Platinum(II) Complexes of NCN-Coordinating 1,3-Bis(2-pyridyl)benzene Ligands: Thiolate Coligands Lead to Strong Red Luminescence from Charge-Transfer States

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• 作者：William A. Tarran ; Gemma R. Freeman ; Lisa Murphy ; Adam M. Benham ; Ritu Kataky ; J. A. Gareth Williams
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 2, 2014
• 年：2014
• 卷：53
• 期：11
• 页码：5738-5749
• 全文大小：498K
• 年卷期：v.53,no.11(June 2, 2014)
• ISSN：1520-510X

文摘

A new family of platinum(II) complexes of the form PtLⁿSR have been prepared, where Lⁿ represents a cyclometalating, NCN-bound tridentate ligand and SR is a monodentate thiolate ligand. The complexes fall into two groups, those of PtL¹SR where HL¹ = 1,3-bis(2-pyridyl)benzene, and those of PtL²SR, where HL² = methyl 3,5-bis(2-pyridyl)benzoate. Each group consists of five complexes, where R = CH₃, C₆H₅, p-C₆H₄-CH₃, p-C₆H₄-OMe, p-C₆H₄-NO₂. These compounds, which are bright red, orange, or yellow solids, are formed readily upon treatment of PtLⁿCl with the corresponding potassium thiolate KSR in solution at room temperature. The replacement of the chloride by the thiolate ligand is accompanied by profound changes in the photophysical properties. A broad, structureless, low-energy band appears in the absorption spectra, not present in the spectra of PtLⁿCl. In the photoluminescence spectra, the characteristic, highly structured phosphorescence bands of PtLⁿCl in the green region are replaced by a broad, structureless emission band in the red region. These new bands are assigned to a 蟺_S/d_Pt 鈫?蟺*_NCN charge-transfer transition from the thiolate/platinum to the NCN ligand. This assignment is supported by electrochemical data and TD-DFT calculations and by the observation that the decreasing energies of the bands correlate with the electron-donating ability of the substituent, as do the increasing nonradiative decay rate constants, in line with the energy-gap law. However, the pair of nitro-substituted complexes do not fit the trends. Their properties, including much longer luminescence lifetimes, indicate that the lowest-energy excited state is localized predominantly on the arenethiolate ligand for these two complexes. Red-emitting thiolate adducts may be relevant to the use of PtLⁿCl complexes in bioimaging, as revealed by the different distributions of emission intensity within live fibroplast cells doped with the parent complex, according to the region of the spectrum examined.