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Issue 6, 2015
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Smaller than a nanoparticle with the design of discrete polynuclear molecular complexes displaying near-infrared to visible upconversion

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Abstract

This work shows that the operation of near-infrared to visible light-upconversion in a discrete molecule is not limited to non-linear optical processes, but may result from superexcitation processes using linear optics. The design of nine-coordinate metallic sites made up of neutral N-heterocyclic donor atoms in kinetically inert dinuclear [GaEr(L1)3]6+ and trinuclear [GaErGa(L2)3]9+ helicates leads to [ErN9] chromophores displaying unprecedented dual visible nanosecond Er(4S3/24I15/2) and near-infrared microsecond Er(4I13/24I15/2) emissive components. Attempts to induce one ion excited-state absorption (ESA) upconversion upon near-infrared excitation of these complexes failed because of the too-faint Er-centred absorption cross sections. The replacement of the trivalent gallium cation with a photophysically-tailored pseudo-octahedral [CrN6] chromophore working as a sensitizer for trivalent erbium in [CrEr(L1)3]6+ improves the near-infrared excitation efficiency, leading to the observation of a weak energy transfer upconversion (ETU). The connection of a second sensitizer in [CrErCr(L2)3]9+ generates a novel mechanism for upconversion, in which the superexcitation process is based on the CrIII-sensitizers. Two successive Cr→Er energy transfer processes (concerted-ETU) compete with a standard Er-centred ETU, and a gain in upconverted luminescence by a factor larger than statistical values is predicted and observed.

Graphical abstract: Smaller than a nanoparticle with the design of discrete polynuclear molecular complexes displaying near-infrared to visible upconversion

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Publication details

The article was received on 01 Aug 2014, accepted on 30 Sep 2014 and first published on 30 Oct 2014


Article type: Paper
DOI: 10.1039/C4DT02336F
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Citation: Dalton Trans., 2015,44, 2529-2540
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    Smaller than a nanoparticle with the design of discrete polynuclear molecular complexes displaying near-infrared to visible upconversion

    D. Zare, Y. Suffren, L. Guénée, S. V. Eliseeva, H. Nozary, L. Aboshyan-Sorgho, S. Petoud, A. Hauser and C. Piguet, Dalton Trans., 2015, 44, 2529
    DOI: 10.1039/C4DT02336F

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