LOW-ENERGY EXCITON LEVEL STRUCTURE AND DYNAMICS IN LIGHT-HARVESTING COMPLEX-II TRIMERS FROM THE CHL A/B ANTENNA COMPLEX OF PHOTOSYSTEM-II

Nonphotochemical hole-burned spectra obtained as a function of burn wavelength at 4.2 K are reported for the isolated LHC II peripheral antenna complex of photosystem II. The lowest-energy state of the trimer complex is shown to lie at 680 nm, 4 nm below the most intense Chl a band at 676 nm. The linear electron-phonon coupling for the 680-nm state is characterized and used to predict that its fluorescence origin should lie at 681 nm, precisely coincident with the observed origin at 4.2 K. The 680-nm band carries the equivalent absorption strength of about one chlorophyll a molecule per C-3 trimer complex, which contains about 27 chlorophyll a molecules. The 680-nm absorption band possesses an inhomogeneous width of similar to 120 cm(-1), and its zero-phonon line distribution function is largely uncorrelated with those of the higher-energy states. Zero-phonon hole widths are used to determine that the fluorescent 680-nm state dephases in 10 ps at 4.2 K. An interpretation of this dephasing is given in terms of the trimer of subunits structure. Based on the satellite hole structure observed upon hole burning into the 680-nm state, two new states at 674 and 678 nm are identified. The possibility that these three states are excitonically correlated is considered. The observed trend in the zero-phonon hole burning efficiency as a function of burn frequency is qualitatively consistent with the states at energies higher than 680 nm having ultrashort lifetimes at 4.2 K.