engleski

The effect of topochemical factors on solid-state photo-dissociation of aromatic C-nitroso compounds

A chemical behavior of nitroso compounds is quite interesting in both biological and chemical sense. In biological systems they appear as intermediates, mostly on the pathways involving transformations of amino groups via oxidation or nitro groups via reduction. They also readily form radicals and radical ions. In chemical systems an intriguing discovery that nitroso dimers in crystals undergo photodissociation has at least two perspectives. The first includes a study of topochemical effects in the solid-state chemical reactivity. The second includes a possibility of application of such effects in the molecular “ON-OFF” switches in the field of molecular electronics. Additionally, since monomers and dimers differ in color, monomers are blue or green and dimers yellowish or colorless, such a photochemically induced solid-state reaction can be visualized, and the effect represents one of the most interesting example of photochromism. A rapidly increasing interest in the solid-state reactions due to their application in the solvent-free synthetic methods is followed by a desire to design new intelligent materials. The efficacy of the solid-state reaction is governed by the topochemical postulate. It stated that reaction is possible only if topochemical postulate is satisfied. For example, a topochemical postulate will be fulfilled only in case when the monomer crystal structure affords close contacts between the reactive centers of neighboring molecules. 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. 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 drastically modifies the reaction rate of these solid-state reactions.

4-halogenonitrosobenzenes (azodioxides); dimerization; molecular “ON-OFF” switches; photodissociation; topochemical effects in solid state

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