Theoretical study on steric deconjugation of poly(3-hexylthiophene) through bromination

Abstract In poly(3-hexylthiophene) (P3HT), it is suggested that bromination disturbs the π conjugation and reduces the carrier mobility. To investigate the deconjugation mechanism, we theoretically studied a key flexibility of the Br-P3HT backbone, namely inter-ring S C C S dihedral torsion, in terms of potential energy curve, geometry-based aromaticity index, and decomposed energies of inter-monomer interaction. The linkage between bromination and the excitation energy was also investigated. We concluded that steric repulsion due to bulky bromo group can cause out-of-plane S C C S torsion of Br-P3HT and consequent shortening of the conjugation length, not electronic substituent effect, leads to blue shift of the S 0 → S 1 excitation energy.