Porphyrin electrode films prepared by electrooxidation of metalloprotoporphyrins
Electrooxidation in organic solvents of the dimethyl esters of several metalloprotoporphyrins (PP) (Ni/sup II/PP, Zn/sup II/PP, Co/sup II/PP, (Fe/sup III/PP)Cl, (Fe/sup III/PP)/sub 2/O, and (Cr/sup III/PP)/sub 2/O) leads to the deposition of thick (approx. 1000 monolayer equivalents), electroactive porphyrin films, which have been characterized by cyclic voltammetry and absorption spectroscopy on transparent SnO/sub 2/ electrodes. The films are stable toward organic solvents and aqueous acids and bases, but are removed by treatment with hot concentrated acids. The resonance Raman spectrum of the NiPP film indicates that one of the two vinyl groups is saturated on most of the porphyrin units. Deposition continues for some minutes after the current is interrupted. This evidence is consistent with a mechanism involving electroinitiated cationic vinyl polymerization. No film is formed if the metal, rather than the ring, is oxidized. Thus the first oxidation step of Co/sup II/PP, to (Co/sup III/PP)/sup +/, does not support film formation (although the potential is as high as for ring oxidation in ZnPP), but the second step, to (Co/sup III/PP)/sup 2 +/, does. Lack of film formation for (Mn/sup III/PP)Cl and (Cr/sup IV/PP)O suggests metal, rather than ring oxidation, to Mn/sup IV/ and Cr/sup V/. However, (CrPP)/sub 2/O oxidation does produce a film, suggesting ring oxidation, analogous to (FePP)/sub 2/O, which also produces a film. However, while (CrPP)/sub 2/O is incorporated intact into the film, the (FePP)/sub 2/O film contains monomer units. Incorporation of other metal ions can be accomplished by soaking a ZnPP-coated electrode in H/sub 2/SO/sub 4/ followed by contact wtih a solution of the metal dihalide in refluxing DMF. The porphyrin sites are accessible to small ions, as shown by chloride coordination of ZnPP film upon soaking in chloride solution. 49 references, 13 figures, 1 table.
- Research Organization:
- Princeton Univ., NJ
- DOE Contract Number:
- AC02-81ER10861
- OSTI ID:
- 5557994
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 105:17
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHROMIUM COMPLEXES
ELECTRODEPOSITION
COBALT COMPLEXES
ELECTRODES
FILMS
SYNTHESIS
IRON COMPLEXES
NICKEL COMPLEXES
PORPHYRINS
ZINC COMPLEXES
DEPOSITION
ORGANIC SOLVENTS
ORGANOMETALLIC COMPOUNDS
OXIDATION
POLYMERIZATION
RAMAN SPECTRA
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
COMPLEXES
ELECTROLYSIS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
LYSIS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SOLVENTS
SPECTRA
SURFACE COATING
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties
400301 - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)