Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives

Sudan Red-7B/Cyclodextrin doped ZnO nanocomposites are synthesized and analyzed by various spectral and microscopic methods. The doping effect of SR7B/CD on ZnO nano investigated by UV-visible, fluorescence, FTIR, DTA, XRD, FE-SEM and TEM methods. The effect of different polarities of the solvents, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), on MV was studied by various spectral methods. The inclusion behaviour of SR7B on both CDs was determined by PM3 method. The solvent and CD studies show that the azo-imino tautomer is present in the SR7B molecule and that, depending upon the polarity of the solvents, absorbance and emission intensities of the azo-imino tautomer is varied. With increasing CD concentrations, the shorter wavelength emission intensity of the SR7B regularly increased while the longer wavelength emission intensity decreased. The horizontal bond length of SR7B is longer than the CD cavities; hence, this molecule is partially encapsulated in the CD cavity. HOMO-LUMO gap for MV/β-CD inclusion complex was more negative, which supports that this complex is more stable than MV/α-CD inclusion complex. Red or blue shifted absorption and fluorescence maxima were seen in SR7B/CD/ZnO nanocomposites than SR7B/CD inclusion complex. Nanoparticle size was measured by TEM-EDS and X-RD methods. TEM image showed that nanosheets are formed in SR7B/CD/ZnO.