Investigation of the S1/ICT equilibrium in fucoxanthin by ultrafast pump-dump-probe and femtosecond stimulated Raman scattering spectroscopy

Time-resolved multi-pulse spectroscopic methods-pump-dump-probe (PDP) and femtosecond stimulated Raman spectroscopy-were used to investigate the excited state photodynamics of the carbonyl group containing carotenoid fucoxanthin (FX). PDP experiments show that S-1 and ICT states in FX are strongly coupled and that the interstate equilibrium is rapidly (< 5 ps) reestablished after one of the interacting states is deliberately depopulated. Femtosecond stimulated Raman scattering experiments indicate that S-1 and ICT are vibrationally distinct species. Identification of the FSRS modes on the S-1 and ICT potential energy surfaces allows us to predict a possible coupling channel for the state interaction.