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

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 mm) 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 mm) 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.