From the viewpoint of developing photoresponsive supramolecular systems in microenvironments to exhibit more sophisticated photo-functions even at the macroscopic level, inorganic/organic hybrid compounds based on clay or niobate nanosheets as the microenvironments were prepared, characterized, and examined for their photoreactions. We show here a novel type of artificial muscle model unit having much similarity with that in natural muscle fibrils. Upon photoirradiation, the organic/inorganic hybrid nanosheets reversibly slide horizontally on a giant scale, and the interlayer spaces in the layered hybrid structure shrink and expand vertically. In particular, our layered hybrid molecular system exhibits a macroscopic morphological change on a giant scale (~1500 nm) compared with the molecular size of ~1 nm, based on a reversible sliding mechanism.
Organic-inorganic hybrids composed of polyfluoroalkyl azobenzene surfactant (abbreviated as C3F-Azo-C6H) and inorganic layered compounds are able to undergo reversible three-dimensional morphology changes such as interlayer space changes and nanosheet sliding in a giant scale due to reversible trans-cis isomerization of the azobenzene moiety upon photo-irradiation. In this paper, we have systematically studied the relationship between the layered hybrid microstructures of C3F-Azo-C6H-clay and their photoreactivity for understanding the mechanism of the photo-induced morphology change. The photoreactivity was found to be very much affected by the surrounding microenvironments. As compared with it in solution, the cis-trans photo-isomerization in C3F-Azo-C6H-clay nano-layered film was substantially enhanced with the quantum yield exceeding unity (Φ = 1.9), while the trans-cis isomerization was rather retarded. The corresponding hydrocarbon analogue of the azobenzene surfactant (C3H-Azo-C6H) did not show such an enhancement. The enhancement was discussed in terms of a cooperative effect among adjacent azobenzene moieties along with polyfluoroalkyl chains and the inorganic clay nanosheet to prevent a dissipation of the excess energy being liberated during the photo-isomerization within the nano-layered microenvironment.
A novel photofunctional material composed of polyfluorinated cationic azobenzene and layered potassium titanoniobate was synthesized and its photochemical behavior was investigated. Although polyfluorinated cationic azobenzene could not be intercalated into the interlayer region of layered potassium titanoniobate directly, the intercalation compound was obtained by guest-guest-exchange with the hexylammonium-TiNbO 5 intercalation compound. X-Ray diffraction, TGA, IR, TEM, UV-visible spectroscopy and elemental analysis results indicated that the polyfluorinated cationic azobenzene was intercalated into the interlayer spaces of the potassium titanoniobate. The AFM image for the intercalated compound with a basal spacing of 3.90 nm was consistent with the X-ray diffraction data. The spectral properties as well as X-ray diffraction results have revealed that the adsorbed polyfluorinated cationic azobenzene molecules form J-like aggregates with bi-layers in the interlayer space of the potassium titanoniobate. The intercalation compound exhibited an excellent reversible cis-trans photoisomerization by successive illumination with UV light at 365 nm and visible light at 458 nm. The basal spacing changed reversibly upon photoisomerization of the intercalated polyfluorinated cationic azobenzene.
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