Combined theoretical and vibrational study of dihexylbithienoquinonoid derivatives with regioregular head-to-head, head-to-tail, and tail-to-tail orientations

We present the results of a theoretical and vibrational spectroscopic study carried out on three different 2,2'-(dihexyl-2,2',5,5'-tetrahydro-2,2'-bithienylidene-5,5'-diylidene)bis(propanedinitrile) isomers, which are compared with the corresponding unsubstituted bithienoquinonoid in the pristine state as solids. In these isomers, the two solubilizing hexyl side chains are attached to preassigned beta-positions: head-to-head (HH), head-to-tail (HT), and tail-to-tail (TT). These materials possess a highly extended pi-electron conjugation, since they bear a pure heteroquinonoid structure in their electronic ground states. Thus, these molecules could be regarded as suitable models of the structural perturbations induced by the ionization in doped polythiophene.