Theoretical analysis of poly(difluoroacetylene)

Abstract

The electronic structure of poly(difluoroacetylene) was investigated with the aim of determining whether it is a good candidate for a conducting polymer with high n-type conductivity. Positions of valence and conduction bands and bandwidths indicate that planar all-trans poly(difluoroacetylene) is p- and n-dopable and that on-chain mobility of electrons and holes is high. Various geometries of oligomers with eight carbon atoms were optimized and compared to those of decacyanooctatetraene and octatetraene. Decafluorooctatetraene has a tendency to adopt nonplanar structures, but the planar trans form lies only 5.44 kcal/mol above the helical minimum. Since the energy for planarization is small, poly(difluoroacetylene) might be planar in the solid state. This is in contrast to the cyano analogue for which the planar trans structure lies 23.26 kcal/mol above the helical minimum. Alternating acetylene and difluoroacetylene units give rise to planar polymers with reduced band gap. Bandwidths, ionization potential, and electron affinity are average between those of the homopolymers.