An intrinsically zwitter-ionic COF: a carboxylic acid and pseudo-tetrahedral sp 3 nitrogen functionalized covalent organic framework with potential for humidity sensing

A carboxylic acid functionalized sp 3 N-rich imine bonded COF shows a humidity-dependent visible color change. This COF is easily exfoliated to nanosheets, which are explored as a potential humidity sensor that detects trace water in organic solvents.