A Ratiometric Fluorescent Probe for K+ in Water Based on a Phenylaza‐18‐Crown‐6 Lariat Ether

• Published in: Chemistry : a European journal 2018-07, Vol.24 (40), p.10116-10121
• Main Authors: Schwarze, Thomas, Riemer, Janine, Holdt, Hans‐Jürgen
• Format: Article
• Language: English
• Subjects: charge transfer; Chemistry; crown compounds; Emission; Fluorescence; Fluorescent indicators; Molecular chains; potassium; ratiometric sensors
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201802306

This work presents two molecular fluorescent probes 1 and 2 for the selective determination of physiologically relevant K+ levels in water based on a highly K+/Na+ selective building block, the o‐(2‐methoxyethoxy)phenylaza‐18‐crown‐6 lariat ether unit. Fluorescent probe 1 showed a high K+‐induced fluorescence enhancement (FE) by a factor of 7.7 of the anthracenic emission and a dissociation constant (Kd) value of 38 mm in water. Further, for 2+K+, we observed a dual emission behavior at 405 and 505 nm. K+ increases the fluorescence intensity of 2 at 405 nm by a factor of approximately 4.6 and K+ decreases the fluorescence intensity at 505 nm by a factor of about 4.8. Fluorescent probe 2+K+ exhibited a Kd value of approximately 8 mm in Na+‐free solutions and in combined K+/Na+ solution a similar Kd value of about 9 mm was found, reflecting the high K+/Na+ selectivity of 2 in water. Therefore, 2 is a promising fluorescent tool to measure ratiometrically and selectively physiologically relevant K+ levels. Potassium probes: Two molecular fluorescent probes are reported for the selective determination of physiologically relevant K+ levels in water based on a highly K+/Na+ selective building block, the o‐(2‐methoxyethoxy)phenylaza‐18‐crown‐6 lariat ether unit. Fluorescent probe 1 showed a high K+‐induced fluorescence enhancement by a factor of 7.7 whereas probe 2 showed a dual emission behavior.