ANALYSIS OF THE TEMPERATURE-DEPENDENCE OF FEMTOSECOND EXCITED-STATE DYNAMICS OF BACTERIORHODOPSIN BY SPIN-BOSON MODEL

The spin-boson model was applied to analyze the temperature dependence of excited state dynamics for the cis-trans photoisomerization of the chromophore in bacteriorhodopsin which was obtained by the Fourier tr ansform of the optical absorption spectrum. The results indicate that the model is valid in the short time region less than about 30 fs and that the excited state dynamics in the time region larger than 30 fs i s dominated by the non-harmonic slow vibrational motion, which is temp erature independent. It is suggested that this specific vibrational mo tions might reflect the ultrafast cis-trans isomerization of the chrom ophore as well as conformation change of the protein environment.