Preparation And Characterizations Of Second-Order Nonlinear Optical Polymeric Film Materials

Recently, various novel and high performance second-order nonlinear optical (NLO) organic polymer materials, owing to their wide application in electro-optical (E-O) modulated devices and advantages superior to inorganic materials, have been prepared and investigated by numerous scientists. It is still considered to be a challenge for researchers to prepare novel polymer lattices with macroscopically non-centrosymmetric structure and in which chromophoric dipolar molecules arranged with orientation. We can define three general approaches to achieving noncentrosymmetric lattices of nonlinear optical chromophores: electric-field poling technique, Langmuir-Blodgett film technique and Layer-by-Lay (LBL) assembly technique. However, the insufficient temporal or mechanical instability shortcomings of NLO LB film materials made by Langmuir-Blodgett film technique restricted their potential applications. Poled polymer materials and NLO assembly film materials offer potential advantages for device application. How to improve the stability, designable and consistent orientation of the materials are the key problems of our reseach. optical sensing, and telecommunications. Simultaneity,inorganic-organic hybrid materials have been developed,the NLO chromophores are incorporated into the inorganic matrix by one or more covalent bonds. These hybrid materials capitalize on the unique properties offered by the two components to generate novel materials with desired characteristics, therefore, they are considered as promising candidate for NLO device applications and have been the subject of NLO materials research. The theory and development of these types of NLO polymer film materials have been reviewed in chapter 1. In this dissertation, we improved the stability of the assembled films by the silicon oxygen meshwork and the photo-cross-linked structure. Inorganic-organic hybrid second-order nonlinear optical multilayer films with photo-cross-linkable structure were fabricated by electric-field-induced layer-by-layer assembly technique. In another, using the sol-gel process and the photo-cross-linked reaction, we have fabricated the photo-cross-linked organic-inorganic hybrid poled second-order NLO films at room temperature.In chapter 2, we have successfully synthesized a new stable chromophore molecule 2-({4-[4-(2-carboxy-2-cyano-vinyl)-phenylazo] -z -phenyl}-methyl -amino)-ethyl acid (DRCB) with high thermal stability, which possesses two negative groups at both ends and still retains the molecular polarity after ionization. The DRCB molecule was assembled with polycationic DAR by electric field-induced Layer-by-Layer assembly technique to fabricate organic second-order NLO multilayer films. Due to the dc electric field effect in assemble processes, in addition to introducing the stable chromophore molecule and the covalently cross-linking structure in the films, the second-order NLO films fabricated in this method have large SHG response, good thermal stability and excellent chemical stability, which offer potential advantages for device application. we had demonstrated that by using the electric-field-induced LbL assembly technique, high stable photo-crosslinked second-order NLO multilayer films could be fabricated on nonconductive substrate materials, for instance using PAA as cladding layer. The PAA supported second-order NLO films are important electro-optical materials.In chapter 3, we have successfully synthesized a novel aromatic diazo groups linked silicon sol (ADS). Inorganic-organic hybrid second-order NLO multilayer films with photo-cross-linkable structure were fabricated with ADS and LMWC molecule by electric-field-induced layer-by-layer assembly technique. Due to introducing the silica oxygen network and the covalently cross-linking structure in the films, in addition to using dc electric field in assemble processes, the second-order NLO films fabricated in this method exhibited high SHG response, good thermal stability and excellent chemical stability. Thus, they should be good candidates for practical electro-photonic applications.In chapter 4, A simple diazo chromophore and"T"type structural alkoxysilane dye have been synthesized. Their structures were verified by FT-IR, UV-vis spectra and 1H-NMR. Followed by a hydrolysis and copolymerization process of the alkoxysilane withγ-glycidoxypropyl trimethoxysilane (KH560) and tetraeth- oxysilane (TEOS), high quality of inorganic-organic hybrid second-order NLO films were obtained by spin-coating. The"T"type structure of the alkoxysilane was found to be effective for improving the temporal stability of the optical nonlinearity, due to the reduction of the relaxation of the chromophore in the film materials. In another, a photo-cross-linked stable organic-inorganic hybrid second-order NLO film was fabricated by sol-gel process with ADS and DRCB. The films were poled under 50 dc voltage electric field at room temperature at the existence of solvents. After the solvents volatilized completely and upon UV irradiation under the electric field, the ionic bonds converted to stable covalent bonds in the system, the orientations of the chromophores were fixed by the photo-cross-linked structures. The order parameter of the fabricated film can retain 99 % after 17 days at room temperature. The stable organic-inorganic hybrid photo-cross-linked NLO films fabricated in this paper had large potential to be applied in electric-optic devices.