Table 3. Carotenoid S₁ (2¹A_g^–) State Lifetimes and Contributions of Carotenoid Excited States to Energy Transfer to BChl a.

				τS1 (ps)
carotenoid	Na	NC=C	NC=O	solventb	LH2c	EffCar S1→B850 (%)d	ΦCar S1→B850 (%)e	ΦCar S2→B850 (%)f	ΦCar→B850 (%)g
neurosporene	9	9	0	22.5	1.2	95	27	60	87
spheroidene	10	10	0	8.5	1.4	84	18	70	88
lycopene	11	11	0	4.4	3.4	23	7	59	66
rhodopin	11	11	0	3.3	2.9	12	3	62	65
spirilloxanthin	13	13	0	1.5	1.4	0	0	46	46
diketospirilloxanthin	15	13	2	0.8	1.1	0	0	41	41

^aTotal number of conjugated double bonds (N = N_C=C + N_C=O).

^bS₁ (2¹A_g^–) state lifetime in solvent calculated as midrange of literature values (RT) given in Table 2.

^cS₁ (2¹A_g^–) state lifetime in LH2 at RT obtained in this work.

^dCarotenoid-to-BChl a energy transfer efficiency for S₁ (2¹A_g^–) obtained from difference between lifetime in solvent and in LH2; this value is the percentage of S₁ (2¹A_g^–) state produced from S₂ (1¹B_u⁺) that gives energy transfer to B850 calculated via eq 1.

^eThe quantum yield of energy transfer from S₁ (2¹A_g^–) to B850; this value is the actual contribution of carotenoid S₁ (2¹A_g^–) state to the overall energy transfer (per photon absorbed to produce the S₂ (1¹B_u⁺) state obtained using eq 2.

^fQuantum yield of energy transfer from the carotenoid S₂ (1¹B_u⁺) state to B850; this value is the actual contribution of the carotenoid S₂ (1¹B_u⁺) state to overall energy transfer.

^gOverall carotenoid-to-BChl a energy transfer yield obtained from comparison of absorptance (1–T) and fluorescence excitation spectra.