Excited state lifetime modulation by twisted and tilted molecular design in carbene-metal-amide photoemitters

Qinying Gu, Florian Chotard, Julien Eng, Antti-Pekka M. Reponen, Inigo J. Vitorica-Yrezabal, Adam W. Woodward, Thomas J. Penfold, Dan Credgington, Manfred Bochmann, Alexander S. Romanov

Research output: Contribution to journalArticlepeer-review

Abstract

Carbene-metal-amides (CMAs) are an emerging class of photoemitters based on a linear donor-linker-acceptor arrangement. They exhibit high flexibility about the carbene-metal and metal-amide bonds, leading to a conformational freedom which has a strong influence on their photophysical properties. Herein we report CMA complexes with (1) nearly coplanar, (2) twisted, (3) tilted, and (4) tilt-twisted orientations between donor and acceptor ligands and illustrate the influence of preferred ground-state conformations on both the luminescence quantum yields and excited-state lifetimes. The performance is found to be optimum for structures with partially twisted and/or tilted conformations, resulting in radiative rates exceeding 1 × 10 6s -1. Although the metal atoms make only small contributions to HOMOs and LUMOs, they provide sufficient spin-orbit coupling between the low-lying excited states to reduce the excited-state lifetimes down to 500 ns. At the same time, high photoluminescence quantum yields are maintained for a strongly tilted emitter in a host matrix. Proof-of-concept organic light-emitting diodes (OLEDs) based on these new emitter designs were fabricated, with a maximum external quantum efficiency (EQE) of 19.1% with low device roll-off efficiency. Transient electroluminescence studies indicate that molecular design concepts for new CMA emitters can be successfully translated into the OLED device.

Original languageEnglish
Pages (from-to)7526–7542
Number of pages17
JournalChemistry of Materials
Volume34
Issue number16
Early online date4 Aug 2022
DOIs
Publication statusPublished - 23 Aug 2022

Keywords

  • Gold complexes
  • photoluminescence
  • light emitting diodes
  • organometallics

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