AB-INITIO STUDY OF THE ELECTRONIC-STRUCTURES OF POLYCYCLOPENTADITHIOPHENE-4-ONE AND POLYDICYANOMETHYLENE-CYCLOPENTADITHIOPHENE - 2 CONJUGATED POLYMERS WITH SMALL BAND-GAPS

Quantum chemical results of the electronic structures of polycyclopent adithiophene-4-one (PCDT) and polydicyanomethylene-cyclopentadithiophe ne (PCNTh), (the two known conjugated polymers consisting of successiv e 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 poly mers on the basis of their geometries as well as their a-bond orders a re 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 gro up. Copyright (C) 1996 Elsevier Science Ltd