SPECTROSCOPIC MEASUREMENTS ON METAL TETRASULPHONATO-PHTHALOCYANINES

An optically transparent thin layer cell was used to obtain light absorption spectra of iron tetrasulphonato-phthalocyanine (FeTSPc) dissolved in both acidic and alkaline solutions, with the iron ion in the first, second and third oxidation state, respectively. Further, electroreflectance (ER) spectra for the complex adsorbed on the basal plane of stress-annealed pyrolytic graphite (BP of SA-Cp) were recorded. The ER spectrum due to the couple Fe(I)/Fe(II)TSPc has, as predicted theoretically, a shape similar to that of the difference spectrum constructed by subtracting the absorption spectra observed for the components of the couple from each other. For the other couple (Fe(II)/Fe(III)TSPc) also, a similarity exists between the electroreflectance spectrum and the constructed difference spectrum in acidic electrolyte. However, there is hardly any resemblance in alkaline solution, indicating that in this electrolyte the surface has a greater influence on the adsorbed complex than in acidic solution. The importance of these observations with respect to the reduction of dioxygen is discussed. © 1990.