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 Kd 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 (Kd=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 (Kd=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.

1,2,3‐Triazol‐1,4‐diyl‐Fluoroionophores for Zn2+, Mg2+ and Ca2+ based on Fluorescence Intensity Enhancements in Water

“…These φ f values are low, caused by a PET process from the aniline unit to the coumarin moiety, which quenches the fluorescence. Further, similar low φ f values were also found for a set of π ‐conjugated 1,2,3‐triazol‐1,4‐diyl–fluoroionophores [11a–e,12a−c] . Herein, the regioisomeric triazole linkage in Zn1 is responsible for a better fluorescence quenching than in Zn3 .…”

“… [12b] Further, in the Na + ‐probes Na1 and Na2 the emission wavelength and quantum yield ( φ f ) depends on the coumarin fluorophore. Thus, we observed for Na2 +Na + a higher Na + induced FEF and a higher φ f caused by the fixed alkylated amino group in position 6 and 8 of the coumarin moiety [12a,c] . Further, for comparison, we synthesized the compound C1 [10b] …”

“…As found out for K1 , K2 , Na1 and Na2 , (cf. Scheme 2) these fluorescent probes work nicely under simulated physiological conditions [12a–c] . Herein, we also want to provide bioorthogonal fluorescent probes, which show cation induced FE in water.…”

“…Na1 and Na2 , Scheme 2). [12a–c] The combination of an 18‐membered crown (aza‐18‐crown‐6) ether and an ethoxymethoxy substituent in ortho position of the aniline unit in K1 enables the selective extracellular K + determination [11a] . The exchange of the aza‐18‐crown‐6 by an aza‐15‐crown‐5 unit (cf.…”

Sulfur Tuning of [1,3]‐Dioxolo[4.5‐f]benzodioxole (DBD) Fluorescent Dyes

“… [5a,b] The outstanding features of these dyes are very large Stokes shifts, long fluorescence lifetimes and high bleaching stability. Meanwhile, we developed numerous applications such as probes for sensing lipophilic environment, [5c] conformational changes of proteins, [5d,e] detecting carbohydrate‐lectin interactions, [5f] ds DNA, [5o] and alkaline cations [5g,h] . Furthermore, fluorescence lifetime based assays [5i,j] and FRET pairs [5k–n] were developed.…”