Electronic chirality inversion of lanthanide complex induced by achiral molecules

Area of Science:

• Coordination Chemistry
• Photophysics
• Spectroscopy

Background:

• Chiroptical activity in metal complexes is typically associated with specific chiral structures (Λ or Δ).
• Understanding the factors influencing chiroptical activity is crucial for developing new optical materials and sensors.
• Previous studies have primarily focused on structural changes to modulate optical properties.

Purpose of the Study:

• To demonstrate a novel mechanism for chiroptical activity inversion in metal complexes.
• To investigate the role of electronic structure changes, independent of chiral coordination geometry, in modulating optical activity.
• To explore the influence of external achiral molecules on the chiroptical properties of lanthanide complexes.

Main Methods:

• Synthesis and characterization of a europium (Eu(III)) complex with (+)-3-(trifluoroacetyl)camphor (+tfc) and triphenylphosphine oxide (tppo).
• Spectroscopic analysis including 1H NMR, photoluminescence, and emission lifetime measurements.
• Circularly polarized luminescence (CPL) measurements to evaluate optical activity in solution.

Main Results:

• Observed CPL sign inversion in the Eu(III) complex without changes in Λ- or Δ-type structure.
• Demonstrated a drastic enhancement in CPL intensity.
• Showed that optical activity modulation is dependent on external achiral molecules (tppo, acetone) interacting with the Eu(III) ion.

Conclusions:

• Established a new mechanism for chiroptical activity inversion driven by electronic structure modifications.
• Highlighted the significant impact of the local coordination environment and external molecules on the optical activity of metal complexes.
• Provided the first evidence of optical activity changes linked to electronic structure rather than solely chiral coordination type.