Tridentate Benzimidazole-Pyridine-Tetrazolates as Sensitizers of Europium Luminescence
摘要:
We report on new anionic tridentate benzimidazole-pyridine-tetrazolate ligands that form neutral 3:1 complexes with trivalent lanthanides. The ligands are UV-absorbing chromophores that sensitize the red luminescence of europium with energy-transfer efficiency of 74-100%. The lifetime and quantum yield of the sensitized europium luminescence increase from 0.5 ms and 12-13% for the as-prepared solids to 2.8 ms and 41% for dichloromethane solution. From analysis of the data, the as-prepared solids can be described as aqua-complexes [Ln(k(3)-ligand)(2)(K-1-ligand)(H2O)x] where the coordinated water molecules are responsible for the strong quenching of the europium luminescence. In solution, the coordinated water molecules are replaced by the nitrogen atoms of the K-1-ligand to give anhydrous complexes [Ln(K-3-ligand)(3)] that exhibit efficient europium luminescence. X-ray structures of the anhydrous complexes confirm that the lanthanide ion (La-III, Eu-III) is nine-coordinate in a distorted tricapped trigonal prismatic environment and that coordination of the lanthanide ion by tetrazolate is weaker than by carboxylate.
制备了一系列三齿苯并咪唑取代的吡啶-2-羧酸,在苯并咪唑环的6位带有卤素,甲基或烷氧基,其中还含有可溶的N烷基链。配体形成中性的九坐标镧,euro和ter络合物,这是通过对八个结构的X射线晶体学分析确定的。镧系元素离子周围的配位多面体接近于三重三角棱镜,其配体以上-下-下的方式排列。配位体充当络合物中的集光生色团,其最大吸收范围为321–341 nm(ε =(4.9–6.0)×10 4 M -1 cm -1)以及21,300至18,800 cm -1之间的三重态能量; 最大的红移发生在溴和电子给体的烷氧基取代基上。配体有效地敏化铕的发光与整体的量子产率()和观察到的寿命(τ OBS)分别达到71%和3.00毫秒,在固体状态下和52%和2.81毫秒,在CH 2氯2在室温下。铕(的辐射寿命5 d 0)电平量τ弧度= 3.6-4.6毫秒和敏化效率η SENS = (τ弧度/τ OBS)对于大