Dual Carbon Dot Ensemble: Visible-Light-Induced Photocatalysis with Reaction Monitoring and Simultaneous Byproduct Scavenging for the ipso-Hydroxylation of Aryl Boronic Acids

Selective oxidative transformations that avoid the use of peroxides, metal catalysts, harsh conditions, toxic reagents, and solvents are indeed crucial for sustainable industrial processes. Herein, we demonstrate the engineering of a carbon dot (CDpc) uniquely designed to fit the profile of a photocatalyst to comply with all the above sustainability factors for the conversion of arylboronic acid to phenol, chosen as a model reaction due to its mild reaction conditions, ease of oxidation, and myriads of readily available derivatives. Additionally, arylboronic acids offer advantages over conventional phenol precursors such as benzenes or aryl halides, which are potentially more toxic and less environmentally friendly, further aligning this study with green chemistry principles. Derived from l-arginine, ethylenediamine, and glucose through controlled hydrothermal pyrolysis, the CDpc photocatalyst preserves key functional groups of the substrates on their surface. The generation of reactive oxygen species (ROS) from CDpc upon visible white LED light (40 W) irradiation enables the ipso-hydroxylation of aryl boronic acids in water at room temperature under aerobic conditions with a high yield and broad substrate scope. Control reactions performed in the presence of various radical/hole scavengers established a type I ROS mechanism to be operative involving superoxide ions. Additionally, a naphthoic acid based CDms was employed to monitor the reaction in real time, taking advantage of its specificity toward boric acid, the sole byproduct of the reaction. A change in emission wavelength and hence fluorescence color from green to blue upon boric acid absorption on CDms embedded in agarose beads not only enables a visual cue toward the progress of the reaction but concurrently scavenges away the boric acid, making purification easy. Thus, for the first time, a dual-CD combo is presented for efficient metal and peroxide-free photocatalysis in water with the provision of simultaneous reaction monitoring and byproduct scavenging.