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 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 =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 =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.