Luminescent Ruthenium(II) Bipyridine-Calix[4]arene Complexes as Receptors for Lanthanide Cations

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• 作者：Paul D. Beer ; Fridrich Szemes ; Paolo Passaniti ; and Mauro Maestri
• 刊名：Inorganic Chemistry
• 出版年：2004
• 出版时间：June 28, 2004
• 年：2004
• 卷：43
• 期：13
• 页码：3965 - 3975
• 全文大小：204K
• 年卷期：v.43,no.13(June 28, 2004)
• ISSN：1520-510X

文摘

The synthesis and photophysical properties of novel luminescent ruthenium(II) bipyridyl complexes containing one,two, or six lower rim acid-amide-modified calix[4]arene moieties covalently linked to the bipyridine groups arereported which are designed to coordinate and sense luminescent lanthanide ions. All the Ru-calixarene complexessynthesized in this work are able to coordinate Nd³⁺, Eu³⁺, and Tb³⁺ ions with formation of adducts of variablestoichiometry. The absorbance changes allow the evaluation of association constants whose magnitudes dependon the nature of the complexes as well as on the nature of the lanthanide cation. Lanthanide cation complexformation affects the ruthenium luminescence which is strongly quenched by Nd³⁺ ion, moderately quenched bythe Eu³⁺ ion, and poorly or moderately increased by the Tb³⁺ ion. In the case of Nd³⁺, the excitation spectra showthat (i) the quenching of the Ru luminescence occurs via energy transfer and (ii) the electronic energy of theexcited calixarene is not transferred to the Ru(bpy)₃ but to the neodymium cation. In the case of Tb³⁺, the adduct'sformation leads to an increase of the emission intensities and lifetimes. The reason for this behavior was ascribedto the electric field created around the Ru calix[4]arene complexes by the Tb³⁺ ions by comparison with the Gd³⁺ion, which behaves identically and can affect ruthenium luminescence only by its charge. However, especially forcompounds 1 and 3, it cannot be excluded that some contribution comes from the decrease of vibrational motions(and nonradiative processes) due to the rigidification of the structure upon Tb³⁺ complexation. In the case of Eu³⁺,compounds 1, 2, and 4 were quenched by the lanthanide addition but the quenching of the ruthenium luminescenceis not accompanied by europium-sensitized emission which suggests that an electron-transfer mechanism isresponsible for the quenching. On the contrary, compound 3 exhibits enhanced emission upon addition of Eu³⁺ (asnitrate salt); it is suggested that the lack of quenching in the [3·2Eu³⁺] adduct is due to kinetic reasons becausethe electron-transfer quenching process is thermodynamically allowed.