Self-assembled molecular films of tetraamino metal (Co, Cu, Fe) phthalocyanines on gold and silver: electrochemical and spectroscopic characterization

Abstract

The formation of molecular films of 2,9,16,23-tetraamino metal phthalocyanines [TAM(II)Pc; M (II) = Co, Cu, and TAM(III)Pc; M = Fe] by spontaneous adsorption on gold and silver surfaces is described. The properties of these films have been investigated by cyclic voltammetry, impedance, and FT-Raman spectroscopy. The charge associated with Co(II) and Co(I) redox couple in voltammetric data leads to a coverage of (0.35 ± 0.05) × 10-10 mol cm^-2, suggesting that the tetraamino cobalt phthalocyanine is adsorbed as a monolayer with an almost complete coverage. The blocking behavior of the films toward oxygen and Fe(CN)₆ ^3-/4- redox couple have been followed by cyclic voltammetry and impedance measurements. This leads to an estimate of the coverage of about 85 % in the case of copper and the iron analogs. FT-Raman studies show characteristic bands around 236 cm^-1 revealing the interaction between the metal substrate and the nitrogen of the -NH₂ group on the phthalocyanine molecules.