Push–pull–pull interactions of 2D imide–imine-based covalent organic framework to promote charge separation in photocatalytic hydrogen production

Abstract

Photocatalytic hydrogen production through water splitting provides a promising route towards renewable energy generation. However, constructing photocatalytically active covalent organic frameworks with high charge separation remains challenging. Herein, we demonstrate for the first time the use of 2D imide–imine-based covalent organic frameworks as new photocatalysts for the hydrogen evolution reaction (HER) under visible light irradiation. The main achievement is incorporating donor and dual acceptors, including weak electron-deficient imine and strong electron-deficient imide groups within the 2D COF backbone that create favorable push–pull–pull intramolecular charge transfer to promote charge separation after photoexcitation. DFT and NBO calculations revealed the strong integration of donor and dual acceptors with a synergistic interplay enhancing spatial charge transfer and separation. The synthesized COFs show significantly high thermal stability >400 °C with a high energy barrier for degradation. Moreover, Py-DNII-COF exhibited a 104-fold enhancement in hydrogen evolution compared to TFPB-DNII-COF. Py-DNII-COF demonstrated excellent stability and hydrogen evolution of 625 μmol h⁻¹ g⁻¹ over 48 hours.