Temperature dependence of electronic energy transfer from a polymer host to a triplet emitter in light emitting diode materials Sang-Hyun Lim a , Xiong Gong b , Jacek Ostrowski b,c , Guillermo C. Bazan b,c , Daniel Moses b , Christopher J. Bardeen a, * a Department of Chemistry, University of Illinois, Urbana, IL 61801, USA b Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, CA 93106-5096, USA c Department of Chemistry, University of California at Santa Barbara, Santa Barbara, CA 93106-5096, USA Received 18 April 2003; in final form 4 June 2003 Published online: 27 June 2003 Abstract We investigate the temperature dependence of electronic energy transfer between a polymer host, poly(N-vinylc- arbazole) blended with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, and the triplet emitter tris[9,9-dihexyl- 2-(phenyl-4 0 -(pyridin-2 00 -yl))fluorene] iridium(III) (Ir(DPPF) 3 ). The photophysics of the blend are similar to those of neat poly(N-vinylcarbazole), with two emitting species corresponding to shallow and deep excimer traps. When the blend is doped with Ir(DPPF) 3 , the deep trap emission is preferentially quenched. This quenching cannot be explained by simple F€ orster energy transfer to the dopant. Instead, the data are consistent with a rapid, temperature-dependent partitioning of the energy between the two host species and the Ir(DPPF) 3 , each of which decays independently. Ó 2003 Elsevier Science B.V. All rights reserved. 1. Introduction Light-emitting diodes based on organic semi- conducting polymers have improved steadily in bothefficiencyandstability,andhavenowreached thestageofcommercialization.Amajoradvancein the field occurred when it was realized that the fraction of triplet excitons created by charge re- combination could be harvested by strongly emit- ting triplet energy acceptors [1]. Since the original demonstration of highly efficient triplet harvesting by Forrest and coworkers [2], a number of other groups have demonstrated efficient electrophos- phorescenceinavarietyoforganic-basedmaterials [3–5]. Recent work by Gong et al. [6–8] has shown that the combination of iridium complexes (tris- [9,9-dihexyl-2-(pyridinyl-2 0 ) fluorene] iridium (III) (Ir(DPF) 3 ), tris-[9,9-dihexyl-2-(phenyl-4 0 -(-pyridin- 2 00 -yl)) fluorene] iridium(III) (Ir(DPPF) 3 ) and tris- [2,5-bis-2 0 -(9,9 0 -dihexylfluorene)iridium](Ir(HFP) 3 ) Chemical Physics Letters 376 (2003) 55–61 www.elsevier.com/locate/cplett * Corresponding author. Fax: 1-217-244-3186. E-mail address: bardeen@uiuc.edu (C.J. Bardeen). 0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00945-X