Engineering of Donor‐Acceptor Nanodomains in Zn‐Salen COFs Enhances Efficient Coupling Photoredox of Oxygen and Indoline

Abstract

ABSTRACT The photocatalytic coupling of molecular oxygen with organic substrates, such as indoline represents a sustainable solar‐to‐chemical strategy. However, designing highly‐efficient organic photocatalysts still remains a significant challenge. Herein, three Zn‐Salen covalent organic frameworks (COFs, Zn‐Salen‐EN, ‐PD, and ‐HATP) with tunable donor‐acceptor (D‐A) nanodomains were synthesized through combining the same Zn‐Salen acceptor units with different electron‐donating linkers including ethylenediamine (EN), 1,2‐phenylenediamine (PD), and 2,3,6,7,10,11‐hexaaminotriphenylene (HATP). Among them, Zn‐Salen‐PD exhibits best activity for the two‐electron photoreduction of O 2 (2e − ORR) to produce hydrogen peroxide (H 2 O 2 ) with a rate of 26 700 µmol g cat −1 h −1 , while simultaneously enabling efficient photocatalytic indoline dehydrogenation to generate indole (2e − IND‐DR). The enhanced performance of Zn‐Salen‐PD stems from its optimal D‐A spatial alignment and a tailored band structure, which achieve a balanced synergy among exciton dissociation, charge carrier lifetime, and electron reduction capability. Moreover, mechanistic insights from in situ spectroscopy and theoretical calculations revealed that ZnN 2 O 2 motifs served as efficient Griffith‐type 2e − ORR active centers, while photoinduced holes accumulated on the donor units to drive 2e − IND‐DR. This work demonstrates that the nanoscale engineering of D‐A structures within metal‐COFs offers a powerful strategy for enabling coupled photoredox transformations.