Cyclophane Host Research Articles

Guest-Mediated Modulation of Photophysical Pathways in a Coronene Bisimide Cyclophane.

The properties and functions of chromophores utilized by nature are strongly affected by the environment formed by the protein structure in the cells surrounding them. This concept is transferred here to host-guest complexes with the encapsulated guests acting as an environmental stimulus. A new cyclophane host based on coronene bisimide is presented that can encapsulate a wide variety of planar guest molecules with binding constants up to (4.29 ± 0.32) × 1010 M-1 in chloroform. Depending on the properties of the chosen guest, the excited state deactivation of the coronene bisimide chromophore can be tuned by the formation of host-guest complexes toward fluorescence, exciplex formation, charge separation, room-temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). The photophysical processes were investigated by UV/vis absorption, emission, and femto- and nanosecond transient absorption spectroscopy. To enhance the TADF, two different strategies were used by employing suitable guests: the reduction of the singlet-triplet gap by exciplex formation and the external heavy atom effect. Altogether, by using supramolecular host-guest complexation, a versatile multimodal chromophore system is achieved with the coronene bisimide cyclophane.

Deracemization of Carbohelicenes by a Chiral Perylene Bisimide Cyclophane Template Catalyst.

Deracemization describes the conversion of a racemic mixture of a chiral molecule into an enantioenriched mixture or an enantiopure compound without structural modifications. Herein, we report an inherently chiral perylene bisimide (PBI) cyclophane whose chiral pocket is capable of transforming a racemic mixture of [5]‐helicene into an enantioenriched mixture with an enantiomeric excess of 66 %. UV/Vis and fluorescence titration studies reveal this cyclophane host composed of two helically twisted PBI dyes has high binding affinities for the respective homochiral carbohelicene guests, with outstanding binding constants of up to 3.9×1010 m −1 for [4]‐helicene. 2D NMR studies and single‐crystal X‐ray analysis demonstrate that the observed strong and enantioselective binding of homochiral carbohelicenes and the successful template‐catalyzed deracemization of [5]‐helicene can be explained by the enzyme‐like perfect shape complementarity of the macrocyclic supramolecular host.

Deracemization of Carbohelicenes by a Chiral Perylene Bisimide Cyclophane Template Catalyst

AbstractDeracemization describes the conversion of a racemic mixture of a chiral molecule into an enantioenriched mixture or an enantiopure compound without structural modifications. Herein, we report an inherently chiral perylene bisimide (PBI) cyclophane whose chiral pocket is capable of transforming a racemic mixture of [5]‐helicene into an enantioenriched mixture with an enantiomeric excess of 66 %. UV/Vis and fluorescence titration studies reveal this cyclophane host composed of two helically twisted PBI dyes has high binding affinities for the respective homochiral carbohelicene guests, with outstanding binding constants of up to 3.9×1010 m−1 for [4]‐helicene. 2D NMR studies and single‐crystal X‐ray analysis demonstrate that the observed strong and enantioselective binding of homochiral carbohelicenes and the successful template‐catalyzed deracemization of [5]‐helicene can be explained by the enzyme‐like perfect shape complementarity of the macrocyclic supramolecular host.

Supramolecular control over pH- and temperature-responsive dialkoxynaphthalene-functionalized poly(2-(dimethylamino)ethyl methacrylate) in water

In the framework of the development of multi-responsive polymer materials, a well-defined copolymer bearing supramolecular recognition units was designed based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and a dialkoxynaphthalene-functionalized monomer (NaphtA). The supramolecular host–guest interactions of this P(DMAEMA-co-NaphtA) copolymer with the electron-deficient CBPQT4+, 4Cl- cyclophane host were studied by 1H NMR spectroscopy, UV–Visible spectroscopy and isothermal titration calorimetry (ITC), revealing, a high association constant of 6.5 × 105 M−1 in water. The addition of CBPQT4+, 4Cl- to a colorless solution of the copolymer in water resulted in a purple solution due to the formation of donor–acceptor inclusion complexes, the intensity being directly proportional to the amount of host added. Investigations on the thermoresponsive behavior of the naphthalene-functionalized copolymer highlighted that the cloud point temperature is directly proportional to the amount of CBPQT4+, 4Cl- host added and can simply be programmed within a temperature window from 30 °C to 48 °C by playing with pH. The dethreading process was studied as function of temperature and anionic exchange of the counterions of the CBPQT4+, 4Cl-. Interestingly, a partial decomplexation was observed by heating the sample above the cloud point temperature while a complete and programmable dethreading was achieved by adding the anionic surfactant sodium dodecyl sulfate (SDS) as a competitive counterion of the host molecule.

Guest-mediated chirality transfer in the host–guest complexes of an atropisomeric perylene bisimide cyclophane host

Chirality transfer upon preferential binding of homochiral guests to one stereoisomer of a conformationally equilibrated atropisomeric cyclophane is reported.

Assembly of [2]Rotaxanes in Water

Two [2]rotaxanes have been assembled in water from modular subunits through CuI‐catalyzed azide–alkyne “click” chemistry. For this purpose, 2,6‐disubstituted naphthalene axles with solubilizing oligo(ethylene glycol) (OEG) chains (n = 1–5) and propargyl terminal groups were synthesized and examined for their propensity to form inclusion complexes with a dicationic Diederich‐type cyclophane host. The dependence of pseudorotaxane formation on the linkers between the naphthalene core and OEG chains, and in the case of ester linkers on different spacer lengths, was analyzed by titration experiments. In addition, the inclusion complexes of two [2]rotaxanes were trapped by using a water‐soluble azide‐functionalized stopper. Repetitive chromatography finally enabled the isolation of both mechanically interlocked [2]rotaxanes.

Host Amplification in a Dithioacetal-Based Dynamic Covalent Library

Molecular amplification in a dithioacetal-based dynamic library is described for the first time. The homatropine induced selection, amplification, and isolation of one cyclophane host demonstrates the utility of dithioacetal exchange for preparing responsive dynamic libraries. Nuclear magnetic resonance and isothermal titration calorimetry analysis suggest that the amplified macrocycle forms a 1:1 complex with the template. This is the first report about a host/guest system involving a dithioacetal cyclophane.

ChemInform Abstract: Pillararene‐Based Supramolecular Polymers: From Molecular Recognition to Polymeric Aggregates

AbstractReview: [47 refs.

Emergent ion-gated binding of cationic host-guest complexes within cationic M12L24 molecular flasks.

"Molecular flasks" are well-defined supramolecular cages that can encapsulate one or more molecular guests within their cavities and, in so doing, change the physical properties and reactivities of the guests. Although molecular flasks are powerful tools for manipulating matter on the nanoscale, most of them are limited in their scope because of size restrictions. Recently, however, increasingly large and diverse supramolecular cages have become available with enough space in their cavities for larger chemical systems such as polymers, nanoparticles, and biomolecules. Here we report how a class of metallosupramolecular cages known as M12L24 polyhedra have been adapted to serve as nanometer-scale containers for solutions of a pseudorotaxane host-guest complex based on a tetracationic cyclophane host, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), and a 1,5-dioxynaphthalene (DNP) guest. Remarkably, the hierarchical integration of pseudorotaxanes and M12L24 superhosts causes the system to express stimulus-responsive behavior, a property which can be described as emergent because neither the DNP⊂CBPQT(4+) nor the M12L24 assemblies exhibit this behavior independently. The DNP-containing M12L24 molecular flasks are effectively "sealed off" to CBPQT(4+) until ions are added as a stimulus to "open" them. The electrolyte stimulus reduces the electrostatic screening distance in solution, allowing favorable DNP⊂CBPQT(4+) host-guest interactions to overcome repulsive Coulombic interactions between the cationic M12L24 cages and CBPQT(4+) rings. This unusual example of ion-gated transport into chemical nanocontainers is reminiscent of transmembrane ion channels which act as gates to the cell, with the important difference that this system is reversible and operates at equilibrium.

Pillararene-based supramolecular polymers: from molecular recognition to polymeric aggregates.

Pillar[n]arenes (P[n]As) and their derivatives, consisting of (substituted) hydroquinone units linked by methylene bridges at para-positions, are new type of cyclophane hosts developed in 2008. Their intrinsic characteristics and properties, such as facile preparation and flexible modification, symmetrical and columnar architectures, very rigid and π-rich cavities, as well as intriguing and peculiar guest complexation capability, make them ideal building blocks for the fabrication of polymeric supramolecules. This Feature Article provides an overview of the construction of pillararene-based supramolecular polymers and covers recent research endeavors of the marriage between pillararene-based host-guest pairs and polymeric aggregates. These polymers are classified into two major classes according to the different types of guest species: (1) supramolecular polymers relying on pillararene-based cationic guest recognition; (2) supramolecular polymers relying on pillararene-based neutral guest recognition. The host-guest motifs, building strategies, topological architectures, stimuli-responsiveness and functionalities are comprehensively discussed.

ChemInform Abstract: Complexes of Neutral Molecules and Cyclophane Hosts

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Surface plasmon resonance study on binding interactions of multivalent cyclophane hosts with immobilized guests

AbstractGuest‐binding affinities of water‐soluble cyclophane heptadecamer (1) and pentamer (2) with immobilized guests such as 1‐pyrenylmethylamine (PMA) and 2‐(1‐ naphthyl)ethylamine (NEA) were investigated by surface plasmon resonance (SPR) measurements. As a typical example, the binding constants (K) for 1 and 2 with the immobilized PMA as a guest were evaluated to be 2.5 × 107 and 2.7 × 106 M−1, respectively, and were much larger than that of a monocyclic reference cyclophane (K, 2.5 × 104 M−1). Interestingly, in the complexation of 1 and 2 with the immobilized guests, more favorable association and dissociation rate constant values (ka and kd, respectively) were observed in comparison with those for the monocyclic cyclophane, reflecting multivalent effects in macrocycles. The multivalent effects in macrocycles as well as molecular recognition abilities of the cyclophane oligomers were confirmed even when the guest molecules were immobilized on SPR sensor chip surfaces. Copyright © 2009 John Wiley & Sons, Ltd.

NMR Studies of Host–guest Complexes Between Monocarboxylic Acids and Amide-based Cyclophanes in Chloroform

Formation of host–guest complexes with acetic acid and benzoic acid was studied by NMR for amide-based octaazacyclophanes having pendant methyl ester arms; the cyclophanes were tetramethyl 2,9,18,25-tetraoxo-1,4,7,10,17,20,23,26-octaaza[10.10]paracyclophane-4,7,20,23-tetraacetate, its meta-isomer and analogues. Amide NH proton and CH2 proton adjacent to amide C = O in every cyclophane host showed down-field NMR shifts in the presence of the guest acids in CHCl3-d, suggesting the formation of 1:1 complexes in which the carboxyl group of an acid molecule formed two hydrogen bonds with the amide NH and C = O moieties of a host molecule. Since the complex formation competed with the dimerization of the guest acids, the monomer–dimer equilibrium was restudied by NMR and the equilibrium constant was determined to be 330 M− 1 for acetic acid and 518 M− 1 for benzoic acid. By using these values, the formation constants of the host–guest complexes were determined to be 8–51 M− 1. The close contact between the host and guest molecules via hydrogen bonding was consistently confirmed by NMR shifts due to the ring current of aromatic group.

Synthesis and solid-state structures of new cyclophane host molecules

Five new cyclophane host molecules (corrals) are prepared by linking together two α,α′-di(4-hydroxyphenyl)-1,4-diisopropylbenzene or α,α′-di(3,5-dimethyl-4-hydroxyphenyl)-1,4-diisopropylbenzene units with two permethylene spacers. Three small cyclophane hosts (boxes) are synthesized by cyclization of α,α′-di(4-hydroxyphenyl)-1,4-diisopropylbenzene with di(bromomethyl)benzene compounds. Solid-state structures of one corral and one box are reported.

Switching Surface Chemistry with Supramolecular Machines

Tethered supramolecular machines represent a new class of active self-assembled monolayers in which molecular configurations can be reversibly programmed using electrochemical stimuli. We are using these machines to address the chemistry of substrate surfaces for integrated microfluidic systems. Interactions between the tethered tetracationic cyclophane host cyclobis(paraquat-p-phenylene) and dissolved pi-electron-rich guest molecules, such as tetrathiafulvalene, have been reversibly switched by oxidative electrochemistry. The results demonstrate that surface-bound supramolecular machines can be programmed to adsorb or release appropriately designed solution species for manipulating surface chemistry.

New Exo-Functional Cyclophane Hosts. Synthesis and Crystal Structures of Inclusion Compounds

The new cyclophane type host compounds 1–3, containing rigid aromatic units and two exo-topic carboxylic acid functions, have been synthesized. Crystalline solvent inclusions, involving the dicarboxylic acid hosts and their corresponding ester intermediates 6 (a–c), namely 1·DMSO (1:4), 2·pyridine (1:3), 3·pyridine (1:4), 6a·pyridine (1:2) and 6a·benzene (1:2), have been prepared and studied using X-ray diffraction on single-crystals. Moreover, X-ray structure analyses of the solvent-free crystals of the 6 (a, b) intermediates were also carried out for comparison. Co-crystals of the carboxylic hosts 1–3 contained H-bonded 1:2 host-guest associates as building blocks, together with additional space-filling guests, whereas only loosely bounded space-filling solvent molecules were found in the two solid inclusion compounds of the 6a cyclophane ester host. In addition to the mentioned conventional H-bond interactions between carboxylic hosts and their guests, the crystal structures proved to be held together by relatively weak C–H…O bonds besides the ordinary van der Waals' interactions. Packing relations, and the effects of structural variations, guest molecules and anisotropic packing forces on the conformation of the semi-rigid cylcophane ring have been discussed and compared in seven crystal structures.

Synthesis and evaluation of new ditopic cyclophane receptors for benzoic acid

AbstractAs potential receptors for a benzoic acid guest, new ditopic cyclophane host molecules, each with a π electron‐rich portion and a pyridine ring‐containing portion, are synthesized. Complexation of benzoic acid guest by the potential molecular receptors is probed by infrared spectroscopy, proton magnetic resonance titration experiments and solid‐state structure determination. Copyright © 2005 John Wiley & Sons, Ltd.

Exo-functional cyclophane hosts. Crystal structures of two respective inclusion compounds

Exo-functional cyclophane hosts. Crystal structures of two respective inclusion compounds

Complexation behavior of a highly preorganized 7,7-diphenylnorbornane-derived macrocycle: towards the design of molecular clocks.

The syntheses of two new cyclophane hosts, 4 and 6, are described. The main difference between them is the higher degree of preorganization of 4 as a consequence of the inclusion of the 7,7-diphenylnorbornane (DPN) subunit. The inner cavity of 4 adopts a belt-shaped structure, while 6 has a twisted geometry. In the solid state, the molecules of macrocycle 6 are stacked along an axis to form nanotubular structures. Compounds 4 and 6 form two of the strongest complexes between arene cyclophanes and Ag(+) reported up to date. The silver cation is located inside the cavity of the macrocycles. The stability of 4.Ag(+) is considerably higher than that of 6.Ag(+). The additional stabilization of 4.Ag(+) is attributed to higher preorganization of macrocycle 4. DNMR experiments as well as theoretical calculations carried out with 4.Ag(+) show evidence of Ag(+)-hopping between two different binding sites inside the macrocycle. This phenomenon could be the basis for the design of molecular clocks.

Synthesis of New Cyclophane Host Molecules and Crystal Structures of Their Compounds with Hydrocarbon Guests

Three new cyclophane host molecules 2, 4, and 6 are prepared by connecting the oxygen atoms of twoα ,α'–di(4-hydroxyphenyl)-1,4-diisopropylbenzene units with two di-, tetra-, and hexamethylene spacers, respectively. Solid-state structures are determined for host 2 with a hexane guest, host 4 with a toluene guest and a solvating toluene molecule, host 4 with a p-xylene guest,and host 6 with two p-xylene guests.