Glover Peter B, Bassett Andrew P, Nockemann Peter, Kariuki Benson M, Van Deun Rik, Pikramenou Zoe
School of Chemistry, The University of Birmingham, Edgbaston B15 2TT, UK.
Chemistry. 2007;13(22):6308-20. doi: 10.1002/chem.200700087.
In this paper we demonstrate that the effect of aromatic C--F substitution in ligands does not always abide by conventional wisdom for ligand design to enhance sensitisation for visible lanthanide emission, in contrast with NIR emission for which the same effect coupled with shell formation leads to unprecedented long luminescence lifetimes. We have chosen an imidodiphosphinate ligand, N-{P,P-di(pentafluorophinoyl)}-P,P-dipentafluorophenylphosphinimidic acid (HF20tpip), to form ideal fluorinated shells about all visible- and NIR-emitting lanthanides. The shell, formed by three ligands, comprises twelve fully fluorinated aryl sensitiser groups, yet no-high energy X--H vibrations that quench lanthanide emission. The synthesis, full characterisation including X-ray and NMR analysis as well as the photophysical properties of the emissive complexes [Ln(F20tpip)3], in which Ln=Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, Y, Gd, are reported. The photophysical results contrast previous studies, in which fluorination of alkyl chains tends to lead to more emissive lanthanide complexes for both visible and NIR emission. Analysis of the fluorescence properties of the HF20tpip and [Gd(F20tpip)3] reveals that there is a low-lying state at around 715 nm that is responsible for partially quenching of the signal of the visible emitting lanthanides and we attribute it to a pi-sigma* state. However, all visible emitting lanthanides have long lifetimes and unexpectedly the [Dy(F20tpip)3] complex shows a lifetime of 0.3 ms, indicating that the elimination of high-energy vibrations from the ligand framework is particularly favourable for Dy. The NIR emitting lanthanides show strong emission signals in powder and solution with unprecedented lifetimes. The luminescence lifetimes of [Nd(F20tpip)3], [Er(F20tpip)3] and [Yb(F20tpip)3] in deuteurated acetonitrile are 44, 741 and 1111 micros. The highest value observed for the [Yb(F20tpip)3] complex is more than half the value of the Yb ion radiative lifetime.
在本文中，我们证明，与近红外发射相反，配体中芳族C-F取代的效果并不总是遵循传统的配体设计理念来增强可见镧系元素发射的敏化作用，对于近红外发射，相同的效果与壳层形成相结合会导致前所未有的长发光寿命。我们选择了一种亚氨基二膦酸酯配体，N-{P,P-二（五氟膦酰基）}-P,P-二五氟苯基膦亚胺酸（HF20tpip），以在所有可见光和近红外发射的镧系元素周围形成理想的氟化壳层。由三个配体形成的壳层包含十二个完全氟化的芳基敏化基团，但没有会淬灭镧系元素发射的高能X-H振动。本文报道了发光配合物[Ln(F20tpip)3]（其中Ln = Nd、Sm、Eu、Gd、Tb、Dy、Er、Yb、Y、Gd）的合成、包括X射线和核磁共振分析在内的全面表征以及光物理性质。光物理结果与先前的研究形成对比，在先前的研究中，烷基链的氟化往往会导致可见光和近红外发射的镧系元素配合物具有更强的发射。对HF20tpip和[Gd(F20tpip)3]荧光性质的分析表明，在715 nm左右存在一个低能态，该低能态导致可见光发射镧系元素的信号部分淬灭，我们将其归因于π-σ*态。然而，所有可见光发射的镧系元素都具有长寿命，出乎意料的是，[Dy(F20tpip)3]配合物的寿命为0.3 ms，这表明从配体框架中消除高能振动对Dy特别有利。近红外发射的镧系元素在粉末和溶液中显示出强发射信号，且具有前所未有的寿命。[Nd(F20tpip)3]、[Er(F20tpip)3]和[Yb(F20tpip)3]在氘代乙腈中的发光寿命分别为44、741和1111微秒。[Yb(F20tpip)3]配合物观察到的最高值超过了Yb离子辐射寿命值的一半。
