Design,synthesis And Properties Of Third-order Nonlinear Optical Materials Of Azobenzene-carbazole

Inertial confinement fusion(ICF)experimental studies require measurement of the spatial distribution of scattered light.The spatial distribution of scattered light can be measured by polarization imaging technology based on optical Kerr effect.The third-order nonlinear optical materials with excellent performance are needed in the measuring optical path.Compared with inorganic nonlinear optical materials,organic polymer nonlinear optical materials have many advantages,such as large nonlinear coefficient,fast response,good molding process property,and can be designed at the molecular level in order to achieve the best performance.The nonlinear functional molecules generally have rigid skeleton and large polarity,stacking effect often leads to the insolubility of polymers.Therefore,host-guest doping technology is an effective method to prepare polymer nonlinear optical materials.Host-guest doped polymer nonlinear optical materials have the advantages of simple preparation and good processing performance,but the material's nonlinear optical properties need to be improved.In this paper,we designed and synthesized azobenzene-carbazole molecules.HMNAC/PMMA polymer third-order nonlinear optical materials were prepared by host-guest doping method.The main contents of this paper are as follows.The effects of basis set on calculation accuracy and time of(hyper)polarizability were studied based on sum-over-states method.The results showed that 2-zeta basis set is suitable for calculating the second-order hyperpolarizability y of molecules in large systems.The polarization functions of high angular momentum increase the calculation time and have limited influence on the calculation accuracy of the second-order hyperpolarizability y.The appropriate dispersion function is beneficial to improving the calculation accuracy of the second-order hyperpolarizability y.Specifically,aug-cc-PVDZ basis set is suitable for calculating the second-order hyperpolarizability y of molecules in large systems.The relationship between molecular structure and nonlinear optical properties was studied at the CAM-B3LYP/aug-cc-PVDZ level.The results showed that increasing the conjugation range of intramolecular delocalized ? electrons and push-pull electron groups are beneficial to enhancing the second-order hyperpolarizability y of molecules.Based on the relationship between molecular structure and properties,azobenzene-carbazole molecules were designed.The electron-hole density distribution studies showed that the nonlinear optical properties of azobenzene-carbazole molecules arise from charge transfer excitation and local excitation,but charge transfer excitation plays a leading role.Based on the designed azobenzene-carbazole molecules,the suitable synthetic route and synthetic method were selected to synthesize the target molecules.The third-order nonlinear optical properties of azobenzene-carbazole molecules were studied by Z-scan technique.HMNAC molecule exhibited excellent third-order nonlinear optical properties.In nanosecond time scale(4ns,532nm),HMNAC molecule exhibited self-defocusing,saturated and reverse saturated absorption properties,the second-order hyperpolarizability ? reaches 2.59 × 10-29esu,the figure of merits FOMs reaches 1.5.In femtosecond time scale(190fs,532nm),HMNAC molecule exhibited self-focusing,saturated and reverse saturated absorption properties,the second-order hyperpolarizability ? reaches 9.31 × 10-32esu,figure of merits FOMs reaches 0.4.HMNAC molecule has no molding process property,and it is difficult to integrate with semiconductor,which limits the application of HMNAC molecule as a nonlinear optical material.Therefore,HMNAC/PMMA polymer nonlinear optical materials were prepared by host-guest doping method.The transmittance,thermal stability and endothermic(exothermic)heat of the samples were studied by ultraviolet-visible absorption spectroscopy,Thermogravimetric Analysis and Differential Scanning Calorimetry respectively.The third-order nonlinear optical properties of samples were studied by means of nanosecond time scale(4ns,532nm)Z-scan technique.Samples showed a transition from saturated absorption to reverse saturated absorption,with the increase of HMNAC molecule concentration and light intensity.This phenomenon was explained by the five-level model.The self-defocusing property of the samples is attributed to the fact that refractive volum ?E of the excited state energy level is smaller than refractive volum ?0 of the ground state energy level.HMNAC/PMMA polymer nonlinear optical materials exhibited excellent third-order nonlinear optical properties.When the mass percentage of HMNAC is 0.15%,the third-order nonlinear optical susceptibility ?(3)of the sample reaches 1.48 × 10-10 esu.HMNAC/PMMA polymer third-order nonlinear optical material is expected to be applied in ICF optical diagnosis,low energy consumption and high contrast all-optical switch,optical communication and other fields.