Photobehaviour of thio-analogues of stilbene and 1,4-distyrylbenzene studied by time-resolved absorption techniques

The photobehaviour of the trans isomers of some thio-analogues of stilbene and distyrylbenzene has been investigated by femtosecond time-resolved absorption techniques. The observed transient spectra were assigned to the S1 → Sn transition by comparison with previous results on time-resolved nanosecond fluorescence decay. Much faster (few ps) dynamics were also observed, assigned to vibrational relaxations to the emitting state or to the involvement of an upper electronic state. For 2,5-di-(2-thienylethenyl)thiophene, the specific role of an upper state was evidenced by a parallel study of the effect of the solvent polarizability on the emission spectrum shape and photophysical properties. In some cases, biexponential decay kinetics confirmed the presence of at least two conformers. For 2,5-distyrylthiophene, the transient was found to be the precursor of T1, as shown by the formation of the T1 → Tn absorption band at a rate corresponding to that of the singlet decay.