biostudies-literatureUnknown5(11)Liu LClassical distance-dependent Dexter energy transfer models fail to account for the complex, geometry-sensitive kinetics observed in flexible and dynamically disordered organic photocatalytic systems. To resolve these persistent inconsistencies, particularly in photosensitized [2 + 2] cycloaddition reactions, we investigate how charge-transfer (CT) intermediates mediate triplet-triplet energy transfer (TTEnT) beyond the conventional Dexter framework. Through a combined approach integrating high-level multistate CASPT2 calculations, ultrafast transient absorption spectroscopy, and electrochemical analysis, we uncover two distinct and previously unrecognized TTEnT pathways: a CT trap mechanism and a CT-mediated sequential TTEnT mechanism in which electron and hole transfer steps bridge the doJACS Au5481-5492https://www.ebi.ac.uk/biostudies/studies/S-EPMC12648329biostudies-literatureA Charge Transfer Mediated Sequential Triplet Energy Transfer Model Beyond the Dexter Limit in Organic Photocatalysis.PMC12648329Liu XQiao YLiu LJie JWang QFeng KFang WChen XSu HShi YfalseA Charge Transfer Mediated Sequential Triplet Energy Transfer Model Beyond the Dexter Limit in Organic Photocatalysis.Classical distance-dependent Dexter energy transfer models fail to account for the complex, geometry-sensitive kinetics observed in flexible and dynamically disordered organic photocatalytic systems. To resolve these persistent inconsistencies, particularly in photosensitized [2 + 2] cycloaddition reactions, we investigate how charge-transfer (CT) intermediates mediate triplet-triplet energy transfer (TTEnT) beyond the conventional Dexter framework. Through a combined approach integrating high-level multistate CASPT2 calculations, ultrafast transient absorption spectroscopy, and electrochemical analysis, we uncover two distinct and previously unrecognized TTEnT pathways: a CT trap mechanism and a CT-mediated sequential TTEnT mechanism in which electron and hole transfer steps bridge the do2025-01-01T00:00:00Z2025 Nov2026-06-05T17:58:55.843Z2026-05-19T03:12:08.525ZS-EPMC126483294131192810.1021/jacsau.5c00968