Molecularly Tuned Carbon Dots for Visible-Light-Driven Boryl Radical Generation via Enhanced Hole Transfer

Carbon-based, metal-free photocatalysts are emerging as sustainable alternatives to transition-metal-based systems due to their tunability, abundance, and environmental friendliness. Among them, carbon dots (CDs) offer unique opportunities in visible-light-driven transformations owing to their excellent photostability, electronic tunability, and surface functionalization capacity. However, the development of structurally defined CD-based catalysts that enable efficient hole transfer, a broad substrate scope, and scalability remains a key challenge. Herein, we report the first bifunctional, quasi-homogeneous CD-based photocatalytic platform that combines visible-light absorption with cooperative hydrogen atom transfer (HAT) catalysis. Using a covalent molecular design, thiol groups were precisely anchored onto the CD surface, enabling fast and efficient hole transfer and promoting the reductive quenching of the excited CD to produce thiyl radicals. This molecular tuning facilitates efficient boryl radical generation via HAT of N-heterocyclic carbene–borane (NHC-BH3), and enables broad substrate applicability on boration of naphthalenes, indoles, alkenes, and polyfluoroarenes. The method is readily scalable, performing smoothly under both gram-scale batch and continuous flow conditions. Detailed mechanistic studies reveal that the thiol groups accelerate excited-state charge separation and act as hole acceptors, highlighting a hole-transfer-driven catalytic mechanism. This work demonstrates how molecularly tailored CDs can serve as multifunctional, metal-free photocatalysts and provides a new blueprint for advancing dual catalytic organic transformations under visible light.