Femtosecond time-resolved spectroscopy of sexithiophene thin single crystals

Pump–probe experiments as a function of probe time delay, wavelength and polarisation have been performed in α-sexithiophene thin single crystals. The characteristics of the observed induced absorption and stimulated emission are explained by the decay of the singlet excitons to the lower Davydov band. The dipole moment of the transition from this state to the ground state is weak and polarised perpendicularly to the long molecular axis.