The synthesis of two new fluorescent molecular sensors based on calix[4]biscrowns is reported. A dioxycoumarin fluorophore was incorporated into one of the crowns or into both crowns, leading to Calix-COU1 and Calix-COU2, respectively. The stability constants of the 1 ∶ 1 and 1 ∶ 2 complexes with potassium and caesium ions in ethanol or acetonitrile were measured. An anticooperative effect was observed when binding a second cation to the 1 ∶ 1 complex owing to electrostatic repulsion. The selectivity of Calix-COU1 in ethanol expressed as the ratio of the stability constants of the 1 ∶ 1 complexes was found to be about 4 × 104 for Cs+versus Na+ and greater than 500 for K+versus Na+. The origin of the cation-induced changes in the photophysical properties is discussed.
The development of highly selective sensors for potassium is of great interest in biology. Two new hydrosoluble potassium sensors (Calix‐COU‐Alkyne and Calix‐COU‐Am) based on a calix[4]arene bis(crown‐6) and an extended coumarin were synthesized and characterized. The photophysical properties and complexation studies of these compounds have been investigated and show high molar extinction coefficients