Fluorescence Quenching of a Europium Coordination Compound for the Detection of Trace Amounts of Water: Uncovering the Response Mechanism by Structural Confirmation

Abstract

The coordination compound Eu(DAF)2(NO3)3 (1, DAF = 4,5‐diazafluorene), which shows strong red fluorescence, has been synthesized and characterized. The luminescence‐quenching effect of 1 has been applied to the detection of water in CH3CN. For the first time, the response mechanism has been uncovered through the confirmation of the structure of the resultant nonluminous compound [Eu(NO3)2(H2O)5](NO3)(DAF)2·H2O (2). The replacement of the coordinated DAF ligands by the added water led to quenching of the emission of the EuIII ion and the simultaneous enhancement of the ligand emission. X‐ray powder diffraction and thermogravimetric analyses also confirmed this mechanism. Theoretical calculations by the semi‐empirical method revealed the origin of the absorption spectra of 1. This fluorometric detection of trace amounts of water in CH3CN by 1 is a direct, rapid, and sensitive method.

7-Dialkylaminocoumarin Oximates: Small Molecule Fluorescent “Turn-On” Chemosensors for Low-Level Water Content in Aprotic Organic Solvents

“…Calculated detection (3σ/S) limits for water using the studied two-component colorimetric and fluorescence “turn-on” 7-dialkylaminocoumarin oxime/F − chemosensors 1 /F − and 2 /F − are amongst the lowest published detection limits for water in MeCN and DMF and chemosensor 1 /F − in particular can compete in sensitivity with chemodosimeters or chemosensors based on interpolymer π-stacking aggregation ( Table 3 ) [ 24 ]. Compared to other “competitive ligand-based” chemosensors for water content in aprotic polar solvents, determined 3σ/S in MeCN for 1 /F − is even lower than that of the most sensitive Eu 3+ luminiscent chemosensor published by Song et al [ 42 ].…”

Chemical Sensors for Water Detection in Organic Solvents and their Applications

“…Few compounds have been reported for moisture detection, working on the principle of metal displacement [19,20] or water acting as a ligand to coordinate with the metal complex based probe. A trace amount of water causes fluorescence change either on‐off [8,21] / off‐on [22,23] or change in color [24] due to the following reasons such as a) partial/complete removal of metal ion from the complexes, b) replacing the ligand attached to the metal complex, c) water interaction or coordination with metal center (Scheme 1A).…”

“…Red luminescence europium based metal complex 34 ( Eu ( DAF ) 2 ( NO 3 ) 3 , where, DAF=4,5‐diazafluorene) [22] was synthesized for the detection of moisture in acetonitrile. The bright red luminescence of the Eu(III) complex was quenched in the presence of water in acetonitrile as well as in solid‐phase.…”

Dynamic Coordination of Eu–Iminodiacetate to Control Fluorochromic Response of Polymer Hydrogels to Multistimuli

“…However, the previous studies on luminescent‐tunable metallopolymers with multistimuli response were only carried out in organic solvents. [2a,3a,13,15] The main obstacle to design luminescent hydrogels is that water molecules can hydrate lanthanides ions, which essentially quenches the luminescence of metals . Hydration of water also weakens the hydrogel networks; that is, without large metal–ligand binding constant, hydrogels based on metal coordination binding are not mechanically strong.…”