Low-lying electronic levels of spheroidene bound to the light-harvesting (LH2) complex of Rhodobacter sphaeroides 2.4.1 as determined by fluorescence and fluorescence—excitation spectroscopy at 170 K

Abstract

Fluorescence and fluorescence—excitation spectroscopy at 170 K of the light-harvesting (LH2) complex of Rhodobacter sphaeroides 2.4.1 has determined the energies of level I (2 1A g −, level III ( 1B u +) and level IV of the bound spheroidene, as the absorptive 0 ← 0 transitions, to be 14500, 18300, 19200 and 23200 cm −1, respectively. Internal conversion in spheriodene and spheroidene-to-bacteriochlorophyll energy transfer, as determined by fluorescence—excitation spectroscopy, suggest two different light-harvesting pathways: (1) capturing the light energy and transferring the singlet energy through level III, and (2) capturing the light energy via level IV and transferring the rest of the singlet energy via level I, after internal conversion (energy dissipation) from level IV to level I.