Excited State Proton Transfer Of NHM-2A,BBTD And 5RMS

Hydrogen bonding is a generally weak interaction in physics,chemistry and biology.Many microcosmic and supermolecular structures involve hydrogen bonding interaction,such as polymers,solute and solvent complexes,proteins and DNA et al.Hydrogen bonding interaction can exist in the ground state and excited state.The excited state hydrogen bonding interactions have been extensively studied,which play an important role in the processes of electron spectra shift,fluorescence quenching,photoinduced electron transfer,internal conversion and intramolecular charge transfer etc.Proton transfer that is basing on hydrogen bonding has been further research and had a wide range of applications,such as laser dyes,LEDs,fluorescence sensor,molecular switch,UV filters and so on.Excited state proton transfer research has attracted much attention.This paper mainly uses Gaussian 09 software to study the proton transfer mechanism of three systems,the calculation process select the density functional theory(DFT)and time-dependent density functional theory(TDDFT)method.In this text,three systems have been researched.They are the chain proton transfer process in ternary complex(NHM-2A)of 9H-pyrido [3,4-b] indole(norharmane,NHM)and acetic acid molecules in the solvent,the coordination or stepwise mechanism of2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol(BBTD)intramolecular proton transfer,as well as the proton transfer of different R substituted in methyl 5-R-salicylates(5RMS).According our researches,the chain proton transfer for the ternary complex(NHM-2A)of NHM with two acetic acid molecules is a gradual transfer process.The fluorescence phenomenon of BBTD has been studied in the experiment.The experiment show that the tautomers of proton transfer are existent by the analyses of analogues,but they can not determine the mechanism of proton transfer in more detail.By calculating the potential energy surface,we clarify that the mechanism of intramolecular proton transfer of BBTD is a stepwise process.Through studying the proton transfer of methyl 5-R-salicylates under different R substituents,theelectron-releasing ability of R substituent group becomes more and more stronger,the potential barrier becomes more lager,and even the proton transfer cannot occur.The theoretical study clearly explains the principle of proton transfer that is not clear in the experiment.