Investigation Of Excited-state Hydrogen Bonding Dynamics And Proton Transfer Process For Different Systems In Liquid Phase

Excited state proton transfer(ESPT)reactions in liquid phase belong to the dynamic behaviors of excited-state hydrogen bond,which is one of the most important reaction processes.With the developments of investigative techniques,dynamic behaviors of excited-state hydrogen bond can be analyzed qualitatively and quantitatively.It is well known the most reactions occurred in organisms located in excited(S1)state.Moreover,the hydrogen bond structures acted as the building blocks widely exist in natural.The proton transfer processes along orientation of hydrogen bond can run from proton donor to proton accepter where the hydrogen bond interaction offers driving force.The proton transfer cannot be performed in the ground(S0)state because of the weak hydrogen bond interaction.However,upon the photo-induced process the hydrogen bond interaction will be enhanced following the molecular transition from the S0 to S1 state,which will facilitates proton transfer reactions.In addition,the photophysical and photochemistry properties will change significantly with the ESPT processes,for example,the dual-fluorescence phenomenon,fluorescence quenching,the big Stokes’ shift and internal conversion(IC)process.The ESPT reactions can be applied for a large amount of fields,for example,the developments of light-emitting materials,the applications of fluorescence probes,the ultraviolet absorptions,solar energy capture and optical storage technologies and so on.With the implementations of calculational chemistry and quantum mechanics,the time dependent density functional theory(TDDFT)will widely be carried out to investigate dynamic behaviors of excited-state hydrogen bond at present.The theoretical methods not only can explain the reaction mechanisms in experiment,but the methods also can estimate the feasibility of research work.In this study,the photophysical and photochemistry properties of ESPT processes will be drastically studied based on TDDFT methods.Herein,the corresponding wave function information can be visually offered,for example,the analysis of bond parameters,the molecular frontier orbitals(MOs),the analysis of infrared vibration frequencies,the analysis of potential energy surfaces and weak interactions.Firstly,the ESPT processes for a new natural product quercetin will be theoretically research in dichloromethane solvent.The results indicate that the excited state intramolecular proton transfer(ESIPT)processes of isomers K1 and K2 are competitive with each other.In addition,the ESIPT reaction of isomer K2 is easier to occur,since the corresponding hydrogen bond interaction is stronger in six-member ring.Secondly,the new competitive mechanism of hydrogen bonding interactions and transition process for the hydroxyphenyl imidazole [1,2] pyridine in mixed liquid solution will be investigated.It concludes that the intramolecular hydrogen bond interaction can impede torsion of molecule.Moreover,the intermolecular hydrogen bond can be taken place after the ESIPT reaction because of the weaker intramolecular hydrogen bond interaction of tautomer.It should be noted that the twisting intramolecular charge transfer(TICT)form can be obtained,since intermolecular hydrogen bond breaks intramolecular hydrogen bond structure.This study further shows that the non-radiative decay process of TICT might go through predominantly the intersystem crossing(ISC)channel on the minimum energy crossing point(MECP)between S1 and triplets(T1)state.