Modulating fluorescence sensing properties of excited-state intramolecular proton transfer (ESIPT)-based metal organic frameworks (MOFs) by metal polarization

Abstract

Al³⁺, Ga³⁺, In³⁺ and ligand 2,5-dihydroxyterephthalic acid (DHBDC) are used to construct the MIL-53 structure, which shows a sensing process based on the mechanism of excited state intramolecular proton transfer (ESIPT). The electron cloud density of the ligand in the framework is regulated by the metal, further adjusting the fluorescence sensing performance of the MOF. As the polarization of the metal weakens, the ligand-to-metal charge transfer ability weakens, the proton transfer ability of the DHBDC ligand increases, and the detection sensitivity increases. This rule was verified in the process of MIL-53-Al/Ga/In for N₂H₄ detection. The detection sensitivity and detection rate were ranked in the order MIL-53-In > MIL-53-Ga > MIL-53-Al. MIL-53-In was successfully applied to construct a high sensitivity, fast detection rate and reusable N₂H₄ sensor. This rule also laid the foundation for the construction of subsequent high-sensitivity fluorescence sensors. In addition, MIL-53-Al/Ga/In exhibits high-performance temperature sensing capabilities, which can achieve temperature sensing of 80–460 K.