Density functional theory investigation on the electronic structure of furo[3,4-b]pyridine-type heterocyclics: from monomer to polymer

The geometries and electronic properties of six polymers based on furo3,4-b]pyridine-type heterocyclics were studied using density functional theory (DFT) at the B3LYP/6-31G(d) level. Bond lengths, bond critical point (BCP) properties, nucleus-independent chemical shift (NICS), and Wiberg bond indexes (WBIs) are analyzed and correlated with conduction properties. The changes of bond length, BCP properties, NICS, and WBIs all show that the conjugational degree is increased with main chain extension. The changes of NICS also show that the conjugation is stronger in the central section than in the outer section. And the HOMO–LUMO energy gap (E _g) is decreased steadily upon chain elongation. The results suggest that the six polymers all have lower energy gaps (in the range of 0.39–0.58 eV), which indicate that these proposed polymers are good candidates for the conductive materials.