93 J. Electroanal. Chem., 266 (1989) 93-108 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Electrochemistry of various substituted aminophenyl iron porphyrins Part I. Redox properties of dissolved, adsorbed and electropolymerized species A. Bettelheim *, D. Ozer and R. Harth Nuclear Research Center-Negeu, P.O. Box 9001, Beer-Shera 84190 (Israel) R.W. Murray Kenan Loboratories of Chemisty?, The University of North Carolina, Chapel Hdl, NC 27514 (U.S.A.) (Received 4 January 1989) ABSTRACT The redox properties of dissolved, adsorbed and electropolymerized films of iron(II1) tetrakis( o- aminophenyl)porphyrin (Fe(U) (o-NH*)TPP), iron(II1) tetrakis( p-aminophenyl)porphyrin (Fe(II1) ( p- NH,)TPP) and iron(II1) tetrakis( p-N, N’-dimethylaminophenyl)porphytin (Fe(II1) (p-NMe,)TPP) have been studied in aqueous solutions. Cyclic voltammetry at glassy carbon electrodes for the complexes dissolved in 1 M HCI showed two Fe(III)/Fe(II) waves with cathodic peak potentials of -0.14 and -0.38 V for Fe(o-NH*)TPP, -0.15 and -0.36 V for Fe(p-NH,)TPP, and -0.17 and -0.45 V for Fe( p-NMe,)TPP. Differential pulse voltammetry also revealed two reduction waves for Fe( o-NH,)TPP adsorbed on a glassy carbon electrode (- 0.16 and + 0.08 V) and only one reduction process for Fe( p-NH,)TPP (-0.24 V) and Fe(NMe,)TPP (-0.25 V). The reduction peak potentials for the polymeric films at pH 3.2kO.2 are -0.22 and +0.12 V for poly[Fe( o-NH,)TPP], -0.22 and -0.07 V for poly[Fe( p-NHz)TPP and - 0.18 and - 0.02 V for poly[Fe( p-NMe,)TPP]. Thin-layer spectroelectro- chemical techniques for the dissolved iron porphyrins and cyclic voltammetry for the polymeric films in strong acidic solutions indicated irreversible changes resulting from a demetallation process occurring upon reduction. The demetallation rate for the Fe(I1) (p-NMe,)TPP compound (8~10~~ ss’) was about 20-fold smaller than that of the Fe(I1) (p-NHz)TPP complex. In contrast, the polymeric films showed high stability at pH > 3: the cyclic voltammetric peak currents decreased by only 2% after 100 subsequent cycles in the potential range + 0.4 to - 0.8 V. l To whom correspondence should be addressed. 0022-0728/89/$03.50 0 1989 Elsevier Sequoia SA