Ultrafast Ootical Nonlinearities And Dynamics Of Heterocyclic Compounds Containing Benzothiazole

Organic nonlinear optical materials have great potential in nonlinear optics due to their low cost,structure flexibility,large nonlinear polarizability and fast response speed.The nonlinear response and photophysical properties of the organic materials are directly related to their molecular structures.Benzothiazole,as a chromophore containing heterocycle,is often used to design nonlinear materials since the high nonlinear hyperpolarizability,chemical and thermal stabilities it possesses.However,to the best of our knowledge,previous studies are mainly focused on the chemical synthesis,theoretical study and second-order nonlinear optical properties,the third-order optical nonlinear properties and ultrafast dynamics are rarely studied systematically.In this dissertation,the ultrafast nonlinear absorption and photo-physical mechanism of a series of benzothiazole derivatives with different structures are investigated using ultrafast tunable laser source and advanced measurement techniques.The relations between the molecular structure and the optical nonlinear response are established.The research contains several aspects:The third-order nonlinear optical properties and ultrafast excited-state dynamics of benzothiazolium salts are studied under different time regimes.Significant nonlinear optical parameters of these two molecules are obtained by z-scan technique.Dynamics analysis for the variations of nonlinear optical response in different time regimes and determination of key parameters are performed via transient absorption experiments.A comparative study on broadband nonlinear optical properties and transient dynamic analysis of a neutral benzothiazole derivative with its corresponding benzothiazolium salt is conducted.Z-scan measurements and transient absorption spectroscopy with 190 fs and 15 ps laser pulses are employed in the research.In addition,the impacts from different solvents are also investigated.A series of benzothiazole derivatives with different substituents attached to the benzothiazole groups are designed and synthesized.The influence of the substituent on linear absorption,fluorescence emission,nonlinear absorption and excited-states dynamics are investigated,Revealing the broadband reverse saturable absorption and excellent optical limiting performance in this material.The optical nonlinear absorption and refraction of a benzothiazolium salt containing thiophene are studied.Z-scan results show large figure of merits,indicating the sample a good all-optical switching material.The excited state absorption and refraction mechanism is investigated via time-solved pump probe technique with a phase object,Consistent fast response rates of nonlinear absorption and refraction confirmed that the sample has excellent properties for all-optical switching.The influence of multiple heterocycle on molecular nonlinear properties are studied.