Ratiometric and Turn-On Luminescence Detection of Water in Organic Solvents Using a Responsive Europium-Organic Framework

Abstract

The development of simple, rapid-response sensors for water detection in organic solvents is highly desirable in the chemical industry. Here we demonstrate a unique luminescence water sensor based on a dual-emitting europium-organic framework (Eu-MOF), which is assembled from a purposely selected 2-aminoterephthalic acid ligand with responsive fluorescence inherent in its intramolecular charge transfer (ICT) process. This ICT process can be rapidly switched-on in the presence of water owing to its ability to boost and stabilize the ICT state. In contrast, the Eu3+ emission within the framework is insensitive to water and can serve as a reference, thus enabling highly sensitive water detection in a turn-on and ratiometric way. In addition, the significant ratiometric luminescence response induced by water makes Eu-MOF undergo a distinct change of emitting color from red to blue, which is favorable for visual analysis with the naked eye. Sensitive determination of water content (0.05–10% v/v) in various organic solvents is achieved in multiple readouts including ratiometric emission intensity, emission color, or the Commission Internationale de l’Eclairage (CIE) chromaticity coordinate. The present Eu-MOF sensor featuring high sensitivity and reusability, self-calibration, simple fabrication and operation, and capability for real-time and in situ detection is expected to have practical applications in water analysis for industrial processes.

Chemical Sensors for Water Detection in Organic Solvents and their Applications

“…Europium‐metal organic framework ( Eu ‐ MOF ) assembled with 2‐amino terephthalic acid ligand has been developed by Y. Zhou and group for the water sensor in the organic solvent [60] . The Eu ‐ MOF act as two emitting centers: Eu 3+ and the ligand.…”

“…The emission spectra were studied from low polar (cyclohexane) to high polar (water) solvents, which underwent a bathochromic shift. The red‐shift is due to the charge [60] transfer nature of the emissive state. The luminescence water responsive Eu ‐ MOF displayed red to blue color change with water content in the range (0.05 to 10 % v/v) in DMF observed under 365 nm light, as shown in figure 5B.…”

“…Europium-metal organic framework (Eu-MOF) assembled with 2-amino terephthalic acid ligand has been developed by Y. Zhou and group for the water sensor in the organic solvent. [60] The Eu-MOF act as two emitting centers: Eu 3 + and the ligand. The emission of the 2-amino terephthalic ligand is a significant switch in the presence of water, whereas the Eu 3 + is unresponsive to water and acts as a reference.…”

“…Displacement of metal from complex or coordination with metal leads to water detection using the metal complex as a chemical sensor. The metal complex of transition and lanthanides ions, [50,51] metal‐based luminescent and phosphorescent nanomaterials, [18a] metal‐organic frameworks (MOFs) [52] and metal‐organic polyhedra (MOPs) [53] are mainly used for moisture detection.…”

Covalent Organic Frameworks with Electron‐Rich and Electron‐Deficient Structures as Water Sensing Scaffolds

“…[ 29,30 ] Recently, luminescent‐based sensors with the advantages of simple operation and low cost for water detection have been developed, for example, organic fluorophores, polymers, Cu nanoclusters, and carbon dots can be used as the probe to detect water through the fluorescence change. [ 31 ] COFs with the advantages of high crystallinity, good stability, structural controllability, and especially porosity can be potential candidates for the application in water detection. But to the best of our knowledge, there are only few reports on the detection of trace amount of water in organic solvents by using COFs.…”