Carbene-metal-amide complexes with bright red and near-infrared thermally activated delayed fluorescence Ikechukwu David Nwosu , Alexander Romanov University of Manchester, UK Two-coordinate carbene-metal-amide (CMA) complexes have recently emerged as new class of organometallic materials for realizing energy efficient Organic Light Emitting Diodes (OLED) [1]. CMA materials are recognized for their excellent photophysical properties such as submicrosecond thermally activated delayed fluorescence (TADF) with near unity efficiency [2]. This is due to their near degeneracy between singlet and triplet charge transfer (CT) excited states and heavy metal atom that enables fast reversed intersystem crossing process between the two CT states. Fast and bright blue to orange luminescent CMA materials exhibiting high quantum yields have been demonstrated [1]. However, there are no reports for red and near-IR CMA materials that exhibit near-unity luminescence efficiency associated with limitations imposed by the energy gap law. To achieve deep- blue emitting CMA materials one can use benzimidazole-type NHC-carbene ligands having a π-extension in the carbene backbone that helps to reduce the LUMO energy level compared with the classical NHC-carbene [3]. In this work we demonstrate that incorporating aza-nitrogen atoms in the π-extension of the NHC-carbene backbone results in significant red shift of the TADF luminescence resulting in bright red emitters with near unity photoluminescence quantum yields (PLQYs). Following this molecular design a series of novel CMA complexes will be presented (Figure 1) that emit bright TADF in the range of 563-832 nm. Varied temperature excited state lifetime measurements enabled us to estimate the singlet-triplet energy gaps to be as low as 30 meV. This parallels well with the fast reverse intersystem crossing rates resulting in efficient TADF having an excited state lifetime down to 300 ns and radiative rates up to 2.87 x 10 6 s -1 . New CMA materials show a superior performance compared with the benchmark phosphors based on iridium(III) or platinum(II).
Figure 1. New CMA complexes showing fast and bright TADF behaviour. References 1. D. Di, A. S. Romanov, L. Yang, J. M. Richter, J. P. H. Rivett, S. Jones, T. H. Thomas, M. A. Jalebi, R. H. Friend, M. Linnolahti, M. Bochmann, D. Credgington, Science , 2017, 356, 159–163 2. P. J. Conaghan, C. S. B. Matthews, F. Chotard, S. T. E. Jones, N. C. Greenham, M. Bochmann, D. Credgington, A. S. Romanov Nat.Commun ., 2020, 11, 1758, DOI: 10.1038/s41467-020-15369-8 3. C. N. Muniz, J. Schaab, A. O. Razgoniaev, P. I. Djurovich, M. C. Thompson, J.Am.Chem.Soc. , 2022, 144, 17916–17928
P24
© The Author(s), 2023
Made with FlippingBook Learn more on our blog