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) x 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)63-/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.

Insights into the surface and redox properties of single-walled carbon nanotube—cobalt(II) tetra-aminophthalocyanine self-assembled on gold electrode

“…Assuming n ≈ 4 for SWCNT redox wave [59] and n = 1 for the CoTAPc, the surface coverages were estimated as 1.1 × 10 −10 mol cm −2 ( 6.6 × 10 13 particles cm −2 ≈ 150 Å 2 per particle) for the Au-AET-SWCNT, and 6. perpendicularly oriented SAMs of Au-AET-SWCNT [10] and CoTAPc [68] and [69] obtained at long deposition times ≥12 h as carried out in this work. If each CoTAPc molecule assumes flat orientation on the SWCNT surface yielding an area close to 200 Å 2 [67], [68], [69] and [70], the coverage should work out to be approximately 1.0 × 10 −10 mol cm −2 .…”

“…CoTAPc has been reported to form SAM on gold electrode (Au-CoTAPc) [68] and [69], hence we carried out CV experiments with Au-CoTAPc (Fig. 4B) with a view to investigating the possible influence of the SWCNT on the electrochemistry of Au-AET-SWCNT-CoTAPc SAM.…”

“…If each CoTAPc molecule assumes flat orientation on the SWCNT surface yielding an area close to 200 Å 2 [67], [68], [69] and [70], the coverage should work out to be approximately 1.0 × 10 −10 mol cm −2 . Thus, the high surface coverage for the CoTAPc is a clear indication of a perpendicular orientation for the CoTAPc.…”

“…Thus, the high surface coverage for the CoTAPc is a clear indication of a perpendicular orientation for the CoTAPc. Interestingly, CoTAPc is also known to prefer perpendicular orientation when adsorbed on a gold surface as a SAM [68] and [69]. Also, the cross sectional area for a single SWCNT of diameter of 1.3 nm redox-active centre of the CoTAPc led to more reversibility and slight enhancement of the peak current.…”

Electrocatalytic and Analytical Response of Cobalt Phthalocyanine Modified Carbon Paste Electrodes Towards Antimalarial Endoperoxide Artemisinin

“…In addition modified electrodes (MEs) can catalyze the oxidation or reduction of analytes that reveal high over voltages at chemically unmodified surfaces and as a result are not compatible to quantify through conventional electrodes [17]. Phthalocyanine as modifier has been shown to have very remarkable properties together with outstanding stability to heat, light and harsh chemical environments [18]. Since metallo-phthalocyanines have well-known catalytic activity towards a wide variety of redox systems [19 -22], various studies are continued to explore the use of phthalocyanine containing carbon paste electrodes as electrochemical sensors in voltammetry and liquid chromatography [17,23].…”