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 (<b>ICCT</b>) 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)