Mechanism of luminescent chemosensor response in europium chelates

The luminescent chemosensor properties of Eu(III) carboxylatodibenzoylmethanates with acetic and acrylic acids as applied to ammonia vapors are studied. Quantitative measurements of the optical response revealed a linear increase in the Eu(III) luminescence intensity with increasing analyte concentration in the range of 3–300 ppm. It is shown that the luminescent response is reversible; the ammonia detection limit is 3 ppm. The optical effect mechanism determined by quantum-chemical modeling consists in the interaction of ammonia with a sensor resulted in the formation of a rigid H$_2$O–NH$_3$ structural fragment, which eliminates the luminescence quenching effect of high-frequency OH vibrations. The chemosensors proposed have high sensitivity and selectivity and, hence, can be promising for creating ammonia sensors used in food safety control and environmental monitoring.