A CATION-SPECIFIC, LIGHT-CONTROLLED TRANSIENT CHROMOIONOPHORE BASED ON A BENZOTHIAZOLIUM STYRYL AZACROWN ETHER DYE

A benzothiazolium styryl azacrown ether dye (1) and its complexation w ith Ba2+ and Na+ cations in acetonitrile solution have been studied by UV-vis absorption and emission spectroscopy, trans-1 is found to act as a normal chromoionophore for Ba2+ and Na+ at high concentration (gr eater than or equal to 10(-2) M) by complexation with the azacrown and as a light-controlled, transient chromoionophore specific for Ba2+ at low concentration (10(-5)-10(-3) M). A quantitative analysis of the c omplexation and thermal reactions following photolysis has enabled a d etailed mechanism to be proposed: trans-1 photoisomerization produces cis-1, which is stabilized in the presence of Ba2+ by dual intramolecu lar complexation of the cation with both azacrown and sulfonate groups .