Mechanism And Regulation Of Excited State Intra-and Inter-Molecular Multiple Proton Transfer

Excited state intramolecular or intermolecular proton transfer(ESIPT)be-longs to one of the most classical chemical reactions involved in hydrogen bonding dynamics.Previously,most reports have summed up the characteristics about E-SIPT,i.e.,dual fluorescence peaks phenomenon.However,given the ESIPT case along with double or multiple hydrogen bonding wires,the possible single or double proton transfer mechanism is not yet clear.In the present work,we mainly focus our attention on exploring excited state multiple proton transfer mechanism and on providing novel attribution for experimental phenomenon.Via constructing poten-tial energy surfaces,we firstly infer the possible ESIPT paths.Based on searching transition state(TS)and simulating imaginary frequencies of TS,we clarify whether ESIPT reaction occurs or not.Further,combining the Born-Oppenheimer approx-imation molecular dynamics(BOMD)with kinetic rate equation,we use several representative molecular systems to verify excited state multiple proton transfer mechanism.On this premise,we also regulate the excited state double proton transfer(ESDPT)process via changing surroundings(i.e.,solvent effects)for sym-metrical and unsymmetrical systems.The most remarkable thing is that we apply the external electric field to investigate ESDPT behavior.For the first time,we present a new mechanism about regulating and controlling stepwise ESDPT reac-tion via external electric field.In addition to these,we also elaborate the ESIPT coupled to aggregation-induced enhanced emission(AIEE)and to thermally active delayed fluorescence(TADF)mechanisms.For the case of excited state intermolec-ular reactions,we clarify how to judge the numbers of solvent molecule participating in the ESIPT reaction and to explore proton relay as well as intramolecular twisting behaviors.It paves the way for further investigating intermolecular multiple hydro-gen bonding interactions in biological processes.The research methods and results adopted in this work could provide good theoretical guidances for experimental design and synthesis of high efficiency luminous materials in future.