Theoretical Studies Of New Nuclear-spin-induced Magneto-optical Effect And Etalloporphyrin Excited States

Nuclear magnetic resonance (NMR) is an important phenomenon that is applied in various fields, from structural characterization to medical imaging. Most NMR and MRI measurements use the traditional nuclear induction methods put forward sixty years ago. In2006, nuclear-spin-induced optical rotation (NSOR) was reported as a novel NMR signal detection method related to magneto-optical effect. In the NSOR, the plane of polarization of linearly polarized light is rotated by spin-polarized nuclei in an NMR sample. Based on Buckingham et al’s theory of antisymmetric polarizability and Faraday effect, we derived an analytical theoretical expression of nuclear-spin-induced optical Faraday rotation (NSOFR). Based on Buckingham and Pople’s theory of magnetic double refraction, we first proposed and theoretically researched a new Cotton-Mouton effect (IBCM) which is induced by the crossed effect between the high dc magnetic field Bo and the nuclear magnetic moment. These two new nuclear-spin-induced magneto-optical effects are closely related to the molecular structure and thus may be developed into new analytical techniques integrating NMR and optical spectroscopy. The metalloporphyrins have long been studied, but details about their excited state structures are still lack. In this thesis, density functional theory (DFT) calculations are used to study Jahn-Teller distortion of zinc-porphyrins in the excited states. The IBCM of porphyrins are also be studied by using DFT. This dissertation is divided into five chapters.Chapter1introduced the basic knowledge of NMR, molecular polarizability, magneto-optical effect and quantum chemistry computational methods. The research backgrounds and developments of nuclear-spin-induced magneto-optical effect and metalloporphyrins are presented in this chapter. The main content of this dissertation is introducd briefly.In Chapter2, based on the thought on the antisymmetric polarizability induced by nuclear magnetic moments and theory of the Faraday effect, an analytical theoretical expression is derived for the nuclear-spin-induced optical Faraday rotation (NSOFR) of diamagnetic saturated molecules in a circular cylinder. That consists of two parts,(?)(1)and(?)(B), induced by the intramolecular and intermolecular hyperfine interaction, respectively. By using them and the Verdet constants, NSOR for1H in water, hexane, cyclohexane and methyl-alcohol in liquid and H2gas have been calculated. The calculated NSOR for water agrees with the experiment and for three hydrocarbons predicts the same order of magnitude as water. For the samples studied (?)(1) and(?)(B) are comparable in magnitude. This part of the work was confirmed by recent experimental study and quantum chemical calculations.In Chapter3, based on Buckingham and Pople’s theory of magnetic double refraction, a theoretical expression is derived for a new Cotton-Mouton effect (IBCM) in liquid induced by the crossed effect between the high dc magnetic field Bo and the nuclear magnetic moment. It contains temperature-independent and-dependent parts. The latter is proportional to the product between anisotropy of polarizability and nuclear magnetic shielding tensor. For this new effect, its order in magnitude for a molecule with large polarizability anisotropy is estimated to be comparable to the nuclear-spin-induced optical Faraday rotation (NSOFR). In the multipass approach, IBCM can be eliminated by time-reversal symmetry arguments, but NSOFR is enhanced. In addition, we derived the expression of optical rotation when Faraday effect and Cotton-mouton effect exist at the same time.In Chapter4, density functional theory was used to calculate the new Cotton-Mouton effect (IBCM) of C6F6and a series of porphyrins. For conjugated molecules that have large polarizability anisotropy, the tempetature-dependent term almost determine the total new Cotton-Mouton effect. We calculate the frequency-dependent polarizability anisotropy and nuclear magnetic shielding anisotropy which are connected with the tempetature-dependent contribution to IBCM. The preferable methods and basis sets for IBCM calculation is tested out. The new effect of porphyrins is strong and comparable with NSOFR, so it may be detected by experiments. Besides, IBCM is found resonance enhanced when the incident light is in resonance with the excitation wavelength of the molecule.In Chapter5, we have studied the first singlet exciting state of Zinc-porphyrins (ZnP, ZnPc, ZnTAP, ZnTBP). It was discovered that Jahn-Teller distorted assuredly occur in the S1state. The stable rectangle geometries can transform to each other through B3g vibration mode of a diamond-like transition state. The dynamic Jahn-Teller effect (DJT) transition energy barriers increase with the degree of the distortion. The degree of distortion is related to configuration interaction. The J-T distortion in T1state is much stronger than the S1state, because of the absence of configuration interaction.