Ruthenium and Osmium Podate Cyclodextrins with Dual-function Recognition Sites for Luminescent Sensing

Abstract

A multifunctionalised podand cyclodextrin ligand, β-CD-(urebpy)⁷, with urea--bipyridine binding sites leads to ruthenium and osmium, {Ru[β-CD-(urebpy)⁷]}[PF⁶]² {Os[β-CD-(urebpy)⁷]}[PF⁶]², cyclodextrins. The bipyridine ligands are preorganised by the cyclodextrin cavity encapsulating the ruthenium and osmium core to give photoactive metallocyclodextrins. The podate cyclodextrin complexes show characteristic ruthenium and osmium tri-bipyridine luminescence. It is demonstrated that the ruthenium cyclodextrins participate in sensing schemes through both the cyclodextrin cavity and the urea cage at the bottom of the cyclodextrin rim. Luminescence quenching of the ruthenium emission is observed by addition of anthraquinone guests in the cyclodextrin cavity or addition of dihydrogen phosphate anion.

Abstract

The podate (left) and wheel (right) cyclodextrin complexes with AQS guest.

Keywords:

• Cyclodextrins
• Molecular devices
• Supramolecular chemistry
• Sensors

Acknowledgements

We thank Professor L. De Cola and Dr R. M. Williams for help with the time-resolved measurements. We are grateful to the Leverhulme Trust (M.C., J.M.H.), the Aventis Foundation (M.J.J.P.S.) and the Royal Society for financial support. We also wish to thank Johnson & Matthey for a loan of ruthenium trichloride.

Notes

The Future of Supramolecular ChemistryThe development of supramolecular systems will be directed towards the design of systems that will either interact with or act as nanoscale devices in a controlled way. For example, the importance of miniature photomolecular devices in nanoscale technology has led to the design of polymetallic supramolecular assemblies. The employment of multi-electron metal centres in a single supramolecular structure provides the basis for the development of molecular energy conversion systems and molecular wires in macromolecular systems, which is a focus of our research.Zoe Pikramenou obtained her BSc from the University of Athens in Greece. She was then awarded an Academy of Athens scholarship to carry out PhD studies in the USA where she joined the group of Professor Daniel G. Nocera (currently at MIT) at Michigan State University to develop optical supramolecules as sensors for aromatic pollutants. Upon completion of the doctorate, she moved to France to join the group of Professor Jean-Marie Lehn as a Marie Curie fellow and later as a Collège de France research fellow to work on photochromic systems based on photoinduced proton transfer. She then moved to the UK to take up an appointment as a lecturer in the University of Edinburgh before she moved to her current lectureship position in the School of Chemical Sciences at the University of Birmingham. Her research interests involve the design of functional supramolecular systems with emphasis on light-activated functions including lanthanide chemistry and photophysics and cyclodextrin receptor chemistry. In the lanthanide field, the group has developed systems for lanthanides, studied controlled formation of lanthanide complexes with different sensitisers and studied the interaction with DNA. In the cyclodextrin field, energy and electron transfer via non-covalent bonds in aqueous assembled metallocyclodextrin-metalloguest systems has been demonstrated.