Linear and nonlinear optical properties of new azo aminosalicylic acid derivatives

4-(3-Allyl-4-oxo-2-thioxo-thiazolidin-5-ylazo) salicylic acid (4-ATS) and 5-(3-allyl-4-oxo-2-thioxo-thiazolidin-5-ylazo) salicylic acid (5-ATS) were synthesized and characterized by different spectroscopic techniques. The XRD patterns of 4-ATS and 5-ATS in powder form were recorded and found to be polycrystalline with monoclinic crystal system. Thin films of 4-ATS and 5-ATS were successfully prepared by thermal evaporation technique onto optical flat quartz substrates. Linear and nonlinear optical properties of 4-ATS and 5-ATS were investigated by spectrophotometric measurements. The spectral distribution of refractive index of 5-ATS thin films showed normal dispersion in the non-absorbing region of spectra, while 4-ATS showed nonlinear response. The optical energy gap and the electronic transition type for 4-ATS and 5-ATS were calculated. The electronic absorption and emission spectra were recorded for