FEMTOSECOND DYNAMICS OF POPULATION AND COHERENCE OF THE S-2 SINGLET EXCITED-STATE OF BACTERIOCHLOROPHYLL (THE Q(X) ABSORPTION-BAND) IN-VIVO AND IN-VITRO

Population relaxation and electronic dephasing of the excited singlet state S-2 Of bacteriochlorophyll a (the Q(x) absorption band) in solution, in photosynthetic reaction centers, and in light-harvesting complexes were measured using four-wave mixing spectroscopy. The observed lifetime and dephasing time constants are 100 - 400 fs. The calculated homogeneous line width is less than 100 cm(-1) in both ethanol solution and in B800-850 light-harvesting complex. The possible role of ultrafast dephasing in the primary processes of photosynthesis is discussed.