Isolation of Unique Dimer Spectra of Dyes From the Composite Spectra of Aggregated Solutions

Aggregation of fluorescein, eosin and rose bengal in aqueous solutions has been studied. Mathematical expressions are derived to calculate the monomer mole fractions in moderately and highly concentrated solutions. The average values of the dimer dissociation constant, Kd, for fluorescein, eosin and rose bengal in aqueous solutions at pH 12 are 0.20, 9.0×10‐3 and 40 × 10‐3 moles/l respectively. A method is developed here to isolate the dimer spectrum from the composite spectrum. The uniqueness of this method is established by comparison with other known methods. The dimer spectra of all the three dyes are reported.