Efficient photothermal catalytic oxidation of 5-hydroxymethylfurfural using stable 4-OH-TEMPO radical

Open-shell organic radicals, characterized by their unique spin states, typically exhibit exceptional photothermal conversion efficiency. However, the development of open-shell organic radical materials with stability and high photothermal properties remains a challenge. Among these radicals, the stable and commercialized 4-OH-TEMPO radical molecule has garnered considerable attention in various organic synthesis reactions owing to its unique redox advantages, but it shows less application comparing with the other open-shell organic radicals in photo-thermal conversion. In this study, 4-OH-TEMPO exhibits favorable photothermal properties upon combination with Cu 2 + , thus it is capable of enhancing the reaction rate of HMF oxidation to DFF by a factor of 10 under LED (400 nm). Under illumination of LED, leading to the complete conversion of HMF and the generation of DFF with a yield of 99.7 % within 30 min. Mechanism study shows that the photothermal effect facilitates the kinetic process of the reaction, and accelerated conversion of 4-OH-TEMPO to the oxidatively active species 4-OH-TEMPO + under light-induced action further increased the reaction rate. This research proffers novel insights and references for 4-OH-TEMPO mediated organic synthesis reactions and the design of free-radical photothermal materials.