Electronic relaxation and vibrational dynamics in a thiophene oligomer studied under the same experimental condition with a sub-5 fs laser

Abstract

Using a sub-5 fs pulse laser, the pump-probe experiment was performed on a quinoid thiophene derivative and both electronic relaxation and vibrational dynamics were clarified with the same experimental data. From the data, two population decay times of the lowest electronic excited state were determined to be 200 fs and 1.8 ps, which can be explained by the assumption that the 2(1)A(g) state lies below the exciton 1(1)B(u) state together with the very low fluorescence quantum efficiency. The relaxation process after excitation by the pump pulse was studied to be 1(1)B(u) -> 1(1)B(u)* -> 2(1)A(g) -> 1(1)A(g). According to the experimental data, the location of the energy level was also discussed. The electronic dephasing time was determined to be 64 +/- 4 fs by utilizing the data in the 'negative time' range. The vibrational dephasing time constant of the most strongly coupled mode with frequency of 1466 cm(-1) was determined to be 520 +/- 20 fs from the widths of the corresponding Fourier power spectra.