Study On Orientation Correlation Strength Of Nitroaniline Molecules Using Hyper-rayleigh Scattering

Hyper-Rayleigh scattering(HRS) possesses remarkable advantages such as compact experimental apparatus, convenient operation and null external electric field. Combining with quantum chemical calculation, HRS is widely applied in the characterization of second-order nonlinear optical property of organic materials; surface effects of nanometer particle and ion detection, etc. At present, HRS, as an alternative of electric field-induced harmonic method, has been becoming a mainstream to study the second-order nonlinear properties of the materials. On the basis of the theory of depolarized Hyper Rayleigh scattering, the primary aim of this thesis is to construct the relevant experimental apparatus, as well as explore the influences of solvent effect,substituent group and strength of orientation correlation on the first-order hyperpolarizability accompanying with quantum chemistry calculation.Based on quantum chemistry calculation, we calculate the first-order hyperpolarizability, the gap between electron highest occupied orbital(HOMO) and electric lowest unoccupied orbital(LUMO), as well as the electron cloud distribution of para-nitroaniline molecule in different solvents. Under such a circumstance, the effects of the solvents on both the charge distribution of solute and the first-order hyperpolarizability are analyzed. Our findings indicate, in contrast to the reported data in the literature, that the uniform variation tendency is presented for the first-order hyperpolarizability of para-nitroaniline calculated by quantum chemistry calculation method, which can provide guidance for choosing suitable solvents to measure the first-order hyperpolarizability of molecule.According to the proposed theoretical model, we successfully set up the depolarized Hyper-Rayleigh scattering experimental configuration. By selecting dimethyl sulfoxide as desirable solvent, the stability of the measurement system is verified by examining the para-nitroaniline’s first-order hyperpolarizability and dependence of scattering rays on polarization. By means of the well-behaved and robust experimental setup, we detect the variations on the first-order hyperpolarizability of the para-nitroaniline whose H atoms at the ortho position to the NH2 is replaced by disparate substituents. In addition, the first-order hyperpolarizability and molecules’ frontier electron orbital of a series of molecules in terms of quantum chemistry calculation method, researches the influences of substituent group on the first-order hyperpolarizability.In view of the developed mechanism of the Hyper-Rayleigh scattering, the interaction potential between induced dipoles is derived. The strengths on orientated correlation of dipole between solute molecules are related to not only the distance between the solute molecules, but also the orientation arrangement of the induced dipole. The vertical and horizontal polarized components of Hyper-Rayleigh scattering light is measured to calculate the depolarization ratio of solute molecules at different concentrations. By dissecting both the first-order hyperpolarizability and depolarization as a function of the concentration of solute molecular, the correlated strength as varying concentration, and the impact of substituent group on first-order hyperpolarizability and local symmetry are extracted respectively. We further evaluate the displacement of intensive orientation correlation between induced molecular dipoles by analyzing the depolarization ratio with alteration of solute molecular concentrations.