Modulation of Pt → Ln Energy Transfer in PtLn2 (Ln = Nd, Er, Yb) Complexes with 2,2′-Bipyridyl/2,2′:6′2′′-Terpyridyl Ethynyl Ligands

Reaction of (CH3)3SiC≡Cbpy (bpy = 2,2′-bipyridyl), (CH3)3SiC≡CC6H4tpy (tpy = 2,2′:6′2′′-terpyridyl), or (CH3)3SiC≡CC6H4C≡Cbpy with Pt(Bu t 2bpy)Cl2 in the presence of KF and CuI gave Pt(Bu t 2bpy)(C≡Cbpy)2 (1), Pt(Bu t 2bpy)(C≡CC6H4tpy)2 (5), or Pt(Bu t 2bpy)(C≡CC6H4C≡Cbpy)2 (9), respectively. Incorporating Ln(hfac)3 (Ln = Nd, Er, Yb; hfac = hexafluoroacetylacetonate) units with 1, 5, and 9 through 2,2′-bipyridyl/2,2′:6′2′′-terpyridyl chelation induces isolation of a series of PtLn2 heterotrinuclear complexes. Upon excitation of the PtLn2 complexes at 350 nm ≤ λex ≤ 500 nm, near-infrared (NIR) luminescence from lanthanide ions is indeed “lighting up” through effective Pt → Ln energy transfer from 3[d(Pt) → π*(Bu t 2bpy)] metal-to-ligand charge transfer transition excited-state of the Pt(Bu t 2bpy)bis(acetylide) antenna chromophore. By successive insertion of phenylene or ethynyl between acetylide and 2,2′-bipyridyl/2,2′:6′,2′′-terpyridyl in the bridging ligands, the rate and efficiency of Pt → Ln energy transfer are tunable. In contrast with quite effective Pt → Ln energy transfer in Pt−C≡Cbpy−Ln (Pt···Ln = 8.6 Å) and Pt−C≡CC6H4tpy−Ln (Pt···Ln = 14.1 Å) arrays, the long-range energy transfer across Pt−C≡CC6H4C≡Cbpy−Ln (Pt···Ln = 14.9 Å) array becomes less efficient.