Electron-transfer kinetics and axial-ligation reactions are explored within films of polymeric Fe, Co, Ni, and Cu tetraphenylporphyrins on electrodes. By sandwiching 100-300-nm films between two electrodes potentiostated so as to reduce and oxidize opposing faces of the polymer film, it was possible to determine that electron mobilities within the porphyrin film vary by over 10/sup 3/ x depending on central metal, porphyrin oxidation state, and axial ligation. Mobilities were measured as electron diffusion coefficients, which, since electron transport occurs by a hopping process, are proportional to the electron self-exchange rate constants of each oxidation state couple. The electron diffusion coefficients in the polymeric porphyrin films are shown to parallel the heterogeneous electron-transfer rate constants that have been determined for solutions of analogous monomeric tetraphenylporphyrins at electrode surfaces. It is concluded that electron-transfer barriers within the polymeric porphyrins are similar to those of dissolved monomers. Such a comparison has not been previously reported for a series of related electron-transfer processes. Electron diffusion coefficients could also be measured for a Fe(III/II) porphyrin film in the absence of liquid solvent.