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

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 (K ) 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 K value of approximately 8 mm in Na -free solutions and in combined K /Na solution a similar K 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.