The effects of oxygen and boron functionalization on the optical properties of dithienothiophenes

We study the optical properties of dithienothiophene functionalized with lateral dimesitylboryl groups and/or oxygen atoms at the central thienyl sulphur atom. The excitation energies of these systems are computed using first-principles time-dependent density functional theory, and the results are discussed and compared with measured absorption spectra. The agreement between theoretical and experimental results is very good. It is found that the oxygen and the boron functionalization modifies the lowest unoccupied molecular orbital, and thus optical properties, in a different way. Moreover if the boron and the oxygen functionalization are combined together, the effects of the former dominate.