Excitation relaxation of carotenoids within the S-2 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 S-2 state wit h an excess energy of approximately 3000 cm(-1). Supplemental data were als o obtained on beta-carotene, Fluorescence kinetics showed an emission wavel ength dependence and therefore the reconstructed transient fluorescence spe ctra 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 e volution were estimated to be similar to 40 fs and 210-260 fs. These relaxa tion times showed vibrational relaxation kinetics in the S-2 state. (C) 199 9 Elsevier Science B.V. All rights reserved.