Ground and excited state chiroptical properties of enantiopure macrocyclic tetranaphthyl lanthanide complexes: controlled modulation of the frequency and polarisation of emitted light

Abstract

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 L^1a/b. In constitutionally isomeric complexes involving a 2-naphthyl linkage, L^2a/b, intramolecular excimer formation is observed by fluorescence emission spectroscopy as being strongest in the protonated ligand itself. The terbium and europium complexes show a well-defined circularly polarised luminescence that is independent of the nature of excitation: UV excitation at 300 nm via the proximate naphthyl antennae in [Tb.L^1a]³⁺ and [Tb.L^1b]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.