Bifunctional photo- and vapochromic behaviors of a novel porous zwitterionic metal–organic framework

A novel zwitterionic metal-organic framework [Zn(Cbdcp)(4,4'-bipy)(0.5)]2H(2)O (Zn-MOF) with large holes was synthesized by utilizing a flexible zwitterionic ligand H3CbdcpCl (Cbdcp = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium) and auxiliary ligand 4,4'-bipy. The framework exhibited photochromic property, and we simulated the competition mechanism between pyridine and 4,4'-bipy through theoretical calculations. The results showed that 4,4'-bipy exhibited stronger electron-accepting ability than pyridine, and O atoms from the benzene carboxylic groups were mainly electron donors. More attractively, the compound also showed significant color change from colorless to yellow when exposed to NH3, ethylamine (EA), and n-propylamine (PA) vapor within just a few seconds. This work provides abundant scope to explore novel MOF materials as colorimetric sensors and a new route to design practical MOFs.