ELECTRIC-FIELD-INDUCED POLARIZATION CURRENT STUDIES IN GUEST-HOST POLYMERS

We apply polarization current measurements to study dipole reorientati on of nonlinear chromophores that are embedded in a polymer matrix. In particular, we apply a step voltage to a thin film of poly(methyl met hacrylate) that is doped with a well-known dipolar chromophore, Disper se Red 1, or an apparently centrosymmetric squarylium chromophore, and measure the isothermal temporal behavior of the current at several te mperatures. By correlating the current with electric-field-induced sec ond-harmonic generation, we find that at very early times, polarizatio n current dominates, while at later times, charge hopping mechanisms p robably dominate. For the centrosymmetric squarylium chromophore dopan t, we find an early-time current suggesting polarization decay with no corresponding second-harmonic signal. This suggests that the squaryli um molecule has a dipole moment that is perpendicular to the dominant axis of the polarizability tenser and is consistent with the presence of the cis isomer. A time-temperature-voltage complimentarity relation ship is also observed.