Theoretical search for low-gap polymers based on polythiophene

Abstract We have performed ab initio Hartree-Fock crystal orbital calculations on a variety of periodic polymers based on thiophene. One of the goals was to find a system with a low fundamental bandgap, which might open the possibility of intrinsic electric conductivity in organic materials. Furthermore, we intended to obtain a relationship between the chemical composition and the value of the gap to be able to predict new systems. Different numbers of benzene rings have been condensed to thiophene, resulting in the lowest bandgap being found with poly(naphthothiophene). Thiophene has also been modified by connecting heterocyclesin the β,β′-positions. Only in the cases of 1.3- and 1,4-diazabenzene is the gap much lower than for polythiophene. Substitutions by the cyano group or hydroxyl group hardly change the energy band structures. Several factors seem to correlate the bandgap with the chemical structure. The dominating one most probably is different for the different chemical classes based on thiophene.