Ultrafast Spectroscopy of Trimeric Light-Harvesting Complex II from Higher Plants

Abstract

Time-resolved femtosecond transient absorption measurements have been carried out at room temperature on light-harvesting chlorophyll a/b protein complex of photosystem II (LHC II) trimers prepared from spinach. Exciting in the chlorophyll (Chl) b region at 650 nm with very low intensity, virtually annihilation-free two-color transient absorption measurement of the kinetics over 100 ps, between 645 and 690 nm, yield global lifetimes of 175 fs, 625 fs, and 5 ps and a long component (≥790 ps) where the three fastest lifetimes reflect Chl b to Chl a energy transfer. Using a camera detection system, kinetics over 400 ps at still low annihilation levels and with much higher spectral resolution have been obtained. Short lifetime components of 180 fs, 480 fs, and 6 ps are comparable with the two-color data, but in addition, 34 and 85 ps components with small amplitudes are resolved and a long component (3.6 ns) is fixed at the longest lifetime value determined by fluorescence. Annihilation statistics have been c...