Theoretical Design And Experimental Preparation Of Ionic Organic Nonlinear Materials

As the carrier of nonlinear optics(NLO)from theory to practical applications,nonlinear optical materials have been highly attracted to date.Among them,organic nonlinear optical materials exhibit strong optical nonlinearity and high flexibility in molecular design,and have been widely applied in terahertz wave generation and detection,second harmonic generation imaging,and etc.Among them,ionic organic nonlinear materials have higher nonlinear properties than neutral molecules at the same molecular weight.Accordingly,two new organic ionic nonlinear optical materials,i.e.4-(4-dimethylaminostyryl)methylbenzothiazole 4-methylbenzenesulfonate(DABT)and 2-(4-hydroxystyryl)methylbenzothiazole mesitylene sulfonate(OHB-TMS),were designed and theoretically and experimentally investigated in this thesis.The main contents are as follows:(1)Material designs:two new organic ionic nonlinear optical materials,including 4-(4-dimethylaminostyryl)methylbenzothiazole 4-methylbenzenesulfonate(DABT)and 2-(4-hydroxystyryl)methylbenzothiazole mesitylene sulfonate(OHB-TMS),were designed.The first hyperpolarizability and other data of these two materials were theorecticaly simulated by first-principles calculations.Results revealed that the first hyperpolarizability of DABT is?_total=117×10^-30 esu,which is stronger than that of OHB-TMS(?_total=60×10^-30 esu)and close to that of the benchmark material DAST(?_total=136×10^-30 esu).Furthermore,the optical properties of DABT,such as the complex permittivity,absorptivity,reflectance,were also simulated,reevaling that the dielectric constant of DABT is lower than that of DAST,thus suggesting that higher terahertz wave generation efficiency might be detected from DABT.Moreover,DABT has the potential to become an Epsilon-near-zero(ENZ)material along the c-axis direction,suggesting great potential applications of DABT in metamaterials.(2)Material preparations:the DABT products were successfully synthesized and purified.And the DABT products were characterized by elemental analysis,high-resolution mass spectrometry,proton nuclear magnetic spectroscopy,and infrared spectroscopy.All the characterization results confirmed that the as-synthesized product was the designed DABT.Furthermore,based on the self-synthesized DABT products,DABT organic single crystals with a maximum size of 8×5×4 mm~3 have been successfully grown for the first time by a method combining the inclined plate and the solvent evaporation.(3)Performance mesurements:the nonlinear absorption of DABT was measured.Results indicated that DABT exhibits a typical saturable absorption effect.Moreover,the modulation depth of DABT solution is 40%,while the modulation depth of DABT thin film reaches 58%,both revealing that DABT is a new third-order nonlinear organic optical material with excellent performance.Thus,one can expect that the novel DABT holds potential applications in Q-switched laser or mode-locked laser.The absorption spectrum of DABT in the terahertz band was tested.The results show that DABT exhibits strong absorption at 1.25-4.25 THz,which is expected to be applied in the fields of light absorption layer of terahertz detectors.