Coupling d⁶ Ir(III) and d⁸ Pt(II) Chromophores

Two classes of widely studied luminescent metal complexes are octahedral d⁶ (i.e., Ir³⁺) and square planar d⁸ (i.e., Pt²⁺) polypyridyl complexes, which have distinctly different photophysics and photoreactivity. In this study we report a series of d⁶-d⁸ Ir^III-Pt^II hybrid complexes arising from coordination of metalloligands IrL₂(benzene-1-thioether-2-thiolate) or Ir(L)₂(benzene-1,2-dithiolate) anion [L = 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dfppy), or 1-phenylisoquinoline (piq)] to Pt(terpy)²⁺ (terpy = 2,2′:6′,2″-terpyridine). X-ray crystal structures of the Ir-Pt complexes show the IrL₂ and Pt(terpy) chromophores are cofacially oriented with interplanar distances of 3.268-3.442 Å. Density functional theory (DFT) calculations show that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in the IrL₂ and the Pt(terpy), respectively. All the complexes display a low-energy absorption band (λ_max = 460-534 nm, ϵ_max = (0.75-2.13) × 10³ M^-1 cm^-1), which is attributed to interchromophore-charge-transfer (ICCT) transition, according to time-dependent DFT calculations. The ³ICCT excited state is emissive, giving long-lived phosphorescence that reaches as low as near-infrared (λ_max = 668-710 nm, τ = 0.17-0.79 μs).