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A new class of benzimidazole-substituted 8-hydroxyquinoline ligands has been prepared that contain a monoanionic tridentate N,N,O-coordinating unit. These ligands form charge-neutral lanthanide complexes of the type [Ln(LR) 3] · nH2O or [Ln2(L2)3] · nH2O (n ) 1-3) with early lanthanides from LaIII to GdIII inclusive. Crystallographic characterization was carried out for 11 complexes with 6 different ligands. In all of these structures, the lanthanide ion was found to be nine-coordinated by three ligands arranged in an “up-up-down” fashion around the metal center. The coordination environment can be described as a tricapped trigonal prism, with N atoms of quinoline rings occupying capping positions. Upon deprotonation of the ligand and complex formation, a new absorption band appears in the visible range of the spectrum with a maximum in the range of 466-483 nm and molar absorption coefficient of (7.2 - 18) × 103 M-1 cm-1. Its origin is likely to be an intraligand phenolate-to-pyridyl charge transfer transition centered on the 8-hydroxyquinolate chromophore. Upon excitation in ligand absorption bands, new NdIII complexes display characteristic metal-centered luminescence in the near-infrared region from 850 to 1450 nm with quantum yields and lifetimes in solid state at room temperature as high as 0.34% and 1.2 μs, respectively.
David Lyndon Emsley, Dominik Józef Kubicki, Daniel Prochowicz, Amita Ummadisingu, Albert Hofstetter
Rosario Scopelliti, Kay Severin, Farzaneh Fadaei Tirani, Bastiaan Kooij, Zhaowen Dong
Kay Severin, Farzaneh Fadaei Tirani, Damien Wen Chen, Jean Charles Edouard de Montmollin, Atena-Bianca Solea