Ultrafast Spectroscopy Study of Energy Transfer, Electron Transfer, and Solvents.

A cavity dumped Kerr-lens mode-locked Ti:sapphire laser and its regenerative amplifier are built. The oscillator generates 15 fs, 40 nJ pulses (0.15 to 1 MHz) with a near Gaussian spectrum ({~}50 nm, FWHM) and its center wavelength can be tuned over 750 -850 nm. The regenerative amplifier generates 60 fs, 40 muJ pulses (0.1 to 6 kHz). The design of the regenerative amplifier is novel: amplification and stretching of pulses are completed simultaneously within the laser cavity without "pre-stretching". The temperature dependent energy transfer in PSI is studied by time resolved fluorescence and simulated with lattice models. The absorption spectra of chlorophyll molecules at various temperatures are calculated. The Forster weak coupling theory and Master equations are used. A new random lattice model with red pigments near P700, is proposed to account for the spatial-spectral correlation in PSI. Red fluorescence at 298K and its kinetics from a Cynaobacterial PSI only mutant, TolE4B, are recorded and modeled by a two-domain antenna model. The ultrafast energy transfer time ({ ~}65 fs) from B to P in the reaction center of Rb. capsulatus is measured. Excited state decays of the special pair of Rb. capsulatus and ten mutants are presented from 17-298 K. We correlate the decay time with mutation-induced changes in the redox potential of the ground state of the special pair. An inhomogeneous model for the electron transfer process is explored. We estimate reorganization energy of <=250 cm^{-1} and {~}500 cm ^{-1} at 292 K and 22 K, respectively. A new spectroscopic technique based on fifth order nonlinear response from a molecule is reported. Both the ultrafast inertial components and much slower dynamics of the solvent are found to be important. Four wave mixing (TA, TG, 2PE, and 3PE) studies of LH2 of Rb. sphaeroides are presented. The models for energy transfer from B800 to B850 are discussed, along with the broadening mechanism and dephasing process in B800.