Femtosecond–picosecond dynamics of the lowest excited singlet state in α-quinquethiophene

A femtosecond photo-induced absorption spectrum has been studied for α-quinquethiophene. The observed stimulated emission with a lifetime of 600±40 fs is ascribed to the transition from the geometrically non-relaxed levels in the lowest excited singlet (S1) state. A picosecond time-resolved Raman spectrum studied by utilizing a time-frequency two-dimensional multiplex CARS spectrometer has provided signals due to the geometrically non-relaxed S1 state as well as the relaxed S1 state.