The triplet (T-1) states of carotenoids (Cars) and bacteriochlorophyll a (BChl) in the LH2 antenna complexes from Rhodobacter sphaeroides GIC, Rba. sphaeroides 2.4.1 and Rhodospirillum molischianum, containing neurosporene, spheroidene and lycopene, respectively, were examined by stationary-state and time-resolved phosphorescence spectroscopy. The T-1 energies of Cars were determined, irrespective of the Car or BChl excitation, to be 7030 cm(-1) (neurosporene), 6920 cm(-1) (spheroidene) and 6870 cm(-1) (lycopene), respectively, whereas that of BChl to be 7590 cm(-1). In the Rba. sphaeroides GIC, the Car and BChl triplet states decayed in similar time constant as the BChl Q(y) state, a fact which indicates that the pair of triplet states decays through the triplet-triplet annihilation mechanism. (C) 2003 Elsevier B.V. All rights reserved.