Abstract: The electrochemical reduction of Basic Blue was investigated by means of thin-layer spectroelectrochemical technique at SnO₂ film optically transparent electrode.The nearly reversible redox peaks of basic blue were shown on the thin layer cyclic voltammogram.Spectroscopic experiment found the cis-trans-tautomerism and the color change effect of basic blue.In the presence of Oxygen, a new peak appears on the cyclic voltammogram and on the spectrum.It was supposed that the basic blue and the oxygen molecule can form a charge transfer complex.The formal potentials and the electron transfer numbers as well as the diffusion coefficient of basic blue were determined by means of thin-layer spectroelectrochemical technique.The possible electrode process was discussed on the basis of these measurements.

Key words: Basic blue, Thin-layer spectroelectrochemistry, Color change effect, Tautomerism, Charge transfer complex