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Excited-State Lifetime Modulation by Twisted and Tilted Molecular Design in Carbene-Metal-Amide Photoemitters

Lookup NU author(s): Dr Julien EngORCiD, Professor Thomas PenfoldORCiD

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

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 × 10⁶ s^–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.

Publication metadata

Author(s): Gu Q, Chotard F, Eng J, Reponen A, Vitorica-Yrezabal J, Woodward A, Penfold TJ, Credgington D, Bochmann M, Romanov AS

Publication type: Article

Publication status: Published

Journal: Chemistry of Materials

Year: 2022

Volume: 34

Issue: 16

Pages: 7526–7542

Print publication date: 05/08/2022

Online publication date: 05/08/2022

Acceptance date: 05/08/2022

Date deposited: 05/08/2022

ISSN (print): 0897-4756

ISSN (electronic): 1520-5002

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.chemmater.2c01938

DOI: 10.1021/acs.chemmater.2c01938

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