Photoreduction of fe(iii) protoporphyrin ix in ethanol-water solutions containing bifunctional ligands

The irradiation of Fe(III) protoporphyrin IX [Fe(III)PPIX) in a thoroughly deoxygenated 35% ethanol-water solution containing pyrazine (pyz) leads to changes in the visible spectrum that are indicative of Fe(II)PP species formation. With a large excess of pyz the spectrum is similar to that of the Fe(II) pyridine hemochrome, suggesting that the monomer Fe(II)PP(pyz)2 is formed. With a lower pyz content, the photochemically formed bis-pyz complex converts to a polymeric Fe(II)PP species. A similar photochemical behaviour is observed when piperazine or 4,4′-bipyridine are used as bridge ligands instead of pyz. The origin of the absorptions characteristic of the photoreaction products is discussed on the basis of the dependence of the spectra on the nature of the bridge ligands. © 1986.