The AIE-active flavonoids in orange peel for photocatalytic oxidation reactions

Abstract

Photochemical organic synthesis has emerged as a prominent and important synthetic methodology in recent years. However, conventional photosensitizers are often expensive and require multi-step synthesis for their preparation. This study utilizes natural flavonoids extracted from citrus peel (Tangeretin, Nobiletin, and Sinensetin) as photocatalysts to achieve the photooxidation of alkenes. Conversion rates of 53.7% for styrene and 66.1% for cyclohexene were attained. Reaction Mechanism Generator (RMG) simulations revealed that alkenes undergo reaction pathways mediated by singlet oxygen or oxygen-free radicals to form the corresponding products, a finding corroborated by a series of control experiments and EPR. These flavonoid compounds exhibit Aggregation-Induced Emission (AIE) characteristics. Upon encapsulation with saponins to form nanoparticles, the conversion rate for cyclohexene was further enhanced to 86.0%. Furthermore, this system successfully achieved the efficient oxidation of benzyl alcohol in an aqueous solvent (52.4% conversion, >99% selectivity). This work establishes a comprehensive green chemistry system encompassing the light source, catalyst, and solvent. The proposed strategy offers a novel approach to the development of natural photocatalysts and sustainable organic synthesis.