Making the golden connection: reversible mechanochemical and vapochemical switching of luminescence from bimetallic gold-silver clusters associated through aurophilic interactions |
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Authors: | Lasanta Tania Olmos M Elena Laguna Antonio López-de-Luzuriaga José M Naumov Panče |
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Institution: | Departamento de Química, Universidad de la Rioja, Grupo de Síntesis Química de La Rioja, UA-CSIC Complejo Científico Tecnológico, E-26001 Logro?o, Spain. |
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Abstract: | Aiming at the development of new architectures within the context of the quest for strongly luminescent materials with tunable emission, we utilized the propensity of the robust bimetallic clusters Au?Ag?(R(I)/R(II))?] (R(I) = 4-C?F?I, R(II) = 2-C?F?I) for self-assembly through aurophilic interactions. With a de novo approach that combines the coordination and halogen-bonding potential of aromatic heteroperhalogenated ligands, we have generated a family of remarkably luminescent bimetallic materials that provide grounds to address the relevance, relative effects, and synergistic action of the two interactions in the underlying photophysics. By polymerizing the green-emitting (λ(max)(em) = 540 nm) monomer Au?Ag?R(II)?(tfa)?]2? (tfa = trifluoroacetate) to a red-emitting (λ(max)(em) = 660 nm) polymer Au?Ag?R(II)?(MeCN)?](n), we demonstrate herein that the degree of cluster association in these materials can be effectively and reversibly switched simply by applying mechanochemical and/or vapochemical stimuli in the solid state as well as by solvatochemistry in solution, the reactions being coincident with a dramatic switching of the intense, readily perceptible photoluminescence. We demonstrate that the key event in the related equilibrium is the evolution of a metastable yellow emitter (λ(max)(em) = 580 nm) for which the structure determination in the case of the ligand R(II) revealed a dimeric nonsolvated topology Au?Ag?R(II)?]?. Taken together, these results reveal a two-stage scenario for the aurophilic-driven self-assembly of the bimetallic clusters Au?Ag?(R(I)/R(II))?]: (1) initial association of the green-emitting monomers to form metastable yellow-emitting dimers and desolvation followed by (2) resolvation of the dimers and their self-assembly to form a red-emitting linear architecture with delocalized frontier orbitals and a reduced energy gap. The green emission from Au?Ag?R(II)?(tfa)?]2? (λ(max)(em) = 540 nm) exceeds the highest energy observed for Au?Ag?]-based structures to date, thereby expanding the spectral slice for emission from related structures beyond 140 nm, from the green region to the deep-red region. |
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