Discrete Heteropolynuclear Yb/Er Assemblies: Switching on Molecular Upconversion Under Mild Conditions

The salts {[Ln2Ln*(Hhmq)3(OAc)3(hfac)2]+ [Ln*(hfac)3(OAc)(MeOH)]−} (Hhmq=2‐methanolquinolin‐8‐oxide, hfac=hexafluoroacetylacetonate; Ln, Ln*=Er, Gd, Yb) feature a discrete heteronuclear cation consisting of two types of lanthanide atoms. The quinolinoxy O‐atom serves as a μ2‐bridge to two Ln atoms a...

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Published in:Angewandte Chemie 2021-10, Vol.133 (41), p.22542-22549
Main Authors: Wang, Jie, Jiang, Yue, Liu, Jiao‐Yang, Xu, Hai‐Bing, Zhang, Yue‐Xing, Peng, Xu, Kurmoo, Mohamedally, Ng, Seik Weng, Zeng, Ming‐Hua
Format: Article
Language:English
Subjects:
Chemistry
Deuteration
discrete lanthanide assemblies
dual lanthanide emission
Erbium
Fluorides
Gadolinium
Irradiation
Luminescence
Mass spectrometry
Mass spectroscopy
molecular upconversion luminescence
multi-responsive photoluminescence
NMR
Nuclear magnetic resonance
Room temperature
Salts
Upconversion
Ytterbium
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Summary:The salts {[Ln2Ln*(Hhmq)3(OAc)3(hfac)2]+ [Ln*(hfac)3(OAc)(MeOH)]−} (Hhmq=2‐methanolquinolin‐8‐oxide, hfac=hexafluoroacetylacetonate; Ln, Ln*=Er, Gd, Yb) feature a discrete heteronuclear cation consisting of two types of lanthanide atoms. The quinolinoxy O‐atom serves as a μ2‐bridge to two Ln atoms and as a μ3‐bridge to all three atoms, with metal⋅⋅⋅metal distances being around 3.7 Å. For 1 ([Yb2Er]+), near‐infrared downshifted luminescence is switched to competitive upconversion luminescence upon irradiation by a 980 nm laser under an extremely low excitation power (0.288 W cm−2) through introduction of fluoride ions. The stability of 1 after addition of fluoride was confirmed by powder X‐ray diffraction and multistage mass spectrometry, associated with the 1H NMR of 6 ([La2Eu]+). More importantly, the at least 20‐fold enhancement of the quantum yield in non‐deuterated solvents at room temperature under low power densities (2 W cm−2) is the highest among the few molecular examples reported. The performance of discrete heteropolynuclear Yb/Er salts is switched from a Yb/Er doublet to competitive upconversion luminescence exploiting fluoride association. A more than 20‐fold enhancement of the relative quantum yield ϕUC under low power densities in non‐deuterated solvents at room temperature was recorded.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.202107637