Effect of a halogenide substituent on the stability and photophysical properties of lanthanide triple-stranded helicates with ditopic ligands derived from bis(benzimidazolyl)pyridine †
作者:Carlos Platas Iglesias、Mourad Elhabiri、Marcel Hollenstein、Jean-Claude G. Bünzli、Claude Piguet
DOI:10.1039/b001818j
日期:——
Bis1-ethyl-2-[6-(N,N-diethylcarbamoyl)-4-halogenopyridin-2-yl]benzimidazol-5-yl}methane (halogeno = chloro, LE; bromo, LF) have been synthesized as ditopic receptors for the development of lanthanide-containing helicates able to couple with biological material and to test the influence of the halogeno substituent on the wrapping process, the structure of the resulting dimetallic edifices, and the photophysical properties of the encapsulated ions. The stability of the [Eu2(L)3]6+ helicates, as determined by NMR competitive titrations, decreases by respectively one (LF) and three (LE) orders of magnitude compared to the value found for the unsubstituted ligand (LB) although it remains large, log β23 = 23.8 (LF) and 21.8 (LE) in acetonitrile. The [Ln2(LE)3]6+ helicates are shown to be isostructural in acetonitrile over the lanthanide series (Pr to Yb) and the crystal structure of [Tb2(LB)3]6+ appears to be a good model for their solution structure, as demonstrated by paramagnetic NMR measurements (lanthanide induced shift method) and relaxation time determination. Ligand LE appears to be a fair sensitiser of EuIII, the quantum yield of [Eu2(LE)3]6+ being 25% larger than that found for [Eu2(LB)3]6+, but the ligand 3ππ* state and Tb(5D4) excited level are in resonance, which limits the sensitisation of TbIII. High resolution luminescence spectra of [Eu2(LE)3]6+, both in solution and in the solid state, are presented and discussed in terms of site symmetry and vibronic coupling mechanisms.
合成了双1-乙基-2-[6-(N,N-二乙基氨基甲酰基)-4-卤代吡啶-2-基]苯并咪唑-5-基}甲烷(卤素=氯,LE;溴,LF)作为双位受体,用于开发能够与生物材料耦合的含镧元素的螺旋体,并测试卤代取代基对包裹过程、所形成的双金属构筑物结构以及封装离子的光物理特性的影响。通过NMR竞争滴定法确定的[Eu2(L)3]6+螺旋体的稳定性与未取代配体(LB)相比,分别下降了一个(LF)和三个(LE)数量级,尽管其仍然较大,在乙腈中log β23为23.8(LF)和21.8(LE)。在乙腈中,[Ln2(LE)3]6+螺旋体在镧系元素(Pr到Yb)间显示出同构性,[Tb2(LB)3]6+的晶体结构似乎是它们溶液结构的良好模型,通过顺磁性NMR测量(镧诱导位移法)和弛豫时间测定得以证明。配体LE对EuIII的灵敏度相当,其量子产率比[Eu2(LB)3]6+大25%。但 ligand 3ππ*状态与Tb(5D4)激发态之间存在共振,这限制了TbIII的敏化。在溶液和固态下,[Eu2(LE)3]6+的高分辨率发光光谱被呈现并讨论,涉及位点对称性和声子耦合机制的问题。