Abstract

Femtosecond time-resolved fluorescence spectroscopy (up-conversion) was applied to directly determine the S₂ lifetime of β-carotene at room temperature. Upon excitation of β-carotene in n-hexane with a 425 nm femtosecond pulse, the fluorescence lifetime was estimated to be 195 ± 10 fs throughout the whole emission wavelength. Absence of dynamic Stokes shift suggests that the intramolecular relaxation processes occur within 50 fs, followed by the internal conversion from S₂- to S₁-state in 195 fs.

© 1994 Optical Society of America