Oueslati Issam, Sa Ferreira Rute A, Carlos Luís D, Baleizão Carlos, Berberan-Santos Mario N, de Castro Baltazar, Vicens Jacques, Pischel Uwe
REQUIMTE/Departamento de Química, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal.
Inorg Chem. 2006 Mar 20;45(6):2652-60. doi: 10.1021/ic051159l.
Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed 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 (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) </= 0.01%) and much shorter lived (tau(lum) = 0.36 ms) than the Tb(III) emission. The latter, on the other hand, reached lifetimes of up to 2.60 ms and quantum yields as high as 12% for one of the ligands. Water/deuterium oxide exchange experiments showed the presence of only one solvent molecule in the coordination sphere of the lanthanides. However, Eu(III) luminescence was efficiently quenched by NH oscillators and the presence of a ligand-to-metal charge transfer state. Near-infrared luminescence of Nd(III) was also generated by energy-transfer sensitization.
两个带有两个氨基聚酰胺桥封端的杯[4]氮杂冠醚用作镧系离子[Eu(III)、Tb(III)、Nd(III)、Er(III)、La(III)]络合的配体。观察到形成了1:2和1:1的络合物，通过紫外吸收和荧光光谱法测定的稳定常数发现通常在log β(11)约为5 - 6和log β(12)约为10的量级。通过1H NMR光谱探究了配体在与La(III)络合时的结构变化。观察到这两个配体具有相反的荧光行为，即金属离子络合时荧光增强（通过阻断胺基的光诱导电子转移）或淬灭（通过镧系元素 - 发色团相互作用）。通过在配体芳香部分的π,π带中激发使长寿命的镧系元素发光得以敏化。通过Tb(III)对配体磷光的淬灭证明了天线三重态的直接参与。一般来说，Eu(III)的发光较弱（Φ(lum)≤0.01%）且寿命比Tb(III)的发射短得多（τ(lum)=0.36 ms）。另一方面，对于其中一个配体，Tb(III)的发射寿命高达2.60 ms，量子产率高达12%。水/重水交换实验表明在镧系元素的配位球中仅存在一个溶剂分子。然而，Eu(III)的发光被NH振荡器和配体到金属的电荷转移态有效地淬灭。Nd(III)的近红外发光也通过能量转移敏化产生。
