engleski

Aromatic C-nitroso compounds as building blocks for new supramolecular assemblies

Aromatic C-nitroso compounds can exist in two different forms, as monomers or dimers (azodioxides). Formation of azodioxide bond strongly depends on the conditions of the environment. The predominant species in solution at ambient temperature are monomers whereas lowering of temperature or crystallization favors dimerization. In solid state, dimerization is dependent not only on electronic factors but also on topochemical effects. If the molecules are favorably oriented in crystal lattice with their nitroso groups in the vicinity they readily form azodioxides. Such azodioxides can undergo photodissociation to monomers in crystal at cryogenic conditions and in turn, by warming above some critical temperature, redimerization occurs. In our recent studies, we tried to expand the current knowledge about the dimerization of aromatic C-nitroso compounds by exploring if it can occur on two-dimensional gold surface through formation of ordered self- assembled bilayers (SABs). SABs could be formed by interactions of nitroso groups exposed at the interface of self-assembled monolayer (SAM) and those present in solution via azodioxide bonds. We have prepared nitrosoaromatic derivatives with one and two nitroso groups functionalized with sulfur headgroups for adsorption on Au(111) surface. Layers of nitrosoaromatic derivatives on Au(111) surface were studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). STM and AFM images revealed that in addition to self-assembly into monolayers, the nitrosoaromatic derivatives are also able to form ordered bilayers. In addition, we examined the ability of aromatic C-nitroso compounds to dimerize on the three-dimensional surface of Au nanoparticles. We have prepared Au nanoparticles capped with nitrosoaromatic derivatives with one and two nitroso group and characterize them by FTIR spectroscopy, UV-Vis spectroscopy and transmission electron microscopy (TEM). It was found that nitroso molecules are present in dimeric form on the gold surface leading to interlinking of Au nanoparticles through azodioxide bonds and their subsequent aggregation.

Aromatic C-nitroso compounds ; Dimerization ; Self-assembled monolayers ; Self-assembled bilayers ; Scanning tunneling microscopy ; Atomic force microscopy

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