Specific recognition of chiral amino alcohols via lanthanide coordination chemistry: structural optimization of lanthanide tris(beta-diketonates) toward effective circular dichroism/fluorescence probing

Lanthanide tris(beta-diketonates) formed stable, 1:1 highly coordinated complexes with amino alcohols, and the resulting complexes exhibited large enhanced fluorescence and intense induced circular dichroism (CD) signals. The stability constants of the highly coordinated complexes were determined for various combinations of lanthanide centers, beta-diketonate ligands, and organic substrates. These revealed that amino alcohol coordinated with the lanthanide center much more strongly than monoamine, monoalcohol, or diol derivative. On the basis of the highly coordinated complexation, several lanthanide tris(beta-diketonates) acted as CD/fluorescence probes specific for amino alcohols. Tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadionato)europium(III) showed enhanced fluorescence in the presence of amino alcohols, while the corresponding ytterbium complex exhibited chirality-dependent CD signals for amino alcohols. In particular, the observed CD spectral profiles related well with the absolute configuration and optical purity of the bound amino alcohol, indicating that the structural optimization of lanthanide tris(beta-diketonates) offered specific sensing of amino alcohols and precise determination of their enantiomer excess percentages.