Photoluminescent Linear Carbene-Silver-Amide Complexes

Two-coordinate, linear carbene-metal-amide (CMA) complexes have gained attention due to their excellent photophysical properties. CMA complexes featuring cyclic (alkyl)(amino)carbenes (CAACs) and copper(I) or gold(I) have been extensively studied. However, CMA complexes with classical N-heterocyclic carbene (NHC) ligands and silver(I) have rarely been studied for photophysical properties. Herein, we report the synthesis and characterization of five linear carbene-silver-amide complexes, [Ag(IPr)(Cbz)], [Ag(IPr)(Cbz^Cl)], [Ag(^AcenaphIPr)(Cbz)], [Ag(^AcenaphIPr)(Cbz^Cl)], and [Ag(^AcenaphIPr)(Cbz^tBu)], respectively, and their photophysical properties. All five complexes have been characterized by ¹H, ¹³C{¹H}, and 2D NMR spectroscopy and high-resolution mass spectrometry. [Ag(IPr)(Cbz)] has also been characterized by single-crystal X-ray diffraction analysis. The organometallic silver(I) complexes have been studied by UV-visible and luminescence spectroscopy. The UV-visible spectra of the complexes feature transitions up to 400 nm. Upon excitation, they show photoluminescence from 360 to 430 nm in solution at room temperature. In all cases, luminescence originates from ligand-centered π-π* transitions and is fluorescent in nature. The excited state lifetimes of the complexes are in the range of 1.3 to 7.8 ns, and quantum yields are in the range of 6.7-33.2% in deaerated THF solutions at room temperature. When the carbene-silver-amide complexes contain carbazolide units or carbazolide with electron-donating groups, high fluorescence quantum yields are obtained. On the other hand, when carbazolide with electron-withdrawing groups is present in the complexes, low quantum yields are detected.