Molecular designing and DFT investigation of novel alternating donor-acceptor dibenzo[b,d]thiophen-based systems: from monomer to polymer

The structures and properties of dibenzo[b,d]thiophene (DBT) based alternating donor-acceptor conjugated oligomers, in which thieno[3,4-b]pyrazine (TP), thieno[3,4-b]thiadiazole (TD), and [1,2,5]thiadiazolo[3,4-e]thieno[3,4-b]pyrazine (TTP) as acceptors, and their periodic polymers were investigated by the density function theory (DFT) at the B3LYP/6-31G(d) level. The bond length, electron density at bond critical points (BCPs) and nucleus-independent chemical shift (NICS) are analyzed and correlated with the conductive properties. NICS shows that the conjugation degree is increased with main chain extension. Research results show the conductive ability of compounds with 1:2 D-A ratio is better than that with 1:1 D-A ratio. The reorganization energies and energy bands also are considered. The results suggest that (BTDDBT) (n) and (BTPDDBT) (n) have small reorganization energy (0.163 and 0.152 eV, respectively) and quite low energy gap (0.73 and 0.56 eV, respectively), which indicate that they may be potential organic conductive materials.