Charge carrier dynamics in pulse-irradiated polyphenylenevinylenes: Effects of broken conjugation, temperature, and accumulated dose

The transient conductivity resulting from nanosecond pulsed ionization of alkoxy-substituted phenylene-vinylene/ethylidene copolymers, ''dMOM-PPV(n)'', with n the fractional vinylene content, has been studied using the pulse radiolysis time-resolved microwave conductivity (PR-TRMC) technique. Minimum values of the sum of the charge carrier mobilities within the bulk solids, Sigma mu(min), have been estimated from the end-of-pulse conductivity. For the freshly precipitated materials at room temperature, Sigma mu(min) decreases gradually with decreasing n from 1.8 x 10(-7) m(2)/(V s) for n = 1 (full conjugation) to 0.4 x 10(-7) m(2)/(V s) for n = 0.57. After annealing dMOM-PPV(1) at 100 and 150 degrees C, Sigma mu(min) at room temperature increased to 3.2 x 10(-7) and 8.0 x 10(-7) m(2)/(V s), respectively. No significant effect of high-temperature annealing was found for n less than or equal to 0.87. On cooling dMOM-PPV(1) from 150 to -50 degrees C, Sigma mu(min) decreased initially with an activation energy of approximately 0.07 eV but approached a plateau at the lowest temperatures. The after-pulse decay of the conductivity was disperse in all cases. First half-lives of several microseconds were found for n = 1. The decay kinetics were independent of the dose in the pulse. Large accumulated radiation doses (up to 1.2 MJ/kg) did not effect the end-of-pulse conductivity but did increase the decay rate. This effect could be reversed by high-temperature annealing.