The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Fraser J Stoddart - One of the best experts on this subject based on the ideXlab platform.
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Cyclophane sustained ultrastable porphyrins
Journal of the American Chemical Society, 2020Co-Authors: Wenqi Liu, Ryan M Young, Michael R Wasielewski, Fraser J Stoddart, Chenjian Lin, Jacob A Weber, Charlotte L SternAbstract:We report the encapsulation of free-base and zinc porphyrins by a tricyclic Cyclophane receptor with subnanomolar binding affinities in water. The high affinities are sustained by the hydrophobic e...
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a dynamic tetracationic macrocycle exhibiting photoswitchable molecular encapsulation
Journal of the American Chemical Society, 2019Co-Authors: Yong Chen, Charlotte L Stern, Long Zhang, Ommid Anamimoghadam, Dengke Shen, Zhichang Liu, Kang Cai, Cristian Pezzato, Yu Liu, Fraser J StoddartAbstract:Designing macrocycles with appropriate molecular recognition features that allow for the integration of suitable external stimuli to control host-guest processes is a challenging endeavor which enables molecular containers to solubilize, stabilize, and separate chemical entities in an externally controllable manner. Herein, we introduce photo- and thermal-responsive elements into a semi-rigid tetracationic Cyclophane, OPVEx2Box4+, that is composed of oligo( p-phenylenevinylene) pyridinium units and the biphenylene-bridged 4,4-bipyridinium extended viologens and adopts a rectangle-like geometry. It transpires that when the photoactive oligo( p-phenylenevinylene) pyridinium unit is incorporated in a macrocyclic scaffold, its reversibility is dramatically improved, and the configurations of the Cyclophane can go back and forth between ( EE)- and ( EZ)-isomers upon alternating blue light irradiation and heating. When the macrocycle is found in its ( EE)-configuration, it is capable of binding various π-electron-rich guests-e.g., anthracene and perylene-as well as π-electron-deficient guests-e.g., 9,10-anthraquinone and 5,12-tetracenequinone-through charge-transfer and van der Waals interactions. When irradiated with blue light, the ( EE)-isomer of the Cyclophane can be transformed successfully to the ( EZ)-isomer, resulting in the switching off of the binding affinity for guest molecules, which are bound once again upon heating. The use of light and heat as external stimuli to control host-guest interactions involving a multi-responsive host and various guests provides us with a new opportunity to design and construct more-advanced molecular switches and machines.
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ExTzBox: A Glowing Cyclophane for Live-Cell Imaging
2018Co-Authors: Indranil Roy, Jiawang Zhou, Michael R Wasielewski, Daniel P Ferris, Sharan Bobbala, Minh T. Nguyen, Siva Krishna Mohan Nalluri, Evan Alexander Scott, Fraser J StoddartAbstract:The ideal fluorescent probe for live-cell imaging is bright and non-cytotoxic and can be delivered easily into the living cells in an efficient manner. The design of synthetic fluorophores having all three of these properties, however, has proved to be challenging. Here, we introduce a simple, yet effective, strategy based on well-established chemistry for designing a new class of fluorescent probes for live-cell imaging. A box-like hybrid Cyclophane, namely ExTzBox·4X (6·4X, X = PF6−, Cl−), has been synthesized by connecting an extended viologen (ExBIPY) and a dipyridyl thiazolothiazole (TzBIPY) unit in an end-to-end fashion with two p-xylylene linkers. Photophysical studies show that 6·4Cl has a quantum yield ΦF = 1.00. Furthermore, unlike its ExBIPY2+ and TzBIPY2+ building units, 6·4Cl is non-cytotoxic to RAW 264.7 macrophages, even with a loading concentration as high as 100 μM, presumably on account of its rigid box-like structure which prevents its intercalation into DNA and may inhibit other interactions with it. After gaining an understanding of the toxicity profile of 6·4Cl, we employed it in live-cell imaging. Confocal microscopy has demonstrated that 64+ is taken up by the RAW 264.7 macrophages, allowing the cells to glow brightly with blue laser excitation, without any hint of photobleaching or disruption of normal cell behavior under the imaging conditions. By contrast, the acyclic reference compound Me2TzBIPY·2Cl (4·2Cl) shows very little fluorescence inside the cells, which is quenched completely under the same imaging conditions. In vitro cell investigations underscore the significance of using highly fluorescent box-like rigid Cyclophanes for live-cell imaging
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probing distance dependent charge transfer character in excimers of extended viologen Cyclophanes using femtosecond vibrational spectroscopy
Journal of the American Chemical Society, 2017Co-Authors: Yilei Wu, Jiawang Zhou, Brian T Phelan, Catherine M Mauck, Ryan M Young, Fraser J Stoddart, Michael R WasielewskiAbstract:Facile exciton transport within ordered assemblies of π-stacked chromophores is essential for developing molecular photonic and electronic materials. Excimer states having variable charge transfer (CT) character are frequently implicated as promoting or inhibiting exciton mobility in such systems. However, determining the degree of CT character in excimers as a function of their structure has proven challenging. Herein, we report on a series of Cyclophanes in which the interplanar distance between two phenyl-extended viologen (ExV2+) chromophores is varied systematically using a pair of o-, m-, or p-xylylene (o-, m-, or p-Xy) covalent linkers to produce o-ExBox4+ (3.5 A), m-ExBox4+ (5.6 A), and p-ExBox4+ (7.0 A), respectively. The Cyclophane structures are characterized using NMR spectroscopy in solution and single-crystal X-ray diffraction in the solid state. Femtosecond transient mid-IR and stimulated Raman spectroscopies show that the CT contribution to the excimer states formed in o-ExBox4+ and m-ExBo...
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cooperative reactivity in an extended viologen based Cyclophane
Journal of the American Chemical Society, 2016Co-Authors: Edward J. Dale, Michal Juricek, Jonathan C Barnes, Nicolaas A Vermeulen, Daniel P Ferris, James J Henkelis, Ilja Popovs, Severin T Schneebeli, Fraser J StoddartAbstract:A tetracationic pyridinium-based Cyclophane with a box-like geometry, incorporating two juxtaposed alkyne functions, has been synthesized. The triple bonds are reactive through cycloadditions toward dienes and azides, promoted by the electron-withdrawing nature of the pyridinium rings, as well as by the strain inherent in the Cyclophane. The cycloadditions proceeded in high yields, with the Cyclophane reacting faster than its acyclic analogue. While the Cyclophane contains two reactive triple bonds, there is no evidence for a stable monofunctional intermediate—only starting material and the difunctional product have been detected by 1H NMR spectroscopy. Molecular modeling of the energy landscape reveals a lower barrier for the kinetically favored second cycloaddition compared with the first one. This situation results in tandem cascading reactions within rigid Cyclophanes, where reactions at a first triple bond induce increased reactivity at a distal second alkyne.
Sambasivarao Kotha - One of the best experts on this subject based on the ideXlab platform.
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diversity oriented approach to Cyclophanes via claisen rearrangement and ring closing metathesis as key steps
Tetrahedron Letters, 2014Co-Authors: Sambasivarao Kotha, Gopalkrushna T WaghuleAbstract:Abstract Among numerous reactions to prepare Cyclophane derivatives, Claisen rearrangement reaction is very useful. We have prepared Cyclophanes containing ethylene oxy bridge by double Claisen rearrangement reaction and ring-closing metathesis reaction as key steps.
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diversity oriented approach to macrocyclic Cyclophane derivatives by suzuki miyaura cross coupling and olefin metathesis as key steps
Journal of Organic Chemistry, 2012Co-Authors: Sambasivarao Kotha, Arjun S Chavan, Mobin M ShaikhAbstract:Palladium-catalyzed Suzuki–Miyaura (SM) cross-coupling reaction with allylboronic acid pinacol ester and titanium assisted cross-metathesis (CM)/ring-closing metathesis (RCM) cascade has been used to synthesize macrocyclic Cyclophane derivatives.
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suzuki miyaura cross coupling and ring closing metathesis a strategic combination for the synthesis of Cyclophane derivatives
ChemInform, 2007Co-Authors: Sambasivarao Kotha, Kalyaneswar MandalAbstract:The synthesis of Cyclophane derivatives through a sequence involving Suzuki–Miyaura cross-coupling between α,α′-dibromo-m-xylene and arylboronic acid derivatives, alkenylation and ring-closing metathesis has been achieved. One of the Cyclophanes was obtained by tandem isomerization and metathesis. Significant magnetic anisotropic effects on the intra-annular hydrogen atoms were observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Ryan M Young - One of the best experts on this subject based on the ideXlab platform.
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Cyclophane sustained ultrastable porphyrins
Journal of the American Chemical Society, 2020Co-Authors: Wenqi Liu, Ryan M Young, Michael R Wasielewski, Fraser J Stoddart, Chenjian Lin, Jacob A Weber, Charlotte L SternAbstract:We report the encapsulation of free-base and zinc porphyrins by a tricyclic Cyclophane receptor with subnanomolar binding affinities in water. The high affinities are sustained by the hydrophobic e...
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probing distance dependent charge transfer character in excimers of extended viologen Cyclophanes using femtosecond vibrational spectroscopy
Journal of the American Chemical Society, 2017Co-Authors: Yilei Wu, Jiawang Zhou, Brian T Phelan, Catherine M Mauck, Ryan M Young, Fraser J Stoddart, Michael R WasielewskiAbstract:Facile exciton transport within ordered assemblies of π-stacked chromophores is essential for developing molecular photonic and electronic materials. Excimer states having variable charge transfer (CT) character are frequently implicated as promoting or inhibiting exciton mobility in such systems. However, determining the degree of CT character in excimers as a function of their structure has proven challenging. Herein, we report on a series of Cyclophanes in which the interplanar distance between two phenyl-extended viologen (ExV2+) chromophores is varied systematically using a pair of o-, m-, or p-xylylene (o-, m-, or p-Xy) covalent linkers to produce o-ExBox4+ (3.5 A), m-ExBox4+ (5.6 A), and p-ExBox4+ (7.0 A), respectively. The Cyclophane structures are characterized using NMR spectroscopy in solution and single-crystal X-ray diffraction in the solid state. Femtosecond transient mid-IR and stimulated Raman spectroscopies show that the CT contribution to the excimer states formed in o-ExBox4+ and m-ExBo...
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intramolecular energy and electron transfer within a diazaperopyrenium based Cyclophane
Journal of the American Chemical Society, 2017Co-Authors: Xirui Gong, Jiawang Zhou, Ryan M Young, Nema Hafezi, Karel J Hartlieb, Claire E Miller, Hai Xiao, Tao Cheng, William A Goddard, Omar K FarhaAbstract:Molecules capable of performing highly efficient energy transfer and ultrafast photoinduced electron transfer in well-defined multichromophoric structures are indispensable to the development of artificial photofunctional systems. Herein, we report on the synthesis, characterization, and photophysical properties of a rationally designed multichromophoric tetracationic Cyclophane, DAPPBox4+, containing a diazaperopyrenium (DAPP2+) unit and an extended viologen (ExBIPY2+) unit, which are linked together by two p-xylylene bridges. Both 1H NMR spectroscopy and single-crystal X-ray diffraction analysis confirm the formation of an asymmetric, rigid, box-like Cyclophane, DAPPBox4+. The solid-state superstructure of this Cyclophane reveals a herringbone-type packing motif, leading to two types of π···π interactions: (i) between the ExBIPY2+ unit and the DAPP2+ unit (π···π distance of 3.7 A) in the adjacent parallel Cyclophane, as well as (ii) between the ExBIPY2+ unit (π···π distance of 3.2 A) and phenylene ring ...
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guest and solvent modulated photo driven charge separation and triplet generation in a perylene bisimide Cyclophane
Chemical Science, 2016Co-Authors: Peter Spenst, Ryan M Young, Michael R Wasielewski, Frank WurthnerAbstract:Cofacial positioning of two perylene bisimide (PBI) chromophores at a distance of 6.5 A in a Cyclophane structure prohibits the otherwise common excimer formation and directs photoexcited singlet state relaxation towards intramolecular symmetry-breaking charge separation (τCS = 161 ± 4 ps) in polar CH2Cl2, which is thermodynamically favored with a Gibbs free energy of ΔGCS = −0.32 eV. The charges then recombine slowly in τCR = 8.90 ± 0.06 ns to form the PBI triplet excited state, which can be used subsequently to generate singlet oxygen in 27% quantum yield. This sequence of events is eliminated by dissolving the PBI Cyclophane in non-polar toluene, where only excited singlet state decay occurs. In contrast, complexation of electron-rich aromatic hydrocarbons by the host PBI Cyclophane followed by photoexcitation of PBI results in ultrafast electron transfer (<10 ps) from the guest to the PBI in CH2Cl2. The rate constants for charge separation and recombination increase as the guest molecules become easier to oxidize, demonstrating that charge separation occurs close to the peak of the Marcus curve and the recombination lies far into the Marcus inverted region.
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energy and electron transfer dynamics within a series of perylene diimide Cyclophane systems
Journal of the American Chemical Society, 2015Co-Authors: Sean T J Ryan, Edward J. Dale, Nicolaas A Vermeulen, Ryan M Young, James J Henkelis, Nema Hafezi, Andreas Hennig, Matthew D Krzyaniak, Athan Fox, Werner M NauAbstract:Artificial photosynthetic systems for solar energy conversion exploit both covalent and supramolecular chemistry to produce favorable arrangements of light-harvesting and redox-active chromophores in space. An understanding of the interplay between key processes for photosynthesis, namely light-harvesting, energy transfer, and photoinduced charge separation and the design of novel, self-assembling components capable of these processes are imperative for the realization of multifunctional integrated systems. We report our investigations on the potential of extended tetracationic Cyclophane/perylene diimide systems as components for artificial photosynthetic applications. We show how the selection of appropriate heterocycles, as extending units, allows for tuning of the electron accumulation and photophysical properties of the extended tetracationic Cyclophanes. Spectroscopic techniques confirm energy transfer between the extended tetracationic Cyclophanes and perylene diimide is ultrafast and quantitative,...
Mobin M Shaikh - One of the best experts on this subject based on the ideXlab platform.
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diversity oriented approach to macrocyclic Cyclophane derivatives by suzuki miyaura cross coupling and olefin metathesis as key steps
Journal of Organic Chemistry, 2012Co-Authors: Sambasivarao Kotha, Arjun S Chavan, Mobin M ShaikhAbstract:Palladium-catalyzed Suzuki–Miyaura (SM) cross-coupling reaction with allylboronic acid pinacol ester and titanium assisted cross-metathesis (CM)/ring-closing metathesis (RCM) cascade has been used to synthesize macrocyclic Cyclophane derivatives.
Murray V Baker - One of the best experts on this subject based on the ideXlab platform.
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formation of dinuclear auii and aui auiii mixed valence complexes is directed by structural constraints imposed by Cyclophane nhc ligands
European Journal of Inorganic Chemistry, 2018Co-Authors: Brian W Skelton, Ahmed Hassoon Mageed, Alexandre N Sobolev, Murray V BakerAbstract:Oxidation of dinuclear AuI complexes containing Cyclophane-bis(NHC) ligands by SOCl2, Br2, and I2 has been investigated. The outcome of the oxidation was dependent on the nature of the Cyclophane-NHC framework. The new complexes were fully characterised by X-ray diffraction and NMR spectroscopy. When the AuI complex contained an o-Cyclophane framework (dictating short intra-cation Au...Au distances), oxidation resulted in dinuclear AuII complexes of form X-AuII(NHC)2-AuII(NHC)2-X (X = Cl, Br, I), Au...Au being in the range (2.6055(3)-2.6501(1) A). These AuII complexes were strongly luminescent. When the AuI complex contained an m-Cyclophane framework (dictating longer intra-cation Au...Au distances), oxidation with SOCl2 or Br2 resulted in dinuclear complexes containing AuI and AuIII centres, of form X-AuIII(NHC)2-X-AuI(NHC)2. NMR studies showed interconversion of AuI and AuIII sites within the complexes occurred on rates comparable to the NMR timescale.
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dinuclear au i n heterocyclic carbene complexes derived from unsymmetrical azolium Cyclophane salts potential probes for live cell imaging applications
Dalton Transactions, 2016Co-Authors: Louise E Wedlock, Peter J Barnard, Aleksandra Filipovska, Brian W Skelton, Susan J Bernersprice, Murray V BakerAbstract:We have synthesized a new series of azolium Cyclophanes and used them as precursors of inherently luminescent dinuclear Au(I)–N-heterocyclic carbene (NHC) complexes. The azolium Cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium Cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium Cyclophanes served as precursors of Au2L22+ complexes (L is a Cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium Cyclophanes, the Au2L22+ complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L22+ complexes had short intramolecular Au⋯Au distances, in the range 2.9–3.3 A, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the Cyclophane bis(NHC) ligands. The complexes having the shortest Au⋯Au distances (i.e., those based on C3-linked Cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au–NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.
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calixarene azolium Cyclophane hybrids synthesis structure and conformations
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2015Co-Authors: Valerie J Hesler, Brian W Skelton, Allan H White, David Brown, Murray V BakerAbstract:The synthesis, structure, and conformational behaviour of three imidazolium Cyclophanes that incorporate one or two 4-tert-butylphenol or 4-tert-butylanisole groups as meta-disubstituted linkers in the macrocycle is described. The Cyclophanes containing anisole moieties adopt a cone conformation in the solid state, which, in solution, is not labile on the NMR timescale. The Cyclophanes containing one or two phenol moieties adopt conformations other than the cone in the solid state and are labile in solution on the NMR timescale. The phenol Cyclophanes are readily deprotonated, and structural and conformational studies for a variety of the associated Cyclophanes are also reported.
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enhanced deep blue emission from pt ii complexes bound to 2 pyridyltetrazolate and an ortho xylene linked bis nhc Cyclophane
Dalton Transactions, 2013Co-Authors: Karen D M Magee, Murray V Baker, David Brown, Phillip J Wright, Sara Muzzioli, Claire M Siedlovskas, Paolo Raiteri, Stefano Stagni, Massimiliano MassiAbstract:The coordination of 2-pyridyltetrazolate and ortho-xylene-linked bis(NHC)Cyclophane to Pt(II) yielded a novel complex characterised by enhanced pure deep-blue emission, whose intensity can be modulated via methylation of the tetrazole ring.
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luminescence studies of the intracellular distribution of a dinuclear gold i n heterocyclic carbene complex
Angewandte Chemie, 2006Co-Authors: Peter J Barnard, Louise E Wedlock, Brian W Skelton, Susan J Bernersprice, Murray V Baker, David A Joyce, James H SteerAbstract:A bidentate Cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid Cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.
