Abstract:

In this study, the electron-deficient pyridinium group and the naphthalene fluorophore were simultaneously introduced to a bipyridyl-containing Zr(Ⅳ) metal-organic framework (MOF) by the N-alkylation post-synthetic modification. The obtained ionic MOF, Zr-bpy-MNap, is nonluminous in the pristine state but shows selective fluorescence turn-on responses to some solvents and ammonia. Test papers were prepared using the MOF for the identification of solvents and detection of ammonia in air. The fluorescence turn-on response is considered to be due to complex host-guest interactions and solvation effects. The MOF is non-fluorescent due to the quenching effects of the host-guest communications between the bromide ion and the framework. On exposure to some solvents or ammonia, the quenching mechanisms are weakened or destroyed by the solvation of bromide or host-guest interactions between ammonia and the framework, resulting in fluorescence turn-on responses. The fluorescence originates from the charge-transfer transition between the naphthyl group and the electron-deficient framework.

Key words: metal-organic frameworks, post-synthetic modification, fluorescence sensor, ammonia