Excitation relaxation of carotenoids within the S2 state probed by the femtosecond fluorescence up-conversion method

Excited-state dynamics of a linear carotenoid, neurosporene, was studied by the femtosecond up-conversion method after excitation to the S2 state with an excess energy of approximately 3000 cm−1. Supplemental data were also obtained on β-carotene. Fluorescence kinetics showed an emission wavelength dependence and therefore the reconstructed transient fluorescence spectra changed with time. The time constant of internal conversion was in the range of 195–280 fs, depending on the wavelengths, and those of spectral evolution were estimated to be ∼40 fs and 210–260 fs. These relaxation times showed vibrational relaxation kinetics in the S2 state.