Electrochemical Deposition of Aggregated Cobalt Sulfophthalocyanines at Gold Surfaces in Alkaline Solutions

In this paper, the method of cyclic voltammetry was used for the first time to study the electrochemical behavior of series of peripheral substituted cobalt phthalocyanines with consistently changing sulfonated fragments (cobalt phthalocyanine tetrasulfonic acid ( CoPcI ), cobalt tetra-4-[(6-sulfo-2-naphthyl)oxy]phthalocyanine ( CoPcII ), cobalt tetra-4-[(6,8-disulfo-2-naphthyl)oxy]phthalocyanine ( CoPcIII ), cobalt tetra-4-[(4-sulfo-1-naphthyl)oxy]-tetra-5-(1-benzotriazolyl)phthalocyanine ( CoPcIV ), cobalt tetra-4-[(1,6-disulfo-2-naphthyl)oxy]-tetra-5-(1-benzotriazolyl)phthalocyanine ( CoPcV ), cobalt tetra-4-[(1,6-disulfo-2-naphthyl)oxy]-tetra-5-(nitro)phthalocyanine ( CoPcVI ), cobalt tetra-4-{4-[1-methyl-1-(4-sulfophenyl)ethyl]phenoxy}-tetra-5-(nitro)phthalocyanine ( CoPcVII ), and cobalt octa-4,5-{4-[1-methyl-1-(4-sulfophenyl)ethyl]phenoxy}phthalocyanine ( CoPcVIII )) in an aqueous alkaline solution. Comparative analysis of the electrochemical behavior depending on the functional substitution in the macrocycle molecule was carried out. For all the compounds, central metal ion oxidation (Co 2+ → Co 3+ ) and reduction (Co 2+ → Co 1+ ) processes, as well as phthalocyanine ring activity were registered. Based on the occurrence of some peaks in the first scan numbers and the appearance/disappearance of other peaks, a hypothesis regarding the mechanism of electrodeposition of cobalt phthalocyanine derivatives at gold electrodes was formulated. It was shown that the electrodeposition process is generally independent on the nature of the substituent in the phthalocyanine macroring. It was also confirmed that react-ing species are adsorbed on the electrode surface without specific diffusion.