Ultrafast Nonlinear Absorption Dynamics Of Benzothiazolate Derivatives

The rapid development of nonlinear optics(NLO)is closely related from the support of nonlinear optical materials,much efforts has been made to optimize the properties of NLO materials.Benzothiazolates are kinds of novel nonlinear optical materials which have potential in applications such as displaying,illumin ating,and dye-sensitized solar cells.Here in this thesis,three different benzothiazolate molecules were investigated.The frontier orbital possession percentage of each group in molecule is calculated via density functional theory(DFT).It is observed that carbazole-based benzothiazolate has the strongest intramolecular charge transfer compared to the other benzothiazolates.The ultrafast nonlinear optics response of three different benzothiazolate are investigated by multi-wavelengths Z-scan,reverse saturable absorption is observed in a wide spectral range from 650 nm to 800 nm.The mechanism of nonlinear absorption in three sample is considered to originat from two-photon absorption and two-photon induced excited-state absorption.The NLO response of three different benzothiazolate is found to be different at 532 nm.The transformation of nonlinear absorption in double benzene-base benzothiazolate is observed.Via femtosecond pump-probe at 515 nm,the origin of this transformation is discussed.The ultrafast excited-state dynamics of three different benzothiazolate are investigated via picosecond pump-probe measurement and femtosecond transient absorption spectra.The excited-state absorption cross section and lifetime of three sample are extracted via the fiiting of Z-scan data and the numerically simulation of kinetic traces based on a simplified energy level model.In addition,the modulation of different benzothiazolate functional substituents on singlet excited-state lifetime of benzothiazolate derivatives is studied,indicating that they can be used as potential materials in nonlinear optical devices.