Photo-induced morphological winding and unwinding motion of nanoscrolls composed of niobate nanosheets with a polyfluoroalkyl azobenzene derivative

Abstract

Photo-responsive nanoscrolls can be successfully fabricated by mixing a polyfluoroalkyl azobenzene derivative and a niobate nanosheet, which is exfoliated from potassium hexaniobate. In this study, we have found that the photo-responsive nanoscroll shows a morphological motion of winding and unwinding, which is basically due to the nanosheet sliding within the nanoscroll, by efficient photo-isomerization reactions of the intercalated azobenzene in addition to the interlayer distance change of the nanoscrolls. The relative nanosheet sliding of the nanoscroll is estimated to be ca. 280 nm from the AFM morphology analysis. The distance of the sliding motion is over 20 times that of the averaged nanosheet sliding in the azobenzene/niobate hybrid film reported previously. Photo-responsive nanoscrolls can be expected to be novel photo-activated actuators and artificial muscle model materials.

Photo-Activated Motion of Layered Hybrids Induced by the High-Order Architecture of Azobenzene Assembly on Niobate Nanosheets and the Microenvironment

“…18,26,27 In these contexts, we have fabricated the layered nanosheet hybrids composed of polyfluoroalkyl azobenzene derivative (C3F-Azo-C6H: Figure 1a), which is originally synthesized in our group, and inorganic nanosheets to bring out potential photo-functions of molecular assembly in a nanosheet microenvironment. 8,11,12,19 For example, in the clay nanosheet microenvironment, C3F-Azo-C6Hs exceeding over the cation exchange capacity have been intercalated into the interlayer spaces of layered clay nanosheets, 11,19 where C3F-Azo-C6Hs were closely packed between the clay nanosheets due to both the strong hydrophobicity and lipophobicity of the perfluorocarbon chain. Furthermore, it has been found that the photoreactivity for cis−trans photo-isomerization has been remarkably enhanced in the clay hybrid, where the quantum yield exceeded unity (Φ cis−trans = 1.9).…”

“…12,27,30 Interestingly, the double-walled nanoscroll can undergo a winding and unwinding motion, which is basically due to the nanosheet sliding within the nanoscroll induced by efficient photo-isomerization reactions of the C3F-Azo-C6H. 12 The maximum nanosheet sliding within some nanoscrolls is estimated to be about 280 nm.…”

“…An inorganic nanosheet prepared by exfoliation from a layered microcrystal has also been expected to be one of the most promising materials providing the microenvironment for supramolecular systems and molecular assemblies because of their characteristics such as the extensively wide and smooth surface area, surface positive/negative charge, flexible interlayer distance, and intercalation ability of functional molecules into the interlayer spaces. − In particular, an organic/inorganic hybrid composed of photo-responsive molecule and inorganic nanosheet is a curious supramolecular system coupled with the nanosheet microenvironment to express various photo-functions such as fluorescence enhancement, highly efficient excitation energy transfer , and chemical reactions, − photocatalysis, , artificial photosynthesis, − photo-activated actuator materials, ,, and so on. It is also noteworthy that further improvement and novel expression of photo-functions have been expected by controlling the dimensionality of nanosheet systems between an exfoliated single nanosheet, stacked nanosheets, nanoscroll, and nanoscroll aggregates. ,, …”

“…In the past several decades, many supramolecular systems and molecular assemblies have been extensively studied for various advanced functions . To develop more sophisticated functions, much attention has been focused to supramolecular systems coupled with a unique surrounding microenvironment: many types of materials such as cyclodextrins, mesoporous materials, − nanosheets, − nanostructured systems, − and so on, have been expected as the microenvironment for supramolecular systems. Their physical and chemical properties, reactivities, and functionalities have been extensively studied from a variety of perspectives.…”

“…Furthermore, it has been found that the photo-reactivity for cis – trans photo-isomerization has been remarkably enhanced in the clay hybrid, where the quantum yield exceeded unity (Φ cis – trans = 1.9) . In the niobate nanosheet microenvironment, C3F-Azo-C6H has similarly been intercalated into the interlayer spaces of layered niobate nanosheets to expand the interlayer distance, ,, which is reversibly changed upon UV- and visible light-irradiations. The expansion ratio of the hybrid, which is defined as the interlayer distance of the most expanded state against that of the most shrunken one, is more than 10% in the niobate nanosheet microenvironment.…”