Since the discovery of MCM-41 more than ten years ago, many investigations have explored the suitability of hexagonal mesoporous silicas for potential practical applications. These range from catalysis and optically active materials to polymerization science, separation technology and drug delivery, with recent successes in the fabrication of hybrid mesoporous organosilicas expected to open up further application possibilities. Because the pore voids of this class of materials exhibit relatively narrow pore size distributions in the range of 2-4 nm in diameter, mesoporous silicas can selectively include organic compounds and release them continuously at a later stage. The functionalization of MCM-41 pore voids with photoactive derivatives provides influence over the material's absorption behaviour, but full control over the release process remains difficult. Here we show that the uptake, storage and release of organic molecules in MCM-41 can be regulated through the photocontrolled and reversible intermolecular dimerization of coumarin derivatives attached to the pore outlets. Successful functionalization requires uncalcined MCM-41 still filled with the template molecules that directed the formation of its pores, to ensure that coumarin derivatives attach preferentially to the pore outlets, rather than their inside walls. We find that this feature and the one-dimensional, isolated nature of the individual pores allow for efficient and reversible photocontrol over guest access to the material's interior.

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A photoresponsive coumarin derivative was grafted on the pore outlet of Si-MCM-41. Irradiation of UV light longer than 310-nm wavelength to this coumarin-modified MCM-41 induced the photodimerization of coumarin to close the pore outlet with cyclobutane dimer. Guest molecules such as phenanthrene neither can enter nor escape from the onedimensional, isolated, individual pores of MCM-41. On the other hand, the irradiation to the dimerized-coumarin-modified MCM-41 with shorter wavelength UV light around 250 nm regenerates the coumarin monomer derivative by the photocleavage of cyclobutane dimer, and guest molecules included inside are released from the pore void. For the first time, this intermolecular reversible photodimerization-cleavage cycle realized photo-switched storage and release of guest molecules from coumarin-modified MCM-41. Coumarin-modified MCM-41 prepared using tetradecyltrimethylammonium bromide as surfactant was able to store 21.6 wt % of phenanthrene as guest molecule after photodimerization and washing with n-hexane. Among the four different methods studied for the modification by the coumarin derivative, a grafting procedure with as-synthesized MCM-41 for short reaction time was found to be the most effective for the dense attachment of coumarin-derived monomer at the pore outlets of MCM-41, which is essential for effective storage-release controlled release.

Silica microcapsules (hollow spheres) were readily prepared by an interfacial reaction using a water/oil/water (W/O/W) emulsion system. A W/O emulsion consisting of an aqueous solution of sodium silicate (WP-1) and an n-hexane solution of Tween 80 and Span 80 (OP) was added to another aqueous solution of a precipitant (WP-2). The reaction of sodium silicate with a precipitant to form silica on this W/O/W emulsion system (WP-1/OP/WP-2) forms the hollow structure spontaneously. Therefore, no core material often utilized in silica hollow sphere fabrication was required in this process. The formation and the particle size of the silica microcapsule depended on the precipitant employed. When NH 4 HCO 3 was used as precipitant, the particle size of the silica microcapsule was successfully controlled by the volume ratio of WP-1/OP/WP-2, the rotation number of the homogenizer, and the concentration of sodium silicate in WP-1. However, this control of the particle size was not achieved when other precipitants such as NH 4 Cl were used. In the case of NH 4 HCO 3 , silica formation takes place at the outer interface between OP and WP-2 on the W/O/W emulsion system. On the other hand, when NH 4 Cl is utilized, silica is yielded at the inner interface between WP-1 and OP. These differences of reaction mechanisms of sodium silicate among precipitants were important factors in the preparation and properties of microcapsules.

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There remains an ongoing interest in molecular nanotechnology. [1][2][3][4][5][6][7][8][9][10] The operational range of molecular motion is too restricted to create macroscopic phenomena. However, in the small spaces of mesopores, molecular movement on the nanometer level is sufficient to dominate the physical and chemical behaviors of guest molecules, for example, as shown by a molecular gating system on a mesopore outlet.[4] The release rates of guest molecules in pore voids are dominated by inactive diffusion in all reported gating systems, [4,[7][8][9][10][11][12] and no acceleration of release has been claimed. Developing on from the primary gating system, [4] here we report a multifunctional, fully controlled storage and release system by installing two photomechanical units that behave as "stirrer" and "gate" functions into mesoporous silica. An enhancement of the release rate of the guest molecule in mesoporous silica is induced by reversible photoisomerization of azobenzene groups attached to the inner surface.A sample of solvent-extracted mesoporous silica (1 A) was modified with 5.6 wt % of N-(3-triethoxysilyl)-propyl-4-phenylazobenzamide inside the pores (1 B), and this modified sample was then loaded with 35.1 wt % of cholesterol (1 C; see Experimental Section). UV/Vis diffuse reflectance spectra were measured on the powdery azobenzene-modified (1 B) and cholesterol-loaded samples (1 C) under various photoirradiation conditions ( Figure 1). As expected, both samples show similar variations in their UV/Vis diffuse reflectance spectra under photoirradiation (Figure 1), indicating that photoisomerization occurs even when a significant amount of cholesterol was loaded into the narrow pores. Irradiation with UV light (l % 360 nm) induced a gradual decrease in the absorption at 340 nm (corresponding to the pp* transition of the trans isomer) with an increase in the absorption at 430 nm (corresponding to the n-p* transition of the cis isomer). The trans-to-cis photoisomerization of the azobenzene group took place in the pore, and it reached a photostationary state after irradiation for 30 min. On the other hand, when UV/Vis light (UV: 80 mW, l % 360 nm; Vis: 54 mW, l % 430 nm) was used to irradiate samples 1 B and 1 C for 10 min, the isomerization reached another photostationary state.Azobenzene moieties are characterized by fast, stable, and reversible photoisomerization by a rotation-inversion mechanism, [13][14][15] which is exploited in various applications. [16][17][18] Here, we used the photoinduced molecular "motion" of azobenzene isomerization to accelerate the release of guest molecules from mesopores. When the trans isomer is irradiated with UV light, an excitation state is achieved and the benzene group rotates and/or inverts to form the cis isomer, while irradiation with visible light turns the cis isomer into the trans isomer. The reversible photoisomerization by UV and visible light creates a continuous rotation-inversion movement, accompanied with stretchshrink motions. During this process, t...

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