Enhancement of electro-optic coefficient of doped films through optimization of chromophore environment

Substantial (>70%) enhancement of the electro-optic (EO) coefficient of NLO films through optimization of host properties and local chromophore environment is discussed. The EO coefficient (r(33)) was determined for common electrooptic 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(33) varied as much as two orders of magnitude in this series. Resonance enhancement and local field effects account for 20-25% of this variation. The remainder is attributed to intermolecular interactions. Electronic and infrared spectroscopy revealed the presence of specific secondary interactions (H-bonding) 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(33) by greater then 70% with respect to a comparable DR1-PMMA system. An ultimate EO coefficient of 15 pm/V for a 25wt% 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