Sensitisation of Eu(III)- and Tb(III)-based luminescence by Ir(III) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms.
Sensitisation of Eu(III)- and Tb(III)-based luminescence by Ir(III) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms.
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DOI：
10.1039/c4dt00292j
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发表时间：
2014-04
影响因子：
4
通讯作者：
Daniel Sykes;Ahmet J. Cankut;N. M. Ali;A. Stephenson;Steven J. P. Spall;S. Parker;J. Weinstein;M. Ward
中科院分区：
文献类型：
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作者：
Daniel Sykes;Ahmet J. Cankut;N. M. Ali;A. Stephenson;Steven J. P. Spall;S. Parker;J. Weinstein;M. Ward
合成了一系列具有镧系离子侧键的蓝光Ir（III）配合物，并用于制备Ir（III）/Ln（III）二元配合物（Ln = Eu，Tb，Gd）。利用光物理研究确定了Ir→Ln（Ln = Tb，Eu）能量转移机制。在Ir/Gd二联体中，直接的Ir→Gd能量转移是不可能的，但仍然发生了基于Ir的发光的显著猝灭;这可以归因于从光激发的Ir单元（*Ir，（3）MLCT/（3）LC激发态）到侧链吡唑基吡啶位点的光诱导电子转移，当与正电性Gd（III）中心配位时，侧链吡唑基吡啶位点成为良好的电子受体。这种电子转移猝灭了Ir基发光，导致形成电荷分离的{Ir（4+）} stec-（吡唑基-吡啶）stec（-）态，其寿命短，可能是由于快速的反向电子转移（<20 ns）。在Ir/Tb和Ir/Eu二元体中，这种电子转移途径再次起作用，并使用从反向电子转移过程释放的能量导致Eu基和Tb基发射的敏化。此外，直接德克斯特型Ir→Ln（Ln = Tb，Eu）能量转移发生在类似的时间尺度上，这意味着有两个平行的机制，激发能可以从 *Ir转移到Eu/Tb中心。敏化Eu基发射的时间分辨发光测量显示了快速和缓慢的上升时间分量，分别与基于PET和基于德克斯特的能量转移机制相关。在Ir/Tb二元组中，Ir→Tb能量转移仅在热力学上是有利的，导致快速的Tb→Ir热激活反向能量转移和非辐射失活，其程度取决于 *Ir和Tb基（5）D4态之间的精确能隙。因此，敏化的Tb（III）基发射是弱的，并且由于反向能量转移而异常短暂，但是尽管如此，代表了由能量供体敏化的Tb（III）的罕见实例，所述能量供体可以使用可见光激发，而不是通常需要的UV激发。
A series of blue-luminescent Ir(III) complexes with a pendant binding site for lanthanide(III) ions has been synthesized and used to prepare Ir(III)/Ln(III) dyads (Ln = Eu, Tb, Gd). Photophysical studies were used to establish mechanisms of Ir→Ln (Ln = Tb, Eu) energy-transfer. In the Ir/Gd dyads, where direct Ir→Gd energy-transfer is not possible, significant quenching of Ir-based luminescence nonetheless occurred; this can be ascribed to photoinduced electron-transfer from the photo-excited Ir unit (*Ir, (3)MLCT/(3)LC excited state) to the pendant pyrazolyl-pyridine site which becomes a good electron-acceptor when coordinated to an electropositive Gd(III) centre. This electron transfer quenches the Ir-based luminescence, leading to formation of a charge-separated {Ir(4+)}˙-(pyrazolyl-pyridine)˙(-) state, which is short-lived possibly due to fast back electron-transfer (<20 ns). In the Ir/Tb and Ir/Eu dyads this electron-transfer pathway is again operative and leads to sensitisation of Eu-based and Tb-based emission using the energy liberated from the back electron-transfer process. In addition direct Dexter-type Ir→Ln (Ln = Tb, Eu) energy-transfer occurs on a similar timescale, meaning that there are two parallel mechanisms by which excitation energy can be transferred from *Ir to the Eu/Tb centre. Time-resolved luminescence measurements on the sensitised Eu-based emission showed both fast and slow rise-time components, associated with the PET-based and Dexter-based energy-transfer mechanisms respectively. In the Ir/Tb dyads, the Ir→Tb energy-transfer is only just thermodynamically favourable, leading to rapid Tb→Ir thermally-activated back energy-transfer and non-radiative deactivation to an extent that depends on the precise energy gap between the *Ir and Tb-based (5)D4 states. Thus, the sensitised Tb(iii)-based emission is weak and unusually short-lived due to back energy transfer, but nonetheless represents rare examples of Tb(III) sensitisation by a energy donor that could be excited using visible light as opposed to the usually required UV excitation.