A series of thiophene oligomers bearing core phenylene and fluorinated phenylene units has been
synthesized as potential semiconductor materials for organic field-effect transistors (OFETs). Polymerization of these compounds has been achieved using Stille and oxidative coupling methods. Functionalization of the phenylene unit with fluorine atoms has a marked effect on the self-assembly and electronic
properties of the parent materials: the optical band gaps and highest occupied molecular orbital levels
are affected with the introduction of fluorine atoms as a result of a combination of inductive effects and
rigidification of the main chain. The design of these materials has focused on the self-assembly and
solution processability of the materials. All the polymers are readily soluble in common organic solvents.
Self-assembly and planarization of the fluorinated materials in the solid state are identified by a combination
of X-ray diffraction studies, absorption spectroscopy, and cyclic voltammetry. The organizational behavior
of the films is in contrast to the conformational freedom observed in solution (absorption spectroscopy)
and in the gas phase (computational studies). Thin-film OFETs have been fabricated for the entire polymer
series. Hole mobilities have been measured up to 10-3 cm2/(V·s), with high current modulation (on/off
ratios up to 105) and low turn-on voltages (down to 2 V). For the Stille coupled polymers, replacement
of the bridging thiophene unit with selenophene generally increases the hole mobility of the polymers.
A novel polythienylenevinylene (PTV) and two new polythiophenes (PTs), featuring fused tetrathiafulvalene (TTF) units, have been prepared and characterized by ultraviolet-visible (UV-vis) and electron paramagnetic resonance (EPR) spectroelectrochemistry. All polymers undergo two sequential, reversible oxidation processes in solution. Structures in which the TTF species is directly linked to the polymer backbone (2 and 4) display redox behavior which is dictated by the fulvalene system. Once the TTF is spatially removed from the polymer chain by a nonconjugated link (polymer 3), the electroactivity of both TTF and polythiophene moieties can be detected. Computational studies confirm the delocalization of charge over both electroactive centers (TTF and PT) and the existence of a triplet dication intermediate. PTV 4 has a low band gap (1.44 eV), is soluble in common organic solvents, and is stable under ambient conditions. Organic solar cells of polymer 4:[6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) have been fabricated. Under illumination, a photovoltaic effect is observed with a power conversion efficiency of 0.13% under AM1.5 solar simulated light. The onset of photocurrent at 850 nm is consistent with the onset of the pi-pi absorption band of the polymer. Remarkably, UV-vis spectroelectrochemistry of polymer 4 reveals that the conjugated polymer chain remains unchanged during the oxidation of the polymer.
[structure: see text] We report the synthesis of a novel end-capped sexithiophene derivative bearing two pendent, fused tetrathiafulvalene (TTF) units linked to the main chain through 1,4-dithiin heterocycles. Cyclic voltammetry and absorption spectroscopy are used to investigate the electronic properties of this hybrid electroactive material. The oligomer has a band gap of 2.1 eV, and the material can be oxidized through the sexithiophene and TTF units simultaneously.
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