Switchable electron-rich biindolizine-based macrocycles: synthesis and redox properties

Abstract

New redox-active cyclophanes, incorporating electrochemically switchable biindolizine units in combination with π-electron-rich hydroquinol units in the ether bridges, have been synthesized by intra- and inter-molecular cyclisation. The electrochemical properties of the cyclophanes, investigated by cyclic voltammetry (CV), are reported. Cyclophanes 5a/6a and 7a, containing 1,4-dioxyphenylene units, showed three reversible redox steps as expected. In contrast, intramolecular interactions occur for cyclophanes 5b/6b and 7b, containing 1,5-dioxynaphthylene as part of the cyclophane ring system. Compounds 5b/6b displayed changes in their electrochemical behaviour upon addition of 2,4,7-trinitrofluoren-9-one but, in general, no influence of potential guests on the half-wave potentials of the biindolizine unit could be established. To have additional possibilities of supramolecular interactions, new 2,2′-heterocycle-disubstituted biindolizines 8 and 9 have been synthesized, which in CV signals a complexation of copper near to the biindolizine redox unit.