Theoretical Study On The Excited Interaction Offormaldehyde With The Hydrogen Bonding Offluorenone,o-Nitroaniline And Uracil

Intermolecular interactions have drawn the interest of both theoretical and experimental chemists.Hydrogen bonding,as a typical non-covalent bond,has been studied by many theoretical and experimental techniques.In recent years,hydrogen bonding excited states have aroused interest in photophysical,photochemical and biological processes.In this paper,the density functional theory?DFT?and time-dependent density functional theory?TD-DFT?were applied to investigate the effects of?1?formaldehyde?CH₂O?and fluorenone?FN?excited states complexes?2?excited states complexes of formaldehyde?CH₂O?and o-nitroaniline?ONA??3?excited states complexes of formaldehyde?CH₂O?and uracil?U?three systems for theoretical study.In this paper,the B3LYP method was used to systematically analyze the bonding nature of fluorenone?FN?,o-nitroaniline?ONA?,uracil?U?with formaldehyde respectively in different electronic states and understand the effects of intermolecular hydrogen bonding and electron excitation on monomers and hydrogen bonding complexes by the spectral analysis.This thesis mainly includes the following contents:1.Time-dependent density functional method was performed to investigate the intermolecular hydrogen bond between fluorenone?FN?and formaldehyde?CH₂O?in the electronically excited states.The geometric structures of the hydrogen bonding complex in the ground state and the first singlet and triplet excited states S₁ and T₁ are optimized respectively by the DFT and TD-DFT methods,the vibrational and electronic absorption spectra and fluorescence spectra are calculated.Two hydrogen bonds C=O???H-C between FN and CH₂O are formed in the complexes,and the intermolecular hydrogen bonds are strengthened by excitation to the electronically excited states S₁and T₁ which are locally excited,where the FN moiety is excited but the CH₂O moiety remains in the ground state.The hydrogen bonds cause a frequency blue shift of the involved CH bond in formaldehyde in the ground state,the electron excitations S₀?S₁ and S₀?T₁ mainly lead to large frequency red shift of the C=O bond in fluorenone.2.To study the hydrogen bonds upon photoexcited,the time dependent density function method?TD-DFT?was performed to investigate the excited state hydrogen bond properties of between o-nitroaniline?ONA?and formaldehyde?CH₂O?.The complex ONA???CH₂O forms the intramolecular hydrogen bond and intermolecular hydrogen bonds.Since the strength of hydrogen bonds can be measured by studying the vibrational absorption spectra of the characteristic groups on the hydrogen bonding acceptor and donor,it evidently confirms that the hydrogen bonds is strengthened in the S₁/S₂/T₁ excited states upon photoexcitation.This article focuses the different effects of electron-excited on hydrogen-bonded complexes and monomers.As a result,the hydrogen bonds cause that the CH stretch frequency of the proton donor CH₂O has a blue shift,and the electron excitation leads to a frequency red shift of N=O and N-H stretch modes in the o-nitroaniline?ONA?and a small frequency blue shift of CH stretch mode in the formaldehyde?CH₂O?in the S₁ and S₂ excited states.The S₁/S₂/T₁ excited states are locally excited states where only the ONA moiety is excited,but the CH₂O moiety remains in its ground state.3.In this thesis,density functional method?B3LYP?with the basis sets aug-cc-pVDZ has been employed to investigate the three hydrogen bond complex systems?U???CH₂O?between uracil and formaldehyde in the ground and the electron excited states.The different effects of electron excitation and hydrogen bond formation on monomer uracil and formaldehyde are also discussed.The analysis of the geometrical configurations,electron absorption and infrared spectra of monomer molecules and hydrogen bond complex molecules?U???CH₂O?showed that both monomer uracil and formaldehyde molecules are both affected by hydrogen bonds and excited states.On the one hand,due to the formation of intermolecular hydrogen bonds between uracil and formaldehyde molecules,the C=O and NH bond length in uracil molecules increase,and the corresponding stretching vibration frequencies are red shifted,and the C=O involved CH₂O bond length increases and the CH bond length shortens,the corresponding C=O stretching vibration frequency of red shift and CH blue shift.On the other hand,when the hydrogen bond complex is excited to the S₁/T₁ electronically excited state,the three hydrogen complexes of HB2:H₂C=O???H-N?U?in the corresponding uracil NH bond is blue shift and formaldehyde C=O bond is red shift.Meanwhile,the intermolecular hydrogen bonds formed by the three hydrogen bond complexes are weakened by excitation to the electronically excited states,except for the enhancement of hydrogen bonds of complex 3 in the S₁ state.