A Metallogel Based on a Zwitterionic Spirocyclic Meisenheimer Complex: Sensing of Fluoride Ions in Water and Moisture Content in Organic Solvents

Abstract

Design and synthesis of stimuli‐responsive materials are highly desired for various practical applications. For this purpose, a picric acid and N,N′‐dicyclohexylcarbodiimide based highly rigid zwitterionic spirocyclic Meisenheimer complex has been applied to produce a metallogel. The Meisenheimer complex does not undergo self‐gelation under any condition. But it forms a stable gel only with Fe3+ ion in a 2:1 ratio in chloroform. Interestingly, the Meisenheimer complex shows bright yellow emission under 366 nm UV light. But the Fe3+ based metallogel does not show any emission under UV irradiation. However, in the presence of fluoride contaminated water, the metallogel surface shows bright yellow emission while checking inside a UV chamber. Thus the non‐fluorescent metallogel was utilized as a sensor of aqueous fluoride ion. The sensor is able to detect aqueous fluoride down to 156 ppb concentration. Like the gel, the dried metallogel solution is also non‐fluorescent in different polar as well as nonpolar organic solvent. But the same solution shows bright yellow emission in the presence of water. The fluorescence intensity was found to increase with an increase in the percentage of water. In this way, the xerogel was utilized as a sensor of undesired water content present in different organic solvents which can detect moisture content with a minimum detection limit of 0.04% for dichloromethane.

Highly Sensitive Water Detection Through Reversible Fluorescence Changes in a syn-Bimane Based Boronic Acid Derivative

“…Current methods for the detection of water in organic solvents tend to rely on spectral monitoring of the solvent to detect signals that correspond to the presence of water, and include the use of FTIR ( Saleh and Tripp 2021 ), Raman ( Yeung and Chan 2010 ), UV-visible ( Mohar 2019 ), and fluorescence spectroscopy ( Zhou et al, 2019 ; Kumar et al, 2016 ). Other methods, including gas chromatography ( Kay et al, 2021 ) and electrochemical methods ( Marecek and Samec 2020 ), have also been reported.…”

Colorimetric sensing of acidic vapour through protonation of a Meisenheimer complex

“…The structure of these compounds is based on the Jackson–Meisenheimer intermediates of aromatic nucleophilic substitution reactions 39,40 . Scientists have applied them in various real‐life applications, including fluoride and cyanide sensors, moisture sensing, 41 as optical probes and electrochromic material, 42 in the preparation of nanostructures, 43 as fluorescent switches at the single molecule level, volatile organic compound sensors, 44 the removal of metal ions, fluoride and oil spills from water, and in stimuli‐responsive materials 35,37,45,46 . In general, the Meisenheimer complex contains a cyclohexadienyl anion system.…”

2,4,7‐Triaminofluorenone as a Multi‐Analyte Colorimetric Sensor of Fluoride, Acetone Vapor, and Other Harmful Compounds

“…With increasing anthropogenic activities and rapid industrial growth, the mineral composition in groundwater has altered a lot and it is heavily contaminated with different toxic metal ions, arsenic, fluoride, etc . Amongst these toxic species, the fluoride present in drinking water is a serious problem around the different corners of the world . The role of fluoride in the living system is complicated and it depends on the concentration of fluoride .…”

“…So designing a fluoride responsive material is very much desired. In recent times, several groups have designed and synthesized various kinds of colorimetric, fluorescent, phosphorescent, chemiluminescent, gel‐based sensors for the quantitative detection of fluoride ion . In this present work, a new colorimetric fluoride sensor has been developed based on a fluorenone derivative.…”

“…[4] Amongst these toxic species, the fluoride present in drinking water is a serious problem around the different corners of the world. [5] The role of fluoride in the living system is complicated and it depends on the concentration of fluoride. [6] The WHO permissible limit of fluoride in drinking water is 1.5 ppm.…”