Abstract
Abstract Nonlinear optics is expected to play a significant role in the fields of optical information processing, optical sensor, and telecommunications. However, characteristic of materials are the critical points. As time goes on, variety materials were developed. Among them, organic polymers are considered the most promising materials because of their rapid responses, higher laser threshold, ease of processing, and flexibility in molecule designs.A novel one-dimension (1-D) stilbene chromophore was synthesized by a facile synthetic approach. By doping chromophores into a soluble polyimide, a series of guest-host nonlinear optical (NLO) polymer were obtained. The guest-host system has faster relaxation than side-chain, main-chain, and network systems because there are no covalent bonds between chromophores and polymer matrices. However, numerous reseach groups try to solve this problem and one of methods is to enlarge the volume of the chromophore. Indeed, the relaxations of the guest-host systems were retarded by increasing the rotational volume of the chromophore. Based on this concept, we choose sulfonyl groups that have larger size as electron acceptors. In addition, we also attach giant imide groups to the chromophores to enhance the stability of the dipole moment. We choose polyimide as polymer matrices because of its excellent mechanical properties, high glass transition temperature, low optical loss and so on. Furthermore, the polyimide we synthesize in this study is soluble in a variety of aprotic solvents. This vantage results in good compatibility between chromophores and matrixes. The thermal stability of the doping systems was measured using DSC and TGA, and it was observed that chromophores sublimates before it decomposed. This is because the existence of polymers reduces the interaction between chromophore itself. We also analyze nonlinear optical properties by measuring second harmonic intensity, and it was found that T0 value reaches 134℃ and possesses thousands of hours for τ value. At last, we discuss the importance of thermal annealing process to the doped system. The result shows that the sample doesn’t undergo thermal annealing process reveals more rapid relaxation. In addition to guest-host system, we also synthesize a second-order NLO polyimide and expected that covalent incorporation restrict the mobility of chromophore effectively. The polyimide-based NLO material was synthesized by the Mitsunobu reaction of poly(hydroxy-imide) with hydroxy-containing NLO chromophore. The primary advantage is that we can prepare pendant NLO material in a mild environment without damage of chromophore during the imidization process at a high ring-closure temperature. A glass transition temperature of 210℃ was observed for the polyimide-based material, which possess a d33 value (53pm/V measured at 1064nm) and exhibit high thermal stability(T0=203℃). Temporal stability was also measured. The d33 value has only 3% decay at 80℃ and remains well at elevated temperatures(retains 80% at 180℃ after 8 days).