Polyvinyl-locked vs free quaterthiophene: effect of spatial constraints on the electronic properties of n-hexyl-quaterthiophene

A soluble, low-weight fraction of poly(a-vinyl, omega-n -hexyl-quaterthiophene), PT4Hex, having n-hexylquaterthiophenes as side-chain groups, is prepared by free-radical polymerization of a-vinyl omega-n-hexyl-quaterthiophene and the corresponding properties compared to those of free di-n-hexylquaterthiophene (T4Hex). Optical analysis (absorption and emission) and X-ray diffraction data indicate that in the polyvinyl-locked architecture the quaterthiophene pendants adopt a cofacial arrangement with a mutual distance close enough for pi-pi orbitals to overlap (similar to 4 angstrom). As a consequence of the close chain packing, a shift of the reduction potential of about 0.5 V toward less negative values with respect to free T4Hex, is found for PT4Hex films. Due to its enhanced electron affinity, PT4Hex displays an electron-acceptor behavior when blended with alkylated and silylated quaterthiophenes acting as donors.