Ester substitution in 2,2′-bithiophene: Analyses of the changes induced in the structural and electronic properties

Ab initio quantum-chemical methods have been used to investigate how the inclusion of ester groups on polythiophene chains can affect some properties of the polymer. For this purpose, MP2/6-31G(d,p) calculations have been performed on three isomers: dimethyl 2,2′-bithiophene-4,4′-dicarboxylate, dimethyl 2,2′-bithiophene-3,3′-dicarboxylate and dimethyl 2,2′-bithiophene-3,4′-dicarboxylate, which mimic the tail-to-tail, head-to-head and head-to-tail polymer linkages. After considering different arrangements of the ester substituents for each isomer, results allow conclude that introduction of ester groups at the 4,4′-positions does not alter the properties of 2,2′-bithiophene. In contrast, 3,3′- or 3,4′-disubstitutions produce significant changes in both the structural and electronic properties. These results may assist in designing soluble polythiophene-based polymers.