fig1

Figure 1. Optimized molecular geometries and frontier molecular orbital distributions of T, TT and DTT using density functional theory by Gaussian 09 at the B3LYP/6-31G(d,p) level. LUMO: Lowest unoccupied molecular orbital; HOMO: highest occupied molecular orbital; T: thiophene; TT: thieno[3,2-b]thiophene; DTT: dithieno[3,2-b:2’,3’-d]thiophene.