Highly Emitting Near-Infrared Lanthanide “Encapsulated Sandwich” Metallacrown Complexes with Excitation Shifted Toward Lower Energy

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• 作者：Evan R. Trivedi ; Svetlana V. Eliseeva ; Joseph Jankolovits ; Marilyn M. Olmstead ; Stéphane Petoud ; Vincent L. Pecoraro
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 29, 2014
• 年：2014
• 卷：136
• 期：4
• 页码：1526-1534
• 全文大小：394K
• ISSN：1520-5126

文摘

Near-infrared (NIR) luminescent lanthanide complexes hold great promise for practical applications, as their optical properties have several complementary advantages over organic fluorophores and semiconductor nanoparticles. The fundamental challenge for lanthanide luminescence is their sensitization through suitable chromophores. The use of the metallacrown (MC) motif is an innovative strategy to arrange several organic sensitizers at a well-controlled distance from a lanthanide cation. Herein we report a series of lanthanide 鈥渆ncapsulated sandwich鈥?MC complexes of the form Ln³⁺[12-MC_{Zn(II),quinHA}-4]₂[24-MC_{Zn(II),quinHA}-8] (Ln³⁺[Zn(II)MC_quinHA]) in which the MC framework is formed by the self-assembly of Zn²⁺ ions and tetradentate chromophoric ligands based on quinaldichydroxamic acid (quinHA). A first-generation of luminescent MCs was presented previously but was limited due to excitation wavelengths in the UV. We report here that through the design of the chromophore of the MC assembly, we have significantly shifted the absorption wavelength toward lower energy (450 nm). In addition to this near-visible inter- and/or intraligand charge transfer absorption, Ln³⁺[Zn(II)MC_quinHA] exhibits remarkably high quantum yields, long luminescence lifetimes (CD₃OD; Yb³⁺, Q_Ln^L = 2.88(2)%, 蟿_obs = 150.7(2) 渭s; Nd³⁺, Q_Ln^L = 1.35(1)%, 蟿_obs = 4.11(3) 渭s; Er³⁺, Q_Ln^L = 3.60(6)路10^鈥?%, 蟿_obs = 11.40(3) 渭s), and excellent photostability. Quantum yields of Nd³⁺ and Er³⁺ MCs in the solid state and in deuterated solvents, upon excitation at low energy, are the highest values among NIR-emitting lanthanide complexes containing C鈥揌 bonds. The versatility of the MC strategy allows modifications in the excitation wavelength and absorptivity through the appropriate design of the ligand sensitizer, providing a highly efficient platform with tunable properties.