Ultra-Stable Metal–Organic Framework with Concurrent High Proton Conductivity and Fluorescence Sensing for Nitrobenzene

Abstract

Luminescent metal–organic frameworks (MOFs) coupled with proton conduction offer wide applications in clean energy and luminescence sensors. High stability and remarkable proton conductivity and sensing are requisites for practical applications. Specifically, high thermal and chemical stabilities under harsh conditions are important but challenging to achieve. Herein, an ultra-stable Cu(I)-tetrazolate MOF, NaCu3(mtz)4 (1, mtz = 5-methyltetrazolate), was prepared. It possesses a 3D framework with 1D channels and exhibits outstanding thermal and chemical stabilities under various conditions, including water, organic solvents, and acidic and basic solutions of wide pH range. The compound exhibits strong green emissions, which can be ascribed to metal-to-ligand charge transfer, and selective fluorescence sensing for pollutant nitrobenzene. Moreover, compound 1 presents a high proton conductivity of over 10–2 S cm–1 at 70 °C and 100% relative humidity. In 1, abundant uncoordinated nitrogen atoms on the pore walls act as H-bonding acceptors to achieve its high proton conductivity under water-assisted conditions. The compound is an unprecedented water-dependent proton conductor of the tetrazole-based MOF, providing a new avenue to design robust and high-performance proton-conductive MOFs.