Hexafullereno-bis-porphyrins as Molecular Reservoirs: Synthesis and Electronic Properties

The use of multiporphyrin arrays as precursors towards the development of electronic/photonic devices has been the subject of much research in recent years. Porphyrins are ideal molecules for such devices as they are fully conjugated and can be functionalised to create rigid arrays with defined geometry that span distances up to 100 Å. The large pi-delocalisation that exists over these porphyrin-based arrays enables them to store and conduct electrons. The impetus for this research has come from Nature where porphyrinoid molecules are used in many electronic processes. We propose the synthesis of covalently linked hexafullereno-bis-(quinone bridged)-porphyrins for the purpose of storing massive amounts of electrons, thereby acting as a `molecular reservoir` of electrons. This molecule is predicted to be chargeable with a practical maximum of 42 reversible electron additions, unprecedented for such a compact molecule. The bridging quinone has the added ability to act as a redox switchable unit or a `molecular dam`, in effect allowing the modulation of electronic communication within the molecule. The synthetic target of this project, a dizinc(II) hexafullereno-bis-(quinone bridged)-porphyrin chelate, will be synthesised using a stepwise approach that utilises a single thermolysis reaction to generate a functionalised porphyrin diene. Isolation of this porphyrin-diene is required to facilitate the controlled synthesis of the annulated array. The isolated diene will then be used in a subsequent Diels-Alder cycloaddition reaction to construct a quinone bridged bis-porphyrin. This bis-porphyrin will then be conjugated to six fullerenes to give the target compound. This approach offers a new methodology for the preparation of multifunctional porphyrin/fullerene arrays using cycloaddition reactions.