Bis-porphyrin arrays. Part 3. The synthesis of model bis-porphyrin dimers and an electrochemical study

We have successfully synthesised exo and endo diphenylacetylene linked bis- porphyrin dimers. We found that the exo-bis-porphyrin dimer could be easily prepared in good yield whilst the endo-dimer was harder to form due to the steric constraints of the meso-substituents. Electrochemical studies indic ated that the porphyrin centred reductions of the bis-porphyrin dimers were dominated by the bis-porphyrin moieties. We found that the first four one- electron reductions of the exo- and endo-bis-porphyrin dimers occurred at s imilar potentials. Finally, at more negative potentials the bis-porphyrin d imers were reduced further which significantly changed the subsequent oxida tion processes. This is thought to be due to a conformational change in the molecule which causes a change in orbital density in the "excited state".