EXCITED-STATE STRUCTURE AND ENERGY-TRANSFER DYNAMICS OF THE BACTERIOCHLOROPHYLL-A ANTENNA COMPLEX FROM PROSTHECOCHLORIS-AESTUARII

Persistent nonphotochemical hole-burning results at 4.2 K are reported for an antenna complex of the photosynthetic bacterium Prosthecochloris aestuarii which consists of a trimer of subunits with each subunit containing seven bacteriochlorophyll a (BChl a) molecules. The data for the Q(y) (S1) region are consistent with an excitonically coupled system and indicate the existence of more than even exciton levels, with two contributing to the lowest energy absorption band at 825 nm. State assignments are discussed in terms of various models, including one that invokes interaction between BChl a belonging to different subunits of the same trimer. Exciton level decay times are reported and discussed in terms of exciton-phonon scattering involving phonon emission. These times are compared to and discussed in terms of the ultrafast (less-than-or-similar-to 100 fs) decay times for the access pigment Q(y) states of the bacterial RC. The hole spectra also allow for the determination of the linear exciton-phonon coupling strength (optical reorganization energy) and the contribution of complex heterogeneity to the line widths of the absorption profiles.