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A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution

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posted on 16.04.2020, 21:45 by Matthias Dorn, Jens Kalmbach, Pit Boden, Ayla Päpcke, Sandra Gómez, Christoph Förster, Felix Kuczelinis, Luca M. Carrella, Laura A. Büldt, Nicolas H. Bings, Eva Rentschler, Stefan Lochbrunner, Leticia González, Markus Gerhards, Michael Seitz, Katja Heinze
Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3dn metal complexes (n ≠ 10) show sizable luminescence at room temperature. Luminescence in the near-infrared spectral region is even more difficult to achieve as further nonradiative pathways come into play. No Earth-abundant first-row transition metal complexes have displayed emission >1000 nm at room temperature in solution up to now. Here, we report the vanadium­(III) complex mer-[V­(ddpd)2]­[PF6]3 yielding phosphorescence around 1100 nm in valeronitrile glass at 77 K as well as at room temperature in acetonitrile with 1.8 × 10–4% quantum yield (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine). In addition, mer-[V­(ddpd)2]­[PF6]3 shows very strong blue fluorescence with 2% quantum yield in acetonitrile at room temperature. Our comprehensive study demonstrates that vanadium­(III) complexes with d2 electron configuration constitute a new class of blue and NIR-II luminophores, which complement the classical established complexes of expensive precious metals and rare-earth elements.