With regard to fluorescence quenching commonly observed during metal-ion detection, "turn-on" chemical sensing has been rarely reported, but could be extremely important because it facilitates the selective recognition of target objects of interest against a dark background. A metal-organic framework (MOF) chemosensor has been prepared that serves as an efficient platform for the selective detection of Cu and Cd ions over other metal ions. In particular, this framework shows the highest fluorescence enhancement (≈60-fold relative to Cd-free MOF) for the hazardous metal ion Cd among luminescent MOFs and displays excellent reusability in repeated cycles. The direct diffusion of Cd into the crystal pores has also been visualized for the first time.

A ZnII‐based metal–organic framework (MOF) serves as an efficient platform for the selective detection of Cu2+ and Cd2+ ions over other metal ions. In particular, this framework shows the highest fluorescence enhancement (≈60‐fold relative to Cd‐free MOF) for the hazardous metal ion Cd2+ among luminescent MOFs. The direct diffusion process of Cd2+ into the crystal pores could be visualized. More information can be found in the Full Paper by C. S. Hong et al. on page 4803 ff.