Stimulus-responsive gels have recently attracted widespread attention as new functional materials for potential applications in sensors, [1] actuators, [2] shape memories, [3] drug delivery devices, [4] and displays. [5] One of the promising properties that organogels based on low molecular mass organic gelators (LMOGs) can offer is their reversible sol-gel phase transition as a result of external stimuli. [6] As far as we know, redoxresponsive organogels from LMOGs, however, are limited. Shinkai and coworkers [7a] reported the first example of organogels of this kind, which contains a redox-active Cu I / Cu II center. Besides, they also synthesized a series of quater-, quinque-, and sexithiophene derivatives bearing two cholesteryl moieties at the a-position. It was found that a sol-gel phase transition can be implemented by addition of oxidizing and reducing reagents.[7b] Zhu and colleagues [7c] prepared an electro-active LMOG containing a tetrathiafulvalene (TTF) entity. The gel formation can be tuned by means of oxidation/ reduction of the TTF group chemically or electrochemically. Although these gel systems are redox responsive, their properties, such as mechanical strength, flexibility, and sensitivity to external stimulus, are far from those required for practical uses. Therefore, creating instant, reversible, redox-responsive, and mechanically flexible organogels still remains a challenge. As a remarkable organometallic compound, ferrocene (Fc) contains an oxidizable metal ion, Fe II , and is a nonpolar compound in the neutral state, and thereby it dissolves readily in hydrocarbon solvents. This property, however, can be easily reversed by simple oxidation of the central ion. Our interest in stimulus-responsive supramolecular gel systems led us to consider the compound as a neutral-cation redox pair that may be employed to tune the gelling ability of a gelator containing it. Actually, the same idea has been adopted by a number of groups for studies of switchable complexation and molecular aggregation in micelles and vesicles. [8] However, all compounds containing the apolar ferrocenyl or charged ferrocenium moiety reported so far do not result in gelation, as documented for a number of solvents. [8b,8c] Introduction of metal ions is a practical way of giving organogels some smart properties.[9] For example, Sijbesma and coworkers [9a] designed and prepared two chloroform gels with reported a palladium-based organometallic LMOG that is able to catalyze C-C bond formation even in the gel state. We report here four novel cholesterol-appended ferrocene derivatives ( Fig. 1a; see Supporting Information for preparation details), and present first evidence for the gelation ability of organometallic compounds of this kind, and particularly the unusual redox-, mechanical-, and ultrasonic-controllable sol-gel phase transition phenomena. These gelators contain one redox-active ferrocenyl moiety and one cholesteryl residue linked by different diamino units. This design was chosen on the basis of the analys...

A series of novel and stable water in oil (W/O) gel-emulsions was created by utilizing a new cholesteryl derivative, a low-molecular mass gelator (LMMGs), as a stabilizer. In the emulsions, n-heptane, n-octane, n-nonane, n-decane, tertiary butyl methacrylate (t-BMA), methyl methacrylate (MMA), or styrene can be used as a continuous phase, water as a dispersed phase, and the stabilizer in the continuous phase is only 2% (w/v). Importantly, the gel-emulsions could be prepared by simple agitation of the mixtures at room temperature, while heating, cooling, and addition of a cosolvent or other additional component are unnecessary. SEM and optical microscopy studies revealed the foam-like structures of the gel-emulsions. Rheological measurements demonstrated that the gel-emulsions are mechanically stable and exhibit typical viscoelastic properties. Surprisingly, the storage modulus, G', and the yield stress of the gel-emulsions with the alkanes as continuous phase decrease along with increasing the volume ratio of the dispersed phase, water, a property different from those of conventional gel-emulsions reported in the literature. From the viewpoint of application, the gel-emulsions as prepared are superior to others due to their simplicity in preparation, less amount of stabilizer needed, and the nonionic nature of the stabilizer, which must benefit practical applications. Furthermore, porous polymer monoliths could be prepared by polymerizing gel-emulsions with organic monomers as a continuous phase.

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This article is intended to provide an overview of recent progress in the studies of cholesterol-based low-molecular mass gelators (LMMGs) with unusual properties, in particular, gelation and selective gelation at room temperature, gel emulsions and gel film formation, etc. Potential applications of the LMMGs in spilled oil collection and water purification are briefly presented.gelation at room temperature, selective gelation, gel emulsions, gel films

With ever-increasing need for thin, flexible, and functional materials in electrochemical systems, various techniques have been explored for creating materials used in fuel cells, batteries, electrochromic devices, solar cells, and sensors. In the present study, a novel ferrocene (Fc) and cholesterol (Chol)-containing oligomer, oligo(FcDC-co-CholDEA), was specially designed and prepared by putting Fc in the main chain and Chol as a side group. MALDI-TOF MS and freezing point depression measurements revealed that in average each oligomer contains three Fc units and three Chol units. Cyclic voltammetric measurements revealed that the oligomer displays superior electrochemical stability if compared with other Fc derivatives containing only one Fc unit and one or two Chol unit and with poly(ferrocenylsilane) with Fc in the main chain. In particular, the Fc-containing oligomer possesses an unusual oxidation center, of which the oxidation potential could be as high as 1.81 V. The oligomer is also superior in self-assembly, as demonstrated by forming an LB film of layered structures. Furthermore, supramolecular films with high mechanical strength in the wet state can be prepared by employing a simple solution casting method. This finding demonstrates that self-assembly is a simple but effective way to create films of potential uses in real-life applications provided proper building blocks are designed and employed.

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