Acid/Base‐ and Anion‐Controllable Organogels Formed From a Urea‐Based Molecular Switch

Hsueh, Sheng-Yao; Kuo, Chih‐Ming; Lu, Tung‐Wu; Lai, Chien‐Chen; Liu, Yi-Hung; Hsu, Hsiu‐Fu; Peng, Shie‐Ming; Chen, Chun‐Hsien; Chiu, Sheng‐Hsien

doi:10.1002/anie.201004090

Cited by 105 publications

(20 citation statements)

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“…Based on the reported macrocycle designed by Chiu and co‐workers,3c, 4a we obtained a ditopicmacrocycle 4 , which contains a 2,6‐pyridinediamide, a polyether chain, and a ferrocenyl unit (Scheme ). The designed bistable [2]rotaxane [ 1 ‐H][PF 6 ] incorporates the ferrocenyl macrocycle 4 4a, 10f, 12 and a dialkylammonium group (DAA + ) and urea station in the thread (Scheme ).…”

Section: Methodsmentioning

confidence: 99%

A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

et al. 2014

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A switchable, bistable molecular shuttle based on dialkylammonium ion and urea functional recognition sites, and a macrocycle bearing a ferrocenyl unit has been constructed, in which the ferrocenyl macrocycle can be easily switched along the thread by addition of acid/base or by addition/removal of acetate anions. The shuttling motion of the macrocycle is accompanied with different fluorescence responses via the adjustment of the photoinduced electron transfer (PET) effect between the ferrocene electron donor and the fluorophores.Mechanically interlocked molecules (MIMs), [1] in particular functional bistable [2]rotaxanes, have attracted much attention in the past few decades due to their challenging construction and potential applications as an excellent framework for the fabrication of molecular machines, such as molecular switches and probes. [2] The shuttling motion of the macrocycle between different recognition sites on the rotaxane thread can be driven by acid/base, [3] ion binding, [4] altering the oxidation state, [5] photochemistry, [6] and solvent changes. [7] Some of these shuttling motions are usually accompanied with remarkable changes in physical properties, such as circular dichroism, [8] conductivity, [9] and fluorescence. [10] Among them, fluorescence change is preferably used as an output signal since it can be easily and remotely detected with low cost.Recently, some successful examples based on bistable [2]rotaxanes with excellent fluorescence responses have been developed, [10] for example, a typical [2]rotaxane with a fluorescent response toward the shuttling movements was reported by Tian and co-workers in 2004. [10a] With further research for switchable rotaxane-containing fluorophores, ferrocene-modified rotaxane attracted more and more attention. [10f, g, k-m] A pyrene/ferrocene-based [2]rotaxane with a three-level lumines-cent response was reported by Mateo-Alonso et al., [10f] and a ferrocene-functionalized molecular shuttle was constructed by Qu and co-workers, in which the fluorescence of the rotaxane can be reduced or enhanced alternately by an adjustable photoinduced electron transfer (PET) process occurring between two ferrocene (Fc) units in the macrocycle and two fluorescent stoppers. [10l] However, it is still a challenge to construct systems in which the shuttling motion of the macrocycle is accompanied with different fluorescence responses, and surely this system would pave the way for constructing more complicated and delicate multilevel molecular switches with optical signals.On the basis of the above-mentioned works and our recent work on a phosphine-oxide-based, three-station molecular shuttle, [4d] and in continuation of research on molecular shuttles, herein we describe an acid/base and anion-responsive bistable molecular shuttle bearing an anthracene stopper on the thread and a ferrocenyl unit on the macrocycle, in which two different states are obtained by using external stimuli (acid/ base and anions). As a result, the fluorescence can be reduced or enhan...

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Section: Methodsmentioning

confidence: 99%

A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

et al. 2014

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“…Responsive 3D self‐assembled materials built on switchable rotaxanes present the interesting potential to modify their supramolecular structure—in shape or volume—by synchronized mechanical actuations, but they remain limited to only few examples in the literature to date. In 2010, the groups of Chen and Chiu reported the discovery of the first organogelator based on a [2]rotaxane . The gelation properties of this molecular machine originate from the presence of a free urea station involved in intermolecular hydrogen bonding interactions leading to the formation of networks of bundled fibers, as determined by TEM and AFM imaging.…”

Section: Molecular Machines In Self‐assembled 3d Materialsmentioning

confidence: 99%

From Molecular Machines to Stimuli‐Responsive Materials

et al. 2019

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Shape-memory effects and mechanical actuations can be indeed generated from objects of various chemical nature [3][4][5] (e.g., metallic alloys, ceramics, liquid crystals, or polymers), and they are often supported by a combination of bottom-up and top-down structural engineering techniques going from surfaces to 3D materials (e.g., supramolecular self-assembly, photopatterning, microfluidics, or inkjet printing). [6,7] Various stimuli can generate their response (e.g., molecules, temperature, light, electrical potential, or mechanical stress) and their functioning principles vary largely from one system to another, involving a number of physical phenomena which can take place at the (macro)molecular level and which are transferred toward higher length scales (e.g., polarity, solubility-such as lower critical solution temperature (LCST), osmotic pressure, surface energy, or phase transition). It should also be mentioned that bio-inspiration is often a driving force in the design of such artificial materials as many smart mechano-active systems with adaptable properties are found in nature (e.g., stiffness change of sea cucumber, adaptive toughness of spider silk, closure of mimosa leaves when touched, or opening of seed pods). [8][9][10] Since the early 2000s, exciting opportunities have emerged in the scientific community for making use of artificial molecular machines as the elementary responsive building blocks in new types of stimuli-responsive materials. This approach is fundamentally disruptive compared to the others developed so far, because it aims to exploit precisely controlled mechanical motions at molecular level (produced by the machines), and to amplify them in collective mechanical motions taking place at larger dimensions up to the material's length scale. The most prominent example of what could be potentially achieved in the far future by such artificial materials is also found in nature, in the form of striated muscle tissue. In muscles, by using adenosine triphosphate (ATP) as chemical fuel, millions of myosin motors, which individually cycle hundreds of few nanometers scale actuations, are able to pull synchronously on sliding actin filaments and to produce micrometric contractions of sarcomeric units. Further hierarchical organizations of sarcomeres in bundled fibrils and fibers result in a macroscopic contraction of the muscle. At that point, and before describing selected examples of (much simpler) artificial systems, it is important for the readers who would not be familiar with molecular machines to first introduce more precisely terms and notions which define their nature and actuation principles. Artificial molecular machines are able to produce and exploit precise nanoscale actuations in response to chemical or physical triggers. Recent scientific efforts have been devoted to the integration, orientation, and interfacing of large assemblies of molecular machines in order to harness their collective actuations at larger length scale and up to the generation of macroscopic motions. Maki...

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“…Intermolecular hydrogen bonds of ureide groups are the common driving force for the formation of supramolecular gels. 7 A variety of LMWGs with mono-urea, 8,9 bis-urea, [10][11][12][13][14][15] trisurea 16,17 and tetrakis-urea 18 structures have been reported. We have also developed C 3 -symmetric tris-urea LMWGs.…”

Section: Introductionmentioning

confidence: 99%

Palladium ion-induced supramolecular gel formation of tris-urea molecules

Aoyama

Sako

Amakatsu

et al. 2014

Polym J

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A multicomponent supramolecular gel constructed from the self-assembly of pyridyl-substituted tris-urea 1 and Pd(OAc) 2 is reported. A mixture of 1 and Pd(OAc) 2 in dimethyl sulfoxide provided a supramolecular gel after brief ultrasound irradiation. The supramolecular gel changed into a sol/solution upon addition of chelating agents such as diamines and bidentate phosphine ligands. Dissociation of the coordination bonds between 1 and the palladium ion via addition of a chelating agent caused the phase transition. The Wacker oxidation of styrene was performed in the supramolecular gel. The reaction in the gel phase required a longer induction period to produce acetophenone than did the reaction in the homogeneous solution.INTRODUCTION Supramolecular gels have potential applications in a wide range of fields in materials science. 1,2 The development of supramolecular gels through the self-assembly of a small molecule, called a low-molecularweight gelator (LMWG), has attracted significant attention in recent decades. 3-6 LMWGs self-assemble by noncovalent interactions, such as hydrogen bonding, π-π interactions, dipole-dipole interactions and solvophobic interactions, to form three-dimensional networks that immobilize fluids. Intermolecular hydrogen bonds of ureide groups are the common driving force for the formation of supramolecular gels. 7 A variety of LMWGs with mono-urea, 8,9 bis-urea, 10-15 trisurea 16,17 and tetrakis-urea 18 structures have been reported. We have also developed C 3 -symmetric tris-urea LMWGs. [19][20][21][22] Supramolecular gels are generally constructed from a single component of LMWGs; however, some are formed from multiple types of small molecules. 23 A metal-ligand coordination bond is a common aspect of the multicomponent supramolecular gels; the advantage in this case is that gel formation can be easily controlled by controlling the formation and dissociation of the metal-ligand coordination bond. Moreover, the metal center of the resulting gel can potentially function as a catalyst for organic reactions. [24][25][26][27][28][29] We have previously reported multicomponent supramolecular gels of trisurea, in which the gelation ability of phenyl-substituted tris-urea was increased by the addition of a small amount of pyridyl-substituted trisurea and metal ion or bis-carboxylic acid. 30 In this paper, we report supramolecular gel formation from pyridyl-substituted tris-urea in the presence of palladium ions in dimethyl sulfoxide (DMSO). The supramolecular gel underwent a gel to sol/solution phase transition upon the addition of chelating agents for palladium ions. The palladium-catalyzed Wacker oxidation of styrene was performed in the gel phase.

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Acid/Base‐ and Anion‐Controllable Organogels Formed From a Urea‐Based Molecular Switch

Cited by 105 publications

References 30 publications

A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

From Molecular Machines to Stimuli‐Responsive Materials

Palladium ion-induced supramolecular gel formation of tris-urea molecules

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