The absorbance and fluorescence properties of indigo carmine (IC) dye have been investigated in various solvents and organized media (beta-, gamma-, 2-hydroxypropyl-beta-, 2,6-Di-O-methyl-beta-cyclodextrins and CTAB and Brij-35 surfactants). A long-wavelength (LW) emission for IC dye in solution is reported that results from the long-wavelength excitation energy of the molecule (~ 609 nm). This emission for IC dye exhibits significant sensitivity to changes in viscosity and hydrophobicity of the microenvironments of the various organized media and solvents used. Induced circular dichroism (ICD) studies of the dye in 2-hydroxypropyl-beta-cyclodextrin indicate an axial inclusion of the molecule along the CD axis of symmetry. The spectral data in organized media are supplemented by photochemical stability and binding studies of the molecule in aqueous solutions of CDs under neutral (pH 7) and basic (pH 12) conditions, at 25 C and 37 C. These data are used to suggest the suitability of the dye as a molecular probe and as a reagent in the development of a hydroperoxide assay.
Eric L. Roberts, Sarah Burguieres, and Isiah M. Warner, "Spectroscopic Studies of Indigo Carmine Dye in Organized Media," Appl. Spectrosc. 52, 1305-1313 (1998)