DFT study of conjugated biheterocyclic oligomers exhibiting a very low HOMO-LUMO energy gap

Density functional theory (DFT) is applied to study the structure and electronic properties of oligomers based on bithiophene bridged by a sp(2) carbon substituted by a chalcogen atom (O, S, Se and Te), and their polybifurane and polybipyrrole analogues. The important reduction of the energy gap which is observed for the whole series of biheterocyclic compounds, when going down the chalcogen group, is explained on the basis of an orbital interaction analysis. Bithiophene polymers bridged by a selenium or a tellurium substituted carbon atom are expected to exhibit very low energy band gaps. (C) 2003 Elsevier B.V. All rights reserved.