Optical Distinction between "Slow" and "Fast" Translational Motion in Degenerate Molecular Shuttles.
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.
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, N9B 3P4, Canada.
V Nicholas
VN
Vukotic
School of Chemistry, Sun Yat-Sen University, Guangzhou, 510275, P.R. China.
Kelong
K
Zhu
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, N9B 3P4, Canada.
Giorgio
G
Baggi
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, N9B 3P4, Canada.
Stephen J
0000-0002-8454-6443
SJ
Loeb
co-conformations; molecular shuttles; optical switches; rotaxanes; supramolecular chemistry