FRET‐Nachweis geometrisch präzise definierter Expansions‐Kontraktions‐Bewegungen im Multinanometerbereich eines Resorcin[4]aren‐Cavitand‐basierten Schalters

Azov, Vladimir A.; Schlegel, Anna; Diederich, François

doi:10.1002/ange.200500970

Cited by 32 publications

(23 citation statements)

References 33 publications

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“…The described class of cavitands provides fascinating modules for molecular switches [9] and, possibly in the future, for molecular machines. Such developments towards technologies and device fabrication greatly benefit from the understanding of the basic physical-organic principles governing the switching process.…”

Section: Discussionmentioning

confidence: 99%

Conformational Behavior of Pyrazine‐Bridged and Mixed‐Bridged Cavitands: A General Model for Solvent Effects on Thermal “Vase–Kite” Switching

Roncucci

Pirondini

Paderni

et al. 2006

Chemistry A European J

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The controllable switching of suitably bridged resorcin[4]arene cavitands between a "vase" conformation, with a cavity capable of guest inclusion, and a "kite" conformation, featuring an extended flattened surface, provides the basis for ongoing developments of dynamic molecular receptors, sensors, and molecular machines. This paper describes the synthesis, X-ray crystallographic characterization, and NMR analysis of the "vase-kite" switching behavior of a fully pyrazine-bridged cavitand and five other mixed-bridged quinoxaline-bridged cavitands with one methylene, phosphonate, or phosphate bridge. The pyrazine-bridged resorcin[4]arene cavitand displayed an unexpectedly high preference for the kite conformation in nonpolar solvents, relative to the quinoxaline-bridged analogue. This observation led to extensive solvent-dependent switching studies that provide a detailed picture of how solvent affects the thermal vase-kite equilibration. As for any thermodynamic process in the liquid phase, the conformational equilibrium is affected by how the solvent stabilizes the two individual states. Suitably sized solvents (benzene and derivatives) solvate the cavity of the vase form and reduce the propensity for the vase-to-kite transition. Correspondingly, the kite geometry becomes preferred in bulky solvents such as mesitylene, incapable of penetrating the vase cavity. As proposed earlier by Cram, the kite form is preferred at low temperatures due to the more favorable enthalpy of solvation of the enlarged surface. Furthermore, the kite conformation is more preferred in solvents with substantial hydrogen-bonding acidity: weak hydrogen-bonding interactions between the mildly basic quinoxaline and pyrazine nitrogen atoms and solvent molecules are more efficient in the open kite than in the closed vase form. Vase-to-kite conversion is entirely absent in dipolar aprotic solvents lacking any H-bonding acidity. Thermal vase-kite switching requires fully quinoxaline- or pyrazine-bridged cavitands, whereas pH-controlled switching is also applicable to systems incorporating only two or three such bridges.

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Section: Discussionmentioning

confidence: 99%

Conformational Behavior of Pyrazine‐Bridged and Mixed‐Bridged Cavitands: A General Model for Solvent Effects on Thermal “Vase–Kite” Switching

Roncucci

Pirondini

Paderni

et al. 2006

Chemistry A European J

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“…This process relies on the expansion and contraction of the flexible, acetylene-expanded cavity of a resorcinarene system. [10] Likewise, the group of Weiss has prepared different pincer-type Abstract: A number of wide-and narrow-rimmed functionalized alkynylcalix[4]arenes have been synthesized by Sonogashira coupling. With respect to their optical properties, these donor-acceptor systems are treated as ensembles of covalently linked, electronically independent tolane subchromophores.…”

Section: Introductionmentioning

confidence: 99%

Alkynyl Expanded Donor–Acceptor Calixarenes: Geometry and Second‐Order Nonlinear Optical Properties

Hennrich

Murillo

Prados

et al. 2007

Chemistry A European J

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A number of wide- and narrow-rimmed functionalized alkynylcalix[4]arenes have been synthesized by Sonogashira coupling. With respect to their optical properties, these donor-acceptor systems are treated as ensembles of covalently linked, electronically independent tolane subchromophores. Linear UV/visible and fluorescence spectroscopic investigations revealed that the charge-transfer character of the electronic transitions in calixarenes, and also the second-order nonlinear optical (NLO) properties depend on the electron-withdrawing nature of the terminal ethynylphenyl substituent (NO(2), CF(3), H). The nitro derivatives display high values of the quadratic hyperpolarizability beta. Not only do the (nonlinear) optical properties of the target compounds depend on the number and relative disposition of the subchromophores, but also on the geometry of the calixarenes. In particular, the opening angle of the calixarene cavity can be determined by the substitution pattern of the calixarene scaffold (wide- versus narrow-rim substitution) and the number of the acetylene functions introduced. Both the NLO properties and the conformational issues are conveniently assessed by using hyper-Rayleigh scattering (HRS) in solution, and supported by X-ray crystallography in the solid state.

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“…Selective functionalization of the rim of resorcin[4]arene cavitands, by attaching long rigid arms bearing terminal chromophores to two wall flaps in the anti-orientation, generates molecular switches featuring large, geometrically well defined contraction/expansion motions. [14][15][16] In the vase conformation, the chromophores are located in close proximity to each other, whereas in the kite conformation they are several nanometers apart. Different interchromophoric interactions in the two states translate into different physical properties that can be utilized to quantify the switching processes.…”

Section: Introductionmentioning

confidence: 99%

Complexation and Dynamic Switching Properties of Fluorophore‐Appended Resorcin[4]arene Cavitands

Shirtcliff

Diederich

2010

Eur J Org Chem

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Fluorophore-appended resorcin [4]arene-based cavitands having pyrene (2) and anthracene (3) moieties attached to the rims were prepared by short synthetic routes. Both undergo reversible temperature-and acid-(CF 3 COOD) induced vase Ǟ kite switching as evidenced by 1 H NMR spectroscopy. The 1 H NMR spectra also suggest that suitably sized solvents, such as [D 8 ]toluene, efficiently solvate the cavity, reducing the conformational flexibility. In [D 12 ]mesitylene, both cavitands undergo remarkably stable host-guest inclusion complexation with cycloalkanes. The larger cavity of 3 preferentially hosts cyclohexane, whereas the smaller cavity of 2 forms the most stable complex with cyclopentane. The propensity for the cavitands to facilitate π-π stacking between the chromophores was confirmed by both 1 H NMR and fluorescence spectroscopy. The interchromophoric interaction is strongly solvent-dependent: π-π stacking between the pyrene moieties of 2 is not as efficient in [D 8 ]toluene, as

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FRET‐Nachweis geometrisch präzise definierter Expansions‐Kontraktions‐Bewegungen im Multinanometerbereich eines Resorcin[4]aren‐Cavitand‐basierten Schalters

Cited by 32 publications

References 33 publications

Conformational Behavior of Pyrazine‐Bridged and Mixed‐Bridged Cavitands: A General Model for Solvent Effects on Thermal “Vase–Kite” Switching

Conformational Behavior of Pyrazine‐Bridged and Mixed‐Bridged Cavitands: A General Model for Solvent Effects on Thermal “Vase–Kite” Switching

Alkynyl Expanded Donor–Acceptor Calixarenes: Geometry and Second‐Order Nonlinear Optical Properties

Complexation and Dynamic Switching Properties of Fluorophore‐Appended Resorcin[4]arene Cavitands

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