Highly Efficient Photolysis via Reversible Triplet–Triplet Energy Transfer

Modulating molecular excited-state dynamics toward the desired bond cleavage pathways while suppressing competing unproductive decay processes is a significant challenge for the rational design of highly efficient photolytic systems. Conventional strategies, relying on covalent molecular engineering or unidirectional photosensitization of photoremovable protecting groups (PPGs), often suffer from limitations such as complex synthesis, compromised physicochemical properties, and inefficient energy utilization. Inspired by the bidirectional energy recycling in reversible triplet-triplet energy transfer (rTTET) systems, we propose an rTTET-mediated photolysis strategy to improve energy utilization efficiency, converting energy that is wasted in conventional TTET strategies into chemical work. This approach establishes an rTTET process between PPGs and carefully selected triplet photosensitizers. A 3-fold enhancement in photolysis quantum yield for typical coumarin-based PPGs was achieved without altering their molecular structures, making this strategy, to our knowledge, the most efficient noncovalent approach reported to date. The underlying principle of this energy-recycling strategy is universal, which can be broadly applied to diverse PPGs and other triplet-state-mediated photochemical processes, paving the way for the rational design of highly efficient photoactive systems.