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Molecules 2012, 17(7), 7824-7842;

Self Assembled Films of Porphyrins with Amine Groups at Different Positions: Influence of Their Orientation on the Corrosion Inhibition and the Electrocatalytic Activity

Department of Analytical Chemistry, Ghent University, Krijgslaan 281-S12, 9000 Ghent, Belgium
Current address: Faculty of Science and Technology, Shinshu University, Tokida, Ueda, Nagano 386-8567, Japan.
Author to whom correspondence should be addressed.
Received: 28 April 2012 / Revised: 8 June 2012 / Accepted: 12 June 2012 / Published: 26 June 2012
(This article belongs to the Special Issue Tetrapyrroles, Porphyrins and Phthalocyanines)
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Self-assembled molecular films of two cobalt porphyrins with amine groups at different positions—(5,10,15,20-tetrakis-(2-aminophenyl) porphyrin-cobalt(II), [Co(II) (T(o-NH2)PP)] and (5,10,15,20-tetrakis-(4-aminophenyl) porphyrin-cobalt(II), [Co(II)(T(p-NH2)PP)]—were formed on a gold substrate. The functionalized surfaces were characterized using Raman spectroscopy, atomic force microscopy and electrochemical methods. Both modified gold surfaces completely mask the charge transfer of a [Fe(CN)6]3−/4− redox couple in solution, indicating the layer is highly resistive in behavior. Electrochemical impedance spectroscopy analyses revealed that the porphyrin film with amine groups at ortho positions shows a higher charge-transfer resistance with a better protective behavior compared to the para position modified surface. Raman, AFM and EIS data suggests that an ortho amine positioned molecule forms a more compact layer compared to the para-positioned molecule. This can be explained in terms of their orientation on the gold surface. [Co(II)(T(o-NH2)PP)] adopted a saddle shape orientation whereas [Co(II)(T(p-NH2)PP)] adopted a flat orientation on the gold surface. The porphyrin modified gold electrode catalyzes the oxygen reduction at lower potentials compared to the bare gold electrode. The shift in the overvoltage was higher in case of molecules with flat orientation compared to the saddle shaped oriented porphyrin molecules on the surface. View Full-Text
Keywords: porphyrin; self assembly; electrocatalysis; orientation porphyrin; self assembly; electrocatalysis; orientation

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Lokesh, K.S.; De Keersmaecker, M.; Adriaens, A. Self Assembled Films of Porphyrins with Amine Groups at Different Positions: Influence of Their Orientation on the Corrosion Inhibition and the Electrocatalytic Activity. Molecules 2012, 17, 7824-7842.

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