Two homochiral EuIII and SmIII enantiomeric pairs showing circularly polarized luminescence, photoluminescence and triboluminescence

Abstract

Two homochiral Eu^III and Sm^III tris(β-diketonate) enantiomeric pairs, based on fluorinated β-diketone (Hbtfa) and enantiopure asymmetric N,N′-donor ligands (L_R and L_S), Λ-Eu(btfa)₃L_R (R-1-Eu)/Δ-Eu(btfa)₃L_S (S-1-Eu) and Λ-Sm(btfa)₃L_R (R-2-Sm)/Δ-Sm(btfa)₃L_S (S-2-Sm) (btfa⁻ = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate and L_R/L_S = (–)/(+)-4,5-pineno-2,2′-bipyridine) were synthesized. The electronic circular dichroism (ECD) spectra confirmed their enantiomeric nature. R-1-Eu/S-1-Eu and R-2-Sm/S-2-Sm exhibit intense characteristic emissions of Eu^III (red) and Sm^III (orange-red) ions both in the solid state and in DCM with long lifetimes and high luminescence quantum yields. For example, the overall quantum yields reach up to 61% and 53% along with very high sensitization efficiency values of 82 and 79 for R-1-Eu in the solid state and in DCM, respectively. Notably, the corresponding values are determined to be 6.5% (solid state) and 3.1% (DCM) for R-2-Sm, which are among the highest quantum yields for rare Sm^III tris(β-diketonate) luminescent complexes reported to date. Furthermore, R-1-Eu and R-2-Sm show a strong triboluminescence (TL) phenomenon visible with the naked eye in daylight. Moreover, R-1-Eu/S-1-Eu and R-2-Sm/S-2-Sm show circularly polarized luminescence (CPL) properties. Particularly, the luminescence dissymmetry factors (g_lum) for R-2-Sm/S-2-Sm are larger than those for R-1-Eu/S-1-Eu despite the fact that Sm^III complexes usually show poorer emission than Eu^III homologues, which is very rare in the reported Eu^III and Sm^III CPL-active complexes.