On the role of excitonic interactions in carotenoid–phthalocyanine dyads and implications for photosynthetic regulation
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In two recent studies, energy transfer was reported in certain phthalocyanine–carotenoid dyads between the optically forbidden first excited state of carotenoids (Car S1) and phthalocyanines (Pcs) in the direction Pc → Car S1 (Kloz et al., J Am Chem Soc 133:7007–7015, 2011) as well as in the direction Car S1 → Pc (Liao et al., J Phys Chem A 115:4082–4091, 2011). In this article, we show that the extent of this energy transfer in both directions is closely correlated in these dyads. This correlation and the additional observation that Car S1 is instantaneously populated after Pc excitation provides evidence that in these compounds excitonic interactions can occur. Besides pure energy transfer and electron transfer, this is the third type of tetrapyrrole–carotenoid interaction that has been shown to occur in these model compounds and that has previously been proposed as a photosynthetic regulation mechanism. We discuss the implications of these models for photosynthetic regulation. The findings are also discussed in the context of a model in which both electronic states are disordered and in which the strength of the electronic coupling determines whether energy transfer, excitonic coupling, or electron transfer occurs.
KeywordsTwo-photon excitation Carotenoids Chlorophylls Carotenoid–phthalocyanine dyads Excitonic interactions
Phthalocyanine (depending on the context Pc also refers to the first excited singlet state of Pc (Qy))
Chlorophyll (depending on the context Chl also refers to the first excited singlet state of Chl (Qy))
Evolution-associated decay spectra
Light-harvesting complex II
This study was supported by the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft (DFG). This study was supported by a Grant from the U.S. Department of Energy (DE-FG02-03ER15393). D.G. and A.M. were supported as part of the Center for Bio-Inspired Solar Fuel Production, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001016. This study was further supported by the Netherlands Organization for Scientific Research (NWO) via the Foundation of Earth and Life Sciences (ALW) and via an NWO visitor grant to T.A.M.
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