TDDFT Study Of Intermolecular Hydrogen Bond,Intramolecular Hydrogen Bond And Their Interaction Of Conjugated Organic Molecules

In recent years, the impact of intramolecular hydrogen bonds and intermolecular hydrogen bonds to the photochemical properties, especially their interaction to the excited state properties in experimental and theoretical research, has caused people’s extensive concern. Experimental study on the direct use of the spectrum or the other experimental methods, with IR, UV-Visible spectroscopy, HNMR spectroscopy and mass spectrometry data analysis and induction, look for the nature and change law of hydrogen bond in photochemistry. In addition to the above equilibrium structure hydrogen bonds research, the study of electronic excited state of ultrafast process gradually develops. With the rapid development of computer science and technology, the theoretical density functional theory calculations (DFT) and time-dependent density functional theory (TDDFT) is also widely applied to the study of hydrogen bonds, which provides a very valuable reference for the relevant scientists. Theoretical study can deeply explain the behavior and mechanism of electron excitation, predict and confirm the spectral phenomenon and give intuitive evidence for the type of excited states and the channels of transition etc., greatly compensating for the lack of experimental methods. It is very common for studying the excited state behavior to use theoretical methods.Study of intermolecular hydrogen bonds in the excited state has been widely reported, in particular for coumarin system formed hydrogen bonds with a small solvent molecule. However, the intramolecular hydrogen bonds properties in excited state, particularly for the influence of intermolecular hydrogen bonds to intramolecular hydrogen bonds properties in excited state, have not been reported. This article basing on the density functional theory and time-dependent density functional theory, using the Gaussian quantum chemistry calculation procedures, theoretical calculations were carried out for different molecular systems including the geometry structure studies, IR studies, excitation mechanism research and frontier molecular orbital analysis. In the first chapter, it mainly introduces photochemistry, electronic excited states and the concepts and the nature of hydrogen bonds. In the second chapter, it mainly gives the important mathematical model and theoretical derivation of density functional theory, the time-dependent density functional theory and a brief introduction of the Gaussian quantum chemistry calculation procedures. In the third chapter, it mainly investigates the properties of methyl salicylate intramolecular hydrogen bond in the excited state, points out its transition mode, transition main channel and charge transfer mechanism, and obtain the conclusion that hydrogen bond is strengthened upon photoexcitation by the geometry and infrared spectrum analysis. In the fourth chapter, it mainly introduces the intermolecular hydrogen bond properties of hydroxycoumarin-methylimidazole in the excited state, and derives a conclusion of Ï€â†'Ï€ transition mechanism by NBO charge analysis and quantitative analysis of the frontier molecular orbitals, improving the achievement of charge transfer mechanism by Mayer. In the fifth chapter, it mainly introduces the intermolecular hydrogen bond properties of methacycline-water in the excited state and its impact on the intramolecular hydrogen bond. Basing on the previous work, we focus on the fact that the formation of intermolecular hydrogen bonds can limit the intramolecular proton transferring upon photoexcitation. The intermolecular hydrogen bond has no significant effect on the excited-state properties.