Femtosecond optical dynamics of α-conjugated hexamethylsexithiophene in solution

The photoexcited state dynamics of methyl-substituted sexithiophene in solution is investigated by using the femtosecond pump and probe technique. Intraband thermalization of S1 could be monitored following the spectral relaxation of the stimulated emission. Electron-ring torsion coupling is proposed to play a fundamental role in this process leading to a more planar geometry of the excited state. The population dynamics is understood taking into account intersystem crossing to the triplet manifold as the main non-radiative decay channel.