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 wa velength at 4.2 K are reported for the isolated LHC II peripheral ante nna complex of photosystem II. The lowest-energy state of the trimer c omplex is shown to lie at 680 nm, 4 nm below the most intense Chl a ba nd at 676 nm. The linear electron-phonon coupling for the 680-nm state is characterized and used to predict that its fluorescence origin sho uld lie at 681 nm, precisely coincident with the observed origin at 4. 2 K. The 680-nm band carries the equivalent absorption strength of abo ut one chlorophyll a molecule per C-3 trimer complex, which contains a bout 27 chlorophyll a molecules. The 680-nm absorption band possesses an inhomogeneous width of similar to 120 cm(-1), and its zero-phonon l ine distribution function is largely uncorrelated with those of the hi gher-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 interpret ation of this dephasing is given in terms of the trimer of subunits st ructure. Based on the satellite hole structure observed upon hole burn ing into the 680-nm state, two new states at 674 and 678 nm are identi fied. The possibility that these three states are excitonically correl ated is considered. The observed trend in the zero-phonon hole burning efficiency as a function of burn frequency is qualitatively consisten t with the states at energies higher than 680 nm having ultrashort lif etimes at 4.2 K.