Carotenoid to chlorophyll energy transfer in light harvesting complex II from Arabidopsis thaliana probed by femtosecond fluorescence upconversion

Trimers of light harvesting complex II from Arabidopsis thaliana were studied by femtosecond fluorescence upconversion. The average lifetime of the carotenoid S2 state was ∼57 fs for wild type trimers and ∼70 fs for trimers from a mutant plant with a distinctly different carotenoid composition. We estimate that ∼56% of the energy transferred from carotenoids to chlorophylls proceeds via the carotenoid S2 state in the wild type and ∼46% in the mutant. By comparison with the fluorescence excitation spectra, we find that ∼20% of the energy transferred in both samples proceeds through the carotenoid S1 state.