Department of Chemistry, Jamia Millia Islamia, New Delhi 110 025, India.
J Fluoresc. 2011 Mar;21(2):673-86. doi: 10.1007/s10895-010-0755-5. Epub 2010 Nov 3.
The electronic absorption, excitation and sensitized visible light emission studies of three praseodymium (III) complexes: [Pr(fod)(3)(bpy)], [Pr(fod)(3)(phen)] and Pr(fod)(3)(bpm) (fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione; bpy=2,2'-bipyridyl, phen=1,10-phenanthroline, bpm=2,2'-bipyrimidine) in a series of non-aqueous solvents is presented. The f-f absorption transitions of Pr(III) are environment sensitive which is reflected by the change in the intensity (oscillator strength) and band shape (stark splitting) upon change in the solvent and/or the ligands. The sensitization of intense Pr(III) emission, in the visible region, of the complexes in solution upon excitation into the ligand centered π→π* absorption band is remarkable. The planar phen has pronounced impact and increases considerably the emission intensity of Pr(III) luminescence than the flexible bpy while bpm has been found least effective in promoting the emission intensity. The intensity of the f-f absorption and sensitized emission are correlated with the nature of the solvents. The donor solvent pyridine enhances the emission intensity of the [Pr(fod)(3)(phen)] drastically and of [Pr(fod)(3)(bpy)] marginally while the luminescent intensity of Pr(fod)(3)(bpm) is decreased. The combined photophysical studies demonstrate that entry of the solvent molecule(s) to inner coordination sphere (complex-solvent interaction) is governed by the structure and basicity of the ancillary heterocyclic ligand attached to the Pr(III) complex. The strong donor DMSO transforms the three complexes into a similar species, [Ln(fod)(3)(DMSO)(2)], which results in similar electronic absorption and emission properties of the complexes in this solvent. The results demonstrate that highly luminescent praseodymium chelates can be designed with ligands containing suitable energy levels and their emission properties can be further modulated through suitable ancillary ligands and donor solvents, thus opening perspectives for applications in electroluminescent devices and luminescent probes.
本文报道了三种镨（III）配合物[Pr(fod)（3）（bpy）]、[Pr(fod)（3）（phen）]和[Pr(fod)（3）（bpm）]（n）（fod=六氟-2,2-二甲基-3,5-辛二酮的阴离子；bpy=2,2'-联吡啶，phen=1,10-菲啰啉，bpm=2,2'-联嘧啶）在一系列非水溶剂中的电子吸收、激发和敏化可见光发射研究。镨（III）的 f-f 吸收跃迁对环境敏感，这反映在溶剂和/或配体变化时强度（振子强度）和带形（斯塔克分裂）的变化上。当配合物在配体中心π→π*吸收带激发时，在溶液中强烈敏化的 Pr(III)发射，在可见光区，是显著的。平面的 phen 对 Pr(III)发光有显著的影响，比灵活的 bpy 大大增加了 Pr(III)发光的强度，而 bpm 则被发现对增强发射强度最有效。f-f 吸收和敏化发射的强度与溶剂的性质有关。供电子溶剂吡啶剧烈增强[Pr(fod)(3)(phen)]的发射强度，对[Pr(fod)(3)(bpy)]略有增强，而Pr(fod)(3)(bpm)的发光强度则降低。综合光物理研究表明，溶剂分子进入内配位球（配合物-溶剂相互作用）是由与镨（III）配合物相连的辅助杂环配体的结构和碱性决定的。强供电子体 DMSO 将三种配合物转化为类似的物种[Ln(fod)(3)(DMSO)(2)]，导致在这种溶剂中配合物具有相似的电子吸收和发射性质。结果表明，可以设计具有合适能级的高发光镨螯合物，通过合适的辅助配体和供电子体进一步调节其发射性质，从而为电致发光器件和发光探针的应用开辟了前景。
