Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements, Lifetime Changes, and on a Ratiometric Response

Abstract Over the years, we developed highly selective fluorescent probes for K + in water, which show K + ‐induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1 – K4 ). In this paper, we introduce selective fluorescent probes for Na + in water, which also show Na + induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2 , 4 , 5 , 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na + responsive ionophore unit and the fluorophore moiety to adjust different K d values for an intra‐ or extracellular Na + analysis. Thus, we found that 2 , 4 and 5 are Na + selective fluorescent tools, which are able to measure physiologically important Na + levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na + levels by fluorescence lifetime changes. Herein, only 8 ( K d =106 m m ) is a capable fluorescent tool to measure Na + levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na + induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 ( K d =78 m m ) showed a ratiometric fluorescence response towards Na + ions and is a suitable tool to measure physiologically relevant Na + levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.