Single bond regulated 1O2 and ‧O2− selective generation of heptazine-based conjugated polymers for high-selectivity photocatalysis

Abstract

In conjugated polymers (CPs) photocatalytic system, the generation of reactive oxygen species (ROS) is regulated by cross-scale factors involving active site, excitonic behavior, and O₂ activation process on the surface. However, research on exploring the domino effect of “structure → excitonic behavior → O₂ activation → photocatalytic reaction” through structural modification at the atomic scale remains at its early stages. Herein, two heptazine-based CPs, CP-DPA, and CP-CZ were successfully prepared by polymerization of precursors formed by reacting diphenylamine (DPA) and carbazole (CZ) with cyameluric chloride, respectively. The minute difference in single bond between DPA and CZ endows the polymers with distinct physicochemical properties. Owing to the rotation between benzene rings, CP-DPA exhibits relatively lower conjugation, resulting in increased exciton binding energy (E_b) and inhibited exciton dissociation. Meanwhile, its more triplet state excitons facilitate energy transfer to generate singlet oxygen. Therefore, CP-DPA shows excellent activity for phenylboronic acid oxidation. Conversely, CP-CZ possesses relatively higher conjugation, minimal E_b and intensified exciton dissociation, which promotes charge transfer to produce superoxide radical. Consequently, CP-CZ displays optimal activity for phenylacetylene oxidation and [3 ​+ ​2] cycloaddition. This work provides new insights into regulating ROS generation by modulating the composition and structure of photocatalysts at the atomic scale.