Controlled assembly of heterometallic lanthanide(III) macrocycles: Incorporation of photoactive and highly paramagnetic metal centres within a single complex

Building on the recent discovery that heterometallic lanthanide complexes can be assembled in a controlled manner using thiol-disulphide chemistry, we now present the assembly of macrocycles that contain both photoactive and highly paramagnetic centres as potential bimodal probes. The assembly of macrocycles M1 and M2 was monitored by UV-visible absorption spectroscopy and electrospray mass spectrometry. Macrocycle M1 contains both Eu ³⁺ and Gd ³⁺ lanthanide centres, and has potential as a dual output probe for visible emission and magnetic resonance imaging measurements. The Eu ³⁺ emission is perturbed compared to an isoabsorptive non-macrocyclic equivalent complex, EuL ^x. Macrocycle M2 incorporates Eu ³⁺ and Nd ³⁺ lanthanide centres for dual optical output in the visible and near-infrared regions of the electromagnetic spectrum. We demonstrate that in M2 there is a quenching effect on the Eu ³⁺ centre, caused by the presence of the proximal Nd ³⁺ centre, attributed to energy transfer from Eu ³⁺ to Nd ³⁺.