Poly(benzothiadiazoles) and Their Derivatives as Heterogeneous Photocatalysts for Visible-Light-Driven Chemical Transformations

Visible-light-driven chemical transformations via photocatalysis have witnessed an explosive growth in the past decade, accompanying the enormous development of the photocatalyst design. Among the intensely investigated systems, molecular photocatalysts as transition-metal complexes and conjugated organic dyes have been established as efficient homogeneous photocatalytic systems for organic photoredox reactions. Nonetheless, heterogeneous photocatalysts possess considerable advantages such as being highly stable, easily separable, and reusable. Especially, the organic, macromolecular heterogeneous photocatalysts have emerged as a nontoxic and potentially more environmentally friendly alternative to the traditional catalytic systems. Among them, poly(benzothiadiazoles) and their derivatives have demonstrated the ability to catalyze various organic photoredox reactions under visible-light irradiation. In this Review, the recent development of metal-free and heterogeneous photocatalytic systems based on poly(benzothiadiazoles) and their derivatives is summarized. An overview of organic photoredox reactions mediated via radicals obtained from the photogenerated electron and hole of the photocatalysts is given, and the underlying mechanisms of photochemical transformations are illuminated. The structural design principles of poly(benzothiadiazoles) for targeted photoredox reactions are also discussed.