A pair of strongly reductive and oxidative photocatalysts for the general upcycling of biomass derivatives and plastic wastes

Tailoring photocatalysts to achieve both strongly reductive and oxidative properties from a common scaffold remains challenging. Herein, we report the development of a pair of photocatalysts, isothiatruxene (ITS) and isosulfonyltruxene (ITSO₂), by modulating the valence states of heteroatoms. ITS exhibits highly reducing power, facilitating selective cleavage of C-O bonds in biomass derivatives despite their negative redox potentials. Upon oxidation of ITS, the resultant ITSO₂ demonstrates strongly oxidizing capacity, enabling metal-free and acid-free upcycling of plastic wastes even with their high redox potentials. By immobilizing ITS and ITSO₂ on polystyrene and oxidized lignin supports, respectively, we have developed recyclable photocatalysts that drive multiple catalytic cycles with high efficiency. Gram-scale upcycling of plastic is achieved by integrating photoredox catalysis with flow chemistry. Mechanistic studies reveal that the excited states of ITS and ITSO₂ can directly activate inert substrates, correlating with their strong redox properties. The newly introduced pair of photocatalysts, characterized by their metal-free nature, concise synthesis <i>via</i> trimerization, and dual photocatalytic capabilities encompassing both strongly reducing and oxidizing properties, show great potential for a wide range of applications. Furthermore, this study presents a sustainable catalytic strategy for synthesizing high-value aromatic compounds directly from biomass derivatives and plastic wastes.