Density functional theory (B3LYP/6-31G*) study of oligothiophenes in their aromatic and polaronic states

In this paper, we report a theoretical study of oligothiophenes (from the dimer to the octamer) in their neutral and oxidized states based on DFT (B3LYP/6-31G*) calculations and focusing the discussion on the influence of chain length on conformational and optoelectronic properties. The bridging effect by CH2, SiH2, C=O and C=C(CN)(2) on the optoelectronic properties of the octamer will then be investigated. The obtained results are close to available experimental ones. While structural parameters of neutral oligomers do not change significantly, the oligomers become planar and show a quinoidal character after oxidation. The bridging by C=C(CN)(2) significantly decreases the octamer's band gap. (c) 2005 Elsevier B.V. All rights reserved.