Synthesis, Time-Resolved Luminescence, NMR Spectroscopy, Circular Dichroism and Circularly Polarised Luminescence Studies of Enantiopure Macrocyclic Lanthanide Tetraamide Complexes

The syntheses and properties of a series of lanthanide complexes (Ln = Eu, Tb, Dy, Yb) of C₄ symmetric chiral tetraamide ligands based on 1,4,7,10-tetraazacyclododecane are reported. The configuration of the chiral centre at carbon in the amide substituent (CH₂NHCO-CH(Me)Ar) determines the helicity of the derived complex and the configuration of the macrocyclic ring. The enantiopure lanthanide complexes do not undergo Δ/Λ interconversion in the temperature range 220 to 320 K and three complexes have been characterised by X-ray crystallography, revealing nine-coordination about the lanthanide ion (Ln = Eu, Dy) with a monocapped square-antiprismatic coordination geometry. The terbium complexes are highly emissive in aqueous solution following excitation into the aryl chromophore (e.g. for [Tb · (R)-7a]³⁺ φH₂O= 0.49; φD₂O= 0.81) and all of the lanthanide complexes exhibit strong circularly polarised luminescence. The ytterbium complexes (e.g. [Yb · (S)-5b]³⁺) shows a strong near-IR CD and circularly polarised luminescence (CPL) associated with the ²F_5/2-²F_7/2 transition. Overall, these emissive complexes allow control in modulating both the frequency and the polarisation of emitted light in aqueous solution.