Enhancement of electrooptic coefficient of doped films through optimization of chromophore environment

The dependence of electrooptic (EO) coefficient on electronic properties of the host polymer and specific chromophore-host interactions were examined. The r(33) of 10 wt % Disperse Red 1 (DR1)- and 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)stryryl)-4H-pyran (DCM)-doped poly(2-vinyl pyridine) films (6.4 and 5.8 pm/V, respectively) was up to 70% larger than comparable poly(methyl methacyrlate)-doped films (3.7 and 3.9 pm/V, respectively) and as much as a factor of 12 larger than comparable polystyrene-doped films (0.5 and 0.4 pm/V, respectively). The variation in EO coefficient was addressed by quantifying the effects of resonance enhancement, local field factors, field responsivity of the host, and specific guest-host interactions. Resonance enhancement and local field effects account for 20-25% of this variation. In contrast, the largest variations in r33 were associated with specific chromophore-host and chromophore-choromphore interactions. These influence the molecular miscibility and thus alter the effective chromophore concentration-and therefore the EO coefficient. An ultimate EO coefficient of 15 pm/V for a 25 wt % DR1-P2VP system was obtained in which specific secondary interactions (hydrogen bonding) occur between chromophore and host. Additionally, synergy between chromophore and a field responsive host (P2VP) may facilitate chromophore orientation and subsequent stability. These results demonstrate the potential associated with modification of guest-host interactions in chromophore-doped polymer films for the development of highly nonlinear, stable EO materials.