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Spectroscopic and Electrochemical Properties of Catenanes Containing the 2,7-Diazapyrenium Unit
Authors:Alberto Credi  Steven J Langford  Anna Prodi  J Fraser Stoddart  Margherita Venturi
Institution:1. Dipartimento di Chimica ‘G. Ciamician’ , Università di Bologna , via Selmi 2, I-40126, Bologna, Italy;2. School of Chemistry , University of Birmingham , Edgbaston, Birmingham, B15 2TT, UK;3. Dipartimento di Chimica ‘G. Ciamician’ , Università di Bologna , via Selmi 2, I-40126, Bologna, Italy;4. Dipartimento di Chimica , Università di Ferrara , via Borsari 46, I-44100, Ferrara, Italy;5. Department of Chemistry and Biochemistry , University of California , 405 Hilgard Avenue, Los Angeles, California, 90095-1569
Abstract:Abstract

The spectroscopic and electrochemical properties of two cyclophanes containing one and, respectively, two 2,7-diazapyrenium electron-acceptor units, and of their 2]catenanes with macrocycles containing two dioxybenzene or dioxynaphthalene electrondonor units have been investigated. The absorption spectra of the catenanes show weak and broad bands in the visible region, assigned to charge-transfer (CT) interactions. The very strong and structured fluorescence (298 K) and the structured fluorescence and phosphorescence (77 K) of the diazapyrenium unit are maintained in the two cyclophanes, but they are no longer present in the 2]catenanes, presumably because of a quenching process caused by the lower energy CT excited states. Each diazapyrenium unit undergoes two distinct reduction processes - only the first one of which is fully reversible - that are hardly affected at all when the diazapyrenium units are incorporated in a cyclophane. In the 2]catenanes, the CT interaction displaces the reduction processes of the diazapyrenium units toward more negative potentials. The results obtained for the diazapyrenium and previously investigated 4,4′-bipyridinium salts, selected cyclophane derivatives, and some 2]catenanes obtained by interlocking the cyclophanes with macrocycles containing two dioxyaromatic electron-donor units are compared and discussed.
Keywords:Catenanes  Photochemistry  Electrochemistry  Charge-transfer
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