Optical properties of some synthesized azo thin films

5-(4′-Alkyl phenylazo)-2-thioxothiazolidin-4-one (PATT-Ln) have been synthesized and characterized with various physico-chemical techniques. Thin films of PATT-Ln have been prepared by the thermal deposition technique in a vacuum of 3 × 10−5 mbar onto optical flat glass substrates. The absorption properties of thermally deposited PATT-Ln thin films were investigated in the wavelength range 190–2500 nm. The type of optical transition near the edge of the band gap is found to be direct allowed transition. The values of the energy gap for derivatives under investigation are calculated and found to be in the range 1.77–2.29 eV dependent on the nature of the substituent. They tend to the increase according to the following order p-(OCH3 < CH3 < H < Cl < NO2) as expected from Hammett’s constant σR.