Derivation and interpretation of the spectra of aggregates. Part 2.—Dimer of Rhodamine B in aqueous solutions

Abstract

The spectral changes with concentration of Rhodamine B in near-neutral aqueous solutions, studied in the visible region, have been interpreted in terms of a monomer-dimer equilibrium and the corresponding species spectra derived. The monomer spectrum has been fitted to a progression involving a single harmonic vibrational mode. The dimer spectrum has been analysed using a vibronic exciton coupling theory suitable for degenerate interactions. A model for the dimer in solution has been proposed that satisfies energetic and spatial requirements and explains the values of the exciton interaction parameters found. The relevance of these findings to the light-fastness of dyes has been referred to briefly.