Molecular meccano, 56 - Anthracene-containing [2]rotaxanes: Synthesis, spectroscopic, and electrochemical properties

Two dumbbell-shaped compounds (8 and 11), each composed of two polyether ch ains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetr aarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-di oxy-anthracene unit, have been synthesized. Two [2]rotaxanes (9.4 PF6 and 1 2.4 PF6) have been prepared by interlocking these dumbbell-shaped compounds (8 and 11) with a bipyridinium-based tetracationic cyclophane (15.4 PF6) - namely, cyclobis(paraquat-p-phenylene). A [3]rotaxane (10.8 PF6) incorpora ting two cyclophane components (15.4 PF6) was also obtained when the 9,10-d ioxyanthracene-containing dumbbell-shaped compound (8) incorporating two 1, 4-dioxybenzene recognition sites was employed. The H-1-NMR spectroscopic in vestigation of the [2]rotaxanes (9.4 PF6 and 12.4 PF6) revealed that the cy clophane component encircles one of the two 1,4-dioxybenzene recognition si tes in the 9,10-dioxyanthracene-containing [2]rotaxane (9.4 PF6) and the 2, 6-dioxyanthracene unit in the other [2]rotaxane (12.4 PF6). These structure s have been confirmed by UV/Vis and electrochemical experiments. Comparison with the spectroscopic properties of simple model compounds shows the pres ence of electronic interactions which lead to (i) the occurrence of very ef ficient energy transfer processes in the dumbbell-shaped components and (ii ) perturbations in the absorption spectra with appearance of two charge-tra nsfer absorption bands and complete luminescence quenching in the [2]rotaxa nes. For the 2,6-dioxyanthracene-containing [2]rotaxane (12.4 PF6), it has been demonstrated that the cyclophane can be displaced from the dioxyanthra cene to the 1,4-dioxybenzene station upon electrochemical oxidation.