PHOTOCHEMISTRY OF SQUARAINE DYES .8. PHOTOPHYSICAL PROPERTIES OF CROWN-ETHER SQUARAINE FLUOROIONOPHORES AND THEIR METAL-ION COMPLEXES

The photophysical properties of a series of red-sensitive, highly fluorescent bis[4-(monoaza-crown ether)phenyl]squaraine fluoroionophores are reported. These dyes are soluble in both polar and nonpolar solvents with fluorescence quantum yield varying from 0.01 to 0.85. These dyes readily form aggregates in aqueous solutions. These aggregates dissociate in beta-cyclodextrin solutions as the dye molecules form 1:1 complex with beta-cyclodextrin. This complexation process is accompanied by a significant enhancement in the fluorescence yields of these dyes. Complexation of the fluoroionophores with alkali-metal ions brings about drastic reductions in their fluorescence quantum yield as well as significant changes in their redox properties.