ELECTROCHROMISM OF METHYLENE-BLUE ABSORBED ON THE BASAL-PLANE OF GRAPHITE

Reflectance measurements were obtained in situ of methylene blue films on a stress-annealed pyrolytic graphite electrode. The optical respon se in the charging region of the double layer was observed for p polar ization in the form of a small bipolar band at 690 nm, red shifted 0.0 8 eV with respect to the monomer species in solution. The band intensi ty was found to depend linearly on the modulation amplitude. On the co ntrary, only tiny changes in band shape and frequency with the bias po tential were detected. The average orientation of the adsorbed dye is discussed together with the role of the Stark effect as a likely band source.