Schiff base COFs for photocatalysis: From fundamentals to applications

In recent times, there has been extensive exploration of Schiff base chemistry or dynamic imine chemistry for synthesis of covalent organic frameworks (COFs). Schiff base COFs are found to be very attractive for the applications in photocatalysis due to their dynamic imine chemistry and π-conjugated structures. Their extensive π-delocalization and donor-acceptor (D-A) framework enhances light absorption, charge separation, and electron transport, allowing for band gap tuning from UV to near-infrared absorption. Consequently, numerous investigations have been conducted to examine and comprehend the photocatalytic efficacy of Schiff base COFs. As a contribution, we present a comprehensive overview of recent advancements in research concerning COFs incorporating Schiff base-type linkages imine, hydrazone, azine, and β-ketoenamine or keto-enol linkages in multiple photocatalytic processes, such as organic transformation, hydrogen (H 2 ) production, carbon dioxide (CO 2 ) reduction, and pollution degradation. This review encompasses discussions on the linkage chemistry, concise synthetic methodologies, and the advantages of employing Schiff base COFs as photocatalysts, which represent a forefront area in materials science research. Additionally, the opportunities and challenges in advancing Schiff base COFs for photocatalysis and strategies to enhance their performance, aiming to inspire further research in this field are discussed. In this review, recent research progresses of COFs involved Schiff base-type linkages such as imine, hydrazone, azine and β-Ketoenamine or keto–enol linkages in photocatalytic applications such as hydrogen (H 2 ) production, carbon dioxide (CO 2 ) reduction, organic transformation, and degradation of pollutants etc. has been described. Moreover, various methods used for the fabrication of COFs including solvothermal, microwave, ionothermal, atmospheric solution, mechanochemical, and interfacial synthesis are also described briefly. The advantages and fundamentals of COFs along with Schiff base linkage COFs for photocatalysis are also highlighted. Lastly, a summary and perspective on the opportunities and challenges for the future development of Schiff base COFs and strategies for enhancing their photocatalytic activity are indicated briefly. • Linkage chemistry for optimizing crystallinity, stability, and functionalization in Schiff base COFs are reviewed. • This work compares conventional and emerging low-energy methods for optimizing synthesis cost, speed and structural quality. • Schiff base linkages contribute to enhance π-conjugation, boosting light absorption and charge transfer. • D-A alternating units in Schiff base COFs form super heterojunctions, enhancing charge separation and reducing recombination. • The D-A architectures, chiral centers, and tunable band gaps enable Schiff base COFs for divers photocatalytic applications.