Dimerization of Nitrosobenzene Derivatives on an Au(111) Surface

Abstract

In this study, we have investigated the ability of C-nitrosobenzenes to dimerize on an Au(111) surface and form ordered self-assembled bilayers (SABs). Use of scanning tunneling microscopy (STM) revealed that nitrosobenzene derivatives are able to form both well-ordered monolayers (SAMs) and bilayers (SABs). High-resolution STM images showed that within SAM regions molecules are arranged into hexagonal structures. Moir e-type superstructure with a periodicity of 1.5 nm was observed, indicating a 3 √ 3 Â 3 √ 3 molecular arrangement. Molecularly resolved STM images showed that within bilayers molecules are also arranged into hexagonally ordered structures at intermolecular spacing of ∼0.4 nm. Furthermore, it was observed that the second layer is better ordered than the first one, probably because of the softer background. Use of atomic force microscopy (AFM), through measured height differences between monolayers and bilayers, further confirmed the formation of SABs. The results of the present study demonstrate that nitrosobenzenes represent convenient molecular models that can be used for systematic design and study of bilayers on metal surfaces. Besides the previously known properties of C-nitroso compounds to form dimers in crystals, here we have found a new situation under which these molecules dimerize, which is, in principle, a 2D crystallization.

Nitrosoarene Dimerization on Two- and Three-dimensional Gold Surfaces

“…The periodicity of the superstructure of 1.5 nm corresponds very well to 3 3 times that of the Au(111) lattice (a = 0.29 nm) indicating a 3 3 3 3  molecular arrangement, same as for SAMs of nitrosoarene derivatives studied in our recent paper. 18 However, on contrary to the molecular adlayers of the recently studied compounds for which higher islands attributed to SABs were detected in the STM images, here we could not observe similar features.…”

“…In contrast to compound 2 and nitrosoarene derivatives studied previously 18 that are all dimers, compound 1 appears as monomer. Dimerization of 1 is prohibited due to the negative charge on the NO-group 24 what can be explained by the contribution of quinoid resonance structure (depicted as structure II in Scheme 2).…”

“…Notably, similar morphology of the surface was observed for adlayers of previously studied compounds. 18 According to STM data, compound 2 forms only a well-ordered SAM with crystalline packing over extended areas. In regard to that, one would expect AFM images displaying uniform molecular layer covering Au(111) terraces.…”

“…The inability to detect SABs regions by STM could be due the length of molecule 2 which is considerably longer in comparison to previously studied molecules. 18 It is possible that during the STM imaging a tip is actually buried within a molecular layer in order to attain tunneling current. Examples of such invasive tip-sample interactions are familiar from the literature.…”

“…In our recent work we have suggested that dimerization of nitrosoarenes is also possible at the metalsolution interface through formation of ordered selfassembled bilayers (SABs) on an Au(111) surface. 18 SABs can be formed by vertical interactions of nitroso-groups exposed at the interface of self-assembled monolayer (SAM) and those present in solution via (O)N=N(O) bonds. Here we extend our knowledge on the nitrosoarene dimerization at the metal-solution interface by investigating how it is affected by structural factors e.g.…”