Study the optical properties of Congo red dye

Abstract

This research included a study of the physical optical properties of Congo red dye that dissolved in distilled water and ethanol solvents at several concentrations (0.2×10-5, 0.5 ×10-5, 1×10-5, 0.2×10-4) mol/L. The physical optical properties of Congo Red films dye, which was prepared by casting method at dye concentration (10-3) M. An ultraviolet-visible spectrophotometer (UV-Vis) used to measure the optical properties [absorbance A, transmittance T, absorption coefficient α, refractive index n, reflection R, extinction coefficient k and energy gap Eg] of dye samples. Based on UV-Visible analysis it found two peaks at wavelengths (330, 490) nm using distilled water, and (328,499) nm using ethanol solution, also it is found one peak was split into two peaks at wavelengths (505,535) nm for dye films, that attitude to dimerization of dye. Absorbency for dye solution using ethanol as solvent is greater than that absorbance using distilled water, this case depends to find the hydroxyl group in ethanol as Auxo group to enhance the color of chromophore groups in this dye and leads to elevated the absorbance of the solution. The energy gap of the dye solution using distilled water as a solvent is less value than using ethanol and equal to 2.1eV and 2.2eV, respectively. This behavior is an attitude to strong hydrogen bond that produced between the lone pair electrons that beyond to heteroatom in dye structure like (N, O, and S) and ethanol and leads to blue shift (small wavelength with large energy).