Early events of energy relaxation in all-trans-beta-carotene following sub-10 fs optical-pulse excitation - art. no. 241104

The rapid internal conversion to the lowest lying 2(1)A(g)(-) state followi ng photoexcitation is studied in all-trans-beta -carotene with unprecedente d time resolution. Visible optical pulses with time duration of 7 fs are us ed to resonantly excite and probe the optical dynamics of the molecule diss olved in solution. A picture for the relaxation dynamics during the first 1 00 fs following photoexcitation is proposed based on time-resolved transmis sion difference spectra and kinetics. Coherent nuclear motion is observed, assigned to impulsive stimulated resonant Raman scattering. Thermalization of the 2(1)A(g)(-) state, evident from excited-state spectral evolution, is rather slow, indicating that the higher lying vibrational levels are popul ated during energy transfer within the photosynthetic systems.