Excited-state intramolecular proton transfer (ESIPT) active interwoven polycatenated coordination polymer for selective detection of Al3+ and Ag+ ions along with water detection in less polar solvents

Abstract

The external stimuli-responsive excited-state intramolecular proton transfer (ESIPT) on/off mechanism is a unique and expedient sensing method that offers easy monitoring through the transition between dual and single-peak emissions. To avail this advantage of ESIPT-based sensing for selective metal ion detection and trace water detection, we have synthesized a 2,5-dihydroxyterephthalate (dht)-based interwoven polycatenated coordination polymer (1). The synthesized compound has been thoroughly characterized using single-crystal and powder X-ray diffraction techniques, along with other physicochemical methods. The synthesized compound exhibits a visual luminescence color change from faint yellow to bright green under UV irradiation in the presence of Al³⁺ ions. This change is attributed to a blue shift in fluorescence maxima of the keto form of the dht ligand in contact with Al³⁺ ions. Additionally, the material detects Ag⁺ ions through an ESIPT-off mechanism. These significant changes in ESIPT – blue shifting for Al³⁺ and ESIPT-off for Ag⁺ – start in just 1 mM aqueous solutions of these ions. Significantly, the ESIPT-off for Ag⁺ is evident even in the presence of other interfering ions. Beyond metal ion detection, this material also offers both qualitative and quantitative sensing of trace amounts of water in various polar organic solvents, such as ethanol (EtOH), tetrahydrofuran (THF), isopropanol (IPA), acetone, and acetonitrile (ACN), through the ESIPT-on/off phenomenon. The activated framework of compound 1 (1′) can detect 2%, 4%, 4%, 3%, and 3% water in acetone, ACN, EtOH, IPA, and THF, respectively; through the conversion from a single to dual hump emission alteration. The respective ESIPT peak shift and ESIPT-on/off in the presence of metal ions and water is explained by the interaction between the host coordination polymer and guest analytes.