Application of time-resolved polarization fluorescence spectroscopy in the femtosecond range to photosynthetic systems.

Time-resolved polarization fluorescence spectroscopy in the femtosecond range was applied to a photosynthetic antenna system. Specific signals of excited states were obtained by simultaneous measurements of fluorescence rise and decay curves and polarized spectroscopy. Relaxation processes of carotenoids, energy transfer from carotenoids to chlorophyll (Chl) a, and energy migration among pigment pools of Chl a and Chl b were clearly resolved. Two new characteristics of carotenoid molecules were revealed only by anisotropy measurements. A new singlet excited state between the well known S2 (1Bu(+)) and S1 (2Ag(-)) states was resolved by an intermediary anisotropy (r(t) = 0.30) for siphonaxanthin in chloroplasts of Codium fragile. Time-dependent changes in anisotropy with an initial value of 0.52 (r(0) = 0.52) were recorded during the relaxation of lutein molecules in the light-harvesting complexes II of Arabidopsis thaliana, and this was interpreted as a strong interaction between two lutein molecules in the pigment-protein complexes. Other examples of the application of this method were also discussed.