Substituent effects on aggregation phenomena in aqueous solution of thiacarbocyanine dyes

摘要

Visible absorption and fluorescence spectra of seven thiacarbocyanine dyes with varying substituents at 5,5'- and meso-positions have been studied suggesting J-aggregate formation in aqueous solutions.The molar extinction coefficients of monomers and dimers(epsilon_M and epsilon_D),the dimer association constant(K_D)and the dimerization enthalpy(DELTAH_D)were determined studying dye concentration and temperature dependencies of absorption spectra.In 0.01 mol/dm~3 KC1 aqueous solutions,J-aggregates were observed due to the association of dimers at a critical dye concentration,which correlated with the K_D value.In addition,the aggregation number,the molar extinction coefficient of the J-aggregate(epsilon_J)and the J-aggregate association constant(K_J)were quantitatively estimated from a modified Harris-Hobbs equation.The J-aggregates were found to be oligomers composed of 20-80 monomers.K_D and DELTAH_D suggested that substituents at the 5,5'-position influenced dimer formation and played an important role in aggregates formation.