Nature of optical transitions in conjugated oligomers. II. Theoretical characterization of neutral and doped oligothiophenes

The optical transitions in α-conjugated oligothiophenes are investigated on the basis of a theoretical approach, including correlation effects; the authors consider both the neutral and doped states. The results are able to provide a coherent interpretation of the sometimes contradictory experimental data. For the neutral oligomers, the authors report the evolution of the lowest energy, dipole-allowed triplet-triplet transition with increasing chain length.