Novel attempts to change the colour of dye molecules utilizing the aggregation mode of saccharides

Ten saccharide-dye (azophenol and azonaphthol) conjugate molecules and four methylated reference compounds were synthesized. The purpose of the present study using these molecules is to change the colour of the common dye moiety, both in solution and in solid by the structural difference in the saccharide moieties and eventually to mimic the colour creation mechanism in a nature's flower family. In azophenol derivatives, the solution (THF) colour was more or less the same but the solid colour was significantly different (yellow-orange-pink). The XRD study established that the colour change is correlated to the crystallinity of the solid samples: the λ_max shifts to shorter wavelength with the increase in the crystallinity. In azonaphthol derivatives, the solution colour was more different than the solid colour. The spectroscopic studies established that this change is due to an azo-hydrazone tautomerism. The colour changes were quantitatively expressed by the CIE L*a*b* colourimetric system. The foregoing results indicate that the colour of the dye molecules can be changed utilizing the intra- and intermolecular hydrogen-bonding interactions among the appended saccharide moieties.