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 C-4 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 Delta/Lambda 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+) phi H2O = 0.49; phi D2O = 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 F-2(5/2)-F-2(7/2) transition. Overall, these emissive complexes allow control in modulating both the frequency and the polarisation of emitted light in aqueous solution.