Design, Synthesis And Properties Of Inorganic-Organic Hybrid Second Order Nonlinear Optical Materials

Over the past two decades, nonlinear optical (NLO) materials have been of great interest due to their potential applications in the fields of optical information processing, optical sensing, and telecommunications. Several chemical methodologies such as inorganic crystal, poled polymers and inorganic-organic hybrid materials have been developed. In the latter, 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.In this thesis, the basic theories of NLO and molecular design theory are briefly introduced, the research progress of second order NLO materials are also reviewed. Research significance and recent progress of inorganic-organic hybrid NLO materials are summarized in detail, based on which, the prospect is looked forward.Four kinds of azobenzene type chromophores which exhibited high transparency in the blue range are synthesized and further react with 3-isocyanatopropyl-triethoxysilane (ICTES) to give alkoxysilane dyes via a urethane reaction. Followed by a sol-gel process of the alkoxysilane dyes, the inorganic-organic hybrid nonlinear optical (NLO) films are successfully prepared. Molecular structures of the resultants are confirmed by elemental analysis, FTIR and ¹H-NMR. The β_CDμ_g values of the chromophores are evaluated by solvatochromic method and the second harmonic coefficients (d₃₃) of the hybrid films are measured by in situ second harmonic generation (SHG) measurement, respectively. The effects of substituent group and position on β_CDμ_g values of thechromophores and J33 values of the films are discussed. The hybrid films exhibited large optical nonlinearity (J33 is 14.3 pm/V) and full transparency in the visible range, which imply that these films are hopeful for laser frequency-doubling in blue range.To meet the thermal stability requirement for electro-optic device application, a new inorganic-organic hybrid second-order NLO films is successfully prepared from a heterocycle chromophore containing benzothiazole unit. Molecular structures of the resultant are confirmed by elemental analysis, FTIR, UV-visible spectra and 'H-NMR. The largest da value of the poled film is 72.1 pm/V. This film exhibits excellent thermal stability of dipole alignment at elevated temperature. The SHG signal of the film has an onset temperature around 160 °C and a half-decay temperature at 215 °C. The (I33 value remains at 94% of its initial value after heating at 120 °C for 6 h.Two kinds of chromophores containing di-hydroxyethyl group are designed and synthesized, based on which, the cross-linked hybrid films are prepared. The da values of these films are 32.5 and 53.4 pm/V, respectively. After heating at 100 °C for 30 min, no obvious decay of the da value is observed, and after heating at 160 °C for 30 min, the d33 value remains at 74% of its initial value.A series of inorganic-organic hybrid films with different matrix are prepared by using TEOS, VTES and AMTES as precursors. The d33 values of the hybrid films increase with augmenting chromophore content, the largest chromophore content is 50 mol%, and the corresponding d^ value is 74.5 pm/V. The precursor AMTES is found to be effective for improving the thermal stability of optical nonlinearity due to the formation of hydrogen bonds between the carbonyl and aniline group, which is confirmed by virtue of FTIR and UV-Visible spectra.The poling process of the inorganic-organic hybrid film is investigated by in situ SHG measurement. An effective chromophore model was proposed to explain the change of SHG intensity in poling process. The structure and morphology of the hybrid film before and after poling are characterized by FTIR and SEM. The influence of poling temperature, poling voltage and poling time on SHG intensity and thermal stability are studied in detail. Based on the dipole model, the relation between polingvoltage and SHG intensity is obtained, which is in good agreement with the experimental results.