Hindered fluorescence quenching in an insulated molecular wire

A 3]rotaxane 2 within 1(2) consisting of an anionic phenylene ethynylene dumbbell 2(4-) threaded through two cationic cyclophanes 1(2+) has been prepared using aqueous Glaser coupling. Stern-Volmer analysis of the fluorescence quenching using three different electron-acceptors (methyl viologen 13(2+), dipropyl-4,4'-bipyridinium disulfonate 14 and anthraquinone-2,6-disulfonate 15(2-)) shows that the threaded cyclophanes inhibit electron-transfer from the excited state of the dumbbell by steric shielding, and by electrostatic shielding in the case of methyl viologen.