Singlet-triplet annihilation in single LHCII complexes

摘要: In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states therefore avoid the production harmful singlet oxygen. The resulting Car lead a non-linear self-quenching mechanism called singlet–triplet (S–T) annihilation that strongly depends on excitation density. this work we investigated fluorescence decay kinetics single immobilized LHCIIs at room temperature found two-exponential with slow (3.5 ns) fast (35 ps) component. relative amplitude fraction component increases increasing intensity, decrease in quantum yield suggests effects. Modulation pattern by means acousto-optic modulator (AOM) furthermore allowed us resolve time-dependent accumulation rate (∼7 μs) quenching species. Inspired singlet–singlet (S–S) studies, developed stochastic model then successfully applied it describe explain all experimentally observed steady-state kinetics. That distinctively identify as S–T annihilation. Quantitative fitting resulted conclusive set parameters validating our interpretation experimental results. obtained can be generalized small molecular aggregates where equilibration time excitations is much faster than annihilation-free excited state lifetime.