engleski

Aromatic dinitroso compounds as supramolecular building blocks

Aromatic C-nitroso compounds can exist in three different forms, as monomers, Z- or E- dimers (azodioxides). Nitroso compounds also exhibit photochromic and thermochromic behavior in solid state. Azodioxides dissociate under UV irradiation at low temperatures and again dimerize at elevated temperatures. Aromatic nitroso compounds with two or more nitroso groups could be used as supramolecular building blocks. Wuest et al. utilized tetranitroso bocks for construction of covalent organic networks (COFs) by polymerization. Supramolecular structures with azodioxides groups could be disassembled or reassembled by applying external stimuli such as UV radiation or heat. Our goal was to prepare aromatic dinitroso compounds with various spacers between two aromatic rings and to investigate their polymerization properties in solid state. Most of the examined dinitroso compounds form oligomers in the solid state which are mainly in E- configuration. Diphenyl-ether derivative doesn’t form dimers because of the quinoid resonance structure, while diphenylmethane derivative forms Z- oligomers. In the case of diphenylmethane derivative, Z- conformers are stabilized by favorable aromatic ring π-π stacking. Monomers are generated upon UV irradiation at cryogenic temperatures. Monomers dimerize by heating the samples to ~150 K. Methane, ethane, biphenyl and benzophenone derivatives form Eoligomers upon redimerization. In the case of diphenylmethane, E- dimers isomerize to thermodynamically more stable Z- conformation upon further heating.

dinitroso ; polymerization ; monomers ; dimers ; supramolecular ; photochemistry ; cryogenic ; switches

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