Nature of the Interaction of N,N′‑Diphenyl-1,4-benzoquinonediimine with Iron Oxide Surfaces and Its Mobility on the Same Surfaces

Short chain aniline oligomers are of interest for applications in organic electronics and as corrosion inhibitors for steel, requiring an improved understanding of their interactions with metal oxide films. Here we investigate the interactions of N,N′-diphenyl-1,4-benzoquinonediimine (B2Q1, oxidized form of an aniline dimer) with iron­(III) oxides. B2Q1 transforms into its semiquinone form when interacting with α-Fe2O3. The resulting charge transfer between B2Q1 and α-Fe2O3 is demonstrated with mid-IR, visible, and Raman spectroscopy. Atomic force microscopy shows the first layer of B2Q1 to be oriented face-on. Thermal analysis also confirms this orientation for submonolayer coverage, whereas molecules start standing up on their edges upon multilayer formation. Thermal analysis shows that the first monolayer of B2Q1 is chemisorbed on the α-Fe2O3 surface, and the following multilayers are strongly interacting with each other. The behavior of the oxidized aniline dimer B2Q1 is in stark contrast to its reduced counterpart (DPPD), which also undergoes charge transfer to iron oxide (in opposite direction). B2Q1 interacts more weakly with the surface, causing it to be more mobile. The mobility of B2Q1 provides a clue toward understanding the self-healing behavior of polyaniline corrosion-inhibiting films on steel.