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Unformatted text preview: Blue-Emitting Iridium Complexes with Substituted 1,2,4-Triazole Ligands: Synthesis, Photophysics, and Devices Enrico Orselli, ²,‡ Gregg S. Kottas,* ,²,‡ Asgeir E. Konradsson, ²,‡ Paolo Coppo, § Roland Fro 1 hlich, | Luisa De Cola,* ,²,‡ Addy van Dijken, ⊥ Michael Bu 1 chel, ⊥ and Herbert Bo 1 rner ¥ Westfa ¨lische Wilhelms-Uni V ersita ¨t Mu ¨nster, Physikalisches Institut, Mendelstrasse 7, 48149 Mu ¨nster, Germany, Center for Nanotechnology (CeNTech), Heisenbergstrasse 11, 48149 Mu ¨nster, Germany, Wolfson Centre for Materials Processing, Brunel Uni V ersity, Uxbridge, Middlesex UB8 3PH, United Kingdom, Westfa ¨lische Wilhelms-Uni V ersita ¨t Mu ¨nster, Organisch-Chemisches Institut, Corrensstrasse 40, 48149 Mu ¨nster, Germany, Philips Research, Philips Natuurkundig Laboratorium, Prof. Holstlaan 4, 5656 AA Eindho V en, The Netherlands, and Philips Research Labs, Weisshausstrasse 2, 52066 Aachen, Germany Received June 6, 2007 Neutral heteroleptic mononuclear iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine- 1,2,4-triazole ligands were synthesized and fully characterized. We investigated the effects of substituents in the 5-position of the triazole ring on the photophysical and electrochemical behavior. Increasing the electron-withdrawing capabilities generally leads to a lowering of the HOMO level with a consequent slight widening of the HOMO- LUMO gap and a blue shift in emission. The complexes reported exhibit high emission quantum yields and long luminescent lifetimes, typical of iridium(III) complexes, and most of them show reversible redox processes in solution. Also, many of the complexes reported here have been obtained as single crystals suitable for X-ray crystallography. Two of the complexes were further tested as phosphorescent dyes in OLED devices and showed high external quantum efficiencies ( ∼ 7%) and color points better than the “standard” for blue iridium(III) bis[(4,6-difluorophenyl)- pyridinato- N , C 2 ′ ]picolinate (FIrpic). We also report the full electrochemical investigation of FIrpic in different solvents. Introduction Iridium(III) organometallic complexes have received a great deal of interest in a variety of photonic applications. In particular, the charged compounds have been intensely studied for use as dopants in light-emitting electrochemical cells (LEECs) 1,2 and the neutral ones in organic/organo- metallic light-emitting diodes (OLEDs). 1- 3 Iridium(III), as other heavy transition metals like ruthenium, osmium, and platinum, harvests both singlet and triplet states from electrically generated excitons, leading to theoretical ef- ficiencies of 100%, whereas fluorescent molecules can only utilize the singlet excitons and thus have a maximum theoretical efficiency of 25%....
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This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at University of Georgia Athens.
- Spring '08