The Research Of Intra-and Inter-molecular Hydrogen Bond Dynamics As Well As Proton Transfer Reaction Of 2,4-DP And BBHQ'

Hydrogen bond exist widely in nature and biological systems and play an indispensable role in our life.In addition,the investigation of hydrogen bond has aroused extensive attention due to their special properties in photophysics,photochemistry and biology,In the past decade.¹–6–6 Firstly,hydrogen bond has a powerful ability to build supramolecules because of their collectively strong directional interaction,which is essential for the construction of fundamental building blocks of life.Secondly,hydrogen bond can be used as the active site for the occurrence of many interactions due to their dynamic features.⁴ Therefore,the further study of hydrogen bond interaction will be critical in the crystal state,solutions and living organisms.Whether intramolecular or intermolecular hydrogen bonds,they play a decisive role in photochemical and photophysical reactions.For instance,Fluorescence quenching,charge transfer?CT?,photoelectron transfer?PET?,fluorescence resonance energy transfer?FRET?,and excited state proton transfer?ESPT?et al.Among them,proton transfer based on hydrogen bonding is the most important reaction in the chemical and biological fields of acid-base neutralization.In particular,excited proton transfer has been applied in many fields,such as the design and application of fluorescent probes,laser dyes and light emitting diodes,ultraviolet absorbers and molecular switches,etc.In this paper,the excited state hydrogen bonds have been investigated using the density functional theory?DFT?and the time–dependent density functional theory?TDDFT?Becke's three-parameter hybrid exchange function with the Lee-Yang-Parr gradient-corrected correlation functional?B3LYP?and?CAM-B3LYP?based on the Gaussian 09 programs.They are concerted mechanisms of excited–state proton intramolecular transfer for bis–2,4–?2–benzoxazolyl?–hydroquinone and its derivatives.The effect of intermolecular and intramolecular hydrogen bonding between 2,4-DP and?MeOH?.For BBHQ?the calculated absorption and emission spectra of BBHQ?and its derivatives are in good agreement with the experimental results.The calculated bond lengths,bond angles and IR vibrational spectra linked with hydrogen bond of molecular BBHQ?in the S₀ and S₁ states demonstrate that the hydrogen bond is strengthened in the S₁ state.Compared to BBHQ?,BBHQ?^–has weak change of hydrogen bond between the S₁ and S₀ states.The calculation results show that there are three stable structures of BBHQ?in the S₁ state.We find that the structure corresponding to the 481nm fluorescence spectrum corresponds to BBHQ?–A rather than BBHQ?^––K.The calculated frontier molecular orbitals?MOs?indicate the nature of the charge distribution and the trend of proton transfer of BBHQ?–A.The constructed potential energy surfaces of BBHQ?and DBHO'further elucidate the proposed mechanism that one–proton or two–proton transfer can happen?stepwise or synchronous?in the S₁states.The proposed ESIPT mechanism can provide a good explanation of the phenomenon of fluorescence quenching of BBHQ?and its derivatives.Finally,the weak interaction types are discriminated through the reduced density gradient?RDG?analyses of BBHQ?and BBHQ?^–.For the 2,4-DP molecular system,we performed the same calculations on optimizing the structure,spectrum calculation,and constructing the potential energy surface.The difference of the second molecular system compared with BBHQ?is that we mainly studied the effect of intermolecular excited hydrogen bonds on proton transfer.The effect of different positions of the excited hydrogen bond on proton transfer is affected by the intermolecular hydrogen bond position.The influence which depending on the position of the intermolecular hydrogen bonds is large,the influence of intermolecular hydrogen bonds on proton transfer is divided into promotion or inhibition.