Charge Transfer on the Surface-Enhanced Raman Scattering of Ag/4-MBA/PEDOT:PSS System: Intermolecular Hydrogen Bonding

A sandwich-structured noble metal-probe molecule-organic semiconductor consisting of Ag nanoparticles (NPs), 4-mercaptobenzoic acid (4-MBA) and different concentrations of poly(styrenesulfonate:poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) was prepared by layer-by-layer assembly. Intermolecular hydrogen bonding was observed to have a significant effect on the surface-enhanced Raman scattering (SERS) of Ag/4-MBA/PEDOT:PSS. Upon increasing the PEDOT:PSS concentration, the characteristic Raman band intensity of 4-MBA was enhanced. In addition, the selected b(2) vibration mode was significantly enhanced due to the influence of the charge transfer (CT) mechanism. The CT degree (rho(CT)) of the composite system was calculated before and after doping with PEDOT:PSS; when the concentration of PEDOT:PSS was 0.8%, the SERS intensity tended to be stable, and rho(CT) reached a maximum. Compared with that of the undoped PEDOT:PSS system, rho(CT) was significantly enhanced after doping, which can be explained by the CT effect induced by hydrogen bonds. These results indicate that hydrogen bonding transfers a charge from the Fermi energy level of Ag to the lowest unoccupied molecular orbital (LUMO) of 4-MBA, and due to the resulting potential difference, the charge will continue to transfer to the LUMO of PEDOT:PSS. Therefore, the introduction of organic semiconductors into the field of SERS not only expands the SERS substrate scope, but also provides a new idea for exploring the SERS mechanism. In addition, the introduction of hydrogen bonds has become an important guide for the study of CT and the structure of composite systems.

Automated summary

A sandwich-structured noble metal-probe molecule-organic semiconductor was prepared by layer-by-layer assembly, with intermolecular hydrogen bonding observed to significantly affect surface-enhanced Raman scattering. The introduction of organic semiconductors expands the scope of SERS substrates and provides a new idea for exploring the SERS mechanism. Hydrogen bonding has become an important guide for studying charge transfer and the structure of composite systems.