Ratiometric Fluorescence Sensing and Real-Time Detection of Water in Organic Solvents with One-Pot Synthesis of Ru@MIL-101(Al)–NH₂

Abstract

Ratiometric fluorescence detection attracts much attention because of its decreased environmental influence and easy-to-differentiate color and intensity change. Herein, a guest-encapsulation metal-organic framework (MOF), Ru@MIL-NH₂, is prepared with 2-aminoterephthalic acid, AlCl₃, and Ru(bpy)₃²⁺ by a simple one-pot method for ratiometric fluorescence sensing of water in organic solvents. The rational selection of the excitation wavelength provides dual emission at 465 and 615 nm from Ru@MIL-NH₂ under a single excitation of 300 nm. High sensitivity, low detection limit (0.02% v/v), wide response range (0-100%), and fast response (less than 1 min) are obtained for ratiometric fluorescence sensing of water under single excitation with Ru@MIL-NH₂ as the probe. Moreover, the result of water content is independent of the concentration of Ru@MIL-NH₂ as the merit of ratiometric fluorescence detection. The response mechanism reveals that the protonation of the nitrogen atom of the MIL-NH₂, the π-conjugation system, and the stable fluorescence of Ru(bpy)₃²⁺ achieve the ratiometric fluorescence. The analysis of real spirit samples confirms the proposed method. A test strip is prepared with Ru@MIL-NH₂ for convenient use. We believe that such turn-on ratiometric host-guest MOFs and the rational selection of excitation wavelength will offer guidance for ratiometric fluorescence detection with wide applications.