Systematic Tuning of the Electronic Effects in Covalent Organic Frameworks for Promoting Photocatalysis

The efficiency of covalent organic framework (COF)-based photocatalysts depends on their electron transfer behavior, which can be rationalized in terms of conjugation effects and induction effects. While conjugation effects have been widely explored in COF-based photocatalysts, induction effects have largely been ignored despite being important to overall photocatalytic activity. Herein, a new isoreticular series of ordered COFs was rationally designed to determine the relative importance of conjugation and induction effects in promoting photocatalytic activity. Systematic component modulation revealed the importance of a balance of conjugation and induction effects in achieving optimum catalytic performance in COF-based photocatalysts. Our study shows that (i) induction effects lead to electrons accumulating in specific positions of COFs, while (ii) p-π and π-π conjugation enables accurate electron transfer to the electron-rich active sites, thereby facilitating photogenerated electron-hole separation and transport and boosting photocatalytic activity. One of our developed COFs (COF-3S) displayed excellent photocatalytic uranium extraction performance in contaminated groundwater and seawater. These results establish that both induction and conjugation effects affect the photocatalytic activity of COFs, which is expected to provide new insight into the rational design of high-performance COF-based photocatalysts.