Molecular excitons of Pyronin B and Pyronin Y in colloidal silica suspension

The electrostatic interactions of the cationic dyes Pyronin B (PyB) and Pyronin Y (PyY) with the negatively charged colloidal silica was investigated by molecular absorption and steady state fluorescence spectroscopy. Both dyes indicated changes in the absorption and emission spectra upon interaction with colloidal silica. A blue shift was observed in the absorption spectra for both dyes with increased dye concentration when the colloidal silica concentration was kept constant. These new bands observed that are higher energy than monomer bands are due to H-aggregates and they were analyzed by using exciton theory and monomer–dimer equilibrium.