Electrònica molecular. De la molècula al dispositiu

En aquest article s'analitzen les característiques estructurals i electròniques de les molècules orgàniques que generen materials amb propietats electròniques amb un especial èmfasi en el disseny del material i la metodologia per a la seva preparació. Es presenta com des de la molècula es crea el material electrònic i com aquest s'utilitza per preparar dispositius posant com a exemple els transistors d'efecte camp i els sensors de pressió i temperatura.The electronic and structural characteristics of organic molecules that generate materials with conducting properties will be analyzed, emphasizing especially the design of the material and the methodology for its preparation. We will review the way to create the material from the molecule and how the material can be used to prepare devices, particularly field effect transistors and pressure and temperature sensors

Tuning crystal ordering, electronic structure, and morphology in organic semiconductors: Tetrathiafulvalenes as a model case

Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF-derivatives are ideal candidates to perform molecule-property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state-of-the-art of the field-effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure-performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p-channel, n-channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source-drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications. Tetrathiafulvalenes are promising active materials in organic field-effect transistors (OFETs), in which they exhibit high performances. An overview is provided of the use of this family of materials as a model building block for OFETs to highlight general concepts of organic semiconductors and their use in devices.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with projects BE-WELL CTQ2013-40480-R and MAT2012-30924, and the Generalitat de Catalunya (2014-SGR-17, 2014SGR97 and XRQTC).Peer Reviewe

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF-derivatives are ideal candidates to perform molecule-property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state-of-the-art of the field-effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure-performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p-channel, n-channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source-drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications

Deposition of composite materials using a wire-bar coater for achieving processability and air-stability in Organic Field-Effect Transistors (OFETs)

Organic thin films based on composite materials of semiconducting dibenzo-tetrathiafulvalene (DB-TTF) and insulating styrenic matrices (Polystyrene (PS10k) and Poly-alpha methylstyrene (PAMS10k) ) have been fabricated by the wire-bar coating technique in ambient conditions (air, light, humidity) and contrasted with the ones prepared by thermally evaporating the organic semiconductor. The transistors fabricated with DB-TTF:PS10k composites show a clear fieldeffect behavior with p-type characteristics, exhibiting charge carriers mobilities in the range of 0.01 cm2/Vs, fully comparable with the films obtained by thermal evaporation. However, while the thermally evaporated films show poor stability in air, the wire-bar coated composites films and devices are highly reproducible and exhibit lower threshold voltage values. Thus, we demonstrate the suitability of the wire-bar technique for manufacturing large area devices.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with project BE-WELL CTQ2013-40480-R, and the Generalitat de Catalunya (2014-SGR-17). F. G. D. P. thanks Universidad Técnica de Ambato and Secretaría de Educación Superior, Ciencia, Tecnología e Innovación for funding through a doctoral scholarship “Convocatoria abierta 2010”.Peer Reviewe

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

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

Single Crystal-Like Performance in Solution-Coated Thin-Film Organic Field-Effect Transistors

In electronics, the fi eld-effect transistor (FET) is a crucial cornerstone and successful integration of this semiconductor device into circuit applications requires stable and ideal electrical characteristics over a wide range of temperatures and environments. Solution processing, using printing or coating techniques, has been explored to manufacture organic fi eld-effect transistors (OFET) on fl exible carriers, enabling radically novel electronics applications. Ideal electrical characteristics, in organic materials, are typically only found in single crystals. Tiresome growth and manipulation of these hamper practical production of fl exible OFETs circuits. To date, neither devices nor any circuits, based on solution-processed OFETs, has exhibited an ideal set of characteristics similar or better than today’s FET technology based on amorphous silicon. Here, bar-assisted meniscus shearing of dibenzo-tetrathiafulvalene to coat-process self-organized crystalline organic semiconducting domains with high reproducibility is reported. Including these coatings as the channel in OFETs, electric fi eld and temperature-independent charge carrier mobility and no bias stress effects are observed. Furthermore, record-high gain in OFET inverters and exceptional operational stability in both air and water are measured.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), the DGI (Spain) project BE-WELL CTQ2013-40480-R, and the Generalitat de Catalunya (2014-SGR- 17). Research in Sweden was fi nancially supported by the Advanced Functional Materials Center at Linköping University, the Önnesjö Foundation, the Knut and Alice Wallenberg Foundation (Power Paper project, scholars), the Swedish Foundation for Strategic Research (SSF, Synergi project). F.G.D.P. thanks Universidad Técnica de Ambato and Secretaría de Educación Superior, Ciencia, Tecnología e Innovación for funding through a doctoral scholarship “Convocatoria abierta 2010.” The authors also thank Witold Tatkiewicz for his help with the ImageJ software.Peer reviewe

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

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.This work was supported by the DGI grant (CTQ2013- 40480-R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), the EU ITN iSwitch 642196, the NANO2FUN Project No. 607721 and the Generalitat de Catalunya (grant 2014-SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015-0496). S.V. is thankful to the LabEx-Chemistry of Complex Systems for a post-doctoral grant (ANR-10-LABX-0026CSC) and to the regional High-Performance Computing (HPC) center in Strasbourg for computational resources. M.S. is enrolled in the Material Science Ph.D. program of UAB and is grateful to MEC for a FPU predoctoral grant.Peer reviewe

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

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 monopyrrolotetrathiafulvalene (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.This work was supported by the EU ITN iSwitch 642196 and “Nano2Fun” 607721 DGI grant (BeWell; CTQ2013-40480-R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), and the Generalitat de Catalunya (grant 2014-SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496). In Denmark, this work was supported by the Danish Council for Independent Research | Natural Sciences (#11-106744). M.S. is grateful to Spanish Ministerio de Educación, Cultura y Deporte for a FPU grant. We thank Vega Lloveras for ESR spectroscopy and Amable Bernabé for MALDI spectroscopy.Peer reviewe

DT-TTF Salts with [Cu(dcdmp)2]−: The Richness of Different Stoichiometries

(DT-TTF)[Cu(dcdmp)(2)] (1), (DT-TTF)(2)[Cu(dcdmp)(2)] (2), and (DT-TTF)(3)[Cu(dcdmp)(2)](2) (3) are three new charge transfer salts obtained by electrocrystallization of the donor DT-TTF (dithiophene-tetrathiafulvalene) with the diamagnetic copper complex [Cu(dcdmp)(2)](-) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 3 crystallize in the triclinic system and consist of out-of-registry layers of mixed stacks of donor and acceptor molecules. (DT-TTF)(2)[Cu(dcdmp)(2)] presents a structure similar to the parent spin-ladder systems with donor stacks arranged in pairs; however, a magnetic spin-ladder behavior is not observed probably due to strong interactions between pairs. Compound 3, despite the mixed nature of the stacks, displays relatively high conductivity (7 S/cm) due to a one-dimensional network of interactions between donors.This work was supported by FCT (Portugal) through contracts PTDC/QEQ-SUP/1413/2012 and UID/Multi/04349/2013 and by DGI, Spain (CTQ2013-40480), the Generalitat de Catalunya (2014SGR0017), the CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), promoted by ISCIII, Spain. R. A. L. S. is thankful to FCT for the PhD grant SFRH/BD/86131/2012.Peer reviewe