Study of magnetic and electrical properties of iodine doped pentacene

Doping of iodine to pentacene (PEN) has been previously reported to cause a drastic transformation from an insulator to a conductor, with conductivity increasing 10(10) times to 150 S cm(-1) at room temperature. ESR was measured at 9.3 GHz and 7.7 MHz over a wide temperature region from 300 to 0.05 K. An anomalous temperature dependence of the g shift was observed, with the g shift and line width showing a change of behavior around 240 K, while no abrupt change in the spin susceptibility or static susceptibility was observed around 240 K. The particular temperature dependence of the conductivity previously observed was attributed to be not due to a transition from a semiconductor to a metal, but it was indicated that relaxation is governed by Elliott's mechanism, with the orbital scattering time having a minimum at 240 K. (C) 1997 Elsevier Science S.A.