EXCITED-STATE DYNAMICS OF RETINAL PROTEINS AS STUDIED BY FOURIER-TRANSFORM OF OPTICAL-ABSORPTION SPECTRUM .1. DEVELOPMENT OF ANALYTICAL METHOD

We significantly improved the analytical method for the study of excited state dynamics of pigments, by means of the time correlation function (tcf) of the vibrational wavepacket which is produced by the Fourier transform of experimentally obtained optical absorption spectra (FTOA). Applying the tcf method to the spectra of rhodopsin at 0-degrees-C and -180-degrees-C, we observed specific peaks which are slightly different between 0-degrees-C and -180-degrees-C in the early time region (1-130 fs) of the absolute value of tcf, representing a characteristic propagation of the wavepacket along a reaction coordinate pertinent to the cis-trans photoisomerization of the chromophore accompanying the motion of protein moiety. From the analysis of phase angle propagation, we obtained a rather small relaxation energy, 6-7 kcal/mol. Based on these results, we can say that FTOA analysis is useful as one of the most powerful techniques for the study of very early procedures in the excited state dynamics of pigments.