CH EM I STRY & CH EM I CAL TECH N OLOGY Vol. 5, N o. 3, 2011 Chemistry Deepali Kelkar and Ashish Chourasia STRUCTURAL PROPERTIES OF POLYTHIOPHENE DOPED WITH FeCl 3 Department of Physics, Institute of Science, Civil Lines, Nagpur – 440 001, India kelkar_ds@rediffmail.com; abchourasiansk@rediffmail.com Received: November 25, 2010 / Revi sed: M arch 03, 2011 / Accepted: M ay 18, 2011  Kelkar D., Chourasia A., 2011 Abstract. Polythiophene is chemically synthesized and doped with FeCl 3 for 2.5, 5 and 10 h. For structural investigation all samples have been characterized using different techniques. The results of elemental analysis show that with the increase of doping duration the Fe content increases while the S content decreases. FTIR spectrum reveals the complex formation between FeCl 3 and polythiophene. UV-Visible results have been used to calculate band gap energy. Analysis of XRD shows that after polythiophene doping by FeCl 3 some modifications in crystal structure and increase in crystallinity take place. Morphological studies using SEM have been carried out. TGA-DTA results indicate the reduction in Tg values with the increase in dopant concentration as well as increase in thermal stability due to doping. Keywords: polythiophene, FTIR, UV-Vis spectroscopy, electron microscopy, TGA-DTA. 1. Introduction Polymer science, both basic and applied, has undergone great development in the last 30 years. The great interest in polymers is due to possibility of combining new chemical functions in a backbone. This opened new fields of applications for macromolecules. After the discovery of iodine doped polyacetylene by McDiarmid and Shirakawa many polymeric structures were synthesized with the aim of improving both the electrical conductivity and the stability of the materials. Polyheterocyclic in particular polythiophene are thermally and environmentally stable [1]. Many researchers have doped polythiophene and/or its derivatives using LiBF 4 , NaAsF 6 , NaPF 6 [2], Bu 4 NClO 4 , Et 4 NBF 4 , Et 4 NBF 6 [3], and iodine [4]. Few groups have reported doping of derivatives of polythiophene by FeCl 3 [5, 6] and fabrication of devices using FeCl 3 doped derivatives of polythiophene [7, 8]. However, poly- thiophene doped with FeCl 3 is not much reported. Hence, in the present work FeCl 3 is used as a dopant. In the present work polythiophene is chemically synthesized, doped with FeCl 3 for different (2.5., 5 and 10 h) durations. For structural investigation, undoped and all doped samples are characterized using different techniques such as elemental analysis, FTIR analysis, UV- Visible spectroscopy, analysis of wide angle X-ray diffraction, and scanning electron microscopy. Thermal analysis using TGA-DTA technique has also been carried out. 2. Experimental 2.1. Chemical Synthesis The polythiophene was chemically prepared by catalytic coupling of the Grignard reagent of 2,5- dibromothiophene (Aldrich) by nickel salt [4]. The general procedure consists of stirring 2,5- dibromothiophene with freshly distilled tetrahydrofuran (THF) with magnesium. The catalyst nickel chloride was introduced at the end. The mixture changed color. After 4 h the mixture was cooled and poured into MeOH-HCl. The obtained solid was then washed in hot methanol and dried. The brown powder was further fractionated into two parts by extracting with hot chloroform (CHCl 3 ).The procedure for chemical synthesis is shown in Fig. 1. S Br Br + Mg S Br MgBr NiCl 2 Catalyst S n Fig. 1. Polythiophene chemical synthesis steps