engleski

Aromatic C-Nitroso Compounds: From Dimerization to Self-Assembly

Aromatic C-nitroso compounds appear in three different forms, as nitroso monomers, and Z- and E-azodioxy dimers. In solid state, aromatic C- nitroso compounds mostly appear as azodioxides, and in solution an equilibrium is established between monomers and dimers. At room temperature, the equilibrium is usually shifted toward nitroso monomers, while dimers can be observed by lowering the solution temperature. Aromatic C-nitroso compounds, which are normally present as dimers in solid state, can sometimes be isolated as metastable nitroso monomers. Monomers can be prepared by cryogenic photodissociation of azodioxides or by sublimation. Warming the crystals of metastable nitroso monomers causes redimerization to starting azodioxides. In some cases, azodioxides thermally dissociate to monomers in solid state. Dimerization and dissociation of aromatic C-nitroso compounds and their dimers, respectively, could be used as a model for studying the thermal organic solid-state reaction mechanisms.1 Adsorption of compounds with exposed aromatic C-nitroso groups on metal surfaces provides possibilities for design of self-assembled bilayers. Bilayers could be formed by interactions of nitroso groups at the monolayer interface and those free in solution through azodioxide bonds (Figure 1a). We studied self- assembly and dimerization of sulphur-containing aromatic C-nitroso compounds on an Au(111) surface. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) indicated that nitrosobenzene derivatives form monolayer and bilayer domains on an Au(111) (Figure 1b).2 More recently, we studied possible dimerization of aromatic dinitroso derivatives, with nitroso groups in mutual meta-position, on gold surface. Compounds with multiple nitroso groups on phenyl ring are interesting because they can interact through azodioxide bonds by forming oligomers and polymers. Our results indicated that aromatic dinitroso derivatives dimerize on gold surface by forming E-azodioxides.3 However, in comparison to mononitroso derivatives, adlayers of aromatic dinitroso compounds are less ordered probably due to the steric hindrance of meta-situated nitroso groups.

Aromatic C-nitroso compunds ; Dimerization ; Solid state ; Self-assembly

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