The advent of supramolecular chemistry 1 has equipped chemists with the synthetic knowledge to construct molecule-level machines 2,3 using template-directed protocols. 4 The concept of nanoscopic machines has been realized in solution, 2,3 at air-water interfaces, 5 on surfaces, 6,7 and in solid-state devices. 8 At a supramolecular level, in complexes we have called 9 pseudorotaxanes, the self-assembly of the components can be reversed upon quelling temporarily the molecular recognition that exists between matching pieces. Thus, a supramolecular machine can be defined 6 as an assembly of two or more molecular components designed to perform mechanical-like motions in response to stimuliswhich include 2,3 chemical, electrochemical, and photochemical pulsessthat can be switched on and off at will. In [2]pseudorotaxanes, the dethreading and rethreading movements of the rod from the ring component are reminiscent 2 of the motions of a linear motor. There are a number of artificial supramolecular machines 2,3 based on [2]-pseudorotaxanes that can be induced to undergo co-conformational changes 10 by chemical, electrochemical, or photochemical means.Although it has been demonstrated 2,3 that pseudorotaxanes thread and dethread in solution, to do useful work and hence realize their potential as machines, they have to be attached to solid supports. Previously, we have shown 6 that photochemically induced threading and dethreading of a pseudorotaxane-based machine does occur when it is attached to a silica surface. Here, we describe (i) the tethering of pseudorotaxanes as gates at the entrances of ∼ 2 nm diameter, cylindrical pores 11 in mesostructured silica (ii) to create nanovalves ( Figure 1) capable of trapping luminescent molecules and able (iii) to release them on demand.The [2]pseudorotaxane [DNPD⊂CBPQT] 4+ was employed as a gatekeeper in the form 6 of a tethered 1,5-dioxynaphthalene (DNP)-containing derivative (DNPD), acting as the gatepost, and cyclobis-(paraquat-p-phenylene) (CBPQT 4+ ), which recognizes DNP units on account of a cooperative array of noncovalent interactions, serving as the gate that controls access in and out of the nanopores. By using tris(2,2′-phenylpyridyl)iridium(III), 12 Ir(ppy) 3 swhich has a diameter of ca. 1 nm and exhibits fluorescent emission at 506 nmsas the trapped molecules, the release process from the nanopores can be followed by fluorescence spectroscopy. The power supply 13 is an external reducing reagent (NaCNBH 3 ) that opens the nanovalve and allows the release of the luminescent molecules. The operation of the nanovalve involves four stages: (i) preparing the container, (ii) filling it, (iii) closing the valve, and (iv) opening the valve to release its contents.The first steps in preparing the nanovalve are making the nanocontainer with gateposts, before filling it with fluorescent molecules and closing the gate. A sol-gel-based dip-coating method was used to effect the rapid synthesis of continuous mesostructured thin films consisting 14 of a 2-D hexagonal array. Calcina...

Methods of making mesostructured sol-gel silicate thin films containing two different molecules deliberately placed in two different spatially separated regions in a one-step, one-pot preparation are developed and demonstrated. When the structure-directing agent is the surfactant cetyltrimethylammonium bromide, the structure is 2-D hexagonal with lattice spacings between 31.6 and 42.1 angstroms depending on the dopant molecules and their concentrations. The three general strategies that are used to place the molecules are philicity (like dissolves like), bonding, and bifunctionality. These strategies take advantage of the different chemical and physical properties of the regions of the films. These regions are the inorganic silicate framework, the hydrophobic organic interior of the micelles, and the ionic interface between them. Luminescent molecules that possess the physical and chemical properties appropriate for the desired strategies are chosen. Lanthanide and ruthenium complexes with condensable trialkoxysilane groups are incorporated into the silicate framework. 1,4-Naphthoquinone, pyrene, rhodamine 6G and coumarin 540A, and lanthanides with no condensable trialkoxysilanes occupy the hydrophobic core of micelles by virtue of their hydrophobicity. The locations of the molecules are determined by luminescence spectroscopy and by luminescence lifetime measurements. In all cases, the long-range order templated into the thin film is verified by X-ray diffraction. The simultaneous placement of two molecules in the structured film and the maintenance of long-range order require a delicate balance among film preparation methodology, design of the molecules to be incorporated in specific regions, and concentrations of all of the species.

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Despite its reputation for lack of reactivity at moderate temperatures, nitrous oxide is capable of oxidizing at least one class of organic compounds, the phosphines, at temperatures at or below 100 °C. The use of supercritical N2O as both the solvent and the reactant simplifies the isolation of the products and allows one to avoid the use of flammable liquid solvents.

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