Stability of reduced polypyrrole

Summary form only given. Electrochemically polymerized polypyrrole(PPy) shows changes in visible light spectrum on reduction revealing changes in electron states of the conjugated double bond. The reduced PPy is unstable to show changes in the visible light spectrum in less than one minute after cutting off applied potential. The absorption peak at 420 nm assigned as /spl pi/ - /spl pi//sup */ transition in the conjugated double bond shrinks fast to show a strong absorption around 800 nm assigned as bipolaron. When the reaction system is purged with nitrogen, the spectral changes slow down significantly to prove that oxygen accererates the structural changes in PPy. It is observed that the spectral changes slow down when hydroquinone is added to the system. The addition of hydroquinone in the system produces little polaron on oxidation of PPy and makes the polymer segments trun directly into bipolaron states. Hydroquinone is ionized in an aqueous system to produce proton which seems to stabilize free radicals in the polaron state. A decrease of pH in the system makes PPy become stable in repeated redox reaction while the polymer shows poor repeatability of cyclovoltammometry in the system with high pH. It is suggested that deprotonation of -NH in the pyrrole ring develops into production of an imine structure to loose the electrochemical reactivity.