Switching Between Singlet and Triplet Excitation in Covalent Organic Frameworks for Highly Efficient Photocatalysis

ABSTRACT Singlet (S 1 ) and triplet (T 1 ) excitation serve as the two primary and competing pathways, playing crucial yet entirely distinct roles in the photocatalytic process. Achieving flexible switching between S 1 and T 1 excitation energies has remained a challenge. Herein, three 2D covalent organic frameworks (COFs) with offset stacking angles of 90°, 105°, and 128° were successfully synthesized by integrating folding building blocks within the skeleton. The results show that the strategic offset stacking can harness efficient π–σ attraction, thereby inducing intersystem crossing from S 1 to T 1 state. The face‐to‐face stacked BDT‐HHTP‐COF tends to follow the electron transfer pathway, thereby generating ·O 2 − . In contrast, BDT‐CTC‐COF with the most optimal offset stacking distance produces high concentrations of 1 O 2 , primarily attributing to the energy transfer pathway. Theoretical calculations prove that the BDT‐CTC‐COF can boost Coulomb interaction, trigger intersystem crossing, and accelerate the transfer of the T 1 exciton to the adsorbed O 2 throughout the matrix of the framework. This switch in the mechanistic pathway is critically important, as the highly electrophilic 1 O 2 exhibits superior efficacy in attacking the electron‐rich aromatic ring of toluene, initiating a selective oxidation process that rapidly achieves over 98% degradation and 80% CO 2 mineralization, representing a 1.5‐fold enhancement compared to the electron transfer‐dominated pathway.