Theoretical Study Of Photochromic Compounds About Pyrazolone Thiosemicarbazone

With the development of the computer technology, quantum chemistry calculation has become a powerful tool for exploring areas of chemistry by the experimental chemists. In this paper, in order to gain a deeper insight into the photochromic compounds, the photochromic mechanism and other properties of two photochromic compounds are investigated on the basis of previously experimental and theoretical work. Furthermore, the complexes of 2-pyridone have also been studied to extend the studies on the quantum chemistry calculations in our lab.Part 1 provides theoretically studies on the geometrical properties and the nature of hydrogen (H-) bonds of PMBP-TSC and PMBP-MTSC. The calculated results show that the electronic structure parameters of two geometries are almost identical. The geometrical difference could arise from the effects of steric hindrance within the molecule, which results in various H-bond modes and increasing the strength of H-bonds. Furthermore, AIM theory is applied to investigate the nature of various H-bonds. Good correlations between H-bond length and AIM parameters have been established, which indicates that the AIM parameters can well describe the H-bond strength of the title compounds and their derivatives.Part 2 is devoted to the photochromic mechanism of PMBP-TSC and PMBP-MTSC. The results, coming from the structure, the population of bonding and the relative stability, as well as the molecular electrostatic potential of the enol and keto forms, offer satisfactory basis for discussing the intermolecular proton transfer. The calculated results of the route between transition state and the equilibrium structures of 2-pyridone and the data derived from Li et al. [56] are applied to determine the reaction path. Part 3 mainly focuses on the coordinated property of PMBP-TSC. The calculated results, merging from the molecular energies, the charge distrubution, frontier orbitals and molecular electrostatic potential of the three isomers, gain a deeper insight into the relationship between the electronic structure and the coordinated properties. It is found that the O, N3, S atoms of the three molecules fit for coordination and the three isomers are sound tridentate ligands. In addition, keto and thiol forms act as aggressive coordinators as that of enol form. These findings are in good agreement with experimental results.Part 4 focuses on the structures and the nature of H-bonds as well as the corrections of six 2HP/2PY complexes. The results of several parameters on single-point CP correction of these complexes are compared against CP-optimized correction. To differentiate between normal H-bond and blue-shifting H-bond, AIM results suggest that it is necessary to supplement information concerning the changes in the X-H bonds. However, the information does not suffice to distinguish between weak normal H-bond and blue-shifting H-bond. NBO analysis reveals a slight decrease in the population of the contactingσ*C-H anti-bonding orbital as the primary reason of the C-H contraction. The correlation analysis shows that the parameters used for describing the properties of H-bonds are correlated and can be used to describe the H-bond strength.