Investigation Of Photoinduced Proton Transfer At Single-Molecule Scale Based On Break-Juntion Technique

The rapid development of computer and information science promotes the birth and development of single-molecule electronics.In order to improve the computing speed of electronic devices,realize the customization of molecular devices and the miniaturization of electronic devices,the mechanism of charge transport at the singlemolecule scale and the structure-property relationship of organic molecules are the hot topics in the field of single-molecule electronics.Stimuli-responsiveness is not only a prerequisite for the functionalization of most molecules,but also provides a good research platform for exploring structure-property relationship of molecules.Compared with other common external stimuli,light has the advantages of high spatial and temporal resolution,non-invasiveness and remote control.By introducing photochromic molecular structure units,molecules and materials can be sensitized to light stimuli.However,this method is limited by the number of the varieties of photochromic molecules.Therefore,finding a more general method to introduce the photo-responsive at the single-molecule scale will greatly promote the investigation of single-molecule optoelectronic devices and the development of single molecule electronics.Therefore,in this thesis,we investigated both the proton transfer process that is common in nature and photo-responsiveness through simple and effective singlemolecule electrical measurements techniques,mechanically controllable break junction(MCBJ)and scanning tunneling microscopy break junction(STM-BJ)technique.On the one hand,we proposed and applied a universal into the single-molecule scale to realize the light control of the non-photoresponsive systems.On the other hand,the thesis also explored the photo-responsive systems with intramolecular hydrogen bonding.The main research contents and conclusions of this thesis are as follows:1.MCBJ technology was used to verify that spiropyrane derivatives,as photoacids,can switch the conductance of azulene derivatives that are not photoresponsive to light at the single-molecule scale;The data of the conductance switching process were analyzed by using the method of automatic trace selection,and the exist of the shift of chemical balance in the system upon irradiation is put forward.Based on DFT calculation and UV-Vis absorption spectrum,the mechanism of conductance change was investigated.The results showed that through proton transfer between molecules,HOMO-LUMO gap was narrowed and the delocalization of electrons was enhanced.The proof-of-principle veryfing of a AND and a OR logic in this dual-responsive system based on the photo-induced proton transfer(PIPT)strategy demonstrated a broad application prospect of this strategy in single-molecule devices.2.The optical conductance switching of schiff base derivative system which can supress the destructive quantum interference(DQI)in single-moleucle junctions based on intramolecular hydrogen bond was verified by STM-BJ technology.The switching ratio of molecules with one intramolecular hydrogen bond and two intramolecular hydrogen bonds was～4.4 and 3.8 respectively.It was found that the system had a concentration dependent effect:the near UV light could not make the 1mM concentration of the molecular solution in the trichlorobenzene(TCB)solvent perform significant color change.The photo-responssive process was further studied by UV-Vis absorption spectrum.Under UV light,photoisomerism induced by excited state proton transfer(ESIPT)was found in the solution with concentration of 0.1Mm.