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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Anthracene as a sensitiser for near-infrared luminescence in complexes of Nd(III),Er(III)and Yb(III);an unexpected sensitisation mechanism based on electron transferf
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Anthracene as a sensitiser for near-infrared luminescence in complexes of Nd(III),Er(III)and Yb(III);an unexpected sensitisation mechanism based on electron transferf

机译：蒽作为Nd（III），Er（III）和Yb（III）配合物中近红外发光的敏化剂;基于电子转移的出乎意料的敏化机理

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The ligand L~1,which contains a chelating 2-(2-pyridyl)benzimidazole(PB)unit with a pendant anthacenyl group An connected via a methylene spacer,(L~1 = PB-An),was used to prepare the 8-coordinate lanthanide(III)complexes [Ln(hfac)3(L~1)](Ln = Nd,Gd,Er,Yb)which have been structurally characterised and all have a square antiprismatic N2O6 coordination geometry.Whereas free L~1 displays typical anthracene-based fluorescence,this fluorescence is completely quenched in its complexes.The An group in L~1 acts as an antenna unit;in the complexes [Ln(hfac)3(L~1)](Ln = Nd,Er,Yb)selective excitation of the anthracene results in sensitised near-infrared luminescence from the lanthanide centres with concomitant quenching of An fluorescence.Surprisingly,the anthracene fluorescence is also quenched even in the Gd(III)complex and in its Zn(II)adduct in which quenching via energy transfer to the metal centre is not possible.It is proposed that the quenching of anthracene fluorescence in coordinated L~1 arises due to intra-ligand photoinduced electron-transfer from the excited anthracene chromophore ~1An* to the coordinated PB unit generating a short-lived charge-separated state [An~(o+)-PB~(o-)] which collapses by back electron-transfer to give ~3An*.This electron-transfer step is only possible upon coordination of L~1 to the metal centre,which strongly increases the electron acceptor capability of the PB unit,such that ~1An* -> PB PET is endoergonic in free L~1 but exergonic in its complexes.Thus,rather than a conventional set of steps(~1An*-> ~3An*-> Ln),the sensitization mechanism now includes ~1An*-> PB photoinduced electron transfer to generate charge-separated [An~(o+)-PB~(o-)],then back electron-transfer to generate ~3An* which finally sensitises the Ln(in)centre via energy transfer.The presence of ~3An* in L' and its complexes is confirmed by nanosecond transient absorption studies,which have also shown that the ~3An* lifetime in the Nd(III)complex matches the rise time of Nd-centred near-infrared emission,confirming that the final step of the sequence is ~3An*-> Ln(III)energy-transfer.
机译：配体L〜1包含一个通过亚甲基间隔基连接的具有侧链蒽基侧基的螯合的2-（2-吡啶基）苯并咪唑（PB）单元（L〜1 = PB-An），用于制备8配位的镧系元素（III）配合物[Ln（hfac）3（L〜1）]（Ln = Nd，Gd，Er，Yb），具有结构特征，均具有方形反棱N2O6配位几何。自由L〜1显示典型的蒽基荧光，该荧光在其配合物中被完全淬灭。L〜1中的An基团充当天线单元;在配合物中[Ln（hfac）3（L〜1）]（Ln = Nd，Er ，Yb）蒽的选择性激发导致镧系中心的敏化近红外发光，同时伴随有荧光的猝灭。提出了在配位的L〜1中蒽荧光的猝灭。发生是由于配位体内光诱导的电子从激发的蒽发色团〜1An *转移​​到配位PB单元，从而产生了短暂的电荷分离状态[An〜（o +）-PB〜（o-）]，该状态被倒塌电子转移产生〜3An *。仅当L〜1与金属中心配位时，此电子转移步骤才可能进行，这会大大增强PB单元的电子受体能力，因此〜1An *-> PB PET为游离的L〜1中的内能，但复合物中的能量是外能的。因此，而不是常规的步骤（〜1An *->〜3An *-> Ln），敏化机理现在包括〜1An *-> PB光致电子转移到产生电荷分离的[An〜（o +）-PB〜（o-）]，然后进行反向电子转移，产生〜3An *，最后通过能量转移使Ln（in）中心敏感。L中存在〜3An *纳秒瞬态吸收研究证实了其及其配合物，该研究还表明Nd（III）配合物中的〜3An *寿命与N的上升时间匹配以d为中心的近红外发射，确认序列的最后一步是〜3An *-> Ln（III）能量转移。

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