A Fourier Transform Infrared Reflection−Absorption Spectroscopy Study of Redox Polyelectrolyte Films

Self-assembled polyelectrolyte multilayer films comprised of poly(allylamine) derivatized with an Os(bpy)2ClPyCH− complex (PAH−Os), and poly(vinylsulfonate), PVS, or poly(styrensulfonate), PSS, have been studied by Fourier transform infrared reflection−absorption spectroscopy. The infrared absorbances of the characteristic SO3-, CH2, NH3+, and aromatic bipyridine and pyridine groups have been characterized, and their intensity increases with the number of self-assembled layers and redox charge. The characteristic infrared signatures are the 1040 cm-1 band assigned to the aromatic ligands in the osmium complex (ν(Py)), PAH−Os, and the 1040 cm-1 (νs(SO3-)) and 1213 cm-1 (νa(SO3-)) bands for SO3 groups in PVS. The νs(SO3-) vibrational mode of PVS senses the local NH3+ environment of the cationic PAH−Os resulting in a band shift of 22 cm-1 for the first polyallylamine layer. Subtractively normalized Fourier transform infrared spectroscopy during the oxidation of the Os centers in the (PAH−Os)n(PVS)m multilayer reveals that different vibrational modes of bipyridine ligands in the osmium redox center of PAH−Os and the sulfonate groups of PVS are affected by charge−ligand electrostatic interaction and dipole reorganization in the multilayers