Ning Yingying, Ke Xian-Sheng, Hu Ji-Yun, Liu Yi-Wei, Ma Fang, Sun Hao-Ling, Zhang Jun-Long
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Department of Chemistry, Beijing Normal University , Beijing 100875, P. R. China.
Inorg Chem. 2017 Feb 20;56(4):1897-1905. doi: 10.1021/acs.inorgchem.6b02481. Epub 2017 Feb 1.
"Configurational isomerism" is an important approach found in naturally occurring chlorophylls to modulate light harvesting function without significant structural changes; however, this feature has been seldom applied in design of antenna ligands for lanthanide (Ln) sensitization. In this work, we introduced a bioinspired approach by orientation of β-dilactone moieties on porphyrinates, namely cis-/trans-porphodilactones, to modulate the energy transfer process from the lowest triplet excited state of the ligand (T) to the emitting level of ytterbium(III) (F, Yb*). Interestingly, near-infrared (NIR) emission of Yb(III) could be switched "on" by the cis-porphodilactone ligand, while the trans-isomer renders Yb(III) emission "off" and the ratio of quantum yields is ∼8. Analysis of the structure-photophysical properties relationship suggests that the significant emission difference is correlated to the energy gaps between T and Yb* (1152 cm in the cis- vs -25 cm in the trans-isomer). More interestingly, due to back energy transfer (BEnT), the Yb(III) complex of cis-porphodilactone exhibits NIR emission with high thermosensitivity (4.0%°C in solution and 4.9%°C in solid state), comparable to previously reported terbium (Tb) and europium (Eu) visible emitters, in contrast to the trivial emission changes of the trans-isomer and porphyrin and porpholactone analogues. This work opens up new access to design NIR emissive Ln complexes by bioinspired modification of antenna ligands.
“构型异构”是天然叶绿素中发现的一种重要方法，可在不发生显著结构变化的情况下调节光捕获功能；然而，这一特性在用于镧系元素（Ln）敏化的天线配体设计中很少被应用。在这项工作中，我们引入了一种受生物启发的方法，通过在卟啉酸盐上定向β - 二内酯部分，即顺式/反式卟啉二内酯，来调节从配体的最低三重激发态（T）到镱（III）的发射能级（F，Yb*）的能量转移过程。有趣的是，顺式卟啉二内酯配体可使Yb（III）的近红外（NIR）发射“开启”，而反式异构体则使Yb（III）发射“关闭”，量子产率之比约为8。结构 - 光物理性质关系分析表明，显著的发射差异与T和Yb*之间的能隙相关（顺式异构体中为1152 cm，反式异构体中为 - 25 cm）。更有趣的是，由于反向能量转移（BEnT），顺式卟啉二内酯的Yb（III）配合物表现出具有高热灵敏度的近红外发射（溶液中为4.0%/°C，固态中为4.9%/°C），与先前报道的铽（Tb）和铕（Eu）可见发射体相当，这与反式异构体以及卟啉和卟啉内酯类似物的微小发射变化形成对比。这项工作为通过受生物启发的天线配体修饰来设计近红外发射的Ln配合物开辟了新途径。
