Electrochromism of Octacyanophthalocyanine Thin Film. Investigation by Means of in situ Visible and Raman Spectroscopies

Abstract The electrochromism of an octacyanophthalocyanine (H2Pc(CN)8) thin film was investigated by in situ visible and Raman spectroscopies in acid and alkaline electrolytes. A new absorption band was observed in the range 700–900 nm of the visible spectra during a reduction of the film. The absorbance reached a constant value at 2 F mol−1 of the cathodic electricity in an alkaline electrolyte. The Raman spectra showed a spectral change in the vibration range which is attributed to the macrocycle and the isoindole moiety; hence, the reduction seems to occur in the azaporphyrin ring. From both the visible and Raman spectra, it was revealed that H2Pc(CN)8 was protonated at the nitrogens in positions 6,13,20,27 by electrochemical reduction. The protonated H2Pc(CN)8 shows absorption in the near-infrared region in both acid and alkaline electrolytes. The mechanism for the formation of protonated H2Pc(CN)8 is considered to be analogous to that of hydrogen evolution in alkaline electrolytes. Both the visible and Raman spectra were reversible during reoxidation.