A cobalt(II) phthalocyanine with indole substituents: formation, characterization and electrocatalytic studies

Herein, we report the formation of a new cobalt(II) phthalocyanine (CoPc) containing peripheral tetra-substituted indole (CoPc-ind, 2) moieties. The derivatized phthalonitrile, 4-(indole-4-oxy)phthalonitrile (1) as well its corresponding metal complex was characterized by NMR (for 1), IR- and UV-Vis spectroscopy as well as TOF mass spectrometry and elemental analysis (for 2). The electrochemical properties of the N-4-macrocyclic metal complex were investigated using cyclic- and square-wave voltammetry as well as corroborated by UV-Vis spectroelectrochemistry. The CoPc was electrodeposited onto the surface of a Pt working electrode followed by the immobilization of multiwalled carbon nanotubes (MWCNTs) onto the modified working electrode surface. The electrocatalytic activity of the resultant modified electrode toward dopamine revealed a lower E value of 80mV versus Ag|AgCl for the modified (2-MWCNTs) Pt electrode compared to the bare Pt electrode (E=280mV vs. Ag|AgCl). The diffusion- and convection-controlled electron-transfer kinetics of the chemically modified electrode were evaluated by chronoamperometry and rotating disk electrode techniques. Electrochemical impedance spectroscopic studies revealed that the 2-MWCNTs Pt electrode had a lower charge-transfer resistance and a higher apparent electron-transfer rate constant. [GRAPHICS]