Sequential donor–acceptor dual modulation in conjugated microporous polymers enables efficient photocatalytic synthesis of symmetric ureas, benzothiazoles and functionalized indoles

Abstract

Donor–acceptor (D–A) conjugated microporous polymers (CMPs) have emerged as promising photocatalysts due to their tunable electronic structures and inherent porosity. However, a detailed molecular-level understanding of how specific monomeric functional groups influence photoinduced charge transfer and enhance reactive oxygen species (ROS)-driven photocatalytic processes remains limited. In this study, we propose a dual functional group modulation strategy to precisely tune the photophysical properties of CMPs for improved photocatalytic efficiency. In the first modification, the electron-withdrawing ketone group of the fluorenone-based acceptor unit in TPA-FLO is converted to an oxime, affording TPA-FLOX. Subsequently, the nitrogen atom in the triphenylamine (TPA) donor unit is replaced with a triazine moiety to yield TRZ-FLOX. Among them, TPA-FLOX exhibited an optimal band gap (2.25 eV), prolonged photoluminescence lifetime, higher oxygen adsorption energy, and enhanced charge transfer dynamics, resulting in superior photocatalytic activity. In this study, we introduced the photosynthesis of disubstituted urea from amine and carbon disulfide in one step using our heterogeneous photocatalysts. TPA-FLOX exhibits exceptional photocatalytic activity for the direct synthesis of diphenylurea from aniline, achieving 99% conversion and 97% isolated yield under visible light within 10 hours. The catalyst displays broad substrate compatibility (12 examples, 37–99% conversion) and excellent recyclability over six cycles. Beyond urea synthesis, TPA-FLOX effectively promoted the C–H thiocyanation of indoles (8 examples) and the photosynthesis of 2-benzothiazoles (12 examples), delivering isolated yields of up to 99% with wide functional group tolerance. Overall, this study demonstrates that oxime functionalization is an effective molecular design strategy for enhancing ROS-mediated photocatalysis by promoting charge separation and oxygen activation and providing a rational pathway for the development of next-generation CMP photocatalysts.