Theoretical Study On The Excited Weakinteraction Between Formaldehyde And Alkalimetal Ions,Isoniazid And Small Molecules

Intermolecular interactions play a very important role in many physical,chemical and biological processes and have attracted the attention of researchers in the past few decades.In recent years,it has been found that the intermolecular weak interaction between the excited states is closely related to the photophysics and photochemical processes.In this paper,the time-dependent density functional theory is used to study the excitation states of?1?formaldehyde and metal ion complexes?2?excited states of isoniazid and formaldehyde complexes?3?excited states of isoniazid and methanol System for theoretical research.In this paper,the bonding properties of formaldehyde and alkali metal ions and excited hydrogen bonds were analyzed by different methods,and the effects of intermolecular weak interaction on the monomer and the effect of excited electrons on the intermolecular weak interaction were systematically analyzed.This paper mainly includes the following three parts.1.The electronically excited states of formaldehyde and its complexes with alkali metal ions are investigated with time-dependent density-functional theory?TDDFT?method.Vertical transition energies for several singlet and triplet excited states,adiabatic transition energies for the first singlet and triplet excited states S₁ and T1,the adiabatic geometries and vibrational frequencies of the ground state S₀ and the first singlet and triplet excited states S₁ and T1 for formaldehyde and its complexes are calculated,better agreement with experiment than the CIS method is obtained for CH₂ O at the TDDFT level.The nonlinear C=O×××M+ interaction in the excited states S₁ and T1 is weaker than the linear interaction in the ground state.In the states S₀ and S₁,the C=O bond is elongated by cation complxation and its stretch frequency is red shifted,but in the state T1 the C=O bond is shortened and its frequency is blue shifted.2.In this paper,the system of excited isoniazid and formaldehyde complex?INH-CH₂O?was calculated by time-dependent density-functional?TDDFT?method at the level of B3 LYP /6-311++G?d,p?.INH-CH₂ O complex has two hydrogen bonds,this paper focuses on the different effects of electron excitation on the two hydrogen bonds of the complex.The results show that thehydrogen bond HB1 formed between the INH molecule and the CH₂ O molecule is strengthened in the excited state,and the HB2 is weakened or even broken at the time of excitation.Infrared spectroscopy analysis showed that the isoniazid and formaldehyde formed intermolecular hydrogen bonds,so that C=O,C-H and N-H bond stretching frequency relative to the monomer is red shifted.Since the occurrence of electron excitation,the C=O and H-C bonds corresponding to HB1 are red shifted,and the C=O bond corresponding to the HB2 is red shifted and the N-H bond stretching vibration is blue shifted.3.In this paper,the system of excited isoniazid and methanol?INH-MeOH?was studied by using time-dependent density functional?TDDFT?theory.The geometrical structure,vibration frequency and electron spectrum of two configurations of INH-MeOH complexes and molecule monomer were calculated at the level of B3LYP/6-311++G*.The HB1 in the complex 1 is enhanced by electron excitation,while the HB2 bond is weakened.The two intermolecular hydrogen bonds C=O×××H-C formed in the complex 2 are enhanced in the S₁ and T1 states relative to the ground state.The excited states S₁ and T1 of the two complexes are locally excited,where isoniazid is excited but methanol remains 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 isoniazid.