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

Abstract

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 Eu³⁺ and Gd³⁺ lanthanide centres, and has potential as a dual output probe for visible emission and magnetic resonance imaging measurements. The Eu³⁺ emission is perturbed compared to an isoabsorptive non-macrocyclic equivalent complex, EuL ^x . Macrocycle M2 incorporates Eu³⁺ and Nd³⁺ 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 Eu³⁺ centre, caused by the presence of the proximal Nd³⁺ centre, attributed to energy transfer from Eu³⁺ to Nd³⁺.

Keywords:

• lanthanide luminescence
• heterometallic complexes
• near-infrared emission
• magnetic resonance imaging

Acknowledgements

We wish to thank the European Community Action Scheme for the Mobility of University Students (ERASMUS), and COST action D38 ‘Metal-Based Systems for Molecular Imaging Applications’ and EPSRC for funding. Some of the spectrometers used in this research were obtained, through Birmingham Science City: Innovative Uses for Advanced Materials in the Modern World (West Midlands Centre for Advanced Materials Project 2), with support from Advantage West Midlands (AWM) and part funded by the European Regional Development Fund (ERDF).