Spectroscopic and electrochemical properties of catenanes containing the 2,7-diazapyrenium unit

The spectroscopic and electrochemical properties of two cyclophanes contain ing one and, respectively, two 2,7-diazapyrenium electron-acceptor units, a nd of their [2]catenanes with macrocycles containing two dioxybenzene or di oxynaphthalene electron-donor units have been investigated. The absorption spectra of the catenanes show weak and broad bands in the visible region, a ssigned to charge-transfer (CT) interactions. The very strong and structure d 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 qu enching process caused by the lower energy C-F excited states. Each diazapy renium unit undergoes two distinct reduction processes - only the first one of which is fully reversible - that are hardly affected at all when the di azapyrenium units are incorporated in a cyclophane. In the [2]catenanes, th e C-F interaction displaces the reduction processes of the diazapyrenium un its toward more negative potentials. The results obtained for the diazapyre nium and previously investigated 4,4 ' -bipyridinium salts, selected cyclop hane derivatives, and some [2]catenanes obtained by interlocking the cyclop hanes with macrocycles containing two dioxyaromatic electron-donor units ar e compared and discussed.