Theoretical studies and spectroscopic investigations of ground and excited electronic states of thiophene oligomers Original Research Article

CNDO/S calculations including single and double excited configurations were performed on thiophene oligomers nT with 2–6 monomer units. In contrast to the results on linear polyenes only single excited configurations are necessary to explain the experimental results. The theoretical energies for the lowest 11B states are in good agreement with the low energy absorption origins and the high energy fluorescence maxima and with the 11B state energies observed at low temperature. The results show that the 21A state lies above the 11B state for 2T–6T. Transient absorption bands measured by picosecond spectroscopy could be assigned to transitions between 11B and higher calculated 1A states of all studied oligomers nT.