Theoretical Investigation into Electronic Structures and Charge Transfer Properties of π-Conjugated System with Different Combinations of Thiophene and Vinyl/Butadiene

A series of combinations of thiophene and vinyl/butadiene were investigated by ab initio and DFT methods to explore their electronic structures and charge transfer properties. The results show that increasing thiophene ring and vinyl number is a rational strategy to raise the HOMO energy levels and lower the LUMO energy levels. Moving the vinyl from the periphery to the core has the slight effect on the HOMO and LUMO energy levels. Furthermore, replacing the middle vinyl and end-capped vinyl of 3b (T5V4) with the butadiene can lower LUMO energy levels and then facilitate the electron injection. Above all, the close hole and electron reorganization energies (?h and ?e) are observed from these compounds. However, the ?es are smaller than their respective ?hs in some compounds, which is relatively rare in organic materials. Especially, the promising ambipolar material 3c (T5B4) is recommended theoretically for possessing the equivalent minimum ?h (0.24 eV) and ?e (0.24 eV). The absorption wavelengths exhibit red shifts with the increasing of the thiophene ring and the vinyl number under the same configuration, which correspond to the reverse order of ?EH-L and Eg. The linear relationships are found between experimental lowest singlet excited energies (Eexp) with theoretical values ?EH-L and Eg.