| 초록 |
We designed and synthesized photorefractive organic glasses which are composed of multifunctional photorefractive chromophore to provide photorefractivity in itself and bulky alkyl group to render it amorphous. Carbazole of multifunctional photorefractive chromophore played dual roles of photoconductor for the build-up of internal space charge field and electron-donor of nonlinear optical chromophore, and push-pull chemical structure induced electrooptic property for the modulation of refractive index. Obtained photorefractive organic glasses formed amorphous thick films with good optical quality despite of their low molar mass and showed photorefractivity through the measurement by two-beam coupling and four wave mixing. To investigate the relationship between charge carrier mobility and response time of grating build-up, we prepared two-component photorefractive materials with photorefractive organic glass and photoconductive organic glass. Response time of hole transporting materials was mainly determined by charge generation efficiency because of high carrier mobility, while that of bipolar materials showing electron mobility as well as hole mobility was affected by the competition between electron transport and hole transport. Since both the mobility and charge generation efficiency were related to highest occupied molecular orbital of materials, it is important to design considering molecular energy level. In addition, high glass transition photorefractive material was prepared by mixing with poly (vinyl carbazole) and photorefractive organic glass and it showed reliable stability toward phase separation and recrystallization due to their good miscibility. Through thermal fixing of chromophore alignment, we obtained the diffraction efficiency at room temperature and photorefractive grating was maintained for three days in dark state, which shows this material is a promising candidate for holographic data storage. |
