Theoretical Study On The Excited-State Proton Transfer Dynamics Of Two Molecules

In this thesis,the two molecules with proton transfer in excited state have been theoretical studied by using density functional theory and time-dependent density functional theory,and B3LYP functional together with TVZP basis set is used for the calculation of excited state hydrogen bonding dynamics.Firstly,the influence of cyanide group substitutent on the excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzothiazole(HBT)has been theoretical studied.It is found that the intramolecular hydrogen bonds of HBT and its cyanide substituted derivatives are significantly strengthened in the first excited(S₁)state,while this trend gets weaken with the increasing of cyano group.The natural population analysis(NPA)is performed to interpret this phenomenon and the calculated results show that the introduction of cyano groups induces intramolecular charge transfer,leading to the decrease of electrostatic interaction of intramolecular hydrogen bond in the S₁ state compared to isolated HBT.Therefore,proton transfer of HBT and its derivatives become difficult with the introduction of cyano groups,which is consistent with the calculated potential barriers of the three molecules in the S₁ state.This work interprets the hindrance of cyanide group on the proton transfer of HBT and its derivatives in the S₁ state,which will bring new theoretical support for the application of cyanide groups in the design of drug molecular.Secondly,the excited-state intramolecular proton transfer(ESIPT)process of 8-hydroxy-quinoline(HQ)and 10-hydroxybenzo[h]quinoline(HBQ)has been studied based on density functional theory and time-dependent density functional theory methods at B3LYP/TZVP theoretical level.The geometric structure and infrared vibrational spectra of HQ analysis show that the intramolecular hydrogen bond is strengthened in the first excited-state,which is different from HQ molecular system due to the influence of the benzene ring in the HBQ framework.The frontier molecular orbitals(MOs)and the Mulliken charge analysis interprets that the nature of hydrogen-bond diversification result from the charge redistribution upon photo-excitation.The potential energy curves indicate that the proton transfer process of HQ can only occur in the first excited-state while the proton transfer process of HBQ can occur both the ground-state and the first excited-state.It is demonstrated that the insertion of benzene ring(HBQ)in the HQ molecular system can change the behavior of the intramolecular hydrogen bond(O-H…N)in the first excited-state and thus may affect proton transfer process to some extent.Finally,the previous work has been summarized and the future research work has been prospected,and the research focus has been changed to practical applications,such as the hydrogen storage mechanism of ammonia-borane hydrogen storage materials,the sun protection mechanism of skin care products,the design and synthesis of drugs.