Received: 5 March 2010, Revised: 4 August 2010, Accepted: 5 September 2010, Published online in Wiley Online Library: 2010 Analysis of the optical properties of poly(3-octylthiophene) partially dedoped E. M. There ´ zio a,b , J. L. Duarte a , E. Laureto a , E. Di Mauro a , I. L. Dias a , A. Marletta b and H. de Santana c * In this work, poly(3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueous media through the oxidation of the monomer, (3-octylthiophene), using a standard three-electrode cell in acetonitrile with 0.05 mol L S1 LiClO 4 or 0.05 mol L S1 Et 4 NBF 4 . The polymeric films were deposited on fluorine tin oxide (FTO). The partial dedoping was obtained in NH 4 OH solution, providing a good chemical stability of the formed material. The films obtained through this method have been characterized by Fourier-transform infrared spectroscopy (FT-IR), electron paramagnetic resonance (EPR), UV–Vis absorption, and photoluminescence (PL) spectroscopy. The FT-IR and EPR spectra together gave the results that led to characterization of two structures (pristine and non-pristine forms of thiophene rings) while forming the P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non-pristine structures) in the polymeric film. Their bands in the PL spectra are wide and asymmetric and their adjustments by Gaussian functions was necessary; this was the main indication that there are two distinct contributions to the emission spectra. These two contributions are attributed to the emission by mixed chains (Gaussian centered at higher energy) and by pristine chains (Gaussian of lower energy) present in the formed polymeric material. Copyright ß 2010 John Wiley & Sons, Ltd. Keywords: electrochemical; photoluminescence; poly(3-octylthiophene); synthesis INTRODUCTION Conjugated polymers have been the object of innumerable studies in the last decades due to their optical and optoelectronic properties, and mechanical characteristics of flexibility and malleability which facilitate the production of devices with an extensive range of applications such as organic light-emitting diode (OLEDs), organic solar cells, integrated circuits, [1] and so on. In spite of the innumerable applications, some physical properties of these materials are not completely understood such as (a) the excitation nature, (b) the non-radiative relaxation of the excited carriers, and (c) their radiative recombination. The physical mechanisms responsible for the conductivity and the light emission vary considerably among these materials and depend on the electronic structure of the atoms and molecules that constitute each material. [2] Among those polymers, the poly(3-alkylthiophenes) (P3ATs) have been provoking a great interest due to their good chemical stability [3,4] and solubility, [3,4] besides possessing some charac- teristics such as electrochromism, [3] solvatochromism, [4] thermo- chromism, [5] electroluminescence, [6,7] and photoluminescence (PL). [6,7] The composed poly(3-octylthiophene) (P3OT) studied in this work belongs to the family of P3ATs. P3OT can be obtained by chemical or electrochemical synthesis starting from the oxidation of the 3-octylthiophene monomer, [3,9,10] and it is a P3AT of short alkyl side chain with eight atoms of carbons. [4] The P3OT, as well as P3ATs in general, have a band gap at 1.92 eV (645 nm). [1,4] However, Wang et al. [4] studied the electroluminescence (EL) of P3OT and identified the appearance of another band in the emission spectrum (2.16 eV). They have also obtained the PL spectrum in which the same band was observed at 2.16 eV (575 nm). However, Wang and collaborators have not explained the reason for the presence of this band. This work intends to objectively answer the question above by studying the optical properties of P3OT thin films synthesized electrochemically, followed by chemical dedoping. This study was complemented by structural characterization of the formed polymer, which made possible to obtain information about the influence of the nature of the film on the P3OT emission spectrum. EXPERIMENTAL Chemicals The 3-octylthiophene (C 12 H 20 S) monomer was purchased from Acros-Organics – 94%; Tetraethylammonium tetrafluoroborate (C 2 H 5 ) 4 NBF 4 ) from Acros-Organics – 99%; and Lithium perchlor- ate (LiClO 4 ) from Acros-Organics – 99%. They were used as supporting electrolyte. All these reagents were used without further purification. (wileyonlinelibrary.com) DOI 10.1002/poc.1802 Research Article * Correspondence to: H. de Santana, Departamento de Quı ´mica – CCE, Uni- versidade Estadual de Londrina, 86051-990, Londrina, Parana, Brazil. E-mail: hensan@uel.br a E. M. There ´zio, J. L. Duarte, E. Laureto, E. Di Mauro, I. L. Dias Departamento de Fı ´sica, Universidade Estadual de Londrina, Londrina, PR, Brazil b E. M. There ´zio, A. Marletta Instituto de Fı ´sica, Universidade Federal de Uberla ˆndia, Uberla ˆndia, MG, Brazil c H. de Santana Departamento de Quı ´mica, Universidade Estadual de Londrina, Londrina, PR, Brazil J. Phys. Org. Chem. (2010) Copyright ß 2010 John Wiley & Sons, Ltd.