Spectroscopic studies of Direct Blue 1 in solution and on cellulose surfaces: effects of environment on a bis-azo dye

The bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) has been studied in solution and on cellophane and cotton surfaces using NMR, resonance Raman, infrared, and UV–visible spectroscopy. The data indicate that Direct Blue 1 is present as the hydrazone tautomer in all of these media, with distinct changes in the spectra with medium showing that the dye is affected by interactions with its environment. In DMF and DMSO solutions, the dye is present as a monomer that is internally hydrogen-bonded. It is also monomeric at low concentrations in aqueous solution, with subtle changes in the Raman spectra from those in DMF and DMSO being attributed to external hydrogen bonding with water. Direct Blue 1 is also present as a hydrazone monomer at low concentrations on cellophane and cotton: the Raman spectra indicate that there is hydrogen bonding with cellulose, and the UV–visible spectra indicate that it experiences an apolar environment which is attributed to its adsorption onto cellulose surfaces.