Spectral and Aggregative Properties of Acid Blue 113 in Aqueous and Aqueous Solutions of Urea and in Colloids of Silver Nanoparticles

Photophysical and association properties of a diazo dye (acid blue 113) in the presence of a structure breaking additive (urea) and Ag nanoparticles (AgNPs) were investigated at different dye and additive concentrations (0–3 mol·L−1 urea and 0.1 mmol·L−1 AgNPs). The ionic dye, with strong hydrophilic character, has an aromatic diazo skeleton and two sulfide functional groups. The dye concentrations ranging from 1 × 10−6 to 5 × 10−4 mol·L−1 were chosen and studied, to avoid formation of the higher-order aggregates. The dye spectra were analyzed using linear and nonlinear decomposition algorithms. Using the least squares fitting approach, the dimerization constant Kd and individual monomer and dimer spectra were determined. A reduction of the dimerization constant for AB 113 in aqueous solutions containing additives was observed. The spectral parameters, structure of the dimeric species and the interaction energy between the monomers in the dye solution were estimated based on the molecular exciton theory.