Electronic structure of the alkyl, benzyl and methoxy derivatives of polythiophene

We present a theoretical investigation of the geometric and electronic structures of some derivatives of polythiophene, namely poly-3-methylthiophene, poly-3-ethylthiophene, poly-3-propylthiophene, poly-3-isopropylthiophene, poly-3-benzylthiophene and poly-3-methoxythiophene. The poly-3-alkyl- and 3-methoxythiophenes have recently attracted a great deal of interest, due to their high conductivities and/or excellent solubility properties. The geometries are optimized with the MNDO semi-empirical method. The MNDO geometries are then used as input for band-structure calculations performed with the VEH (Valence Effective Hamiltonian) technique. We mainly discuss electronic properties such as ionization potentials, bandwidths, band gaps and electron affinities, which are important with regard to the conductivities that could be reached upon doping the polymer.