Some transition metal complexes of the type [ML2]center dot nH(2)O (n = 0 or 2) of the title ligand, 4-(2-thiazolylazo)resorcinol, HL (TAR) have been synthesized and characterized by various analytical and physicochemical (elemental, thermal analyses, AAS, electrolytic conductance and magnetic susceptibility measurements) and spectral (UV-vis and IR) techniques for structure determination and optical properties. The complexes have the formulae [ML2] for M = Fe(II), Cu(II) and Zn(II); [CdL2]center dot 2H(2)O. An octahedral structure is proposed for all complexes. IR spectra show that the ligand is coordinated to the metal ions in a tridentate manner with ONN donor sites of the resorcinol OH, azo N and thiazole N. The effect of varying pH and solvent on the absorption behavior of the ligand and complexes has been investigated. The optical constants such as, refractive index, extinction coefficient, dielectric constant were determined for the ligand and its complexes. These parameters changed with different metal complexes. The optical absorption data revealed that the band gap of the films was direct transitions. The optical band gap and Urbach energy of the films were determined using the known theory. The optical dispersion parameters were determined according to Wemple and DiDomenico method. (C) 2009 Elsevier B.V. All rights reserved.