Espectroscopia Raman por elipsometria aplicada a moléculas orgânicas

Abstract

In this work we show the potencial of the ellipsometric Raman spectroscopy technique (ERS) in obtaining additional information about the structures of various organic materials, complementary to other optical spectroscopy techniques, through the study of polarization of the scattered light. The ERS technique was developed in the material spectroscopy group and presented for the first time to the scientific community in an article by me and collaborators entitled "ellipsometric Raman spectroscopy" published in 2016. The ERS relates the polarization of scattered light by calculating Stokes parameters, with the structure of molecules. Through the Stokes parameters, several physical parametersare calculated, for example, degree of polarization (P) and asymmetry factor (g), the latter can be related to the Raman optical activity signal (ROA - short for Raman optical activity) which is used to characterize secondary protein structures. In the poly (methyl methacrylate) (PMMA), the polymer-solvent interaction in chloroform, tetrahydrofuran (THF) and toluene was analyzed. The ERS demonstrated that the solvents chloroform and THF interact with the polymeric matrix in an anisotropic manner, mainly with the methyl branch and toluene in an isotropic manner in the analyzed regions. In addition, she was able to identify the temperature relaxations 𝛾 and 𝛽 of the PMMA. In bovine serum albumin (BSA - short for bovine serum albumin), its structural conformation in changing the chemical environment from pH 2 to 12 was studied. In order to analyze this change, optical absorption, circular dichroism, photoluminescense, Raman scattering measurements were performed and tia total agreement of these resulta with the literature was verified. Through the ERS technique, as it is a technique capable of observing localized changes, it was observed that the aromatic amino acids rotate in relation to the main chain in a way that at more acidic pH they are unmasked from within the BSA structure and for more basic means they get more embedded in the protein. This is just one of the additional information removed by the ERS, in the text other surprising information will be addressed. The chiral conjugated polymer (1R, 2R) diaminocyclohexane, which is a new material in the literature and was studied in its polymeric form (named in this work by SW254) and in the form of oligomer (named in this job by SW203). For the optical characterization the most varied spectroscopic technique were used, among them, the circular excitation dichroism and the ERS. Among several relevant results, we highlight the ability to control the polarization of light through the excitation length and the asymmetry caused by exciton coupling between the benzene and stylbenzene groups. Dias e tão characteristics make (1R, 2R) diaminocyclohexane a promising material and can be used for the manufacture of metamaterials.