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Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals

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Symmetry and Rigidity for Boosting Erbium-Based Molecular Light-Upconversion in Solution.

Soroush Naseri¹, Inès Taarit¹, Hélène Bolvin²

¹Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai E. Ansermet, 1211, Geneva 4, Switzerland.

Angewandte Chemie (International Ed. in English)

|October 17, 2023

Summary

Stable, low-symmetry molecular complexes significantly enhance light upconversion. This breakthrough boosts near-infrared to visible green light conversion efficiency by up to 1000 times, opening new possibilities for optical applications.

Keywords:

Erbium Heteroleptic Complexes Molecular Upconversion Single Molecule

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Area of Science:

Inorganic Chemistry
Materials Science
Photophysics

Background:

Single-center molecular upconversion previously limited to highly symmetrical homoleptic complexes like [Er(Lk)3]3+.
Excited-state absorption (ESA) mechanism is key for upconversion but requires optimized molecular designs.
Development of stable, low-symmetry heteroleptic adducts is crucial for improved performance.

Purpose of the Study:

To design and synthesize novel heteroleptic erbium complexes, [LkEr(hfa)3], for enhanced single-center upconversion.
To investigate the influence of ligand properties (π-electron delocalization, flexibility, heavy atom effect) on upconversion efficiency.
To achieve significant boosts in near-infrared to visible green light conversion yields.

Main Methods:

Synthesis of heteroleptic erbium complexes [LkEr(hfa)3] where Lk are polyaromatic tridentate ligands and hfa- is hexafluoroacetylacetonate.
Characterization of the synthesized complexes.
Measurement of upconversion quantum yields using linear optics at room temperature, monitoring the 801 nm (NIR) to 542 nm (green) emission.

Main Results:

Successfully synthesized stable, low-symmetry heteroleptic complexes [LkEr(hfa)3].
Demonstrated significant enhancement of upconversion quantum yield, up to three orders of magnitude (1000x).
Correlated the observed efficiency boost with ligand properties: extended π-electron delocalization, flexibility, and heavy atom effect.

Conclusions:

Low-symmetry heteroleptic complexes [LkEr(hfa)3] are superior to previous homoleptic designs for molecular upconversion.
Ligand design plays a critical role in optimizing excited-state absorption and boosting NIR-to-visible light conversion.
These findings pave the way for more efficient molecular-based optical upconversion technologies.