Theoretical Investigation Of Charge Transfer Complex And Molecular Antisymmetric Polarizability

This dissertation is devoted to study of the basic properties of intermolecular charge transfer complexes including structures, binding energies and spectra. Meanwhile, some new problems related to the antisymmetric polarizability have been studied theoretically. The dissertation is divided to six chapters.Chapter 1 introduced the basic knowledge of charge transfer complex, quantum chemistry computational methods, Raman scattering and molecular polarizability, non-linear optics and hyperpolarizability. Atoms in Molecules theory and Natural Bond Orbital theory were briefly introduced. The research backgrounds and main contents of the dissertation were also presented in this chapter.Chapter 2 studied the structure and spectroscopy of imidazole (Im)-chloranil (CA) charge transfer complex. The UV-Vis spectra of the complex were measured in chloroform, and the stoichiometry of the Im-CA complex was determined as 1:1 by applying Benesi-Hildebrand's equation and Job's continuous variation method. DFT and MP2 calculations have been performed to study the possible stable structures and binding energies of the Im/CA complex. The calculations located four conformations (denoted as S1-S4). The bonding characteristics of these conformers have been investigated with NPA, AIM and NBO analysis. The electronic excitation energies of the complex (S1) were calculated with TDDFT, CIS(D) and CC2 methods, and observed UV-visible spectrum of the complex was analyzed based on the computed results.Chapter 3 studied the ground state structures and binding energies of the 2AP-DDQ charge transfer complex with DFT method. Optimization and frequency calculations located four possible conformations, denoted as S1, S2, S3 and S4. The bonding characteristics of these conformations have been investigated with NPA, AIM and NBO analysas. The electronic excitation energies of the complex (S2 and S3) were calculated with TDDFT, the results of theoretical calculations were consisted with experimentally observed UV-visible spectrum of the complex.Chapter 4 studied the structures and binding energies of the naphthalene-TCNQ and anthracene-TCNQ complexes with DFT method. The contribution of electron correlation to the binding energy was discussed. NPA and frontier orbital interaction were applied to investigate the quantity of charge transfer. AIM theory was applied to investigate the bonding characteristics of the two complexes. The aromatic criterions of the electron density at bond critical point and nucleus-independent chemical shift (NICS) were applied to investigate the aromaticity variations of the monomers and the complexes.Chapter 5 studied intensity relation between IR-UV doubly resonant sum-frequency vibrational spectra and antisymmetric resonant vibrational Raman scattering, and an approximate expression of their intensity ratio was given. Based on the intensity ratio expression and the related experimental data of IR and antisymmetric resonant vibrational Raman spectra, hypothetical DR-SFVS of ferrocytochrome c and HbO₂ have been sketched. The experimental investigation on IR-visible DR-SFVS of ferrocytochrome c and HbO₂ may be a test of the related theory.In Chapter 6, antisymmetric resonant vibrational transition polarizabilities for even-electron systems with the ground and excited vibronic states belonging to the real representations have been deduced to be zero under the adiabatic approximation by the time-reversal symmetry and group theory. Beyond the adiabatic approximation the non-adiabatic corrections to them are non-zero, particularly in the degenerate or near degenerate electronic states, such as Jahn-Teller and pseudo Jahn-Teller cases where adiabatic approximation breaks down. The conclusions agree with the experiments of antisymmetric vibrational Raman scattering. The compact expressions for the non-resonant and resonant antisymmetric transition polarizabilities are given in the Appendix.