Enhanced protonation ability of covalent organic frameworks via N , O -bidentate chelation for photocatalytic H 2 evolution.

Inspired by the bidentate coordination chemistry of metal ions, we incorporated hydroxyl (OH) and methoxy (OMe) groups into the skeleton of imine-linked COFs to improve their protonation ability via intramolecular hydrogen bonds (O-H⋯NC). In comparison with the pristine COFs possessing monodentate nitrogen coordination sites, OH and OMe functionalized COFs with ( N , O )-bidentate chelating sites exhibited up to 13.8 times faster photocatalytic hydrogen evolution rates (HERs).