Synthesis of some new tetra-arylporphyrins for studies in solar energy conversion

Abstract

The synthesis of tetra-arylporphyrins, for studies in solar energy conversion, is described. They are derived from 5,10,15,20-meso-tetrakis(4-hydroxyphenyl)porphyrin (4) which, in basic media, forms a green intermediate that is probably the tetraphenoxide (6). The porphyrins (10) and (13), were synthesised as prospective sensitisers for catalysed microheterogenous water photo-oxidation. U.v./visible spectroscopy demonstrates that the porphyrin (10) aggregates in aqueous solution. Cyclic voltammetry shows that the porphyrin (13) behaves as a typical viologen with bulky substituents. A pentameric porphyrin (15) was synthesised and characterised in order to model energy transfer in photosynthetic chlorophyll antennae. There is some evidence that weak singlet-energy transfer occurs between the porphyrin sub-units of the pentamer.