Photochemical studies of new benzothiazole- and benzoselenazole-derived aminosquarylium dyes

In this work, new modified squarylium dyes, namely two new groups of benzothiazole- and benzoselenazole-derived squarylium dyes, were studied. An extensive photochemical characterization of all dyes was performed and the following parameters were studied: quantum yields of singlet oxygen formation, fluorescence quantum yields and fluorescence lifetimes. Depending on the nature of the substituent located in the squaric ring, significant results were obtained. The laser flash photolysis technique was used to determine triplet-triplet absorption spectra, in ethanol. In chloroform, photoproducts resulting from a reaction of the excited squarylium dye in the singlet state with CHCl3 were observed. A solute-solvent complex was detected, the primary product formed after excitation, being the complex [SQ+ ⋯ CHCl2 ⋯ Cl−].The effect of two different counterions (CF3SO3− and I−) was also addressed by these techniques providing new insights about the external heavy atom effect mechanism.