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.