Picosecond-transient spectra of oligothiophenes in solution

The transient spectra of T in dioxane are shown in the Figs. 17.4 and 17.5. At first 

For oligomers T with n = 4, 5, 6, also fast arising A1 bands occur at longer wavelengths. Thereby induced fluorescence was also registered. The induced fluorescence of 5T is very well seen in Fig. 17.4b. 

We compared the band shape of the measured induced fluorescence band with the well-known stationary fluorescence band, shown in Fig. 17.3 b. Thereby we found a good agreement of the maximum position but deviation in band form. This difference is mainly caused by the different Einstein coefficients for spontaneous and stimulated emission. 

The bands A2 also appear at the larger T, but more delayed as at 3T. They shift more to longer wavelengths than the corresponding F spectra, so that the superposition of F and A2 becomes weaker. On the other hand, the A1 bands become wider and thereby they overlap the A2 bands. At long delay the A2 bands solely exist, whereas A1 and F decrease. 

These bands are identical with triplet absorption bands reported from nanosecond to microsecond laser flash experiments [10]. 

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