Monocyclometalated (C N) Gold(III) Metallacycles: Tunable Emission and Singlet Oxygen (¹ O₂ ) Generation Properties

The synthesis, characterization and photoluminescent properties of four cyclometalated (C N)-type gold(III) complexes bearing a bidentate diacetylide ligand, tolan-2,2'-diacetylide (tda), are reported. The complexes exhibit highly tunable excited state properties and show photoluminescence (PL) across the entire visible spectrum from sky-blue (λ_PL =493 nm) to red (λ_PL =675 nm) with absolute PL quantum yields (PLQY) of up to 75 % in solution, the highest PLQY found for any monocyclometalated Au(III) complex in solution. As a consequence of the use of the strongly rigidifying diacetylide bidentate ligand, a significant increase in the excited state lifetimes (τ₀ =16-258 μs) was found in solution and in thin films. The complexes showed remarkable singlet oxygen generation in aerated solution with absolute singlet oxygen quantum yield (ϕ^1Δ ) values reaching up to 7.5×10^-5 and singlet oxygen lifetimes (τ₀ ^1Δ ) in the range of 66-95 μs. Furthermore, the radiative and non-radiative rates of singlet oxygen were determined using the ϕ^1Δ and τ₀ ^1Δ values and correlations are drawn between the formation of singlet oxygen and its interaction with cyclometalated (C N) gold(III) complexes.