Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 140, Issue 42, Pages 13719-13725Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b07271
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Funding
- National Science Foundation CAREER Award [DMR-1554918]
- China Scholarship Council [201709480009]
- National Science Foundation [DMR-1654140]
- Academic Research Fund [RG2/16]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Direct For Mathematical & Physical Scien [1554918] Funding Source: National Science Foundation
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Triplet triplet energy transfer (EnT) is a fundamental activation pathway in photocatalysis. In this work, we report the mechanistic origins of the triplet excited state of carbazole-cyanobenzene donor-acceptor (D-A) fluorophores in EnT-based photocatalytic reactions and demonstrate the key factors that control the accessibility of the (LE)-L-3 (locally excited triplet state) and (CT)-C-3 (charge-transfer triplet state) via a combined photochemical and transient absorption spectroscopic study. We found that the energy order between (CT)-C-1 (charge transfer singlet state) and (LE)-L-3 dictates the accessibility of (LE)-L-3/(CT)-C-3 for EnT, which can be effectively engineered by varying solvent polarity and D-A character to depopulate (LE)-L-3 and facilitate EnT from the chemically more tunable (CT)-C-3 state for photosensitization. Following the above design principle, a new D-A fluorophore with strong D-A character and weak redox potential is identified, which exhibits high efficiency for Ni(II)-catalyzed cross coupling of carboxylic acids and aryl halides with a wide substrate scope and high selectivity. Our results not only provide key fundamental insight on the EnT mechanism of D-A fluorophores but also establish its wide utility in EnT-mediated photocatalytic reactions.
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