Web Release Date: January 15,
Amino Group Position Dependent Orientation of Self-Assembled Monomolecular Films of Tetraaminophthalocyanatocobalt(II) on Au Surfaces
Department of Chemistry, Gandhigram Rural University, Gandhigram-624 302, Dindigul, India
Received September 14, 2007
In Final Form: November 3, 2007
Abstract:
Self-assembled monomolecular films of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4
-CoIITAPc) and 2,9,16,23-tetraaminophthalocyanatocobalt(II) (4
-CoIITAPc) on Au surfaces were prepared by spontaneous adsorption
from solution. These films were characterized by cyclic voltammetry and Raman spectroscopy. Both the surface
coverage (
) and intensity of the in-plane stretching bands obtained from Raman studies vary for these monomolecular
films, indicating different orientations adopted by them on Au surfaces. The 4-CoIITAPc-modified electrode exhibits
an E1/2 of 0.35 V, while the 4-CoIITAPc-modified electrode exhibits an E1/2 of 0.19 V, corresponding to the CoII/CoIII
redox couple in 0.1 M H2SO4. The estimated from the charge associated with the oxidation of Co(II) gives (2.62
± 0.10) × 10-11 mol cm-2 for 4-CoIITAPc and (3.43 ± 0.14) × 10-10 mol cm-2 for 4-CoIITAPc. In Raman spectral
studies, the intensity ratio between in-plane phthalocyanine (Pc) stretching and the Au-N stretching was found to
be 6.6 for 4-CoIITAPc, while it was 1.6 for 4-CoIITAPc. The obtained lower and intensity ratio values suggest
that 4-CoIITAPc adopts nearly a parallel orientation on the Au surface, while the higher and intensity ratio values
suggest that 4-CoIITAPc adopts a perpendicular orientation. The electrochemical reduction of dioxygen was carried
out using these differently oriented Pc's in phosphate buffer solution (pH 7.2). Both the Pc's catalyze the reduction
of dioxygen; however, the 4-CoIITAPc-modified electrode greatly reduces the dioxygen reduction overpotential
compared to 4-CoIITAPc-modified and bare Au electrodes.
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