Picosecond Spectroscopy of Solutions, Proteins and Photosynthetic Membranes

Abstract

The photophysics of tryptophan is discussed and a model capable of rationalizing the photophysics of almost twenty derivatives of tryptophan is proposed. The model is based on conformers about the Cα—Cβ bond and the relative rates of charge transfer from indole to various electrophiles. Three new tryptophan derivatives were synthesized to test the model. Accurate predictions concerning the relative fluorescence lifetimes and the form of the fluorescence decay law are made for tryptophan and seventeen of its derivatives, including the three new derivatives.The fluorescence decay kinetics from chloroplasts from green plants are described. New data are presented on the fluorescence decays obtained from genetic mutants of chlamydomonas which lack specific components of the photosynthetic apparatus. The interpretation of the green plant chloroplast data in terms of the two photosystems and the light harvesting array is discussed in terms of the data from the mutant algae. Our data indicate that the major short component (∼100 ps) obtained in the fluorescence decay of chloroplasts results from photochemical trapping by both photosystem I and photosystem II.A synchronously pumped dye laser which produces two, independently tunable, synchronized picosecond pulse trains will be described. An application of the laser to time and frequency resolved polarization spectroscopy will be given. The results are used to estimate the homogeneous linewidth of the S0 → S1 transition of a large molecule in solution. The optical heterodyne technique is applied to separate the real and imagninary contributions of the third order nonlinear susceptibility.