Crown ether derivatives of squaraine: new near-infrared-absorbing, redox-active fluoroionophores for alkali metal recognition

Abstract

Three monoaza crown ether bisphenylsquaraine dyes, 1–3, with excellent solubilities in both polar and non-polar solvents, have been synthesised. The fluorescence yields of these red-sensitive dyes are dependent on the solvent polarity. They are capable of binding quantitatively with alkali metal ions, Li^–, Na⁺, K⁺, as is seen from their fluorescence quenching and shift in the oxidation potentials. The fluorimetric and electrochemical experiments indicate the potential application of these dyes for cation recognition.