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Published December 11, 2013 | Supplemental Material
Journal Article Open

Relative Unidirectional Translation in an Artificial Molecular Assembly Fueled by Light


Motor molecules present in nature convert energy inputs, such as a chemical fuel or incident photons of light, into directed motion and force biochemical systems away from thermal equilibrium. The ability not only to control relative movements of components in molecules but also to drive their components preferentially in one direction relative to each other using versatile stimuli is one of the keys to future technological applications. Herein, we describe a wholly synthetic small-molecule system that, under the influence of chemical reagents, electrical potential, or visible light, undergoes unidirectional relative translational motion. Altering the redox state of a cyclobis(paraquat-p-phenylene) ring simultaneously (i) inverts the relative heights of kinetic barriers presented by the two termini—one a neutral 2-isopropylphenyl group and the other a positively charged 3,5-dimethylpyridinium unit—of a constitutionally asymmetric dumbbell, which can impair the threading/dethreading of a [2]pseudorotaxane, and (ii) controls the ring's affinity for a 1,5-dioxynaphthalene binding site located in the dumbbell's central core. The formation and subsequent dissociation of the [2]pseudorotaxane by passage of the ring over the neutral and positively charged termini of the dumbbell component in one, and only one, direction relatively defined has been demonstrated by (i) spectroscopic (1H NMR and UV/vis) means and cyclic voltammetry as well as with (ii) DFT calculations and by (iii) comparison with control compounds in the shape of constitutionally symmetrical [2]pseudorotaxanes, one with two positively charged ends and the other with two neutral ends. The operation of the system relies solely on reversible, yet stable, noncovalent bonding interactions. Moreover, in the presence of a photosensitizer, visible-light energy is the only fuel source that is needed to drive the unidirectional molecular translation, making it feasible to repeat the operation numerous times without the buildup of byproducts.

Additional Information

© 2013 American Chemical Society. Received: September 11, 2013; Published: October 30, 2013. This work was supported by the Non-Equilibrium Energy Center (NERC), which is an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences award DE-SC0000989. M.R.W., R.M.Y., D.T.C., and S.M.D. are supported by the Argonne Northwestern Solar Energy Research (ANSER) Center, which is an EFRC funded by the DOE-BES under award DE-SC0001059 (light-driven experiments). W.G.L. and W.A.G. are supported by the National Science Foundation (NSF) (CMMI-1120890 and EFRI-ODISSEI-1332411). W.A.G. is also supported by the World Class University (WCU) Program (R-31-2008-000- 10055-0) funded by the Ministry of Education, Science and Technology, Republic of Korea. H.L. is thankful for a Chinese Government Award for Outstanding Self-Financed Students Abroad. P.R.M thanks the US-UK Fulbright Commission for an All-Disciplines Scholar Award. A.C.F. acknowledges support from a National Science Foundation (NSF) Graduate Research Fellowship. C.K. thanks the Royal Society in the U.K. for support as a Newton Fellow Alumnus.

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