Highly Luminescent Dinuclear Platinum(II) Complexes Incorporating Bis-Cyclometallating Pyrazine-Based Ligands: A Versatile Approach to Efficient Red Phosphors

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• 作者：Stacey Culham ; Pierre-Henri Lano毛 ; Victoria L. Whittle ; Marcus C. Durrant ; J. A. Gareth Williams ; Valery N. Kozhevnikov
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：October 7, 2013
• 年：2013
• 卷：52
• 期：19
• 页码：10992-11003
• 全文大小：593K
• 年卷期：v.52,no.19(October 7, 2013)
• ISSN：1520-510X

文摘

A series of luminescent dinuclear platinum(II) complexes incorporating diphenylpyrazine-based bridging ligands (LⁿH₂) has been prepared. Both 2,5-diphenylpyrazine (L²H₂) and 2,3-diphenylpyrazine (L³H₂) are able to undergo cyclometalation of the two phenyl rings, with each metal ion binding to the two nitrogen atoms of the central heterocycle, giving, after treatment with the anion of dipivaloyl methane (dpm), complexes of formula {Pt(dpm)}₂Lⁿ. These compounds are isomers of the analogous complex of 4,6-diphenylpyrimidine (L¹H₂). Related complexes of dibenzo(f,h)quinoxaline (L⁴H₂), 2,3-diphenyl-quinoxaline (L⁵H₂), and dibenzo[3,2-a:2鈥?3鈥?c]phenazine (L⁶H₂) have also been prepared, allowing the effects of strapping together the phenyl rings (L⁴H₂ and L⁶H₂) and/or extension of the conjugation from pyrazine to quinoxaline (L⁵H₂ and L⁶H₂) to be investigated. In all cases, the corresponding mononuclear complexes, Pt(dpm)LⁿH, have been isolated too. All 12 complexes are phosphorescent in solution at ambient temperature. Emission spectra of the dinuclear complexes are consistently red shifted compared to their mononuclear analogues, as are the lowest energy absorption bands. Electrochemical data and TD-DFT calculations suggest that this effect arises primarily from stabilization of the LUMO. Introduction of the second metal ion also has the effect of substantially increasing the molar absorptivity and, in most cases, the radiative rate constants. Meanwhile, extension of conjugation in the heterocycle of L⁵H₂ and L⁶H₂ and planarization of the aromatic system favored by interannular bond formation in L⁴H₂ and L⁶H₂ leads to further red shifts of the absorption and emission spectra to wavelengths that are unusually long for cyclometalated platinum(II) complexes. The results may offer a versatile design strategy for tuning and optimizing the optical properties of d-block metal complexes for contemporary applications.