Ga3+/Ln3+ Metallacrowns: A Promising Family of Highly Luminescent Lanthanide Complexes That Covers Visible and Near-Infrared Domains

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• 作者：Chun Y. Chow ; Svetlana V. Eliseeva ; Evan R. Trivedi ; Tu N. Nguyen ; Jeff W. Kampf ; Stéphane Petoud ; Vincent L. Pecoraro
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 20, 2016
• 年：2016
• 卷：138
• 期：15
• 页码：5100-5109
• 全文大小：516K
• 年卷期：0
• ISSN：1520-5126

文摘

Luminescent lanthanide(III)-based molecular scaffolds hold great promises for materials science and for biological applications. Their fascinating photophysical properties enable spectral discrimination of emission bands that range from the visible to the near-infrared (NIR) regions. In addition, their strong resistance to photobleaching makes them suitable for long duration or repeated biological experiments using a broad range of sources of excitation including intense and focalized systems such as lasers (e.g., confocal microscopy). A main challenge in the creation of luminescent lanthanide(III) complexes lies in the design of a ligand framework that combines two main features: (i) it must include a chromophoric moiety that possesses a large molar absorptivity and is able to sensitize several different lanthanide(III) ions emitting in the visible and/or in the near-infrared, and (ii) it must protect the Ln³⁺ cation by minimizing nonradiative deactivation pathways due to the presence of −OH, −NH and −CH vibrations. Herein, a new family of luminescent Ga³⁺/Ln³⁺ metallacrown (MC) complexes is reported. The MCs with the general composition [LnGa₄(shi)₄(C₆H₅CO₂)₄(C₅H₅N) (CH₃OH)] (Ln-1, Ln = Sm³⁺–Yb³⁺) were synthesized in a one pot reaction using salicylhydroxamic acid (H₃shi) with Ga³⁺ and Ln³⁺ nitrates as reagents. The molecular structure of [DyGa₄(shi)₄(C₆H₅CO₂)₄(C₅H₅N) (CH₃OH)] was obtained by X-ray analysis of single crystals and shows that the complex is formed as a [12-MC_Ga(III)shi-4] core with four benzoate molecules bridging the central Dy³⁺ ion to the Ga³⁺ ring metals. The powder X-ray diffraction analysis demonstrates that all other isolated complexes are isostructural. The extended analysis of the luminescence properties of these complexes, excited by the electronic states of the chromophoric ligands, showed the presence of characteristic, sharp f–f transitions that can be generated not only in the NIR (Sm, Dy, Ho, Er, Yb) but also in the visible (Sm, Eu, Tb, Dy, Tm). All Ln-1 complexes possess very high quantum yield values with respect to other literature compounds, indicating a good sensitization efficiency of the [12-MC_Ga(III)shi-4] scaffold. Especially, as of today, the Yb-1 complex exhibits the highest NIR quantum yield reported for a lanthanide(III) complex containing C–H bonds with a value of 5.88(2)% in the solid state. This work is a significant step forward toward versatile, easily prepared luminescent lanthanide(III) complexes suitable for a variety of applications including highly in demand biological imaging, especially in the NIR domain.