Characterizing and Circumventing Intermolecular Electrostatic Interactions in Highly Electro-Optic Polymers
- PDF / 475,880 Bytes
- 11 Pages / 414.72 x 648 pts Page_size
- 111 Downloads / 200 Views
Abstract In general, polymers possessing non-resonant electro-optic activities exceeding 20 pm/V require chromophores with strong electron withdrawing groups (cyanovinyls, carbon acid moieties, etc.) as well as highly polarizable bridges. Although much progress has been made on designing and preparing materials with molecular "electrooptic" activities, their incorporation into polymers to show comparably large bulk electro-optic activities has been met with little success. We report here the mature of the difficulty of the translation of microscopic to macroscopic electro-optic activity. The optimization of molecular activity increases intermolecular electrostatic interactions between chromophores, and these interactions impede induction of polar acentric order in the polymers. Theoretical analysis of the problem is presented, as well as one example of a material that is designed to circumvent these interactions. The resulting material possesses electro-optic coefficients as high as 29 pm/V and optical losses as low as 1.5 dB/cm.
Introduction For many electro-optic devices to reach commercial viability, their drive voltages (V,) must be in the digital range. This in turn necessitates electro-optic coefficients on the order of 30 pm/V for organic polymeric materials. It is generally regarded that conventional electrooptic chromophores such as stilbene and azobenzene type chromophores possess insufficiently large molecular first hyperpolarizabilities to achieve this goal. In recent years tremendous progress has been made in optimizing the nonlinear optical response of organic molecules for electro-optic application, such that when incorporated into polymers in identical manner as with conventional materials electro-optic coefficients far exceeding 30 pm/V may be expected.(]) Unfortunately, incorporation of these chromophores into polymers to show the expected large electro-optic responses have been generally met with disappointingly poor results. We have recently shown that this is primarily due to 199
Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
intermolecular electrostatic interactions between chromophores.(2) In this communication we report our recent progress in the theoretical understanding of this phenomenon, its effect on the poling behavior of chromophores, and present results on a representative material that has been designed to circumvent these interactions.
Experimental General. The polymer DH-TCV chromophore was prepared as shown in figure 1. The thermosetting polyurethanes were prepared as shown in figure 2. Full details of the synthesis of the chromophore and polymer will be published elsewhere. Optical spectra were obtained from a Perkin-Elmer Lambda-4C UV-Vis spectrophotometer or a Hitachi U-
2000 spectrophotometer. Dipole moments were calculated from the concentration dependence of dielectric constant of solutions containing the chromophores, where 1,4dioxane was used as the solvent and dielectric constants were measured at 100 kHz. Ionization potentials were estimated
Data Loading...
