The Theoretical Study Of The Intermolecular Hydrogen Bonding For Several Hydrogen Bonded Complex Systems

Hydrogen bonding widely exists in nature. It appears in many disciplines, so it has attracted more and more attention in recent years. Hydrogen bonding usually forms among molecules, sometimes among intramolecules. This kind of weak interaction is a little stronger than intermolecular forces, but weaker than the covalent and ionic bonds, while its stability is weaker than both the covalent and ionic bonds. Hydrogen bonding has a significant impact on the structure and property of the whole molecular system, especially on the photochemical behavior for a complex molecular system. But how does the hydrogen bonding affect the whole complex molecular system? This needs us to explore the impact of hydrogen bonding on ground state and excited state photochemistry in complex. Therefore, this thesis focuses on the role of the hydrogen bonding in the ground state and excited state.To get better understanding of the effects of hydrogen bonding on the molecular system, experimental and theoretical methods are employed to study the hydrogen bonding. Femtosecond time-resolved spectroscopy technology and time-dependent density functional theory (TDDFT) become the most widely-used method. TDDFT, a calculation method of quantum chemistry, is massively adopted, because it has the advantages of small amount of calculation and simple process.This thesis focuses on theoretical research on three different kinds of hydrogen bonding systems by applying the method of quantum chemistry, and further studies how hydrogen bonding affects the three systems in the ground state and excited states. For hydrogen bonding complexes formed by 9-hydroxy-9-fluorene carboxylic acid with some common solvent molecules (formic acid, acetic acid, propionic acid and formamide and water), density functional theory (DFT) and TDDFT are employed to optimize conformations and simulate spectra. By comparing the bond length of hydrogen bonds in the ground and excited states, we can draw a conclusion: in the excited state,intermolecular hydrogen bond C=O…H and intramolecular hydrogen bond 0-H…O strengthen, but intermolecular hydrogen bond O-H…O weakens. The infrared spectrum of 9OH and C=O of the hydrogen bonding complexes show that linear relation exists between frequency shift and bond length stretch. All C=O in complexes have a larger red shift, compared to that of 9OH. The infrared spectrum of C=O will have more redshift in excited state than in ground state.DFT and TDDFT are applied to investigate the hydrogen bonding of complex formed of Pistagremic acid with formic acid, acetic acid, propionic acid and formamide. The electronic absorption spectrum of all complexes have blueshift compared to that of monomer, with the degree of blueshift decreases in the order of complexes of formic acid, acetic acid, propionic acid and formamide. The intermolecular hydrogen bonding between Pistagremic acid and methanol, ethanol led to a redshift for electronic absorption spectrum, but electronic absorption spectrum have a blueshift in the complexes formed between Pistagremic acid and one water molecule, two water molecules, respectively.For the system of N-methylformamide-water, ground state conformations of NMF monomer and complexes NMF-(H2O)2,3 are optimized by using DFT, while electron transition energy and corresponding oscillator strength are calculated by using TDDFT. Intermolecular hydrogen bonding interaction of cis-NMF-(H2O)2,3 is stronger than that of trans-NMF-(H2O)2,3. The trans-NMF-(H2O)2,3 has more obvious electronic absorption spectra redshift than cis-NMF-(H2O)2,3, indicating that trans-NMF-(H2O)2,3’s hydrogen bonds in excited states are stronger than those of cis-NMF-(H2O)2,3.