Incorporation of Fused Tetrathiafulvalenes (TTFs) into Polythiophene Architectures: Varying the Electroactive Dominance of the TTF Species in Hybrid Systems

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-C61 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 π−π 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.