Design, Synthesis And Nonlinear Optical Properties Of Hybrid Materials Based On Conjugated Polyenes

Optical telecommunications and public networking required high-speed optical-electrical data interconversion,which in turns drives a vast need for advanced,extremely efficient device components such as waveguides,switches,emitters and detectors.Development of nonlinear optical(NLO)materials has been of great interest due to their potential applications in the fields.The hybrid materials,which are composites on the nanometer scale,exhibit unique properties,enhanced performance.Therefore,they are considered as promising candidate for NLO device applications and have been the subject of NLO materials research.In this thesis, the recent progress in the field of second-order NLO polymers with specific focus on their characterization methods,molecular design theory,materials synthesis and chromophore orientation techniques are reviewed.Research significance and recent progress of inorganic-organic hybrid NLO materials are summarized in detail,based on which,the prospect is looked forward.A series of alkoxysiyl functionalized NLO precursor are synthesized and characterized in detailed.We also report the influence of structure modifications on the chemical and optical characterizations of hybrid sol-gel films.An in situ second-harmonic generation(SHG)measurement is established.The SHG is a coherent technique giving the fast,electronic in origin,second-order NLO susceptibility at a given,measurement frequency.A Y-cut quartz wedge is used as reference,and the interference fringes agree with theoretical prediction.The distributions of d₃₃on hybrid films on different substrates are also analyzed after corona poling.The measurement of NLO films on ITO substrates presents some advantages over normal glass substrates.These studies provide informative data to the optimization of the poling process.Two kinds of ring-locked isophorone type chromophore which exhibit high thermal stability are synthesized and further form alkoxysilane dyes via a urethane coupling reaction. The flash column chromatography was useful to purify alkoxysilane dyes,even those with low melting point.Followed by a sol-gel process of the alkoxysilane dyes,the hybrid NLO films are successfully prepared and characterized.Molecular structures of the resultants are confirmed by elemental analysis,FTIR and ¹H-NMR.The second harmonic coefficients(d₃₃) of the hybrid films are measured by in situ second harmonic generation(SHG)measurement. The hybrid films exhibited large optical nonlinearity(d₃₃is 46.3 pm/V).The effects of the substitution of the hydroxymethyl diphenylamino group for a hydroxyethyl methylamino group onβ_CTμ_g values of the chromophores,the dispersion of NLO molecules,d₃₃values and the temporal stabilities of the films are discussed.To meet the thermal stability requirement for electro-optic device application,a new hybrid second-order NLO films is successfully prepared from chromophore containing triphenylamino unit.Molecular structures of the resultant are confirmed in detailed.The variation of chromophoric structures on NLO properties was investigated,indicating that the cyano substitution on the vinylene bridge of chromophore would greatly enhance the temporal stability.The film poled at 200℃for 1h with cyano substitution exhibits excellent thermal stability of dipole alignment at elevated temperature.The d₃₃value of the film has an onset temperature around 115℃and a half-decay temperature at 145℃.This work provides a potential design strategy based on molecular engineering which would lead to more stable dipole orientation.But the incorporation of cyano group also lowered the d₃₃value of the film due to additional interaction.A NLO chromophore with strong tricyanofuran(TCF)acceptor and a triphenylamino molecule were synthesized and reacted with ICTES to form two functionalized silicon alkoxide precursors.A series of hybrid films with different matrix are prepared by using different precursors,eg.tetraalkoxysilane(TEOS)and 3-(trimethoxysilyl)propyl methacrylate(TSPM), etc.Thermal stabilities and aggregation behaviors of the NLO chromophores in hybrid films were studied by UV-Vis spectra.A high concentration of silane precursor with triphenylamine or methacrylate is used as spacing group,which are found useful to abate dipolar chromophore interactions and consequent aggregation problems.The triphenylamino precursor is found to be effective for improving the film formation ability due to the formation of Ph₃HN⁺(Si-O)^- unit, which is confirmed by virtue of FTIR.Second-order NLO properties and temporal stability of sol-gel films were also investigated by in situ SHG measurement.Hybrid films containing NLO active chromophores were prepared through the polyaddition of methacrylate and hydrolytic polycondensation of sila-functional alkoxy groups of TSPM which is capable of forming carbon-carbon and siloxane chains,respectively.The NLO-active chromophores are designed and synthesized to be covalently grafted to the carbon-carbon or the siioxane chains.The comparative study of the two different incorporation methods reveals that the poled hybrid film with NLO-active chromophores bonded to siloxane chains would possess a higher d₃₃value(81.3 pm/V)and a more stable dipolar orientation.The corresponding d₃₃values of the hybrid film with NLO-active chromophores bonded to carbon-carbon chains is 30.4 pm/V.Nonlinear optical properties such as fast response time and large third-order nonlinearity are essential for several current and future devices in optical computing,real time holography, optical correlators and phase conjugators.The origin of the third-order optical nonlinearity arises from nonlinear refraction and nonlinear adsorption.The Z-scan technique is a very important yet simple method for characterizing the optical nonlinearities.In order to study the optical nonlinearities of CS₂ and the dimethylformanide(DMF)solution of four stilbene derivates,the nonlinear absorption and the refraction coefficients were measured by using the single-beam Z-scan technique.In the Z-scan measurement,the 5 ns laser pulses at 532 nm wavelength were delivered.The thermal effect of the laser should be taken into consideration in this study.