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Phosphorescent, Cyclometalated Cinchophen-Derived Platinum Complexes: Syntheses, Structures, and Electronic Properties

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journal contribution
posted on 06.07.2015, 00:00 by Oliver J. Stacey, James A. Platts, Simon J. Coles, Peter N. Horton, Simon J. A. Pope
The syntheses of nine new monometallic heteroleptic platinum complexes [Pt­(L1–4)­(acac)], [Pt­(L1)­(hmacac/hfacac)], [PtCl­(L1)­(py)], [Pt­(L1)­(8-Q)], [Pt­(L1)­(bpy)]­(PF6) (where L1 = 2-phenyl-4-ethyl-quinolinecarboxylate; L2/L3 = N-functionalization of 2-phenyl-N-aryl/alkyl-quinoline-4-carboxamides; L4 = 2-phenyl-4-quinolinecarboxylic acid (cinchophen); acac = acetylacetonato; hmacac =2,2,6,6-tetramethyl-3,5-heptanedionate; hfacac = hexafluoroacetylacetonate; py = pyridine; 8-Q = 8-quinolinato; bpy =2,2′-bipyridine) are described from precursor dimeric Pt­(II) species via an intermediate DMSO adduct of the general form [PtCl­(L1–4)­(DMSO)]. Single crystal X-ray diffraction studies were undertaken on three complexes, [Pt­(L1)­(acac)], [PtCl­(L1)­(DMSO)], and [Pt­(L1)­(bpy)]­(PF6). The structures show that the complexes each adopt a distorted square planar geometry (most severely in the case of [Pt­(L1)­(bpy)]­(PF6)) with indications of intermolecular Pt–Pt interactions in one example. The complexes were investigated using 195Pt­{1H} NMR spectroscopy, revealing varied chemical shifts that were strongly dependent upon the specific coordination environment of Pt­(II). Luminescence studies showed the complexes possess a phosphorescent character with tunable emission wavelengths between 605 and 641 nm and luminescent lifetimes up to ∼450 ns. Supporting TD-DFT studies provided descriptions of the HOMO and LUMO energy levels of the key complex types, confirming an MLCT contribution to the lowest energy absorption that generally correlated well with the experimental spectra. The contribution of the Pt­(5d) center to the calculated HOMOs was strongly ligand dependent, whereas the LUMOs are generally localized over the quinoline component of the cyclometalated ligand.