Aminoboranes as Rationally Tuned Organic Photosensitizers for Energy Transfer Catalysis

We report a new class of rationally designed organic photosensitizers based on boron-nitrogen-substituted scaffolds, capable of mediating challenging triplet energy transfer (EnT) reactions under visible-light irradiation. Guided by DFT and TD-DFT calculations, we modulated the twisted intramolecular charge transfer (TICT) character of the excited state through strategic substitution on the carbazole-borane framework, allowing fine-tuning of both absorption and triplet energy levels (E_T = 63-70 kcal mol^-1). The most effective catalyst outperformed traditional Ir- and xanthone-based sensitizers across benchmark EnT reactions, including E/Z isomerizations, [2 + 2] photocycloadditions, and [1,3]-sigmatropic rearrangement. This B-N system enables the sensitization of coumarin-related substrates with E_T ≥ 65 kcal mol^-1, which was previously inaccessible to fully organic EnT photocatalysts. These results establish a new design principle for modular, high-energy triplet sensitizers based on organic aminoborane scaffolds.