Charge-Transfer and Ligand-Localized Photophysics in Luminescent Cyclometalated Pyrazolate-Bridged Dinuclear Platinum(II) Complexes

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• 作者：Arnab Chakraborty ; Joseph C. Deaton ; Alexandre Haefele ; Felix N. Castellano
• 刊名：Organometallics
• 出版年：2013
• 出版时间：July 22, 2013
• 年：2013
• 卷：32
• 期：14
• 页码：3819-3829
• 全文大小：579K
• 年卷期：v.32,no.14(July 22, 2013)
• ISSN：1520-6041

文摘

We present the synthesis, photophysical characterization, and electrochemistry of three series of cyclometalated binuclear platinum(II) complexes, each bridged by two 3,5-disubstituted pyrazolate ligands (渭-R₂pz). These neutral compounds have the general formula [CNPt(渭-R₂pz)]₂, where CN is a cyclometalating ligand corresponding to 2-(2鈥?thienyl)pyridine (thpy), 1-phenylisoquinoline (piq), or 7,8-benzoquinoline (bzq) with R = H, Me, ⁱPr, Ph, corresponding to series I鈥揑II dimers, respectively. Systematic variation of the cyclometalating ligands in addition to the bridging pyrazolates renders colorful structures exhibiting a range of electrochemical and spectroscopic behavior with absorption and photoluminescence properties tuned over a wide portion of the visible spectrum. Steric bulk introduced into the 3,5-positions on the pz bridges readily modulates intramolecular d⁸鈥揹⁸ metal鈥搈etal 蟽 interactions strongly affecting the frontier orbitals鈥?electronic structure, manifested by changes in absorption and emission energy, excited-state lifetime, and photoluminescence quantum yield. Cyclic voltammetry revealed the presence of two very closely spaced reversible CN ligand-based reductions ranging between 鈭?.97 and 鈭?.56 V vs Fc⁺/Fc, and the first metal鈥搈etal-centered oxidation wave was found to be reversible in dichloromethane and irreversible in coordinating THF in most instances. All the complexes of series I displayed triplet ligand-localized excited states at all temperatures, while an increase of steric bulk in the pz bridge in the two other molecular series resulted in a variation of photophysical behavior ranging from charge transfer to ligand localized, including admixture behavior.