Unlocking same‐sign CPL: solvent effects on spectral form and racemisation kinetics in nine‐coordinate chiral europium(III) complexes

De Rosa, Davide F.; Starck, Matthieu; Parker, David; Pal, Robert

Abstract

Understanding the factors that shape the circularly polarised luminescence (CPL) emission profiles of europium(III)-based CPL emitters to have specific sign properties, e. g. monosignate individual CPL transitions, is key to design novel complexes for applications ranging from advanced security inks to bio-probes for live cell imaging. In order to correlate structure and spectral characteristics, a photophysical and kinetic investigation has been conducted on a series of coordinatively saturated nine-coordinate europium(III) systems based on 1,4,7-triazacyclononane. We highlight that lanthanide emission is sensitive to changes in the ligand field by showing the linear dependence of total emission intensity ratios as a function of solvent polarity, for europium(III) complexes displaying an internal charge transfer (ICT) excited state. This sensitivity increases by a factor of 20 when studying changes in CPL spectra, rendering these complexes accurate probes of local polarity. Solvent polarity, solvent-specific effects, and the nature of the chromophores’ coordinating donor atoms strongly influence the kinetic stability of europium(III) complexes with respect to enantiomer interconversion. Notably, we show that the choice of donor groups to coordinating to europium(III) and the nature and polarity of the solvent affects the rate of racemisation, leading to systems with very long half-lives at room temperature in non-polar media.

Citation

De Rosa, D. F., Starck, M., Parker, D., & Pal, R. (2023). Unlocking same‐sign CPL: solvent effects on spectral form and racemisation kinetics in nine‐coordinate chiral europium(III) complexes. Chemistry - A European Journal, https://doi.org/10.1002/chem.202303227

• Journal Article Type: Article
• Acceptance Date: Dec 11, 2023
• Online Publication Date: Dec 20, 2023
• Publication Date: Dec 20, 2023
• Deposit Date: Dec 11, 2023
• Publicly Available Date: Jan 4, 2024
• Journal: Chemistry - A European Journal
• Print ISSN: 0947-6539
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.1002/chem.202303227
• Public URL: https://durham-repository.worktribe.com/output/2022825