Asymmetric Chiral Photocatalysts

Abstract

Traditional photocatalysts generally have a limitation of weak photoresponsiveness. Although current modification methods can improve light absorption and photoresponsiveness by increasing the surface area and optimizing the bandgap width, the vast majority of visible light has not been effectively utilized. Inorganic chiral photocatalysts can be synthesized using chiral solvents, additives, or templates as inducers. For nonpure phase inorganic chiral photocatalysts, their three-dimensional chiral nematic structure can be used to selectively reflect circularly polarized light, thereby reducing light energy loss and improving the photocatalyst’s light absorption capacity. It is worth noting that the photoactivity of these materials is not dependent on the specific chiral orientation of the structure. For pure phase inorganic chiral photocatalysts, the chirality index and radius would affect the band gap of the photocatalyst. Therefore, by adjusting these parameters, the band structure can be optimized to utilize more visible light, thereby improving the light absorption capacity. Compared to traditional thermal or electrocatalysis, asymmetric photocatalytic reactions offer two distinct advantages: (1) using light as an energy source can reduce dependence on fossil fuels and help achieve a more environmentally friendly and energy-efficient process; (2) photocatalytic reactions, operating through excited-state processes, can achieve transformations that are difficult or impossible to realize through conventional thermal or electrocatalytic methods. Therefore, the development of efficient asymmetric photocatalysts is a core requirement in the field of asymmetric photocatalysis. In contrast, single and dual functional chiral photocatalysts integrate visible light excitation and stereo control in the same catalyst, allowing the induced free radical intermediates to be placed in a chiral configuration. The introduction of chiral structures facilitates the rational design of photocatalytic systems, enabling precise control over the catalytic activity and selectivity. This review delves into the role of chiral ligands in regulating the conformational, electronic, and spatial structures during catalytic reactions, providing important insights for designing catalysts with higher activity and selectivity. Additionally, it summarizes the relationship between chiral ligands and catalytic reaction mechanisms, offering the potential to uncover key steps and reaction kinetics in the catalytic processes. This could provide a more systematic theoretical framework for the precise design of catalysts, thus promoting the widespread industrial application of asymmetric catalytic reactions.