In situ ESR-UV-Vis-NIR spectroelectrochemical study of the p-doping of poly[2-(3-thienyl)ethyl acetate] and its hydrolyzed derivatives

The electrochemical oxidation of the chemically prepared polymer poly[2-(3-thienyl)ethyl acetate] (PTEtAc), its partially hydrolyzed derivative PTEtAcOH and the fully hydrolyzed compound poly[2-(3-thienyl)ethanol] (PTEtOH) was studied by in situ electron spin resonance (ESR)/UV-Vis-NIR spectroelectrochemistry. The spectroelectrochemical response of these films on ITO substrates was analyzed with respect to the influence of the functionalized alkyl side chain on polymer doping. The simultaneous use of both electron spin resonance and UV-Vis-NIR spectroscopy allows the analysis of the nature, extent and stability of the charge carriers electrogenerated during p-doping. It was found that PTEtAc has a higher capacity for charged species due to the flexibility of the longer side chains making the redox states more stable at different doping levels. At low doping levels the charged states are dominated by polaronic species while at high doping levels bipolarons and diamagnetic polaron pairs are formed. The presence of the OH groups in the polymer side chains of the hydrolyzed derivatives favors hydrogen bonds. These interactions by hydrogen bonding fix the conjugated chains thus making a charge–discharge reaction more difficult. At high doping levels the hydrolyzed polymers favor the formation of polaron pairs.