Three‐Dimensional Spirobifluorene‐Based COF for Metal‐Free Photocatalytic CH Oxidation Reaction

Three‐dimensional covalent organic frameworks (3D COFs) have emerged as promising materials for photocatalysis due to their interconnected pore channels, low density, high surface area, and robust chemical stability. However, the rational design and synthesis of 3D COFs with tailored photoresponsive properties remains a significant challenge. In this work, we incorporate two photoactive building blocks, spirobifluorene and N , N , N ′, N ′‐tetra(p‐aminophenyl)p‐phenylenediamine (TPDA), and successfully fabricate a novel 3D COF, designated TPDA‐COF, via solvothermal synthesis. Structural characterization unambiguously confirms its crb topology, whereas nitrogen adsorption measurements reveal a high BET surface area of 1747 m 2 g −1 . Importantly, spectroscopic and electrochemical studies demonstrate that TPDA‐COF exhibits pronounced semiconductor behavior under visible‐light irradiation. Electron paramagnetic resonance spectroscopy provides direct evidence for the generation of superoxide radical anions (O 2 •− ) via photoinduced electron transfer from TPDA‐COF to molecular oxygen (O 2 ). Leveraging this property, we employ TPDA‐COF as a heterogeneous photocatalyst for the α‐selective oxidation of N‐substituted tetrahydroisoquinolines (THIQs) under mild conditions using O 2 as a green oxidant. The reaction proceeds with high efficiency and selectivity, demonstrating the capacity of the 3D framework to promote aerobic oxidative transformations. This study illustrates the structural benefits of 3D COFs and their potential as tunable sustainable photocatalysts for organic synthesis.