Synthesis and binding properties of calix[4]biscrown-based fluorescent molecular sensors for caesium or potassium ions

摘要

The synthesis of two new fluorescent molecular sensors based on calix[4]biscrowns is reported. A dioxycoumarinnfluorophore was incorporated into one of the crowns or into both crowns, leading to Calix-COU1 and Calix-COU2,nrespectively. The stability constants of the 1 : 1 and 1 : 2 complexes with potassium and caesium ions in ethanol ornacetonitrile were measured. An anticooperative effect was observed when binding a second cation to the 1 : 1 complexnowing to electrostatic repulsion. The selectivity of Calix-COU1 in ethanol expressed as the ratio of the stabilitynconstants of the 1 : 1 complexes was found to be about 4 × 104n for Csnu0001 versus Nau0001 and greater than 500 for Ku0001 versusnNau0001. The origin of the cation-induced changes in the photophysical properties is discussed.