Fast and bright phosphorescence from linear gold complexes with diamidocarbene ligands Charlotte Riley, Alexander Romanov University of Manchester, UK N-heterocyclic carbenes have emerged as a highly promising class of ligands in organometallic chemistry, paving the way towards various complexes with enhanced catalytic activity, medicinal applications, and materials for optoelectronic applications [1]. Bright luminescent carbene copper(I) halide or pseudohalide complexes with linear geometry have been recently demonstrated based on cyclic(alkyl)aminocarbene (CAAC) and diamidocarbene (DAC) ligands [2,3]. However, similar carbene gold(I) and silver(I) halide complexes are practically non-emissive due to the low-lying energy of the d-orbitals and the large energy gap between HOMO and LUMO energy levels. Here, we present a series of DACAu(I) halide and pseudohalide complexes with particularly bright photoluminescence quantum yields up to 90% (Figure 1). We explain this effect due to the strong π-accepting character of the carbonyl groups of the DAC carbene, significantly stabilising the LUMO energy level of the carbene, thus reducing the energy gap and enabling bright phosphorescence even for the gold complexes. All compounds DAC-Au-X (X=Cl, Br, I SCN or OTf) demonstrate not only bright phosphorescence in the range 480–520 nm but also very short excited state lifetimes as low as 1.1 μs resulting in high radiative rate constants ( k r > 2.6x10 5 s -1 ). These values are on par or superior to some of the most efficient heavy metal emitters based on iridium(III), platinum(II) or gold(III) complexes. Our reactivity study of DAC Mes AuCl revealed that the amide bond is vulnerable to nucleophilic attack, i.e., a strong base such as KO t Bu results in cleavage of the carbene backbone and formation of the neutral trigold cluster.
Figure 1. Linear DAC Mes gold complexes and trigold cluster showing bright phosphorescence 430-550 nm with PLQY up to 90% and short excited state lifetime down to 1 µs References 1. C.A. Smith, M.R. Narouz, P.A. Lummis, I. Singh, A. Nazemi, C.-H. Li, C. M. Crudden, Chem. Rev. 2019, 119, 8, 4986; 2. A.S. Romanov, D. Di, L. Yang, J. Fernandez-Cestau, C.R. Becker, C.E. James, B. Zhu, M. Linnolahti, D. Credgington, M. Bochmann. Chem. Commun., 2016, 52, 6379; 3. S. Shi, L. R. Collins, M.F. Mahon, P.I. Djurovich, M.E. Thompson, M.K. Whittlesey, Dalton Trans., 2017,46, 745.
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