Multi-NIR-Emissive Materials based on Heterolanthanide Molecular Assemblies
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Multi-NIR-Emissive Materials based on Heterolanthanide Molecular Assemblies Flavia Artizzu,1 Francesco Quochi,2 Luciano Marchiò,3 Michele Saba,2 Angela Serpe,1 Andrea Mura,2 Maria Laura Mercuri,1 Giovanni Bongiovanni2 and Paola Deplano1,2 1 Dipartimento di Scienze Chimiche e Geologiche and INSTM, University of Cagliari, SS 554 Bivio per Sestu, I-09042, Monserrato-Cagliari, Italy 2 Dipartimento di Fisica, University of Cagliari, SS 554 Bivio per Sestu, I-09042, MonserratoCagliari, Italy 3 Dipartimento di Chimica, University of Parma, Parco Area delle Scienze 17A, I-43100 Parma, Italy ABSTRACT ErxYb(3-x)Q9 (1, x = 1, 2), NdYb2Q9 (2), NdEr2Q9 (3) and NdErYbQ9 (4), have been obtained through a simple molecular strategy, by controlling reactant stoichiometry. In 2-4, the templating effect of the molecular framework allows to control the metal distribution across the coordination sites where the central position is occupied by the larger Nd ion and the terminal ones by the almost vicariants Yb3+ and Er3+, drastically reducing molecular speciation. Remarkably, 4 represents the first example of a discrete molecular entity containing three different Ln ions simultaneously emitting in three different spectral regions in the NIR, upon single visible wavelength excitation. Highly transparent and homogeneous doped silica glasses have been prepared, which show the same optical properties of the incorporated complex in solution. INTRODUCTION Heterometallic assemblies containing two or more different lanthanide (Ln) ions as carriers of distinctive functionalities are particularly attractive as they can open unprecedented possibilities toward multifunctional materials where different physical properties can coexist or be in interplay thanks to intermetallic communication. In particular, heterometallic luminescent materials hold potential for the development of highly performing multi-colored emitters for optical applications (optical fibers and amplifiers, lasers, luminescent barcodes).[1-4] However, controlled codoping of inorganic glassy or polymeric matrices so far studied for these purposes is often an intrinsically difficult task and estimated efficiencies of these materials are crucially dependent on the Ln3+ doping concentration.[3,4] A strategy to achieve composition control relies on the encapsulation of selected Ln ions into the same molecule to afford optically active materials where metal centers sit at fixed positions and short distance (within few Å) in a predesigned architecture. The trinuclear Ln3Q9 (Q=8-quinolinolate) molecular framework has shown to be particularly suitable for preparing heterolanthanide multi-emissive assemblies, providing: i) high coordinating ability; ii) excellent “antenna” properties of the Q ligand allowing indirect excitation of the emitting Ln ions; iii) short intermetallic distances (< 3.5 Å) for efficient intermetallic communication; iv) high stability and capability to undergo processing procedures without alterations.[5-7] In addition, the incorporation of the Ln ions into an organic fr
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