| The study of host-guest chemistry is crucial to the field of supramolecular chemistry,among which,cucurbituril is the latest fourth-generation macrocyclic host substance.Its unique structural characteristics have received extensive interest.The fields of assembly,controllable molecular switches,nanomedicine,and nanocatalysis have increasingly broad application prospects.However,the current characterization methods of the cucurbituril host and guest systems cannot provide information about the structure of the cucurbituril host and guest molecules,and the study at the molecular level that reveals the interaction between the cucurbituril host and guest molecules still lacks.Raman spectroscopy,as an analytical technique providing molecular "fingerprint"information,can detect physical and chemical processes at the molecular level.The realization of tip-enhanced Raman spectroscopy(TERS),which simultaneously obtains the morphology and chemical fingerprint information with the single-molecule detection sensitivity and(sub-)nanometer spatial resolution,has unique advantages in studying various chemical changes at the nanometer scale.In the TERS study,the tip plays a decisive role in enhancing the Raman signal.However,the pursuit of higher enhancement has always been desired.The way to fabricate high-quality TERS tips with a good reproducibility is one of the essential problems limiting the development of TERS.Therefore,this thesis will first introduce the current research status of cucurbituril host-guest chemistry,as well as the history and application of a series of Raman spectroscopies with different characteristics and advantages.Then,we will devote ourselves to the development of high-stability and high-sensitivity TERS,and apply to it the research on the host-guest system of cucurbituril.The main research results and conclusions of this thesis are as follows:(1)We developed of a method to prepare Au tips with a high TERS activity.The STM-TERS Au tip with consistent and highly reproducible apex obtained by electrochemical etching was further treated by chemical methods to enhance the TERS signal by an order of 2 to 30 folds.The reason for the increase in signal is due to the monoatomic protrusions on the surface of the tip.The related performance of the tip was verified,and it is found that this method can both improve the TERS signal of the tip and ensure that the STM imaging ability and TERS spatial resolution of the tip will not be sacrificed.(2)We applied TERS to study the cucurbituril host and guest systems.The system studied here is cucurbit[7]uril(CB[7])as the host molecule and electrochemically active viologen derivative(S-EV+)as the guest molecule.We used surface-enhanced Raman spectroscopy(SERS)to study the effect of intermolecular interactions caused by CB[7]inclusion on the molecular structure of S-EV+.Meanswhile,it was found that the 633 nm laser would cause S-EV+ molecules to bind in a double-end way in the nanoparticle gap.The EC-SERS results illustrated that CB[7]would gradually separate from the guest molecule with the reduction of S-EV+.Whereas,on the well-defined Au(111)single-crystal surface,the interaction of guest molecules with nano-scale spacing will be significantly weaker than the closely arranged guest molecules under the control of cucurbituril with the TERS and EC-TERS results.The improvement of the preparation method of Au-TERS tip has further enhanced the sensitivity of TERS.Moreover,the study of the intermolecular interaction of cucurbituril-encapsulated redox guests further demonstrates the advantages of enhanced Raman spectroscopy in obtaining structural information of the molecule itself.In addition,the application of TERS in the field of cucurbituril host and guest system shows that TERS is a powerful technique to characterize small changes in intermolecular interactions at the nanoscale and molecular level,and paves the path for TERS to in-situ study single molecule in the electrochemical system. |
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