PHOTOCHEMISTRY OF SQUARAINE DYES .6. SOLVENT HYDROGEN-BONDING EFFECTS ON 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 excited singlet lifetimes of 0.48-2.5 ns in these solvents. Although the photophysical properties of the dyes are independent of solvent polarity in the hydrocarbon solvents, in alcoholic solvents a marked hyposchromic shift in the absorption and emission spectra and a reduction in lifetimes of excited state have been observed. These effects have been correlated with the hydrogen bond donating ability of the alcoholic solvents.