Theoretical investigation on the oligothienoacenes under the influence of external electric field

Theoretical investigation on a series of oligothienoacenes has been carried out at the B3LYP/6-31G* level by considering the influence of the external electric field. With the electric field increasing, the carbon–carbon single bonds become shorter and the carbon–carbon double bonds become longer, resulting in a better conjugation. Due to the different electron density, the charge mobility of the sulfur is more obvious than that of the carbon. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap decreases with the EF intensity increasing. The applied EF also changes the spatial distribution of the molecular orbits: LUMO and several higher orbitals shift to the high potential side, whereas HOMO and several lower ones shift to the low potential side. All these features behave more pronounced with increasing conjugated chain length.