Effects of Molecular Rigidity on Electric Field Induced Alignment and Orientational Stability of Dipolar Chromophore Com
- PDF / 268,334 Bytes
- 7 Pages / 420.48 x 639 pts Page_size
- 85 Downloads / 216 Views
EFFECTS OF MOLECULAR RIGIDITY ON ELECTRIC FIELD INDUCED ALIGNMENT AND ORIENTATIONAL STABILITY OF DIPOLAR CHROMOPHORE COMPOSITES H.E. KATZ, M.L. SCHILLING, G. WASHINGTON, C.W. DIRK, W.R. HOLLAND, T. FANG, AND K.D. SINGER AT&T Bell Laboratories 1D-250, 600 Mountain Avenue, Murray Hill, NJ 07974 and Princeton, NJ 08540
ABSTRACT The relationship between the supramolecular conformational structure of assembled chromophores and their susceptibility to electric field poling is of interest for maximizing the bulk alignment achievable in an electro-optic material. We have employed solution phase dielectric constant measurements to investigate possible enhancements in dipolar susceptibility as a function of connectivity and state of aggregation in rationally synthesized chromophore assemblies, including conformationally defined head-to-tail oligomers. On the other hand, conformationally unrestricted, highly dipolar azo dyes behave as relatively isolated molecules even when present in supersaturated solutions and in close proximity on polymer chains.
INTRODUCTION The 4-amino-4'-(2,2-dicyanovinyl)azobenzene (DCV) chromophore has been utilized in the fabrication of polymeric materials with large, stable optical nonlinearities (1). These materials display larger second order nonlinear optical responses relative to corresponding nitro-substituted azo dye materials by virtue of the higher 13value associated with DCVsubstituted donor-acceptor compounds (2). In principle, it should also be possible to enhance the bulk hyperpolarizability by increasing the electric field orientability of the active moieties. This could be accomplished via designed molecular assembly in which individual chromophore dipole moments are additive (3). This would be in contrast to conformationally unrestricted aggregation in which dipole moments would tend to align antiparrallel and electric field poling would be less efficient. We have evaluated head-to-tail assemblies of cyanovinyl chromophores for enhanced orientability relative to individual chromophore moieties. These pseudodimeric and higher oligomeric chromophore chains are unique because they incorporate strongly electron donating and accepting groups in segments whose relative conformations are defined. Dipole moment measurements were carried out on the pseudodimers and on appropriate smaller model compounds. Enhancements in effective dipole moment were observed, and are in agreement with those predicted from x-ray crystallography of close analogues. According to preliminary
Mat. Res. Soc. Symp. Proc. Vol. 173. @1990 Materials Research Society
544
data, a tetrameric sample is sufficiently extended in a PMMA film to allow the fabrication via poling of an electro-optic and birefringent film. In order to explore the possibility of undesigned aggregation affecting the electric field orientability of a nonlinear optical chromophore, we first performed concentration-dependent dielectric measurements on liquid solutions containing DCV dyes. Data were obtained on both monomeric and polymeric DCV sol
Data Loading...
