Controlling the Photoluminescence from a Laser Dye through the Oxidation Level of Polypyrrole a Marcos J. L. Santos, Emerson M. Girotto, Alexandre G. Brolo* Introduction Conducting polymers are useful materials for a wide range of devices, including solar cells, chemical sensors, actuators, and smart windows. [1–4] Their optical and electronic properties, such as conductivity, and electrochromism, depend on reversible redox processes. Other attractive properties of conducting polymers for practical applica- tions are their low cost, easy synthesis, and processability. The electroluminescent behavior of conducting polymers has received a lot of attention, since this property is explored in organic light emitting devices (OLED). [3,5] Attempts to enhance the photoluminescence (PL) of conducting polymer-based materials focused on polymers with a light emitting group chemically attached to the side chain. [3,6] In this work, we investigated a hybrid system obtained by embedding a dye [oxazine 720 (oxa720)] into a conducting polymer film [polypyrrole (ppy)]. Interestingly, it was observed that the PL of the dye was controlled by the oxidation level of the polymer. Hence, in contrast to earlier works, [3,6] the controlled light emission was an extrinsic property of the resulting material. Moreover, the light emission of the embedded dye was switched on and off by the applied potential. The response of the fluorescence behavior of the dye to the applied potential was interpreted by considering both the conformation rearrangement of the polymeric chains at different oxidation levels, and a quenching mechanism mediated by the distance between the emitter and the polymeric chains. [7] Communication A. G. Brolo, M. J. L. Santos Department of Chemistry, University of Victoria, P.O. Box 3065, V8W 3V6, Victoria, British Columbia, Canada E-mail: agbrolo@uvic.ca E. M. Girotto Departamento de Quı ´mica, Universidade Estadual de Maringa, Av. Colombo 5790, CEP 87020-900, Maringa, Parana, Brazil a : Supporting information for this article is available at the bottom of the article’s abstract page, which can be accessed from the journal’s homepage at http://www.mrc-journal.de, or from the author. In situ spectroelectrochemistry was used to study the emission of the laser dye oxazine 720 (oxa720) embedded into a polypyrrole (ppy) matrix. The photoluminescence (PL) of the dye was found to be controlled by the oxidation level of ppy. It is suggested that a Fo ¨rster resonance energy transfer (FRET) mechanism is involved in the potential-controlled PL. FRET calculations were used to determine the dependence of the apparent distance between the dye molecules and the polymer chain with the oxidation level of ppy. In the reduced state, at 0.9 V, an efficient FRET process quenches the PL from the dye due to the short distance between the dye molecules and the polymer chains. In the oxidized state, at þ0.9 V, the FRET efficiency is only 24% leading to higher PL intensity, due to the larger distance between the donor (oxa720) and the acceptor (ppy). Macromol. Rapid Commun. 2010, 31, 289–294 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.200900489 289