The electronic and structural properties of nonclassical bicyclic thiophene: Monomer, oligomer and polymer

The nonclassical thiophenes have received a great deal of attention because of their unusual electronic structure in several decades. Based on DFT approach, the structural and electronic properties of thieno[3,4-c][1,2,5]thiadiazole, as well as of its co-oligomers and copolymers with benzene and thiophene, are investigated theoretically. The changes of nucleus-independent chemical shifts (NICSs) as a method examining conjugational degree are reported. The results show that the conjugational degree is increased with the increase of polymeric number. The density of state (DOS) and crystal orbital overlap population (COOP) are also investigated. The band structure analysis shows that the benzene and thiophene substitutes have quite low energy gap (0.23 and 0.32 eV, respectively). Therefore, those substitutes are implied as intrinsic conductors.