Marta Mas-Torrent

Novel small molecules for organic field-effect transistors: towards processability and high performance

The processing characteristics of organic semiconductors make them potentially useful for electronic applications where low-cost, large area coverage and structural flexibility are required. This critical review gives a general introduction about the current standing in the area of OFETs focusing on the new processable small molecules that have been recently reported for their use as organic semiconductors. A general description of the OFETs device operation and the transport mechanisms that dominate organic semiconductors is provided, followed by an overview of the strategies and materials employed to fabricate p-type, n-type and ambipolar OFETs. Some new tendencies and applications that are currently being developed employing OFETs are also described, such as the preparation of electronic paper, sensors or light emitting transistors (85 references).

Role of molecular order and solid-state structure in organic field-effect transistors.

3.2. Intermolecular Interactions 4840 3.3. Single-Crystal OFETs 4841 3.3.1. Fabrication 4841 3.3.2. Crystal Anisotropy 4842 3.3.3. Patterning of Single Crystals 4843 3.4. Correlation of Crystal Structure with Mobility in TTF Derivatives 4843 4. Polymorphism 4844 4.1. Pentacene and Related Acenes 4845 4.2. Oligothiophenes 4847 4.3. Tetrathiafulvalenes 4849 5. Influence of the Interfaces 4850 5.1. Organic Semiconductor/Dielectric Interface 4850 5.2. Organic Semiconductor/Metal Interface 4852 6. Summary 4852 Author Information 4852 Biographies 4852 Acknowledgment 4853 References 4853

A robust molecular platform for non-volatile memory devices with optical and magnetic responses

Bistable molecules that behave as switches in solution have long been known. Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of memory devices when immobilized in substrates. Here, we report a highly robust surface-confined switch based on an electroactive, persistent organic radical immobilized on indium tin oxide substrates that can be electrochemically and reversibly converted to the anion form. This molecular bistable system behaves as an extremely robust redox switch in which an electrical input is transduced into optical as well as magnetic outputs under ambient conditions. The fact that this molecular surface switch, operating at very low voltages, can be patterned and addressed locally, and also has exceptionally high long-term stability and excellent reversibility and reproducibility, makes it a very promising platform for non-volatile memory devices.

Tetrathiafulvalene derivatives for organic field effect transistors

Great interest in organic field-effect transistors (OFETs) has emerged in the last years due to their potential applications. Here we highlight the very recent use of tetrathiafulvalene derivatives for fabricating OFETs either from vacuum deposition or from solution. These materials are extremely promising owing to their facile processability and high device performance.

High‐Performance Single Crystal Organic Field‐Effect Transistors Based on Two Dithiophene‐Tetrathiafulvalene (DT‐TTF) Polymorphs

Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the -phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules.

Attaching Persistent Organic Free Radicals to Surfaces: How and Why

Attaching Persistent Organic Free Radicals to Surfaces: How and Why Marta Mas-Torrent,* N uria Crivillers, Concepci o Rovira, and Jaume Veciana* Institut de Ci encia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), ICMAB-CSIC, 08193 Bellaterra, Spain ISIS CNRS 7006, Universit e de Strasbourg, 8 all ee Gaspard Monge, 67000 Strasbourg, France

A Three-State Surface-Confined Molecular Switch with Multiple Channel Outputs

A self-assembled monolayer of a tetrathiafulvalene derivative on indium tin oxide is shown to operate as a ternary redox switch in which the magnetic and optical outputs are employed to provide a readout of the state. This surface-confined molecular switch exhibits excellent reversibility and stability and is thus promising for the development of molecular electronics.

Field effect transistors based on poly(3-hexylthiophene) at different length scales

In this paper we report on thin film transistors based on drop casting solutions of regioregular poly(3-hexylthiophene) (P3HT) over prefabricated gold electrodes. This polymer is known to self-organize into a lamellar structure in chloroform resulting in high field-effect mobilities. We studied the dependency of the charge carrier mobility of devices prepared from solution in chloroform with electrode spacings ranging from 5 µm to 20 nm. It was found that the overall trend was that the mobility decreased as the electrode spacing was made smaller, indicating that the transport properties on closely spaced electrodes were dominated by the contacts. Applying an ac voltage during the preparation of such films resulted in lower mobilities. However, P3HT in p-xylene forms fibres, which were aligned between the electrodes by applying an ac field. Films of aligned fibres with mobilities as high as 0.04 cm2 V−1 s−1 were prepared.

Organic radicals on surfaces: towards molecular spintronics

The novel and exciting field of molecular spintronics has recently attracted a great deal of interest and promising results have already been reported. The utilisation of organic radicals that could favour spin polarisation and conservation during transport offers new possibilities; however, first a fundamental investigation of these materials, especially those deposited on surfaces, is required. Here we highlight our recent results regarding the functionalisation of surfaces with polychlorotriphenylmethyl (PTM) radicals following five different strategies in which interactions of different nature are involved (i.e. van der Waals, electrostatic, coordination bond and covalent bond). In all cases, it was proved that the magnetic character of the molecule persists on the surface.

Self-assembled monolayers of electroactive polychlorotriphenylmethyl radicals on Au(111).

Two new polychlorotriphenylmethyl (PTM) derivatives bearing a thioacetate and a disulfide group have been synthesized to anchor on gold substrate. On the basis of these molecules, three strategies were followed to prepare self-assembled monolayers (SAMs) of electroactive PTMs. The resulting SAMs were fully characterized by contact angle, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The high coverage surface and stability of the SAMs were demonstrated by cyclic voltammetry. In addition, the electrochemical experiments proved that these SAMs are bistable since it is possible to reversibly switch between the PTM radical state to the corresponding anion. The magnetic response was investigated by electron paramagnetic resonance. We observed that when the PTM SAMs are in their radical form they confer magnetic functionality to the surface, whereas when they are in the anionic state, the surface is diamagnetic. Thus, the PTM-modified substrates are multifunctional surfaces since they combine magnetic and electroactive properties. The reported results show the high potential of these materials for the fabrication of surface molecular devices.