PM IRRAS Studies of Organized Molecular Films at a Gold Electrode Surface

This feature article illustrates the potential of polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) to provide molecular-level information about the structure, orientation and conformation of constituents of thin films at electrode surfaces. PM IRRAS relies on the surface selection rules stating that the p-polarized IR beam is enhanced, while the s-polarized beam is attenuated at the metal surface. The difference between p- and s-polarized beams eliminates the background of the solvent and provides IR spectra at a single electrode potential. In contrast, two other popular in situ IR spectroscopic techniques, namely, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) and surface-enhanced infrared reflection absorption spectroscopy (SEIRAS), provide potential difference spectra to remove the signal from the bulk solution. In this feature article, we provide a brief tutorial on how to run the PM IRRAS experiment and describe the methods used for background elimination first. The application of the PM IRRAS in the biomimetic research is then illustrated by three examples: construction of a tethered bilayer, reconstitution of colicin into a phospholipid bilayer and determination of the orientation of nucleolipids in a monolayer assembled at a gold electrode surface. Finally, the structural changes of graphene oxide during its electrochemical reduction are described to highlight the promising application of PM IRRAS in materials science.