Energies and excited-state dynamics of , and states of carotenoids bound to LH2 antenna complexes from purple photosynthetic bacteria

Time-resolved pump–probe stimulated-emission and transient-absorption spectra were recorded after excitation with ∼30 fs pulses to the 1 B u + ( 0 ) and optically-forbidden diabatic levels of carotenoids, neurosporene, spheroidene and lycopene having n = 9–11 double bonds, bound to LH2 antenna complexes from Rhodobacter sphaeroides G1C, 2.4.1 and Rhodospirillum molischianum. The low-energy shift of stimulated emission from the covalent 1 B u - ( 0 ) and 3 A g - ( 0 ) levels slightly larger than that from the ionic 1 B u + ( 0 ) state suggests the polarization, whereas more efficient triplet generation suggests the twisting of the conjugated chain in Cars bound to the LH2 complexes, when compared to Cars free in solution.