One- and two-photon pump–probe optical spectroscopic measurements reveal the S 1 and intramolecular charge transfer states are distinct in fucoxanthin

Abstract

The ultrafast relaxation kinetics of fucoxanthin in polar and non-polar solvents have been studied by femtosecond dispersed one- and two-photon pump–probe spectroscopies. Transient absorption kinetics of the lowest singlet S 1 (2 1 A g - ) state and/or intramolecular charge transfer (ICT) state after excitation to the optically allowed S 2 ( 1 1 B u + ) state depend strongly on solvent polarity. Transient absorption spectra and the kinetics of absorbance changes after direct two-photon excitation to S 1/ICT depend strongly on excitation energy in non-polar solvent. The results suggest that the ICT state is a distinct state from S 1 in polar solvent.