Department of Chemistry, University of Eastern Finland, FI-80101 Joensuu, Finland.
Department of Chemistry, University of Manchester, Oxford Rd., Manchester M13 9PL, UK.
Molecules. 2023 May 28;28(11):4398. doi: 10.3390/molecules28114398.
Gold-centered carbene-metal-amides (CMAs) containing cyclic (alkyl)(amino)carbenes (CAACs) are promising emitters for thermally activated delayed fluorescence (TADF). Aiming at the design and optimization of new TADF emitters, we report a density functional theory study of over 60 CMAs with various CAAC ligands, systematically evaluating computed parameters in relation to photoluminescence properties. The CMA structures were primarily selected based on experimental synthesis prospects. We demonstrate that TADF efficiency of the CMA materials originates from a compromise between oscillator strength coefficients and exchange energy (ΔE). The latter is governed by the overlap of HOMO and LUMO orbitals, where HOMO is localized on the amide and LUMO over the Au-carbene bond. The S ground and excited T states of the CMAs adopt approximately coplanar geometry of carbene and amide ligands, but rotate perpendicular in the excited S states, resulting in degeneracy or near-degeneracy of S and T, accompanied by a decrease in the S-S oscillator strength from its maximum at coplanar geometries to near zero at rotated geometries. Based on the computations, promising new TADF emitters are proposed and synthesized. Bright CMA complex (CAAC)Au(carbazolide) is obtained and fully characterized in order to demonstrate that excellent stability and high radiative rates up to 10 s can be obtained for the gold-CMA complexes with small CAAC-carbene ligands.
金中心卡宾金属酰胺（CMAs）含有环状（烷基）（氨基）卡宾（CAACs），是热活化延迟荧光（TADF）的有前途的发光体。为了设计和优化新的 TADF 发射器，我们报告了超过 60 种具有各种 CAAC 配体的 CMA 的密度泛函理论研究，系统地评估了与光致发光性质相关的计算参数。CMA 结构主要基于实验合成前景进行选择。我们证明，CMA 材料的 TADF 效率源自振子强度系数和交换能（ΔE）之间的折衷。后者由 HOMO 和 LUMO 轨道的重叠决定，其中 HOMO 定域在酰胺上，LUMO 在 Au-卡宾键上。CMA 的 S 基态和激发 T 态采用卡宾和酰胺配体的近似共面几何形状，但在激发 S 态中垂直旋转，导致 S 和 T 的简并或近简并，同时 S-S 振子强度从共面几何形状的最大值降至旋转几何形状的近零。基于计算，提出并合成了有前途的新 TADF 发射器。获得了亮的 CMA 配合物（CAAC）Au（咔唑化物），并对其进行了全面表征，以证明具有小 CAAC-卡宾配体的金-CMA 配合物可以获得极好的稳定性和高达 10 s 的高辐射速率。
