High Pressure Spectroscopy Investigation On Proton Transfer In Co-Crystal

Proton transfer(PT)can be thought to be one of the most basic processes.When the strength of inter-or intra-molecular hydrogen bond becomes strong with the distance between proton donator and proton acceptor shortened,if there are some perturbations in this system,the equilibrium of hydrogen-bond formation will be broken.When the covalent interaction D-H is broken,protons bind to proton acceptor A to form a new covalent bond.The hydrogen-bond formation D…H-A transforms into the formation of D…H-A.Co-crystal is the kind of neutral complex composed of two or more components obtained from vapor,solution or melt.Co-crystal is general y accepted to be supermolecule compound which have some specific function.The components of co-crystal are mainly held together by hydrogen bond.The properties of the co-crystal are usual y determined,on the one hand,by the structure of the molecule and the three-dimensional arrangement in the crystal lattice,on the other hand,by proton transfer through hydrogen bonds.As a hydrogen bond system,proton transfer can be induced by external compression,which determines the electrical,optical and electrical properties of the substances.Therefore,the investigation of proton transfer in co-crystal can give an insight into the influences of proton transfer on the structure and properties of crystal and are relevant for the synthesis of specific material in the future.High pressure is a better method for changing the intermolecular interactions and inducing the proton transfer.In this thesis,we report the detailed geometric information of proton transfer compound,the mechanisms of pressure-induced proton transfer and the structural change of components.Because the verification of proton transfer process is very complicated,the occurrence of proton transfer cannot be confirmed only by our experimental method.So there are some requests that:(1)Proton transfer in co-crystal cannot occur or occur in part at ambient condition.(2)The occurrence of proton transfer at high pressure or high temperature has been report.Therefore,1:1 stoichiometric proton transfer complex(SQBP)given by squaric acid and 4,4'-bipyridine become the object of my investigation.Using a combined high pressure Raman measurement,high pressure infrared measurement and high pressure UV-visible absorption spectroscopy,we obtained the following original results:We carried out in-situ high pressure Raman measurements of SQBP up to 20 GPa and in-situ high pressure infrared measurements up to 10.6 GPa.A solid-solid phase transition together with doubly proton transfer phenomenon was confirmed by Raman and infrared spectroscopy at about 1.5 GPa,which was further characterize using high pressure Uv-Visible spectra,and the emergence of C=O vibrational mode in Raman spectra indicating a symmetric structure of SQ with four C=O bond was formed.The planar BP molecular structure result in ? electron delocalization effects in BP which possibly lead to the occurrence of proton transfer.Additionally,Raman intensity analysis suggested a secondary phase transition with planar BP molecular structure in the pressure range of 4-6 GPa,which was also confirmed by infrared spectroscopy.The planar BP molecular structure result in ? electron delocalization effects in BP which dominated the intensity enhancement of C=O stretching mode in SQ.This is the first observation of proton acceptor's electronic delocalization enhance the proton donor's normal modes.