Unraveling exciton relaxation and energy transfer in LH2 photosynthetic antennas

A long-standing uncertainty has been resolved concerning the early time evo lution of light excitations in LH2 antennas of purple photosynthetic bacter ia. Both isolated and native membrane-embedded LH2 antenna complexes were c omprehensively studied using femtosecond time-resolved transient absorption spectroscopy together with conventional absorption and fluorescence emissi on spectroscopies at low temperatures. The results show that exciton relaxa tion within isolated LH2 complexes is characterized by subpicosecond time c onstants, while spectral evolution associated with energy transfer between the antenna complexes in photosynthetic membranes is characterized by time constants greater than or equal to 1 ps.