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

Abstract

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.

Isomerism‐Activity Relation in Molecular Electrocatalysis: A Perspective

“…This is mainly because, we have observed that short-range interactions often interconnects the nature of functionality as well as isomerism with their electrochemical activation, and such interactions are often substituent specific which offers a plethora of opportunities for researchers working in the domain of molecular electrocatalysis. We also note that often this isomerism-induced activation is interpreted as exclusively arising from the orientation of the molecules with respect to the anchoring electrode [50,51]. It is worthy to mention that such solid conclusions can be arrived only by examing the electrochemical behavior of the molecules by keeping their orientation the same without which there will be elements of ambiguity.…”

Covalent Immobilization of Organic Photosensitizers on the Glass Surface: Toward the Formation of the Light-Activated Antimicrobial Nanocoating

“…For AA, the signals arising from the C–S–C vibrations, C–N–C stretching vibrations, and the C–C stretching within the phenothiazine ring are observed at 900, 1384, and 1634 cm −1 , respectively [ 46 ]. The specific bands coming from APTPP are located at 1002, 1240, 1331, and 1555 cm −1 and correspond to the in-plane bending deformation of the phenyl rings, the C m –H bending, the symmetric stretching of the pyrrole half-ring, and the symmetric stretching of C β –C β , respectively [ 47 , 48 ].…”

Stable nano-sized copper and its oxide particles using cobalt tetraamino phthalocyanine as a stabilizer; application to electrochemical activity

“…15,16,[32][33][34] Phthalocyanine macrocycles are promising as good electrocatalysts since they are chemically and electrochemically stable, and have been shown to exhibit substantial catalytic activity in a wide variety of redox processes. 34,35 Cobalt phthalocyanines have been known to be good catalysts for the reduction of small molecules like oxygen. 34,35 The main aim of the oxygen reduction studies is to increase the rate of the electroreduction of oxygen in order to improve the efficiency of the oxygen (air) electrode of the fuel system.…”