Subunit Variation to Uncover Properties of Polyazine-Bridged Ru(II), Pt(II) Supramolecules with Low Lying Charge Separated States Providing Insight into the Functioning as H2O Reduction Pho

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• 作者：Jessica D. Knoll ; Samantha L. H. Higgins ; Travis A. White ; Karen J. Brewer
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：September 3, 2013
• 年：2013
• 卷：52
• 期：17
• 页码：9749-9760
• 全文大小：551K
• 年卷期：v.52,no.17(September 3, 2013)
• ISSN：1520-510X

文摘

Two new structurally diverse polyazine-bridged Ru(II),Pt(II) tetrametallic complexes, [{(Ph₂phen)₂Ru(dpp)}₂Ru(dpp)PtCl₂](PF₆)₆ (1a) and [{(Ph₂phen)₂Ru(dpp)}₂Ru(dpq)PtCl₂](PF₆)₆ (2a) (Ph₂phen = 4,7-diphenyl-1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline), as well as their trimetallic precursors have been synthesized to provide a comparison for detailed analysis to elucidate component effects in the previously reported photocatalyst [{(phen)₂Ru(dpp)}₂Ru(dpq)PtCl₂](PF₆)₆ (4a) (phen = 1,10-phenanthroline). Electrochemistry shows terminal Ru based highest occupied molecular orbitals (HOMOs) with remote BL鈥?(BL鈥?= bridging ligand coupling central Ru and cis-PtCl₂ moiety) based lowest unoccupied molecular orbitals (LUMOs). Population of a lowest-lying charge separated (³CS) excited state with oxidized terminal Ru and reduced remote BL鈥?via intramolecular electron transfer is predicted by electrochemical analysis and is observed through steady-state and time-resolved emission studies as well as emission excitation profiles which display unusual nonunity population of the lowest lying emissive Ru鈫抎pp ³MLCT (metal-to-ligand charge transfer) state. Each tetrametallic complex is an active photocatalyst for H₂ production from H₂O with 2a showing the highest activity (94 TON (turnover number) in 10 h, where TON = mol H₂/mol catalyst). The nature of the bridging ligand coupling the trimetallic light absorber to the cis-PtCl₂ moiety has a significant impact on the catalyst activity, correlated to the degree of population of the ³CS excited state. The choice of terminal ligand affects visible light absorption and has a minor influence on photocatalytic H₂ production from H₂O. Evidence that an intact supramolecule functions as the photocatalyst includes a strong dependence of the photocatalysis on the identity of BL鈥? an insensitivity to Hg(l), no detectable H₂ production from the systems with the trimetallic synthons and cis-[PtCl₂(DMSO)₂] as well as spectroscopic analysis of the photocatalytic system.