PHOTOCHEMISTRY OF SQUARAINE DYES .6. SOLVENT HYDROGEN-BONDING EFFECTSON THE PHOTOPHYSICAL PROPERTIES OF BIS(BENZOTHIAZOLYLIDENE)SQUARAINES

The photophysical properties of two bis(benzothiazolylidene)squaraine dyes have been studied in aromatic hydrocarbon and alcoholic solvents. These dyes exhibit fluorescence quantum yields of 0.06-0.52 and excit ed singlet lifetimes of 0.48-2.5 ns in these solvents. Although the ph otophysical properties of the dyes are independent of solvent polarity in the hydrocarbon solvents, in alcoholic solvents a marked hyposchro mic shift in the absorption and emission spectra and a reduction in li fetimes of excited state have been observed. These effects have been c orrelated with the hydrogen bond donating ability of the alcoholic sol vents.