Electron spin resonance and relaxation studies on conducting poly(tetrathiafulvalenes)

Abstract

Magnetic properties and the relaxation behavior of paramagnetic centers in various poly(tetrathiafulvalenes) with semiconductor properties have been studied by electron spin resonance (ESR) and electron spin echo (ESE) in the temperature range of 2 to 400 K. AT room temperature the iodine doped polymers have a DC conductivity between 10−9 S cm−1 and 10−4 S cm−1 that increases with temperature. The existence of two types of paragmagnetic centers is confirmed by ESR line shape simulation and by saturation experiments. The electron spin echo registration of ESR spectra and the measurement of relaxation times allow the separate study of the temperature dependence of the paramagnetic centers with relaxation times longer than 300 ns. The relations between the spin concentration and the conductivity of the samples are discussed by means of a model based on polarons, bipolarons, and trapped radicals.