Electrochemical and spectroelectrochemical studies of β-phosphorylated Zn porphyrins

The electrochemical and spectroelectrochemical properties of two β-phosphorylated Zn porphyrins, [2-diethoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (1) and [2-diisopropoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (2), are reported in CH ₂ Cl ₂ and PhCN containing tetrabutylammonium perchlorate (TBAP) or tetrabutylammonium hexafluorophosphate (TBAPF₆) as supporting electrolyte. Under certain solution conditions, three one-electron reductions are observed, with the last process being attributed to the product of a chemical reaction following formation of the porphyrin dianion. Two or three oxidations are observed for the same compounds, again depending upon the solution conditions. In some cases, two well-defined and well-separated one electron oxidations are observed but in others the first one-electron abstraction to give the porphyrin radical cation is split into two redox processes, separated from each other by 110–140 mV. This splitting of the first oxidation into two processes is attributed to linking of the two porphyrins which results when a P = O unit of the phosphoryl substituent on one porphyrin binds to the Zn ( II ) center of a second porphyrin, resulting in dimer formation. The interaction between the two macrocycles is discussed in terms of the difference in potentials between the two split redox processes (ΔE_1/2) and the overall data is compared with that for other porphyrin dimers and bis-macrocycles reported in the literature.