TY - JOUR
T1 - Carotenoid Singlet Fission Reactions in Bacterial Light Harvesting Complexes As Revealed by Triplet Excitation Profiles
AU - Yu, Jie
AU - Fu, Li Min
AU - Yu, Long Jiang
AU - Shi, Ying
AU - Wang, Peng
AU - Wang-Otomo, Zheng Yu
AU - Zhang, Jian Ping
N1 - Funding Information:
The project was supported by the Natural Science Foundation of China (21673288, 21173265; 21411130185). We are indebted to Prof. A. V. Nemukhin at the Research Computing Center of the M.V. Lomonosov Moscow State University for stimulating discussion.
Publisher Copyright:
© 2017 American Chemical Society.
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2017/11/8
Y1 - 2017/11/8
N2 - Carotenoids (Cars) in bacterial photosynthesis are known as accessory light harvesters and photoprotectors. Recently, the singlet fission (SF) reaction initiated by Car photoabsorption has been recognized to be an effective excitation deactivation channel disfavoring the light harvesting function. Since the SF reaction and the triplet sensitization reaction underlying photoprotection both yield triplet excited state Cars (3Car∗), their contribution to the overall 3Car∗ photoproduction are difficult to disentangle. To tackle this problem, we resorted to the triplet excitation profiles (TEPs), i.e., the actinic spectra of the overall 3Car∗ photoproduction. The TEPs combined with the conventional fluorescence excitation spectra allowed us to extract the neat SF contribution, which can serve as a spectroscopic measure for the SF reactivity. This novel spectroscopic strategy was applied to analyze the light harvesting complexes (LHs) from Tch. tepidum and Rba. sphaeroides 2.4.1. The results unambiguously showed that the SF reaction of Cars proceeds with an intramolecular scheme, even in the case of LH1-RC from Rba. sphaeroides 2.4.1 likely binding a secondary pool of Cars. Regarding the SF-reactivity, the geometric distortion in the conjugated backbone of Cars was shown to be the structural determinant, while the length of the Car conjugation was suggested to be relevant to the effective localization of the geminate triplets to avoid being annihilated. The SF reaction scheme and structure-activity relationship revealed herein will be useful not only in deepening our understanding of the roles of Cars in photosynthesis, but also in enlightening the applications of Cars in artificial light conversion systems.
AB - Carotenoids (Cars) in bacterial photosynthesis are known as accessory light harvesters and photoprotectors. Recently, the singlet fission (SF) reaction initiated by Car photoabsorption has been recognized to be an effective excitation deactivation channel disfavoring the light harvesting function. Since the SF reaction and the triplet sensitization reaction underlying photoprotection both yield triplet excited state Cars (3Car∗), their contribution to the overall 3Car∗ photoproduction are difficult to disentangle. To tackle this problem, we resorted to the triplet excitation profiles (TEPs), i.e., the actinic spectra of the overall 3Car∗ photoproduction. The TEPs combined with the conventional fluorescence excitation spectra allowed us to extract the neat SF contribution, which can serve as a spectroscopic measure for the SF reactivity. This novel spectroscopic strategy was applied to analyze the light harvesting complexes (LHs) from Tch. tepidum and Rba. sphaeroides 2.4.1. The results unambiguously showed that the SF reaction of Cars proceeds with an intramolecular scheme, even in the case of LH1-RC from Rba. sphaeroides 2.4.1 likely binding a secondary pool of Cars. Regarding the SF-reactivity, the geometric distortion in the conjugated backbone of Cars was shown to be the structural determinant, while the length of the Car conjugation was suggested to be relevant to the effective localization of the geminate triplets to avoid being annihilated. The SF reaction scheme and structure-activity relationship revealed herein will be useful not only in deepening our understanding of the roles of Cars in photosynthesis, but also in enlightening the applications of Cars in artificial light conversion systems.
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U2 - 10.1021/jacs.7b09809
DO - 10.1021/jacs.7b09809
M3 - Article
C2 - 29053262
AN - SCOPUS:85033218698
VL - 139
SP - 15984
EP - 15993
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 44
ER -