Effect of substitution group variation on the optical functions of -5-sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline thin films

-5-Sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline (SAHQ)-x ligands, x = NO₂ or CH₃ or Cl have polycrystalline structure in as synthesized condition. Thermally evaporated thin films of SAHQ-x have crystal structure depending on the substitution group; SAHQ-NO₂ and SAHQ-Cl films have nano-crystalline structure with different degree of crystallinity and SAHQ-CH₃ film has amorphous structure. The changes in optical functions and therefore optical constants with substitution group variation have been calculated by using spectrophotometer measurements of the transmittance and reflectance at nearly normal incidence of light in the wavelength range 200–2500 nm. Substitution group variation influences the refractive index, dispersion parameters, optical functions and bond length of SAHQ. It has no influence on mobility, relaxation time and plasma frequency of charge carriers. The obtained optical energy gaps for SAHQ-x ligands, x = NO₂ or CH₃ or Cl are 1.89, 2 and 2eV, respectively.