Chiroptical Spectroscopic Studies on Lanthanide Complexes with Valinamide Derivatives in Solution

Abstract

Ligands based on 2,2’‐bipyridine and valinamide moieties induce circularly polarized luminescence in their europium complexes. Both the R and S enantiomers of the complexes were successfully obtained. Single‐crystal X‐ray analysis of the racemic crystal confirmed that the ligand is coordinated to the europium ion in a tetradentate fashion. The π‐electronic system of the ligand is co‐planar with the valinamide moiety, and acts as an efficient photoantenna to sensitize europium luminescence by UV excitation. The luminescence quantum yield (QY) of europium in the valinamide‐containing complex was 44 % in acetonitrile. The glum value to evaluate the circularly polarized luminescence was relatively high at |0.13| estimated from their magnetic dipole transitions around 593 nm. For comparison, we prepared hexadentate europium complexes in the S‐ and R‐forms derived from two bipyridine moieties linked by ethylenediamines. The determined QYs were 18 % (S) and 16 % (R), and the glum value |0.12| for the hexadentate complexes. The photophysical properties of the gadolinium complexes of the ligands were also evaluated.

Quantifying the Overall Efficiency of Circularly Polarized Emitters

“…In this contribution, whenever possible, both the transitions were examined and the corresponding values reported in Table 8. The complexes present extinction coefficients in the range 11 000–80 000 m −1 cm −1 , [2, 103, 106–108, 110–117] except for Eu 4 ( L21 ) 4 ( L′ ) 4 and Eu 4 ( L10 ) 4 ( L′ ) 4 , which show extinction coefficients of 600 000 m −1 cm −1 and 800 000 m −1 cm −1 , respectively [118] . In combination with their high quantum yields (0.68 for Eu 4 ( L21 ) 4 ( L′ ) 4 and 0.81 for Eu 4 ( L10 ) 4 ( L′ ) 4 ), they are endowed with outstanding B CPL values (1122 m −1 cm −1 and 3240 m −1 cm −1 , respectively) for the 5 D 0 7 F 1 transition.…”

Temperature-Dependent Circularly Polarized Luminescence Measurement Using KBr Pellet Method

“…Also, in the field of biomolecules, CPL of green fluorescent protein has been reported, but the g lum value of 1.8 × 10 −3 is small (Goto et al, 2010). In addition, in lanthanoid complexes, the CPL signal associated with f → f transitions has a large g lum , but the CPL band is very sharp (Brittain and Richardson, 1976;Zinna and Bari, 2015;Hasegawa et al, 2020).…”

Biomolecule‐Based Circularly Polarized Luminescent Materials: Construction, Progress, and Applications

“…[58] The results showed that whether amino acids induce detectable CPL depends on the ligand of the Eu III complex. Hasegawa et al, [59] Wu et al, [60] and Okutani et al [61] also indicated that the association of amino acids with Eu III complexes may be an effective way to design a CPL system.…”