Three-motif thienothiophene-based covalent organic frameworks with tailored acceptor-donor-acceptor architecture for enhanced photocatalytic aerobic oxidation.

Abstract

Covalent organic frameworks (COFs) capable of molecular-level design and synthesis for property modulation have been widely employed in photocatalytic aerobic oxidation reactions. Herein, we report the synthesis of two novel three-motif covalent organic frameworks (COFs) composed of thieno[3,2-b]thiophene and triphenylamine as common building blocks, namely COF-TDBT-TPE (where TDBT represents the two-motif molecular junction monomer consisting of thieno[3,2-b]thiophene and triphenylamine, and TPE represents tetraphenylethylene) and COF-TDBT-Py with pyrene. Density functional theory (DFT) calculations reveal that, compared with the donor-donor-acceptor (D-D'-A) architecture of COF-TDBT-Py, the acceptor-donor-acceptor (A-D-A') architecture of COF-TDBT-TPE endows this COF with higher charge mobility and effectively suppresses charge recombination within the COF framework. Photoelectrochemical measurements further demonstrate that COF-TDBT-TPE possesses a narrower optical bandgap and enhanced photocurrent response. Consequently, COF-TDBT-TPE exhibits superior photocatalytic activity compared with COF-TDBT-Py (yields of 98.7% vs 87.3% for benzimidazole synthesis and 93.1% vs 80.7% for benzylamine oxidative coupling), while also showing excellent substrate universality and reusability. This three-motif construction strategy regulates the electronic structure and conjugation system of thiophene-based COFs by designing and introducing different building units, thereby effectively enhancing photocatalytic performance, increasing the structural design flexibility of photoactive COFs, and providing a new approach for constructing efficient COF photocatalysts for diverse aerobic oxidation reactions.