Direct photoexcitation of borate complexes for radical generation: A platform from organic synthesis to chemical biology

Photochemical reactions enable access to reactive intermediates and bond-forming pathways that are often inaccessible under conventional thermal conditions. Among these, photoredox catalysis has become a powerful method for generating radicals, but it typically relies on multistep electron- and energy-transfer processes that can limit the efficiency and design of reaction. Herein, we present the development of borate complexes that can be directly excited by light to generate carbon-centered radicals, which provides a simpler and more versatile alternative to the aforementioned methods. The initial boracene-based systems enable visible-light-driven cleavage of carbon-boron bonds to form alkyl radicals with strong reducing capability. To improve functional group compatibility, a second-generation complex prepared from widely available boronic acids was developed. These systems enable diverse reactions, including carbon-carbon bond formation and transformations of biologically relevant molecules. Furthermore, extension to deep-red and near-infrared light allows radical generation under lower-energy irradiation, which is advantageous for practical and biological applications. Finally, this approach enables a new type of photocaged molecule that releases bioactive compounds with precise spatial and temporal control, as demonstrated for acetylcholine in cellular and neural imaging. These studies highlight the direct excitation of borate complexes as a versatile platform for bridging synthetic chemistry and chemical biology.