Electronic structure and optical physical properties of oligothiophenes

Photoinduced dynamics of oligothiophenes were studied theoretically with quantum chemical method as well as 2D real space analysis method. The transition energies in absorption and fluorescence are red shifted with the increase of the units. For the oligothiophenes with small units, the excitation is delocalized on the whole units for absorption and fluorescence; while with the increase of the units, the excitation is localized on the center in fluorescence, though the excitation is still delocalized on the whole unit in absorption. The bond lengths are compared at the ground state and the relaxed excited state, which reveal the changes of the structures of them on the photoinduced dynamics.