Angewandte Chemie - International Edition
Angewandte Chemie - International Edition
5 years ago

Optical Distinction between “Slow” and “Fast” Translational Motion in Degenerate Molecular Shuttles

Optical Distinction between “Slow” and “Fast” Translational Motion in Degenerate Molecular Shuttles
Giorgio Baggi, Stephen J. Loeb, Kelong Zhu, V. Nicholas Vukotic
A series of six [2]rotaxane molecular shuttles was designed which contain an axle with a benzo-bis(imidazole) core (in either a neutral or dicationic form) and a single 24-membered, crown ether wheel (24C6, B24C6, or DMB24C6), and the shuttling rates of the ring along the axle were determined. The charged versions showed much slower shuttling rates as a result of the increase in noncovalent interactions between the axle and wheel. The [2]rotaxane with a B24C6 wheel shows a difference in fluorescence between the charged and neutral species, while the [2]rotaxane with a DMB24C6 wheel exhibits a difference in color between the charged and neutral compounds. These changes in optical properties can be attributed to the structural differences in the co-conformations of the [2]rotaxane as they adapt to the changes in acid/base chemistry. This allowed the relative rate of the translational motion of a molecular shuttle to be determined by observation of a simple optical probe. Set the wheels in motion: The dicationic and neutral forms of a degenerate molecular shuttle containing an axle with a benzo-bis(imidazole) core show very different shuttling rates as a result of differences in the noncovalent interactions between the axle and wheel in the two forms. Acid/base chemistry can be used to control the shuttling, which is signaled by an optical output: a change in color or fluorescence.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201612549

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