Multi-functional lanthanide coordination polymers for multi-modal detection of nitroaromatics and trace water in organic solvents

Abstract

Multifunctional materials used for multimodal sensors are of great significance both for enriching variety of materials and overcoming the shortcomings of traditional single signal sensors. This work reports the ultrafast preparation of multifunctional coordination polymer (CP) spheres with metalloligand Ru (II)[4,4′-(COOH)2-bpy]3▪Cl2 (L) and Gd3+ ions. Gd-L CPs were used for multi-modal detection of nitroaromatic explosives and trace water in organic solvents with their red fluorescence and magnetic resonance response. The red fluorescence was derived from the ligand, which is electron-rich because of the bipyridine rings. There were different emission behaviors when Gd-L CPs reacted with nitroaromatic explosives that have various electron-deficient properties through electron transfer donor–acceptor mechanism. The changes in the emission depended closely on the nitroaromatic explosives ability to withdraw electrons. Gd-L CPs also showed magnetic resonance response with r1 of 12.1 mM−1s−1 due to the integration of the paramagnetic property of Gd3+ ions. Smart sensing of trace water in organic solvents was achieved by magnetic signals. The fluorescence of Gd-L CPs was enhanced and there was a tiny blue-shift in protonic solvents with increased polarity. The fluorescence sensor used in detecting trace water had a consistent result like the MR response. Thus, Gd-L CPs enabled the use of fluorescence and magnetic resonance sensors simultaneously for the first time to overcome the shortcoming of single modal sensor and expand the application of magnetic resonance relaxation.