Monocyclometalated gold(III) monoaryl complexes - A new class of triplet phosphors with highly tunable and efficient emission properties

Highly tunable and rich phosphorescent emission properties based on the stable monocyclometalated gold(III) monoaryl structural motif are reported. Monochloro complexes of the type cis-[(N^C)Au(C₆H₂(CF ₃)₃)(Cl)] N^C=2-phenylpyridine (ppy)] (1), [N^C=benzo[h]quinoline (bzq)] (2), [N^C=2-(5-Methyl-2-thienyl)pyridine (5m-thpy)] (3) were successfully prepared in modest to good yields by reacting an excess of 2, 4, 6-tris(trifluoromethyl)phenyl lithium (LiFmes) with the corresponding dichloride complexes cis-[(N^C)AuCl₂]. Subsequent replacement of the chloride ligand in 1 with strong ligand field strength such as cyanide and terminal alkynes resulted in complexes of the type cis-[(ppy)Au(Fmes)(R)] R=CN (4), I (5), Cï£C=C₆H ₅ (6) and Cï£C=C₆H₄N(C ₆H₅)-p (7). Single crystal X-ray diffraction studies of all the complexes except 7 were performed to further corroborate their chemical identity. Thermogravimetric analysis (TGA) studies of the uncommon cis configured aryl alkyne complex 7 confirmed the high stability of this complex. Detailed photophysical investigations carried out in solution at room temperature, at 77a K (2-MeTHF) in rigidified media, solid state and 5a wt % PMMA revealed the phosphorescent nature of emission in these complexes. Additionally, their behavior was found to be governed based on both the nature of the cyclometalated ligand and the electronic properties of the ancillary ligands. Highly efficient interligand charge transfer in complex 7 provides access to a wide range of emission colors (solvent-dependent) from deep blue to red with phosphorescence emission quantum yield of 30 % (441a nm) and 39 % (622a nm) in solution and solid state, respectively, and is the highest reported for any Au^III complexes. DFT and TDDFT calculations carried out further validated the observations and assignments based on the photophysical experimental findings. Shining like gold: Introduction of the tris(trifluoromethyl)phenyl group gave rise to stable monocyclometalated gold(III) monoaryl complexes with highly tunable and rich emission properties. A highly efficient interligand charge transfer allowed for the significant tuning of the phosphorescence emission energies across the visible spectrum (see figure).