| A hydrogen bond(H-bond) is a week type of intermolecular interaction, which occurs when a hydrogen atom bonded to a strongly electronegative atom approaches a nearby electronegative atom. It plays a key role in molecular structures and properties and the function of biological organisms.Unlike covalent and ionic bonding, which involve massive shifts of electronic structure of molecule, the rearrangements caused by H-bonding are much more subtle. Therefore, it has been urgent to explore a kind of effective method to study H-bond.Surface-enhance Raman scattering(SERS) spectroscopy offers rich chemical and structural information, and has single-molecule sensitivity. It has developed into a remarkable analysis technique, especially in the field of surface and interface. Considering the unique advantages of SERS, we explored the influence of intermolecular H-bonds in a system by SERS spectroscopy for the first time. We found the frequency shifts and the changes in the intensities of the molecules in an intermolecular H-bond system from the SERS spectroscopy, and discussed the effect of H-bonds on the electronic structure of the molecules and the charge transfer transition in the system. Moreover, we proposed a label-free approach for enantioselective discrimination. This thesis mainly includes the following four aspects:(1) Exploring the effect of intermolecular H-bonds on molecular electronic structure. We employed layer-by-layer assembly methods to fabricate an 132 intermolecular H-bond system consisted by p-mercaptobenzoic acid or p-aminothiophenol molecule and aniline or benzoic acid molecule. It is found that some frequency shifts and the changes in the relative intensities of molecule appeared in the SERS spectra. Furthermore, we observed an obvious positive correlation between these changes and the amount of the H-bond in the system. This study verified the feasibility of the SERS spectroscopy for exploring the intermolecular H-bond, and it provides a reliable basis in the future study of H-bond.(2) The influence of H-bond on the charge-transfer(CT) in the system. Our previous work showed that the relative intensity of the probe molecules in the SERS spectra changes with the formation of H-bond in the system. In addition, the b2-type mode of the molecule were selectively enhanced with increasing the concentration of H-bond in the system. The temperature-dependent SERS experiments and their two-dimensional correlation analysis further demonstrated that intermolecular H-bonds would increase of the conjugation of the system, and result in the changes in the electronic structure of the molecules. Therefore, it is concluded that intermolecular H-bonds can promote the CT transition between the substrate and the adsorbed molecules.(3) A label-free method for enantioselective discrimination of the chiral alcohols by SERS. Based on the effect of intermolecular H-bonds on molecular electronic structures and the CT transition in the system, we proposed a generic, label-free method for enantioselective discrimination of chiral alcohols, in which we choose an achiral molecule, p-mercaptopyridine, as a chiral selector. In our method, the distinction between the two enantiomers can be realized based on the difference in the SERS spectra of chiral selectors in different chiral environments, without either chiral reagents or circularly polarized light.(4) Exploring the mechanism of the label-free enantioselective discrimination. On the basis of the differentiate SERS spectra of the chiral selector depending on different chiral environments, we performed a series of wavelength-dependent and concentration-dependent SERS experiments and nuclear magnetic resonance(NMR) experiments to propose a preliminary explanation. It is manifested that different CT transitions involved in the enantioselective process. This enantioselective discrimination method break the limitation of traditional methods of chiral discrimination, affording new insights into the future field of chiral discrimination. |
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