Study of third-order optical non-linearity and electrical conductivity of sol-gel processed silica: poly(2-bromo-5-methoxy-p-phenylene vinylene) composite Chichang J. Wung, Kwang-Sup Lee and Paras N. Prasad* Photonics Research Laboratory. Department of Chemistry, State University of New York at Buffalo, Buffalo, NY 14214, USA and Jong-Chul Kim and Jung-II Jin Department of Chemistry, Korea University, Seoul 136-701, Korea and Hong-Ku Shim Department of Chemistry. Korea Advanced Institute of Science and Technology, Taejeon 305- 701, Korea (Received 29 November 1991; accepted 27 January 1992) A novel sol gel processed silica: poly(2-bromo-5-methoxy-p-phenylene vinylene)/silica composite was prepared using a soluble precursor. The optical properties of this material have been investigated using u.v.-visible and FTi.r. spectroscopy. The densification process was monitored by d.s.c, and t.g.a. The third-order non-linear susceptibility Z 13) has been investigated for both the pure polymer and its sol,el composite at 602 nm using femtosecond degenerate four-wave mixing. A relatively large ~(3) value with a subpicosecond response is observed. The electrical conductivities of AsF 5 doped polymer and composite films were studied using four-probe measurement. (Keywords: sol-gel; composite; poly(p-phenylene vinylene); non-linear optics) INTRODUCTION Recently the sol-gel process for making organic/inorganic composites has received significant attention from material scientists. Specifically, there has been increased interest in these materials as optical layers for advanced photonics applications. One of the most important material properties in photonics is the non-linear optical effect because of its importance for optical signal processing 1-4. Conjugated polymers containing extensive g-electron delocalization have emerged as an important class of third-order non-linear optical materials because of the large r~-electron contribution to the optical non-linearity 1. The non-linear optical response time for these materials has been shown to be in the subpicosecond region 1. The large optical non-linearity and the fast response time mean that conjugated polymer systems are of great importance in optical signal processing. Unfortunately, most organic polymers have generally not been found to be good photonic media due to high optical losses. Inorganic glasses, however, are excellent photonic media because of their high optical quality and extremely low optical losses. Therefore, combining inorganic glass and *To whom correspondenceshould be addressed organic polymer is one of the best ways to obtain materials with large non-linearity and low optical losses. Sol-gel methods have been actively studied as possibly superior routes for the preparation of ceramics, glasses and composites 5 v due to the potential advantages v lo and uniqueness of this process compared to conventional melt/sintering techniques. Since the sol-gel process involves the use of low viscosity solutions as the starting reagents, there are several clear advantages: (i) high degree of homogeneity, (ii) better control of stoichi- ometry; (iii) low processing temperature, (iv) less con- tamination and (v) ease of preparation of thin films. Generally speaking, the sol-gel composites can be made either by cogelation of monomers or oligomers with alkoxide or by impregnation in porous gels. Nevertheless, not all polymers can form a sol-gel composite by cogelation or impregnation with alkoxide. We have developed a new route for preparing optical quality composite by mixing the precursor polymer with the inorganic glass precursor and conversion to final polymer/silica composite by thermal treatment. This process is suitable when the polymer is processible through a suitable precursor polymer which can be dissolved together with the alkoxide in a common solvent without any phase separation or precipitation. 0032-3861/92/194145q37 ~ 1992 Butterworth-HeinemannLtd. POLYMER, 1992, Volume 33, Number 19 4145