Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Abstract

Two macrobicyclic ligands derived from an 18-membered tetralactam ring and 2,2'-bipyridine or 2,6-bis(pyrazol-1-yl)pyridine moieties, 1 and 2, respectively, form stable complexes with Gd III , Eu III , and Tb III ions in aqueous solution. The ligand-based luminescence is retained in the Gd III cryptates, whereas this radiative deactivation is quenched in the Eu III and Tb III cryptates by ligand-to-metal energy transfer, resulting in the usual metal-centered emission spectra. Singlet-and triplet-state energies, emission-decay lifetimes, and luminescence yields were measured. [Tb & 1] 3 cryptate shows a long luminescence lifetime (t 1.12 ms) and a very high metal luminescence quantum yield (F 0.25) in comparison with those reported in the literature for Tb 3 complexes sensitized by a bipyridine chromophore. By comparison to [Ln & 1] 3 , [Ln & 2] 3 presents markedly lower luminescence properties, due to worse interaction between the 2,6-bis(pyrazol-1-yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu & 2] 3 do not match. The effects of H 2 O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground-state are also reported.Introduction. ± The increasing interest in Eu 3 , Tb 3 luminescent probes is fully justified by their high sensitivity, especially in biological systems. These ions exhibit relatively efficient long-lived luminescence (ms range) when raised to their excited states, which permits easy temporal resolution from the short-lived (sub-ms range) fluorescence background of biological materials [1]. Eu 3 and Tb 3 ions are used as structural and analytical luminescent probes and stains for biomolecular systems [2], and the luminescence of Eu 3 and Tb 3 organocomplexes is exploited in bioanalytical assays such as immunoassays, nucleic acid hybridizations, enzyme assays, or receptor assays (for recent reviews, see [3]). Lanthanide complexes have also been shown to be excellent donors in luminescence resonance energy transfer (LRET) for homogeneous immunoassays [4] and to measure both static and time-varying distances [5]. In addition, the use of macrocyclic Eu and Tb complexes as luminescent sensors for pO 2 , pH and other bioactive ions has been recently reported [6].In attempts to optimize the luminescent properties of Eu 3 and Tb 3 complexes, a great deal of effort has been devoted to the synthesis of a range of different ligands. Many photoactive ligands, including those based on b-diketones (see, e.g., [7]),

Terras raras: aplicações industriais e biológicas

“…Em sistemas biológicos os elementos terras raras têm sido extensivamente estudados, devido às suas propriedades excepcionais, principalmente, as espectroscópicas e magnéticas [42][43][44][45][46][47][48][49][50][51][52][53][54][55] . Esses elementos são geralmente usados como sondas espectroscópicas no estudo de biomoléculas e suas funções, especialmente proteínas que se ligam ao cálcio.…”

“…Também, a carga positiva extra dos íons lantanídeos, comparadas com a do íon Ca(II), na maioria dos casos, contribui para maior estabilidade dos complexos formados com proteínas. Em vista disso, os íons de terras raras inibem a maioria das enzimas cálcio dependentes [42][43][44][45][46][47][48][49][50][51][52][53][54] .…”

Influence of electric field on photoluminescence of lanthanide-doped nematic liquid crystal

“…Complexes with an asymmetric coordination sphere have the intensity ratio I( 5 D 0 -7 F 2 )/ I( 5 D 0 -7 F 1 ) ranging between 8 and 12 while in those with a centrosymmetric environment the ratio is usually lower than 1 [14][15][16]. This value depends on the efficiency of intramolecular energy transfer from the triplet state of the ligand to the emitting state of Eu 3+ , the former must therefore be sufficiently higher in energy than the luminescent state 5 D 0 of the metal ion.…”

Síntese, caracterização e propriedades espectroscópicas de criptatos de lantanídeo do tipo [Ln<FONT FACE=Symbol>Ì</FONT>(bipy)2py(CO2Et) 2(3+)]

“…Criptatos com íons lantanídeos apresentam boa solubilidade em água e elevadas estabilidades cinética e termodinâmica 19 . Os principais estudos fotofísicos mostram que estes criptatos populam eficientemente o nível emissor ( 5 D 0 para o európio e 5 D 4 para o térbio) do íon metálico através de processos não-radiativos, fornecendo assim, altos rendimentos quânticos de emissão, em solução aquosa 20 . Devido aos criptatos de lantanídeos apresentarem grande aplicabilidade em sistemas biológicos [21][22][23] , há uma necessidade crescente de pesquisas de novos criptatos projetados para estes fins.…”