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Twisted Carotenoids Do Not Support Efficient Intramolecular Singlet Fission in the Orange Carotenoid Protein

George A. Sutherland Orcid Logo, James P. Pidgeon Orcid Logo, Harrison Lee, Matthew S. Proctor, Andrew Hitchcock Orcid Logo, Shuangqing Wang, Dimitri Chekulaev, Wing Chung Tsoi Orcid Logo, Matthew P. Johnson, C. Neil Hunter Orcid Logo, Jenny Clark Orcid Logo

The Journal of Physical Chemistry Letters, Volume: 14, Issue: 26, Pages: 6135 - 6142

Swansea University Authors: Harrison Lee, Wing Chung Tsoi Orcid Logo

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Abstract

Singlet exciton fission is the spin-allowed generation of two triplet electronic excited states from a singlet state. Intramolecular singlet fission has been suggested to occur on individual carotenoid molecules within protein complexes provided that the conjugated backbone is twisted out of plane....

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Published in: The Journal of Physical Chemistry Letters
ISSN: 1948-7185 1948-7185
Published: American Chemical Society (ACS) 2023
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa63765
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Abstract: Singlet exciton fission is the spin-allowed generation of two triplet electronic excited states from a singlet state. Intramolecular singlet fission has been suggested to occur on individual carotenoid molecules within protein complexes provided that the conjugated backbone is twisted out of plane. However, this hypothesis has been forwarded only in protein complexes containing multiple carotenoids and bacteriochlorophylls in close contact. To test the hypothesis on twisted carotenoids in a “minimal” one-carotenoid system, we study the orange carotenoid protein (OCP). OCP exists in two forms: in its orange form (OCPo), the single bound carotenoid is twisted, whereas in its red form (OCPr), the carotenoid is planar. To enable room-temperature spectroscopy on canthaxanthin-binding OCPo and OCPr without laser-induced photoconversion, we trap them in a trehalose glass. Using transient absorption spectroscopy, we show that there is no evidence of long-lived triplet generation through intramolecular singlet fission despite the canthaxanthin twist in OCPo.
Keywords: Carotenoids, orange carotenoid protein, OCP, OCPo, OCPr, intramolecular singlet fission
College: Faculty of Science and Engineering
Funders: G.A.S. and C.N.H. acknowledge ERC Synergy Grant 854126. J.P.P. thanks the EPSRC for support through a Doctoral Training Partnership Scholarship (EP/R513313/1). The authors thank the EPSRC for a Capital Equipment Award (EP/L022613/1 and EP/R042802/1) which funded the Lord Porter Laser facility used in this study. J.C., C.N.H, G.A.S. and S.W. thank the EPSRC for funding through EP/S002103/1 and EP/T012455/1. J.C. and S.W. also thank the EPSRC for funding through EP/N014022/1. M.S.P. and M.P.J. were supported by Leverhulme Trust award RPG-2019-045. A.H. acknowledges The Royal Society (award URF\R1\191548). H.K.H.L. and W.C.T. acknowledge the SPECIFIC Innovation and Knowledge Centre (EP/N020863/1) grant for providing financial support.
Issue: 26
Start Page: 6135
End Page: 6142