It is difficult to examine solid/solid and solid/liquid interfaces because such interfaces are buried. We have applied sum frequency generation (SFG) vibrational spectroscopy to study interfaces involving polymers and/or biological molecules such as proteins and peptides in situ in real time at the molecular level. This talk will focus on our recent progress in using SFG to study molecular orientations of semiconducting polymers at solid/solid interfaces, molecular interactions between 2D materials (e.g., graphene, MoS2, WS2) and peptides or protein molecules, and surface immobilized peptides. Our SFG studies are supplemented by attenuated total reflectance (ATR)-FTIR and circular dichroism (CD) spectroscopy as well as all-atom and coarse-grain molecular dynamics simulations. It was found that interfacial orientations of semiconducting polymers are influenced by polymer side chains and substrate surface hydrophobicity, and such interfacial orientations are well correlated to polymer solar cell conversion efficiency. Biological molecules interact with different 2D materials very differently. On graphene, pi-pi interactions play an important role. On MoS2, hydrophobic interaction is the determining factor. Using SFG, we also elucidated the effects of surface immobilization sites on peptides, chemical environments, and substrate surface properties on surface immobilized peptide structure and function.

Molecular structures of polymer and biological molecules at buried interfaces studied by sum frequency generation vibrational spectroscopy

2019 Fall National Meeting

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