071. Link to article and accepted manuscript (open access). ICMAB-CSIC and NANOMOL press releases.

The magnetic properties of a nanoscale system are inextricably linked to its local environment. In adatoms on surfaces and inorganic layered structures, the exchange interactions result from the relative lattice positions, layer thicknesses, and other environmental parameters. Here, we report on a sample-dependent sign inversion of the magnetic exchange coupling between the three unpaired spins of an organic triradical molecule embedded in a three-terminal device. This ferro-to-antiferromagnetic transition is due to structural distortions and results in a high-to-low spin ground-state change in a molecule traditionally considered to be a robust high-spin quartet. Moreover, the flexibility of the molecule yields an in situ electric tunability of the exchange coupling via the gate electrode. These findings open a route to the controlled reversal of the magnetic states in organic molecule-based nanodevices by mechanical means, electrical gating, or chemical tailoring.

Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration

H. Yuan, E. Debroye, K. Janssen, H. Naiki, C. Steuwe, G. Lu, M. Moris, E. Orgiu, H. Uji-i, F. De Schryver, P. Samorì, J. Hofkens, M. Roeffaers

J. Phys. Chem. Lett., 2016, 7, 561–566. Link to article (open access).

Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degradation pathways. Here, we apply simultaneous luminescence and electron microscopy on perovskites for the first time, allowing us to monitor in situ morphology evolution and optical properties upon perovskite degradation. Interestingly, morphology, photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degradation driven by electron beam (e-beam) or by light. A transversal electric current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degradation results in material decomposition to scattered particles and shows little PL spectral shifts. The differences in degradation can be ascribed to different electric currents that drive ion migration. Moreover, solution-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphology. Our results reveal the essential role of ion migration in perovskite degradation and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphology and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degradation and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using scanning electron microscopy or transmission electron microscopy techniques.

Influence of the supramolecular order on the electrical properties of 1D coordination polymers based materials

C. Musumeci, S. Osella, L. Ferlauto, D. Niedzialek, L. Grisanti, S. Bonacchi, A. Jouaiti, S. Milita, A. Ciesielski, D. Beljonne, M. W. Hosseini, P. Samorì

Nanoscale, 2016, 8, 2386–2394. Link to article and accepted manuscript (open access).

The generation, under self-assembly conditions, of coordination polymers on surface based combinations of a terpyridine–antracene–pyridine based tecton and Co(II) or Pd(II) cations is primarily governed by the coordination geometry of the metal center (octahedral and square planar respectively). While the octahedral Co(II) based polymer self-assembles in insulating films exhibiting randomly oriented crystalline domains, the planarity of Pd(II) based polymers leads to the formation of conductive π–π stacked fibrillar structures exhibiting anisotropically oriented domains. In the latter case, the favorable Pd–Pd and anthracene–anthracene wavefunction overlaps along the fiber direction are responsible for the large electronic couplings between adjacent chains, whereas small electronic couplings are instead found along individual polymer chains. These results provide important guidelines for the design of conductive metal coordination polymers, highlighting the fundamental role of both intra- as well as inter-chain interactions, thus opening up new perspectives towards their application in functional devices.

Switching Diarylethenes Reliably in Both Directions with Visible Light

S. Fredrich, R. Göstl, M. Herder, L. Grubert, S. Hecht

Angew. Chem. Int. Ed., 201655, 1208–1212. Link to article and accepted manuscript (open access). Selected as a Hot Paper.

A diarylethene photoswitch was covalently connected to two small triplet sensitizer moieties in a conjugated and nonconjugated fashion and the photochromic performance of the resulting compounds was investigated. In comparison with the parent diarylethene (without sensitizers) and one featuring saturated linkages, the conjugated photoswitch offers superior fatigue resistance upon visible-light excitation due to effective triplet energy transfer from the biacetyl termini to the diarylethene core. Our design makes it possible to switch diarylethenes with visible light in both directions in a highly efficient and robust fashion based on extending π-conjugation and by-product-free ring-closure via the triplet manifold.

An Electrically Driven and Readable Molecular Monolayer Switch Based on a Solid Electrolyte

E. Marchante, N. Crivillers, M. Buhl, J. Veciana, M. Mas-Torrent

Angew. Chem. Int. Ed., 2016, 55, 368–372. Link to article and accepted manuscript (open access). Selected as a Hot Paper.

The potential application of molecular switches as active elements in information storage has been demonstrated through numerous works. Importantly, such switching capabilities have also been reported for self-assembled monolayers (SAMs). SAMs of electroactive molecules have recently been exploited as electrochemical switches. Typically, the state of these switches could be read out through their optical and/or magnetic response. These output reading processes are difficult to integrate into devices, and furthermore, there is a need to use liquid environments for switching the redox-active molecular systems. In this work, both of these challenges were overcome by using an ionic gel as the electrolyte medium, which led to an unprecedented solid-state device based on a single molecular layer. Moreover, electrochemical impedance has been successfully exploited as the output of the system.

Au nanoparticle scaffolds modulating intermolecular interactions among the conjugated azobenzenes chemisorbed on curved surfaces: tuning the kinetics of cistrans isomerisation

C. Raimondo, B. Kenens, F. Reinders, M. Mayor, H. Uji-i, P. Samorì

Nanoscale, 2015, 7, 13836–13839. Link to article (open access).

π–π Intermolecular interactions among adjacent conjugated azobenzenes chemisorbed on (non-)flat Au surfaces can be tuned by varying the curvature of the Au nanoparticles. Here we show that such interactions rule the thermal cistrans isomerization kinetics, towards a better control on the azobenzene bistability for its optimal integration as a responsive material.

Self-Assembly of an Amphiphilic π-Conjugated Dyad into Fibers: Ultrafast and Ultrasensitive Humidity Sensor

M. A. Squillaci, L. Ferlauto, Y. Zagranyarski, S. Milita, K. Müllen, P. Samorì

Adv. Mater., 2015, 27, 3170–3174. Link to article and accepted manuscript (open access). COVER PAGE. CNRSCNRS Alsace, SCFFRCLabEx CSC and Conectus Alsace press releases.

The self-assembly of an amphiphilic monomolecular electron acceptor–donor dyad into electroactive π–π stacked fibrillar structures can be triggered by irradiation with visible light. These fibers, exposing hydrophilic ethylene glycol in their external shell, show unique characteristics as resistive humidity sensors that exhibit high sensitivity and ultrafast response.








Optically switchable transistors comprising a hybrid photochromic molecule/n-type organic active layer

K. Börjesson, M. Herder, L. Grubert, D. T. Duong, A. Salleo, S. Hecht, E. Orgiu, P. Samorì

J. Mater. Chem. C20153, 4156–4161. Link to article (open access).

Organic semiconductors can be easily combined with other molecular building blocks in order to fabricate multifunctional devices, in which each component conveys a specific (opto)electronic function. We have fabricated photoswitchable hybrid thin-film transistors based on an active bi-component material, consisting of an n-type fullerene derivative and a photochromic diarylethene that possesses light-tunable energy levels. The devices can be gated in two independent ways by either using an electrical stimulus via the application of a voltage to the gate electrode or an optical stimulus causing interconversion of the diarylethene molecules between their two isomers. Fine control over the device output current is achieved by engineering the diarylethenes' LUMO that can act as an intra-gap state controlled by a distinct wavelength in the UV or in the visible range. Importantly, the devices based on a mixed diarylethene/fullerene active layer preserve the high mobility of the pristine semiconductor.

Modulating the charge injection in organic field-effect transistors: fluorinated oligophenyl self-assembled monolayers for high work function electrodes

O. Fenwick, C. Van Dyck, K. Murugavel, D. Cornil, F. Reinders, S. Haar, M. Mayor, J. Cornil, P. Samorì

J. Mater. Chem. C, 20153, 3007–3015. Link to article (open access). COVER PAGE. Selected as a Hot Paper.

The rapid increase in charge carrier mobility in organic field-effect transistors (OFETs) in the past few years, with a number of reports >10 cm2 V−1 s−1, calls for a simultaneous improvement in charge injection at the electrode–semiconductor interface. Chemical modification of the electrodes with self-assembled monolayers (SAMs) allows the optimization of three key properties for lowering the contact resistance, thus fine-tuning the charge injection into OFET channels: the electrode work function, the surface energy of the modified electrodes and tunnelling resistance of the SAM. Understanding of the interplay of these properties is of vital importance for organic device design. In this paper, we report a model study based on the modulation of all three of these properties via chemisorption of fluorinated mono- or biphenylthiol molecules (PFBT and PF2BT, respectively) onto gold electrodes. Density functional theory simulations confirm the higher work function of the PFBT monolayers compared to PF2BT and provide evidence that this work function difference is entirely due to differences in the bond dipole to the gold surface. This observation is of importance for the development of future SAM molecules both for organic electronics and across the field of surface chemistry. Incorporation of these SAM-modified Au surfaces as the source and drain electrodes of an OFET with prototypical polymer semiconductors exhibiting different transport levels makes it possible to unravel the role of energetic alignment as well as surface energy and tunnelling resistance on the device performance. Interestingly, our results show that it is not always the high work function PFBT-modified electrodes that give the lowest contact resistance.