Design And Synthesis Of Electro-optic Chromophores And Their Dendritic Modification

In 21th century, organic nonlinear materials have been fully studied for their great potential application in electro-optic (EO) fields. Recently, the studies of organic EO materials are focused on the following aspects: 1) optimizing the properties of the EO materials; 2) design and synthesis of dendritic materials; 3) resolving physical and chemical problems in EO devices fabrication, such as selecting cladding materials, matching solubility, electric resistance and refractive index between the cladding layer and core layer, improving poling efficiency and eliminating film defects.According to the key project titled"Study on Reflective-Polymer-Waveguide Electro-Optic Modulator and Relevant Devices", which were financially supported by National Natural Science Foundation of China, this paper focused on the design and synthesis of organic EO materials, and the EO materials designed and prepared are summarized as follows:A novel multiple chromophore-containing crosslinkable NLO dendrimer: D-1 (NLO-18);A crosslinking polymer prepared by side-chain dendritic polymer (Part A) and dendron-modified chromophore (Part B): P-1 (NLO-19);7 kinds of novel NLO chromophores based on diazo-thiophene: NLO-1~NLO-5, NLO-12, NLO-14;10 kinds of novel single and multiple dendron-modified NLO chromophores: NlO-6~NLO-11, NLO-13, NLO-15~NLO-17;2 kinds of NLO active organic-inorganic hybrid materials: P-2 (NLO-20) and P-3 (NLO-21). There are 21 materials have been designed and synthesized, among which 18 kinds are never reported. The structure of the materials is detailed in the attached sheets.1. Design and synthesis of multiple chromophore-containing crosslinkable NLO dendrimer D-1 (NLO-18)This dendrimer was constructed using a trihydroxyphenyl ethane as the central core and crosslinkable trifluorovinylether-containing chromophores as the exterior moieties. The diazo chromophore with high molecular first order hyperpolarizability was designed and synthesized in our own laboratory. In order to improve the photo-stability of the material, diazo bonds instead of C=C bonds were used in the conjugating molecule. The preparation and purification of the dendritic moieties containing trifluorovinylether groups were somehow difficult work. The preparation schedule of the dendrimer is new and the obtained material (D-1) exhibits high-temperature stability (Td-243℃), perfect solubility and low optical loss.2. Design and preparation of A-B type crosslinking polymer containing quasi-dendrimer chromophore P-1(NLO-19)Part A (polymer 1) was prepared by the reaction of DTFVA and poly (4-vinylphenol), and part B (NLO-16) was dendron modified EO chromophore. The EO crosslinking polymer was prepared by poling and curing the Part A and Part B, both of which were modified by crosslinkable dendrons containing trifluorovinylether groups. This process is similar to that of crosslinking polymers which has long-term alignment stability. The method is simple and feasible, and many other high performance EO polymers will be obtained by changing the chromophores (Part B).3. Design and synthesis of novel EO chromophores based on diazo-thiophene (NLO-1~NLO-5)Because of the complex structure of the chromophore based on diazo-thiophene, the yield of the final product was quite low, and it was a challenge to get enough materials for property studies and device fabrication. In order to solve this problem, the synthesis chemistry of the chromophores has been fully studied, and the procedure were simplified and optimized. As a result, the total yields of the 6 key steps were promoted 5 times, and enough amounts of EO materials were obtained easily and efficiently. Thermal tests indicate that the diazo-based chromophores possess high decomposition temperatures of 220-230℃, and EO coefficient of chromophores doped polymer films is about 17 pm/V at 1315 nm. These results indicate that the chromophores are promising candidates for EO devices applications.4. Design and synthesis of novel single or multiple dendron-modified EO chromophores (NLO-6~NLO-17)Crosslinkable or bulky dendrons attached to the chromophores were designed and synthesized. In molecule design, alkyloxy groups instead of alkyl groups were introduced to the thiophene spacers to improve the photo-stability of the chromophores, and hydroxyl groups as dendron forming site were introduced to the ends of substituents of the thiophene spacers. In preparation, a new reaction to convert THP protective group of the hydroxy group to acetyl protective group was found. The results indicate that the introduction of the dendrons improved the solubility and stability (Td-290℃).5. Design and preparation of the organic-inorganic hybrid materials with EO activity (P-2 (NLO-20) and P-3 (NLO-21))We report an alternative approach based on post-function to prepare EO active organic-inorganic composites, in which the NLO prepolymer were prepared by post-diazo coupling reaction, and the crosslinking hybrid materials were obtained by poling and curing of the prepolymer films. There are several advantages as follows: 1) simple and reasonable, high yield and mild reaction condition; 2) excellent solubility of the prepolymer; 3) perfect film formability; 4) great freedom and flexibility for synthetically tailoring.