Ultrafast strokes shift and excited-state transient absorption of coumarin 153 in solution

Transient absorption and gain spectra of coumarin 153 in polar solvents are studied by the pump/supercontinuum probe (PSCP) technique with 40 fs time resolution. Vibrational frequencies in the ground and excited state of the chromophore are obtained from the early transient spectra. At later time, the gain band experiences a considerable red shift with two isosbestic points which appear successively, while a pronounced excited-state absorption band at 428 nm changes only negligibly. These observations are compared to the results from semi-empirical calculations for higher excited states. They are not fully consistent with relaxation due to pure solvation and may indicate an intramolecular process.