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Optical Distinction between “Slow” and “Fast” Translational Motion in Degenerate Molecular Shuttles
Author(s) -
Vukotic V. Nicholas,
Zhu Kelong,
Baggi Giorgio,
Loeb Stephen J.
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201612549
Subject(s) - rotaxane , chemistry , axle , molecular machine , fluorescence , translational motion , molecule , stereochemistry , photochemistry , nanotechnology , materials science , supramolecular chemistry , optics , organic chemistry , physics , classical mechanics , thermodynamics
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.