Electroactive organic polymers are not only attractive from the viewpoint of their solid-state propertiesÐlike electrical conduction or electrochromism [1] Ðbut also as promising candidates in molecular electronics, [2] including as switches for information storage, an area dominated by smaller molecules.[3±5] While photochemically induced switching in polymers has received much attention, [6] other external stimuli like thermal treatment, [7] chemical or redox interactions, [8] and their combination to make multifunctional polymers [9] are also attractive. Motivated by this promise, one of our objectives is the preparation of chiral redox-polymer systems.[10]Tetrathiafulvalene (TTF) derivatives are good candidates as components of these polymers because of their reversible and tunable redox properties. [11,12] They show two reversible one-electron oxidation processes to form the cation radical and the dication. As a scaffold for these units we chose the poly(isocyanide)s, [13] which can assume chiral conformations and organize electroactive groups. [8,12,14] This manuscript describes a chiral TTF-substituted poly(isocyanide) [15] that shows reversible interconversion between three univalent and two very broad mixed-valence redox states ( Fig. 1) that have different chiroptical properties, behavior that is not shown by the monomer. The TTF derivative, 2 (Scheme 1), bearing a phenyl isocyanide group and two stereogenic centers to induce diastereoselectivity in the polymerization, acts as our monomer. Long alkyl chains are present to ensure the solubility of the resulting polymer. The synthesis of 2 was performed following a multistep synthetic route, [16] the last step of which is the conversion of the formamide 1 to the isocyanide 2 by dehydration with diphosgene. Treatment of 2 with NiCl 2´6 H 2 O as a catalyst in CH 2 Cl 2 gave poly(isocyanide) 3 in 85 % yield (Scheme 1). The conversion of the monomer into the polymer was confirmed analytically.The IR spectrum of 3 showed a broad band from the imine groups attached to the polymer backbone at approximately 1642 cm ±1 and no signal corresponding to the isocyanide moi-
This tutorial review discusses different techniques for the preparation and deposition on surfaces of organic nanostructures -monolayers, nanowires, nano-dots and other aggregates -with emphasis on the key role that chemical design and non-covalent interactions (between molecules themselves and molecules and surface) play in the definition of the final structure and its properties. The characterisation of the nanostructures and the important effects of postdeposition treatment are also touched upon. The tetrathiafulvalene (TTF) unit is used as the example to demonstrate the general principles that are applicable for these different nanoscale architectures, because of the interest of this family of compounds in molecular electronics.
The self-assembly of a series of tetrathiafulvalene (TTF) derivatives at the interface between non-volatile organic solutions and the graphite surface has been studied by scanning tunnelling microscopy (STM). The TTFs have been prepared such that they bear none, one, two (in different constitutions) or four alkyl chains of different lengths and different functional groups. The STM images reveal that the packing of the TTF cores can effectively be controlled by changing the substitution pattern on the heterocycle. Several structures are seen at the interphase-parquettype packing, single and double core tapes, and even isolated molecules-all of which have the TTF core essentially coplanar with the surface. Molecular modelling has shown that several orientations of the molecules are practically equal in energy on the graphite, which explains the polymorphous packing of some of the molecules. Solvent effects also play a role in determining the 2D structures.
We report on the preparation of high performance field-effect transistors (FETs) based on large areas of aligned films of a TTF derivative, namely, tetrakis-(octadecylthio)-tetrathiafulvalene (TTF-4SC18). TTF-4SC18 assembles into one-dimensional stacks in which the long alkyl chains promote intermolecular π−π overlapping due to their extremely closely packed nature. The films were prepared from solution by zone-casting, a simple technique that does not require the use of preoriented substrates. The films were characterized by AFM and X-ray, indicating an extremely high crystalline quality. The TTF molecules are tilted with respect to the substrate surface and are well-aligned in the casting direction. More than 40 FETs were measured, showing a remarkable reproducibility of their performance. The average charge carrier mobility value measured along the casting direction was about 0.006 cm2/V s for a channel length L = 100 μm and about 0.01 cm2/V s for L = 80 μm and L = 50 μm. The FET mobilities determined in the direction perpendicular to the orientation were ca. 1 order of magnitude lower. We found that all the devices after annealing exhibited an enhanced performance with FETs mobilities about 1 order of magnitude higher. The best devices revealed a charge carrier mobility close to 0.1 cm2/V s with an on/off ratio of the order of 104.
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