Quantitative Analysis Of Liquid/air Interface Of Chiral Molecules Using Sum Frequency Generation Twin Polarization Angle Method

Recently, interface is becoming more and more important in the research and in-volving fields of chemistry, physics, material science, biology etc.. Due to the uniqueinterfacial sensitivity and interfacial specificity of the second-order nonlinear opticaltechniques, the applications of these techniques, such as Sum frequency generationand Second harmonic generation, are becoming more and more universal. The investi-gation of chiral interface is a key field of interfacial science. Comparing to the linearoptical methods such as CD, ROA, etc., the chiral response detected by second-orderoptical methods are much bigger and more sensitive to molecular structures, whichmakes second-order optical methods essential to the interfacial chirality detection andanalysis. In the past few years, our group have developed several analyzing methodsof second harmonic generation linear dichroism(SHG-LD). Using these methods, wecan obtain the susceptibility proportions, relative phases and interfacial refractive in-dexes, as well as the degree of chiral excess from chiral interfaces. In this thesis, weapplied the SHG-LD technique to study the chiral Langmuir monolayer composed ofachiral DiA molecules. Based on the analyze results from DiA langmuir monolayerunder various conditions, the substantial issues concerning magnetic dipole chiral con-tribution and the interfacial isotropic'fake'chiral contribution are elucidated. We alsodeveloped twin polarization angle method to characterize the chiral interface using sumfrequency generation technique analogously. The study on limonene liquid/air inter-face, demonstrated feasibility and accuracy of twin polarization angle method.The orgnization of this thesis is as follows:Chapter 1: The developments of interfacial science and the application of second-order nonlinear optics on interface researches are reviewed. The developments of thechiral detection on interface are also reviewed. The overview of this entire dissertationis provided.Chapter 2: The principle and basic functions of nonlinear optics, the methods of sum frequency generation detection and the relations between macroscopic suscepti-bilities and microscopic polarizabilities are introduced. The analyzing routines of SFGsuch as using polarization selection rules, changing the experimental conformations,using the Null angle method etc. are demonstrated.Chapter 3: The chiral detecting and analyzing methods of second harmonic gen-eration linear dichroism are introduced. The origins of interfacial chirality and dis-tinguishing methods of rotational"true"chirality and anisotropic"false"chirality areexplained. The investigation on the chiral responses from DiA Langmuir monolayerunder various conditions and the quantifies results of the DiA interfacial orientationangle and molecular abundance elucidate the chiral response origins of DiA Langmuirmonolayer.Chapter 4: The chiral detection method is extended to sum frequency genera-tion and the twin polarization angle(TPA) method is developed. The advantages ofTPA method is demonstrated by simulation results. The analyzing methods for rela-tive phases between susceptibilities are proposed and the experimental setups of TPAmethod are illustrated. The results of the chiral detection on limonene liquid/air inter-face demonstrates the applicability and accuracy of TPA method and analysing methodfor relative phases. Several experiential conclusions are also acquired from the experi-mental results.Chapter 5: Conclusions and perspective.