Correlation of electron spin concentration and conductivity in the ladder polymer BBL as a function of electrochemical potential

We present results of electron spin resonance (ESR) experiments on benzimidazobenzophenanthroline (BBL) samples in which the relative concentration of unpaired electrons was monitored as a function of electrochemical doping potential and the number of electrons per repeat unit (ERU). An increasing spin concentration along with increasing conductivity at low doping levels (less than 1/2 ERU) indicates that the conducting species have spin 1/2. An increasing spin concentration along with decreasing conductivity at intermediate doping levels (between 1/2 and 1 ERU) indicates that conduction in dry BBL involves a redox hopping process. The polymer has 2 ERU when fully doped.