The Electrochemical Ageing of Poly(o-Toluidine) Studied by Fluorescence Spectroscopy

M. I. FLORIT; W. A. MARMISOLLÉ; D. POSADAS

Sevilla, España

Congreso; 59th Annual Meeting of the International Society of Electrochemistry; 2008

International Society of Electrochemistry

Conducting polymers such as Polypyrrole, Poly(aniline) and Poly(thiophene) shows a phenomenon of ageing after electrochemical reduction. This phenomenon is similar to that of physical ageing found in all amorphous materials and may also be related to the conformational changes in proteins brought about by electron transfer reactions. Electrochemical ageing has been studied by different techniques such as volume changes, voltammetry, UV-vis spectroscopy and electron paramagnetic resonance. In this work we studied the changes in the fluorescence spectra of poly(o-toluidine) (POT) in acid aqueous media, during the electrochemical ageing. POT films were electrosynthesized on the gold electrodes by cycling the potential between -0.1V and 0.8V vs. SCE in 0.5M toluidine and 3.7M H2SO4 solution. The experimental set up for the electrochemical fluorescence mesurements consisted of the following items. The electrochemical cell was a square quartz fluorescence cell of one centimeter. The working electrode was a gold plate (1.0 by 1,4 cm) arranged in the diagonal of the cell. The auxiliar electrode was a platinum wire and a Saturated Calomel Electrode (SCE) was employed as the reference electrode. The fluorescence spectra were taken with a Perkin Elmer LS 50B Model Luminiscence Spectrometer. The excitation radiation was 315 nm and the spectra were recorded in the range 325nm < ë< 600nm. Experiments with different polymer thicknesses and in different sulphuric acid concentrations were carried out. The fluorescence spectra of POT at different potentials in acid media were similar to those reported by previous workers. The ageing experiments were conducted as follows. After obtaining a stationary voltammetric profile, the potential was held at a value corresponding to the reduced state (E ≈ -0.2V vs. SCE) and the fluorescence spectra were recorded as a function of the waiting time, ta. As ta is increased all the band of the spectra between 350nm < ë < 450nm increase in intensity, particularly the peaks at about 374 and 425 nm. As with other ageing experiments the peak intensity shows a linear dependence with the logarithm of ta. These results can be interpreted by a self inhibitory Elovich type of kinetics where the activation energy depends linearly on the extent of the process.