<title>Enhancement of electro-optic coefficient of doped films through optimization of chromophore environment</title>

Abstract

Substantial enhancement of the electro-optic (EO) coefficient of NLO films through optimization of host properties and local chromophore environment is discussed. The EO coefficient was determined for common electro-optic chromophores disperse Red 1 (DR1) and 4-(dicyanomethylene)- 2-methyl-6-(4-dimethylaminostryl)-4H-pyran (DCM) doped in poly(styrene) (PS), poly(2-vinyl pyridine) (P2VP), poly(methyl methacrylate((PMMA), poly(cyclohexyl methacrylate), and styrene-methyl methacrylate copolymers. The r<SUB>33</SUB> varied as much as tow orders of magnitude in this series. Resonance enhancement and local field effects account for 20-25 percent of this variation. The remainder is attributed to intermolecular interactions. Electronic and IR spectroscopy revealed the presence of specific secondary interactions between chromophore-host and chromophore- chromophore. These influence the molecular miscibility and thus alter the effective chromophore concentration and therefore the EO coefficient. Additionally, synergy between the chromophore and a field-responsive host facilitates chromophore alignment. A combination of these effects observed in a DR1-P2VP system leads to an enhancement in r<SUB>33</SUB> by greater than 70 percent with respect to a comparable DR1-PMMA system. An ultimate EO coefficient of 15 pm/V for a 25 wt percent DR1-P2VP system was obtained. These results demonstrate the potential associated with modification of guest-host interactions for the development of highly nonlinear, stable EO polymer systems.