Ab initio study of the electronic structures of polycyclopentadithiophene-4-one and polydicyanomethylene-cyclopentadithiophene: Two conjugated polymers with small band gaps

Quantum chemical results of the electronic structures of polycyclopentadithiophene-4-one (PCDT) and polydicyanomethylene-cyclopentadithiophene (PCNTh), (the two known conjugated polymers consisting of successive bithiophene units bridged by an electron accepting carbonyl group in PCDT and a dicyanomethylene group in PCNTh), obtained with the aid of ab initio Hartree-Fock crystal orbital method are reported. Both polymers on the basis of their geometries as well as their a-bond orders are found to have benzenoid-like structures. It is shown that the small band gap values of these polymers as compared with polythiophene (PTP) arise mainly due to the strong bonding interaction between the LUCO of the bithiophene skeleton and the LUMO of the electron accepting group. Copyright (C) 1996 Elsevier Science Ltd