Available online at www.sciencedirect.com Spectrochimica Acta Part A 71 (2008) 621–627 A spectroelectrochemical study on single-oscillator model and optical constants of sulfonated polyaniline film Mujdat Caglar a,∗ , Saliha Ilican a , Yasemin Caglar a ,Y¨ ucel S ¸ ahin b , Fahrettin Yakuphanoglu c , Deniz H ¨ ur b a Anadolu University, Faculty of Science, Department of Physics, 26470 Eskisehir, Turkey b Anadolu University, Faculty of Science, Department of Chemistry, 26470 Eskisehir, Turkey c Firat University, Faculty of Arts and Sciences, Department of Physics, 23169 Elazig, Turkey Received 11 December 2006; accepted 10 January 2008 Abstract The optical properties of sulfonated polyaniline (SPAN) thin film prepared by electrochemical method have been investigated. Polychromic behavior of SPAN thin film (transparent yellow-green-dark blue) was observed when the cyclic voltammograms were taken between -0.25 V and +1.90 V (vs. Ag/AgCl, sat.) during the growth of polyaniline film. In situ UV–vis spectra of the polymers-indium tin oxide (ITO) glass electrode were taken during the oxidation of the polymers at different applied potentials. The direct band gap values of SPAN thin film changed from 3.771 eV to 3.874 eV with the applied potentials. From in situ UV–vis spectra, the optical constants such as refractive index and dielectric constant of the SPAN thin film were determined. The important changes in absorption edge, refractive index and the dielectric constant were observed due to the applied potentials. The refractive index dispersion curves of the film obey the single-oscillator model and oscillator parameters changed with the applied potentials. The most significant result of the present work is in situ spectroelectrochemical method, which can be used to modify the optical band gaps and constants. © 2008 Elsevier B.V. All rights reserved. PACS: 78.20.Ci; 78.30.Jw Keywords: Polyaniline; Sulfonated polyaniline; Spectroelectrochemistry; Optical constant; Single-oscillator model 1. Introduction Conducting polymers have been widely investigated for their promising applications in gas sensors, batteries, light emission diodes, solar cells, electrochromic devices (ECDs), etc. Polyani- line (PANI) is very popular conductive organic semiconductors. They exhibit p-type semiconductivity at all temperatures. A large number of studies on polyaniline have shown that its chemical and physical properties strongly depend upon the method of the preparation and the composition of the solution [1,2]. Extensive studies in this field led to the synthesis of water- soluble derivatives of polyanilines. Sulfonated polyaniline (SPAN) is the first reported self-doped water-soluble conduc- tive polyaniline derivative [3]. SPAN is interesting in view of its unique electroactive properties in a wide range of solutions ∗ Corresponding author. Tel.: +90 222 3350580/5738; fax: +90 222 3204910. E-mail address: mcaglar@anadolu.edu.tr (M. Caglar). (particularly in neutral aqueous solutions). Easy processability, which arises because of its solubility in a range of solvents, is preferred for wide variety of potential applications [4,5]. The good environmental stability of the parent polyaniline is further improved by the presence of the –SO 3 - group on the phenyl rings due to its strong electron-withdrawing properties. It has also been shown that SPAN has better thermal stability than its parent, polyaniline doped with HCl [6]. The direct band gap of PANI generally observed between 3.6 eV and 4.0 eV [7]. Polymers have attracted great interest in the fields of integrated optics and optical interconnects. The potential appli- cability of organic and polymeric materials to integrated optics is large owing to both their microscopic and bulk properties. The refractive index and optical band gap are the fundamental parameters of an optical material, since these are closely related to the electronics of the material. A knowledge of the refrac- tive index and optical band gap for an organic thin film, and the relationship of N to aromatic –* band transitions are crucial for understanding and optimizing organic electronic and optical 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.01.022