Synthesis and properties of end-capped sexithiophenes incorporating the ethylene dithiothiophene unit

Two new end-capped sexithiophene derivatives (10a and 10b) have been synthesised and characterised by absorption spectroscopy, cyclic voltammetry and UV-vis spectroelectrochemistry. Both oligomers undergo two reversible, sequential oxidation processes (10a: E-1(1/2) = +0.61 V, E-2(1/2) + 0.97 V; 10b: E-1(1/2) 5 +0.70 V, E-2(1/2) + 0.91 V vs. Ag/AgCl) and the electronic band gaps of the materials are ca. 2.2 eV (solid state). Sexithiophene 10a has been incorporated as an electron donor material, with C-60 as acceptor, in a bilayer photovoltaic device. The power conversion efficiency is a modest 0.12%, whilst the maximum IPCE at 350 nm gave an external quantum efficiency of ca. 12%.