The synthesis and optical properties of the 5,5',6,6'-tetraphenyl-2,2'-bi([1,3]dithiolo [4,5-b] [1,4]dithiinylidene)-2,3-dichloro-5, 6-dicyano-p-benzoquinone (DDQ) complex thin film were investigated by the optical characterization. The optical constants such as refractive index, extinction coefficient and absorption coefficient were determined using the transmittance T(lambda) and reflectance R(lambda) spectra and the refractive index dispersion was analyzed using single oscillator of Wemple-Didomenico model. The single oscillator energy Eo and the dispersion energy E-d were calculated. The effect of temperature on refractive dispersion and optical band gap E-g is also discussed. As a result, the annealing temperatures have an important effect on refractive index of thin film. (c) 2007 Elsevier B.V. All rights reserved.