Tunable light‐emission properties of solution‐processable N‐Heterocyclic carbene cyclometalated gold(III) complexes for organic light‐emitting diodes

Robert Malmberg, Tobias von Arx, Monirul Hasan, Olivier Blacque, Atul Shukla, Sarah K. M. McGregor, Shih-Chun Lo, Ebinazar B. Namdas, Koushik Venkatesan*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

N-Heterocyclic carbene (NHC) cyclometalated gold(III) complexes remain very scarce and therefore their photophysical properties remain currently underexplored. Moreover, gold(III) complexes emitting in the blue region of the electromagnetic spectrum are rare. In this work, a series of four phosphorescent gold(III) complexes was investigated bearing four different NHC monocyclometalated (C^C*)-type ligands and a dianionic (N^N)-type ancillary ligand ((N^N)=5,5’-(propane-2,2-diyl)bis(3-(trifluoromethyl)-1 H-pyrazole) (mepzH2)). The complexes exhibit strong phosphorescence when doped in poly(methyl methacrylate) (PMMA) at room temperature, which were systematically tuned from sky-blue [λPL=456 nm, CIE coordinates: (0.20, 034)] to green [λPL=516 nm, CIE coordinates: (0.31, 0.54)] by varying the monocyclometalated (C^C*) ligand framework. The complexes revealed high quantum efficiencies (ϕPL) of up to 43 % and excited-state lifetimes (τ0) between 15–266 μs. The radiative rate constant values found for these complexes (kr=103–104 s−1) are the highest found in comparison to previously known best-performing monocyclometalated gold(III) complexes. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of these complexes further lend support to the excited-state nature of these complexes. The calculations showed a significant contribution of the gold(III) metal center in the lowest unoccupied molecular orbitals (LUMOs) of up to 18 %, which was found to be unique for this class of cyclometalated gold(III) complexes. Additionally, organic light-emitting diodes (OLEDs) were fabricated by using a solution process to provide the first insight into the electroluminescent (EL) properties of this new class of gold(III) complexes.

Original languageEnglish
Pages (from-to)7265-7274
Number of pages10
JournalChemistry - A European Journal
Volume27
Issue number25
Early online date24 Mar 2021
DOIs
Publication statusPublished - 3 May 2021

Keywords

  • cyclometallation reactions
  • gold
  • luminescence
  • N-heterocyclic carbenes
  • organic light-emitting devices

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