NONPHOTOCHEMICAL HOLE-BURNING OF THE REACTION-CENTER OF RHODOPSEUDOMONAS-VIRIDIS

Reddy et al. (Science, accepted) have reported persistent, nonphotochemical hole-burned (NPHB) spectra for the Q(y) states of the reaction center of Rhodopseudomonas viridis. The photoinduced structural transformation was shown to be highly localized on the special pair. This transformation leads to a red shift of the special pair's lowest-energy absorption band, P960, of 150 cm-1 and a comparable blue shift for a state at 850 nm, which, as a consequence, could be assigned as being most closely associated with the upper dimer component. Additional experimental results are presented here together with a theoretical analysis of the extent to which the NPHB spectra provide information on the contribution from the bacteriochlorophyll monomers of the special pair to the Q(y) states that absorb higher in energy than P960. Structured photochemical hole-burned (PHB) spectra of P960 are also presented that underscore the importance of strong electron-phonon coupling from a broad distribution of modes with a mean frequency of 30 cm-1 for an understanding of the P960 absorption profile. These spectra also identify the zero-phonon hole of the strongly damped special pair marker mode (145 cm-1) and its associated phonon sideband structure. Calculated spectra are presented which are in good agreement with the experimental PHB spectra.