Molecular structural engineering of donor–acceptor-based porous organic polymers for sulfide photooxidation in water: a sustainable approach

The utilization of mild and environment-friendly reaction conditions for the photocatalytic oxidation of sulfides to highly valuable sulfoxides represents a sustainable approach that is highly desirable yet quite challenging. Herein, we present a novel approach to enhance the photocatalytic oxidation of sulfides in water by molecular structural engineering of donor–acceptor (D–A) based polymeric networks. By incorporating electron-deficient heptazine or triazine units as acceptors and electron-rich 2,5-diamino fluorene as donors, a synergistic effect is achieved, promoting efficient charge separation upon light absorption. The two polymeric networks namely HEP-FL and TZ-FL efficiently carried out selective oxidation of sulfides to sulfoxide with 100% conversion within 1.3 h and 3.5 h, respectively under blue light irradiation. Through advanced spectroscopic and electrochemical measurements, the correlation between molecular structures and optoelectronic properties is elucidated, unveiling tunable band structures and exciton binding energies. Notably, the heptazine-containing polymeric network (HEP-FL) exhibited superior charge separation efficiency and enhanced catalytic activity, attributed to improved electron delocalization and reduced exciton binding energy. Additionally, we have performed green metrics calculations for the synthesis of sulfoxide using HEP-FL as a photocatalyst to prove the sustainability of the reaction system. These findings underscore the significant prospects of donor–acceptor-based polymeric networks as highly effective photocatalysts for selective oxidation reactions, highlighting their potential to advance environmentally conscious practices in organic synthesis and industrial applications.