engleski

From the topochemical postulate to molecular switches

A rapidly increasing interest in the solid-state reactions due to their application is followed by a desire to design new intelligent materials. It is known that the efficacy of the solid-state reaction is governed by the topochemical postulate which says that the reaction is possible only if topochemical postulate is satisfied. As a part of the study of the effects of topochemical factors on the solid state organic compounds, we report the results of research including the photo-dissociation of aromatic C-nitroso compounds. The discovery that nitroso dimers in crystals undergo photodissociation has at least two perspectives, the study of topochemical effects in the solid-state chemical reactivity, and the possibility to apply this effect in the molecular OFF-ON switches in molecular electronics. In this special case a topochemical postulate will be fulfilled only in case when the monomer crystal structure affords close contacts between the reactive centers of neighboring molecules. Dimerization of 4-bromnitrosobenzene and 4-iodonitrosobenzene was studied under three different topochemical environments: (i) strong topochemistry in the cryogenic conditions where the starting monomers have been obtained by photolysis of crystals of the corresponding dimers at 14 K, (ii) looser topochemistry in the freshly sublimed crystals of monomers and (iii) randomly distributed monomer molecules in thin layers prepared by cryogenic deposition on CsI plate. It was demonstrated that the change in topochemistry and modifying structure at the molecular level drastically modifies the reaction rate and affect a bulk physical property (reactivity) of a solid.

Topochemical postulate ; Molecular switches ; Photo-dissociation ; C-nitroso compounds

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