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 (CH 2 NHCO-CH(Me)Ar) determines the helicity of the derived complex and the configuration of the macrocyclic ring. The enantiopure lanthanide complexes do not undergo D/L 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)- 3 ) shows a strong near-IR CD and circularly polarised luminescence (CPL) associated with the 2 F 5/2 ± 2 F 7/2 transition. Overall, these emissive complexes allow control in modulating both the frequency and the polarisation of emitted light in aqueous solution.

A palladium porphyrin has been covalently linked to a chiral lanthanide complex and effectively sensitises near-IR emission from Nd and Yb; sensitisation is enhanced in the absence of oxygen and in the presence of a nucleic acid.

No abstract

This work describes the measurement and analysis of circular polarization in the luminescence (CPL), in the near-IR spectral region, from chiral complexes of Yb(III) and Nd(III) in solution. The experimental technique is based upon previous measurements of CPL in the visible region. Instrumentation design, performance, and calibration are discussed. The experimental technique has been applied to several related complexes of Yb(III) and Nd(III) with chiral macrocyclic ligands based on 1,4,7,10-tetraazacyclododecane that have approximate C 4 symmetry. In addition, CPL from D 3 complexes of Yb(III) with 2,6-pyridinedicarboxylate, which were prepared as a solution of enriched enantiomers by the addition of (+)-dimethyltartrate, is also presented. It is demonstrated that CPL from the 2F5/2 → 2F7/2 transition of Yb(III) at 980 nm is particularly suited for CPL studies because this transition satisfies magnetic-dipole selection rules. The luminescence from the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 transitions of Nd(III) centered at 880 and 1060 nm, respectively, showed only weak CPL signals. The usefulness of these types of polarization measurements in the near-IR is discussed.

Circular dichroism spectroscopy has revealed that strong exciton coupling occurs between adjacent pairs of 1-naphthyl chromophores in the chiral sodium, calcium and europium complexes of the macrocyclic tetraamide L1a@b. In constitutionally isomeric complexes involving a 2-naphthyl linkage, L2a@b, intramolecular excimer formation is observed by Ñuorescence emission spectroscopy as being strongest in the protonated ligand itself. The terbium and europium complexes show a well-deÐned circularly polarised luminescence that is independent of the nature of excitation : UV excitation at 300 nm via the proximate naphthyl antennae in [Tb.L1a]3`and [Tb.L1b]3`followed by intramolecular energy transfer results in mirror-image circularly polarised emission spectra. The lanthanide complex serves to modulate both the frequency and polarisation of the incident light in a controlled manner.