A dynamic Eu(III)-macrocycle served as the turn-on fluorescent probe for distinguishing H 2 O from D 2 O.

H 2 O and D 2 O are an important pair of analogues, and their high-efficient detections are closely related to fields of chemical industry, food processing, semiconductor, environmental monitoring, etc. Because of their extremely similar physical and chemical properties, H 2 O and D 2 O can be mutually soluble in any ratios, and it is generally thought that the discrimination of H 2 O and D 2 O is an enormous challenge. Herein, upon the fact that vibrational frequency of O-H is greater than O-D, we design a dynamic Eu(III)-macrocycle Eu-2 a with two emitters which exhibits the imine bond breakage of macrocycle emitter H 2 L2 a in H 2 O or D 2 O, resulting in the turn-on fluorescence of Eu(III) emitter. For their differential fluorescence sensing signals of Eu-2 a on three emission bands (433, 500 and 615 nm), the statistical analysis method is employed to produce fully separated fingerprints and thus high-throughput discrimination of 13 common solvents, especially the H 2 O and D 2 O. Fluorescent titration experiments by instrumental or smartphone-based analysis method also prove the successful determination of proportional H 2 O/D 2 O mixtures together with the good sensitivity and wide linear response range. Moreover, this H 2 O-triggered fluorescent complex Eu-2 a used as the fluorescence ink also shows its potential in information encryption application. This article must be a valuable reference for the areas of lanthanide-based luminescent material, multianalyte detection and information encryption.