The signal intensity gradually increased with the doping time, indicating increase of spin concentration with doping time. However, g-value and peak width also increased with doping. Neugebauer et al. reported occurrence of strong charge carrier localization with doping confirmed with IR spectroscopic and electrochemical analysis for PITN-methine. The increase of the peak width in the ESR measurements indicates that charge carriers (polarons (radical cations) and bipolarons (dications)) generated by the iodine doping may be localized.