Using Acetate Anions To Induce Translational Isomerization in a Neutral Urea‐Based Molecular Switch

Huang, Yufang; Hung, Wei-Chung; Lai, Chih-Sheng; Liu, Yi-Hung; Peng, Shie‐Ming; Chiu, Sheng‐Hsien

doi:10.1002/ange.200702197

Cited by 56 publications

(29 citation statements)

References 41 publications

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“…As expected, a mixture of 1-pentanol and the [2]rotaxane [7-H] [PF 6 ] did not gel after sonication. This result supports our proposed model and confirms the importance of the C=O groups of the pyridinediamide unit in the gelation of [5-H] 6 ] also acts as a two-way-controllable molecular switch: the degree of solvent exposure of the hydrogen-bond-donating urea station (and, therefore, the degree of intermolecular hydrogen bonding) and the orientation of the hydrogen-bond-accepting C=O groups of the interlocked macrocycle appear to be responsible for the observed gel-sol transitions in 1-pentanol. The concept might be useful for the design of functional molecular aggregates based on interlocked molecular switches.…”

supporting

confidence: 92%

“…The binding constant for the assembly formed from the macrocycle 1 and dibenzylammonium hexafluorophosphate ((DBA)PF 6 ) in CD 3 NO 2 is (300 AE 30) m À1 , and 1 interacts only negligibly with diphenylurea derivatives in this solvent. [6,8] 6 ] in CD 3 NO 2 shows cross-signals between the ethylene glycol protons of the macrocyclic unit and the aromatic protons of the 3,5-di-tert-butylphenyl stopper adjacent to the DBA + center, however, no crosssignals are seen between the macrocyle and the stopper unit adjacent to the urea station.…”

mentioning

confidence: 78%

“…The reaction of the macrocycle 1, [6] the amino-terminated salt [2-H][PF 6 ], [7] and the isocyanate 3 in CH 3 NO 2 gave the dumbbell-shaped salt [4-H] 6 ] in 49 and 46 % yield, respectively (Scheme 1). The binding constant for the assembly formed from the macrocycle 1 and dibenzylammonium hexafluorophosphate ((DBA)PF 6 ) in CD 3 NO 2 is (300 AE 30) m À1 , and 1 interacts only negligibly with diphenylurea derivatives in this solvent.…”

mentioning

confidence: 99%

“…When we used Et 3 N/trifluoroacetic acid (TFA) as the operating acid/base pair, we observed similar reversible switching of the rotaxane [5-H] + in CD 3 NO 2 (see the Supporting Information). We grew single crystals suitable for X-ray crystallography by liquid diffusion of hexanes into a solution of [5-H] 6 ] (12 mg) to 1-pentanol (0.6 mL) and subsequent sonication led to gelation of the solvent; [11] the solution state was regenerated after adding 1 equivalent of tBuOK. Interestingly, the addition of aqueous HClO 4 (1 equivalent) to the latter solution returned the system to a gel state; one such gel-sol phase transition cycle is shown in Figure 3 a. Migration of the interlocked macrocyclic unit from the DBA + station to the urea station and back again was also evident in 1 6 ] in 1-pentanol are related to the location of the interlocked macrocyclic unit.…”

mentioning

confidence: 99%

“…We grew single crystals suitable for X-ray crystallography by liquid diffusion of hexanes into a solution of [5-H] 6 ] (12 mg) to 1-pentanol (0.6 mL) and subsequent sonication led to gelation of the solvent; [11] the solution state was regenerated after adding 1 equivalent of tBuOK. Interestingly, the addition of aqueous HClO 4 (1 equivalent) to the latter solution returned the system to a gel state; one such gel-sol phase transition cycle is shown in Figure 3 a. Migration of the interlocked macrocyclic unit from the DBA + station to the urea station and back again was also evident in 1 6 ] in 1-pentanol are related to the location of the interlocked macrocyclic unit. The intermolecular accessibility of the urea station presumably plays the major role in effecting the aggregation of these [2]rotaxanes through intermolecular hydrogen bonds and the subsequent sol-gel phase transitions.…”

mentioning

confidence: 99%

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

et al. 2010

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Low-molecular-weight organogels have applications in several fields, including molecular sensing, [1] nanostructure assembly, [2] and drug delivery. [3] Ideally, these materials would switch reversibly between their solution and gel states through the addition or removal of heat, electrons, or ions.[4] Although these modes of operation are similar to those employed for switches based on interlocked molecules, organogels formed from pseudorotaxane-or rotaxane-type gelators are rare. Indeed, we are aware of only a few previously reported examples, all of which feature long alkyl chains or cholesterol units incorporated into the molecular structures to assist the gelation process.[5] Predicting the molecular structures of potential gelators and their preferred solvents remains difficult, and developing new rotaxane-based gelators that do not feature commonly used types of gelation units (e.g., long alkyl chains, steroids) in their structures is particularly challenging. Herein we report the serendipitous discovery of a urea-based [2]rotaxane that behaves as both a molecular switch and an organogelator; both functions are mediated by acid/base and anion control.The reaction of the macrocycle 1, ] in CD 3 NO 2 shows cross-signals between the ethylene glycol protons of the macrocyclic unit and the aromatic protons of the 3,5-di-tert-butylphenyl stopper adjacent to the DBA + center, however, no crosssignals are seen between the macrocyle and the stopper unit adjacent to the urea station.As expected, addition of potassium tert-butoxide (1 equivalent) to a solution of the [2]rotaxane [5-H][PF 6 ] (CD 3 NO 2 , 13.6 mm) resulted in significant shifts in the locations of many of the signals in the 1 H NMR spectrum (Figure 1). The significant downfield shift of the signal for the macrocyle NH protons, and the appearance of signals for the formerly severely broadened urea protons suggested the formation of hydrogen bonds to the carbonyl group of the urea station (Figure 1 b)

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supporting

confidence: 92%

mentioning

confidence: 78%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

et al. 2010

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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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Efficient Solvent‐Free Syntheses of [2]‐ and [4]Rotaxanes

et al. 2008

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Rotaxanes have potential applicability as molecular actuators and switches within mesoscale molecular electronic devices. [1] Among the protocols devised for preparing rotaxanes, threading followed by stoppering [2] has attracted the most attention. Nevertheless, synthesizing rotaxanes in high yields by this approach can be challenging because several factors affect the formation of the precursor pseudorotaxanes in solution-for example, low association constants for the interactions between the thread-and beadlike components, the use of competing solvents and/or elevated temperatures, and the formation of interfering by-products during the stoppering process.[3] Although solvent-free conditions [4] would, in theory, minimize the degree of dissociation of the pseudorotaxane complexes during the stoppering reaction and allow high-order rotaxanes to be generated more efficiently, a new challenge arises in choosing a suitable stoppering reaction that can be performed by grinding a wellmixed solid phase. To the best of our knowledge, only two types of rotaxanes have been synthesized through solid-tosolid grinding: one through the reaction of a mixture of bis-pphenylene[34]crown-10, a benzyl bromide derivative incorporating a bipyridinium recognition site, and a pyridinecontaining stopper, [5] and the other through ball-milling of polypseudorotaxane complexes-comprising a-cyclodextrin and poly(tetrahydrofuran) components-with isocyanate stoppers.[6] Both of these cases gave low-to-moderate yields of their desired products (< 45 %), thus suggesting that these reactions are not suitable for the efficient syntheses of higherorder rotaxanes. Herein, we report a new solid-state ballmilling reaction that produces both [2]-and [4]rotaxanes efficiently and in high yield.The formation of imines through the dehydration of aldehydes and primary amines can be achieved in high yield by solid-state ball-milling. [7] As imines are in general easily hydrolyzed, we were not inclined to use this condensation reaction to construct higher-order rotaxanes. Instead, we turned our attention toward the formation of hexahydropyrimidines by condensing carbonyl compounds with 1,3-diamines.[8] We chose 1,8-diaminonaphthalene (3) as a suitable diamine for the reaction with a threadlike moiety terminated with a formyl group because of its steric bulk and the stability of the resulting dihydropyrimidine stopper units.[9]Previously, we reported that the oxygen-deficient macrocycle 1 forms a complex with a dibenzylammonium (DBA) ion in CD 3 CN (K a = 200 m À1 ).[10] Thus, as the first step toward preparing a [2]rotaxane under solvent-free conditions from such components, we concentrated an equimolar mixture of the macrocycle 1 and the dialdehyde 2-H·PF 6 in CH 3 CN under reduced pressure to afford a white solid, which we assumed to contain predominantly the (Figure 1). After 1 h, these signals were predominant (Figure 1 e), so we subjected the mixture to column chromatography and isolated the [2]rotaxane 4-H·PF 6 in 80 % yield.[11] The yield in...

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Using Acetate Anions To Induce Translational Isomerization in a Neutral Urea‐Based Molecular Switch

Cited by 56 publications

References 41 publications

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

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

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

Efficient Solvent‐Free Syntheses of [2]‐ and [4]Rotaxanes

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