A fluoroionophore for detection of potassium ions: 9-anthryl-substituted azacrown ether covalently linked to a 1,3-alternate calix[4]arene

N-(9-methyl-anthracene)-25,27-bis(1-propyloxy)calix[4]arene azacrown-5 (11) and its model compound N-(9-anthrylmethyl)aza-18-crown-6 (1) were synthesized and tested as fluoroionophores for the selective detection of potassium ions with a view to the use of II in the fabrication of potassium ion sensors. Compound II consists of a 1,3-alternate calix[4]arene group covalently linked to an azacrown ether that is N-substituted with a fluorescent anthracene group. This compound acts as an 'off-on' fluorescent indicator for ion complexation. In dichloromethane solution, compound II exhibits good sensitivity to potassium ions and forms a 1:1 fluoroionophore-ion complex. Studies demonstrate that II is selective for potassium over other alkali metal cations, with excellent selectivity over sodium and lithium (log K-K N-a similar to log K-K.L1 less than or equal to -3.5) and moderate selectivity over rubidium and cesium (log K-K (Rb) similar to log K-K,K-CS similar to -1). Sensitivity of II to potassium is considerably enhanced in dichloromethane in comparison to methanol/dichloromethane mixtures, presumably due to two effects: a hydrogen-bonding interaction of methanol with the azacrown nitrogen atom, and poor solvation of the ion by dichloromethane, the latter creating a driving force for complexation. (C) 2002 Elsevier Science B.V. All rights reserved.