Molecular orbital study of the electronic absorption spectra of dithienyls

The localized orbital method has been used in an SCF study of the electronic absorption spectra of the three isomers of dithienyl. Transition energies are computed for planar, perpendicular, and polyconfigurational descriptions of the molecule. Band intensities are calculated for the planar conformers. The results show that: (1) the coplanarity of the two thiophene rings in dithienyl is not significantly distorted; (2) excited states of dithienyls arise from substantial configuration interaction; and (3) the charge transfer wave function contributes significantly to the excited state.