Calix[4]azacrowns as Novel Molecular Scaffolds for the Generation of Visible and Near-Infrared Lanthanide Luminescence

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• 作者：Issam Oueslati ; Rute A. S&aacute ; Ferreira ; Luí ; s D. Carlos ; Carlos Baleizã ; o ; M&aacute ; rio N. Berberan-Santos ; Baltazar de Castro ; Jacques Vicens ; and Uwe Pischel
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：March 20, 2006
• 年：2006
• 卷：45
• 期：6
• 页码：2652 - 2660
• 全文大小：171K
• 年卷期：v.45,no.6(March 20, 2006)
• ISSN：1520-510X

文摘

Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation oflanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, andstability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally onthe order of log s/gifchars/beta2.gif" BORDER=0 ALIGN="middle">₁₁ s/entities/ap.gif"> 5-6 and log s/gifchars/beta2.gif" BORDER=0 ALIGN="middle">₁₂ s/entities/ap.gif"> 10. The structural changes of the ligands upon La(III) complexation wereprobed by ¹H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely,fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (vialanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence wassensitized by excitation in the s/gifchars/pi.gif" BORDER=0 >,s/gifchars/pi.gif" BORDER=0 >* band of the aromatic moieties of the ligands. The direct involvement of theantenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III)luminescence was weak (s/gifchars/Phi.gif" BORDER=0 >_lum s/entities/le.gif"> 0.01%) and much shorter lived (s/gifchars/tau.gif" BORDER=0 >_lum = 0.36 ms) than the Tb(III) emission. Thelatter, on the other hand, reached lifetimes of up to 2.60 ms and quantum yields as high as 12% for one of theligands. Water/deuterium oxide exchange experiments showed the presence of only one solvent molecule in thecoordination sphere of the lanthanides. However, Eu(III) luminescence was efficiently quenched by NH oscillatorsand the presence of a ligand-to-metal charge transfer state. Near-infrared luminescence of Nd(III) was also generatedby energy-transfer sensitization.