Highly efficient phosphorescence from cyclometallated iridium(III) compounds: Improved syntheses of picolinate complexes and quantum chemical studies of their electronic structures

Robert D. Sanner, Nerine J. Cherepy, H. Paul Martinez, Hung Q. Pham, Victor G. Young

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Abstract

We report a new method to make heteroleptic cyclometallated iridium(III) complexes that employs 1,2-dimethoxyethane (DME) instead of the commonly used 2-ethoxyethanol for the addition of ancillary ligands to chloro-bridged dimeric iridium species. Thus, picolinic acid was quickly and cleanly added to [(F2ppy)2Ir(Cl)]2 (where F2ppy = 2-(4′,6′-difluorophenyl)pyridinato) with base under DME reflux to afford (F2ppy)2Ir(picolinate) (FIrpic) in excellent yield. The high purity of the products obviates the need for further purification, an improvement over the common route in which column chromatography is required. We prepared eleven picolinate complexes by this route, eight of which were characterized by single crystal x-ray diffraction. The complexes possess the same distorted octahedral geometry with two bidentate phenylpyridine ligands and one bidentate 2-picolinate ligand. All of the compounds exhibited efficient phosphorescence with colors ranging from blue to orange; photophysical measurements revealed emission quantum yields as high as 0.92, while most surpassed 0.5. Time-dependent density functional theory calculations, coupled with the use of natural transition orbitals (NTOs), allowed a detailed interpretation of the electronic structures for the complexes. The nature of the acceptor orbital for the lowest-energy triplet state NTO was found to be an important predictor for the emission spectra of FIrpic and its congeners.

Original languageEnglish (US)
Article number119040
JournalInorganica Chimica Acta
Volume496
DOIs
StatePublished - Oct 1 2019

Bibliographical note

Funding Information:
We would like to thank Prof. Laura Gagliardi (University of Minnesota) for helpful discussions on the quantum chemical calculations. Work at Lawrence Livermore National Laboratory was performed under the auspices of the U.S. DOE under Contract No. DE-AC52-07NA27344 and was supported by the single-crystal diffraction data on several complexes presented herein. The Bruker AXS D8 Venture diffractometer was purchased through a grant from NSF/MRI (#1229400) and the University of Minnesota. The computational part of this research (H.P.) was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-FG02-17ER16362. The authors acknowledge the Minnesota Supercomputing Institute (MSI) for providing computing resources. U.S. DOE National Nuclear Security Administration, Defense Nuclear Nonproliferation Research and Development under Contract No. DE-AC03-76SF00098 . We thank the X-Ray Crystallographic Laboratory, LeClaire-Dow Instrumentation Facility, Department of Chemistry, University of Minnesota, for its contribution. The authors would like to acknowledge Mr. James T. Moore and the X-Ray Crystallography course CHEM5755 for assistance in collecting

Keywords

  • Blue emission
  • DFT calculations
  • FIrpic synthesis
  • OLED
  • Phosphorescent iridium complex
  • Photoluminescence

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