Attachment of four oligomeric (MW 550) ethylene glycol chains to tetraphenylporphyrin results in a highly viscous, room temperature melt-a hybrid redox polyether-that is highly concentrated in porphyrin sites (similar to 0.4 RI) and will dissolve LiClO4 electrolyte. Microelectrode voltammetry in undiluted, free base and Co and Fe-metalated melts yields apparent diffusion coefficients that for 1.2 M LiClO4 electrolyte vary by > 10(3)-fold, from a high of 6.2 x 10(-9) cm(2) s(-1) for the ring reduction of the free base to a low of ca. 3 x 10(-12) cm(2) s(-1) for the Co(II/III) oxidation in a Co-metalated melt. Taking the latter as measuring the true physical self-diffusivity of the porphyrins, electron self-exchange rate constants are found for four porphyrinic redox couples (free base (0/1-), Co(II/I), Fe(II/I), and Fe(III/II) give 3.6 x 10(6), 1.2 x 10(5), 3.7 x 10(5), and 1.1 x 10(4) M-1 s(-1), respectively). An activation study yields large free energy activation barriers for these couples, and exponential pre-factors in the 10(13)-10(14) s(-1) range, The polyether appendages provide a weakly coordinating ''solvent'' for the porphyrin centers, and the introduction of ligands like pyridine and carbon monoxide at the gas/melt interface causes changes in Fe(III/II) voltammetry consistent with axial coordination in the semisolid melt. The axial coordination and voltammetric change is reversed by removing the ligand from the bathing gas.