Structure dependence of optical properties of bridged bis-thienyls. I. Simple five-membered aromatic bridges

Abstract

The torsional dependence of the heat of formation (ΔHf), averaged electronic polarisabilities (〈α〉) and second-order hyperpolarisabilities (〈γ〉), lowest singlet–singlet and singlet–triplet transition energies of neutral analogues of α-terthiophenes (compound T1) like 2,5-di(2′-thienyl)-furane (compound F1), 2,5-di(2′-thienyl)-pyrrole (compound P1), 2,5-di(2′-thienyl)-[1,3,4]oxadiazole (compound F2), 2,5-di(2′-thienyl)-[1,3,4]thiadiazole (compound T2) and 2,5-di(2′-thienyl)-[1,3,4]triazole (compound P2) has been studied by semi-empirical AM1 and ZINDO/S methods. The molecules P1 and F1 are more planar than T1. Replacing carbon atoms (CH groups) in β-positions of the central ring in T1, P1 and F1 by nitrogens slightly forces the structure to planarity what is connected with higher effectiveness from the charge transfer point of view. On the other hand, the small decrease in the wavelengths of electron spectra as well as electro-optical properties is expected with this central ring modification. The shape of 〈α〉 and 〈γ〉 torsion dependence is of nearly squared-sine type with minimum at perpendicular conformations.