Abstract:

Six types of donor-acceptor conjugated oligomers were designed by choosing [1,2,5]thiadiazolo-[3,4-g]quinoxaline(TQ) as the acceptor and thiophene(Th), thieno[3,2-b]thiophene(TTh) or pyrrole(Py) as the donor unit. B3LYP method was employed to investigate the electronic structure and properties of the designed oligomers. The atoms-in-molecules(AIM) topological analysis and nuclear-independent chemical shift(NICS) results show that the conjugational degree is increased with main chain extension and thus leads to a decrease in HOMO-LUMO energy separation. In addition, the vertical ionization potential decreases and the vertical electron affinities of these oligomers increase with an increase in polymeric number. The molar ratio of donor to acceptor unit(D-A ratio) plays a very important role on the electronic properties. It is found that the intramolecular charge transfer increases and the HOMO-LUMO energy separation decreases with an increase in the ratio of donor unit. However, the effects of D-A ratio on the electronic properties become weaker as the polymer chain becomes longer. The unusually large intramolecular charge transfer caused by the intramolecular hydrogen bond reveals that pyrrole is not only a strong electron donor, but also a potential hydrogen bond donor. The theoretical results suggest the corresponding copolymers of the designed oligomers should be the good candidates for conducting materials due to the narrow HOMO-LUMO energy separation(< 1 eV).

Key words: Conjugated oligomer, Molar ratio of donor to acceptor, Electronic property, Nuclear-independent chemical shift