Which one is Bulkier: the 3,5-Dimethylphenyl or the 2,6-Dimethylphenyl Group? Development of Size-Complementary Molecular and Macromolecular Rotaxanes
Chemistry, an Asian journal | 3 Feb 2018
H Sato, D Aoki and T Takata
We developed novel size-complementary molecular and macromolecular rotaxanes using a 2,6-dimethylphenyl terminal as the axle-end-cap group in dibenzo-24-crown-8-ether (DB24C8)-based rotaxanes, where the 2,6-dimethylphenyl group was found to be less bulky than the 3,5-dimethylphenyl group. A series of molecular and macromolecular rotaxanes that bear a 2,6-dimethylphenyl group as the axle-end-cap were synthesized using unsubstituted and fluorine-substituted DB24C8. Base-induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size-complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate-determining step to be the step that the wheel is getting over the end-cap group, and the deslipping proceeded via a hopping-over mechanism. Finally, the present deslipping behavior was applied to a stimulus-degradable polymer as an example for the versatile utility of this concept in the context of stimulus-responsive materials.
* Data courtesy of Altmetric.com