Versatile Supramolecular Nanovalves Reconfigured for Light Activation

Authors

  • T. D. Nguyen,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
    2. Current address: Advanced Technology and Systems Analysis Division, Center for Naval Analyses, 4825 Mark Center Dr., Alexandria, VA 22311, USA
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  • K. C.-F. Leung,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
    2. Current address: Center of Novel Functional Molecules, Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, P.R. China
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  • M. Liong,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
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  • Y. Liu,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
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  • J. F. Stoddart,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
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  • J. I. Zink

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
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  • We thank Professor Mark Thompson (University of Southern California) for providing us with a sample of Ir(ppy)3. We acknowledge a discussion with Drs. Alberto Credi and Edward Plummer about possible pathways of light activation, Dr. Johnny Skelton for early help with experimental setup and, Dr. Sourav Saha for manuscript preparation. The powder XRD instrument used in this work was obtained under equipment grant number DMR-0315828. This research was supported by NSF grants DMR-0346601 and CHE-0507929.

Abstract

All autonomous machines share the same requirement—namely, they need some form of energy to perform their operations and nanovalves are no exception. Supramolecular nanovalves constructed from [2]pseudorotaxanes—behaving as dissociatable complexes attached to mesoporous silica which acts as a supporting platform and reservoir—rely on donor-acceptor and hydrogen bonding interactions between the ring component and the linear component to control the ON and OFF states. The method of operation of these supramolecular nanovalves involves primarily the weakening of these interactions. The [2]pseudorotaxane [BHEEEN ⊂ CBPQT]4+ [BHEEEN ≡ 1,5-bis[2-(2-(2-hydroxyethoxy)ethoxy)ethoxy]naphthalene and CBPQT4+ ≡ cyclobis(paraquat-p-phenylene)], when this 1:1 complex is tethered on the surface of the mesoporous silica, constitutes the supramolecular nanovalves. The mesoporous silica is charged against a concentration gradient with luminescence probe molecules, e.g., tris(2,2′-phenylpyridyl)iridium(III), Ir(ppy)3 (ppy = 2,2′-phenylpyridyl), followed by addition of CBPQT·4Cl to form the tethered [2]pseudorotaxanes. This situation corresponds to the OFF state of the supramolecular nanovalves. Their ON state can be initiated by reducing the CBPQT4+ ring with NaCNBH3, thus weakening the complexation and causing dissociation of the CBPQT4+ ring away from the BHEEEN stalks on the mesoporous silica particles MCM-41 to bring about ultimately the controlled release of the luminescence probe molecules from the mesoporous silica particles with an average diameter of 600 nm. This kind of functioning supramolecular system can be reconfigured further with built-in photosensitizers, such as tethered 9-anthracenecarboxylic acid and tethered [Ru(bpy)2(bpy(CH2OH)2)]2+ (bpy = 2,2′-bipyridine). Upon irradiation with laser light of an appropriate wavelength, the excited photosensitizers transfer electrons to the near-by CBPQT4+ rings, reducing them so that they dissociate away from the BHEEEN stalks on the surface of the mesoporous silica particles, leading subsequently to a controlled release of the luminescent probe molecules. This control can be expressed in both a regional and temporal manner by the use of light as the ON/OFF stimulus for the supramolecular nanovalves.

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