Orientational decay in poled second-order nonlinear optical guest-host polymers : temperature dependence and effects of poling geometry

The orientational decay of chemically and thermally stable high-temperature chromophores doped into thin films made from polyimides and a variety of other polymeric hosts has been investigated. The chromophores are aligned using electric field poling and second-harmonic generation (SHG) is used to probe the decay of the electric field poling induced alignment. The decay rate of the SHG signal from films poled using both a corona discharge and side-by-side in-plane electrodes was measured. When electrodes are chosen so that the effects of charge injection are minimized, little difference has been observed between the orientational decays from films poled using the two methods for either an amorphous preimidized polyimide host or a highly anisotropic film poled during imidization. The films imidized during poling showed significant orientational stability at 250 °C for over 15 h after a fast initial partial decay. In addition, the decay of the SHG signal was measured as a function of temperature below the glass transition in a wide variety of different polymer host systems. The temperature dependence of the decay was found to be non-Arrhenius, but could be strongly correlated with the glass transition temperature of the guest-host system using an empirical relationship similar to the Williams–Landel–Ferry or Vogel–Tamann–Fulcher equation.