Conformation-Locking in Thiazole-Rich Mixed-Linkage Covalent Organic Frameworks for Spontaneous Exciton Dissociation and Efficient Photocatalysis.

Abstract

The formidable exciton effect inherent in organic semiconductors fundamentally restricts free charge carrier generation, thereby impeding photocatalytic redox efficiency. Facilitating spontaneous exciton dissociation and lowering exciton binding energy are essential for maximizing charge utilization. Herein, we report a conformation-locking strategy to engineer a thiazole-rich mixed-linkage donor-acceptor conjugated covalent organic framework (SBt-Tapt) via post-synthetic cyclization. The seamless integration of sulfur heteroatoms into a rigid, thiazole-bridged framework significantly enhances π-conjugated and electronic polarizability. Crucially, this structural reinforcement lowers the exciton activation energy below to 25 meV, triggering spontaneous exciton dissociation, extending carrier lifetimes, and yielding a proliferation of free charge carriers at room temperature. Mechanistic insights elucidate that the thiazole moieties synergistically activate adjacent phenyl units for O2 reduction while simultaneously lowering the energy barrier for H2O oxidation at benzothiophene sites. This dual-pathway mechanism drives efficient H2O2 photosynthesis with robust operational stability exceeding 100 h. Notably, utilizing phenolic pollutants as proton donors, SBt-Tapt delivers an exceptional H2O2 evolution rate of 8.99 mmol gcat -1 h-1 alongside effective pollutant mineralization. This study elucidates a profound structure-activity relationship (SAR) and establishes conformation locking as a potent excitonic engineering paradigm for developing high performance organic photocatalysts.