Facile Catch and Release of Fullerenes Using a Photoresponsive Molecular Tube

A Dynamic and Responsive Host in Action: Light-Controlled Molecular Encapsulation

The rational design of a flexible molecular box, oAzoBox⁴⁺, incoporating both photochromic and supramolecular recognition motifs is described. We exploit the E↔Z photoisomerization properties of azobenzenes to alter the shape of the cavity of the macrocycle upon absorption of light. Imidazolium motifs are used as hydrogen‐bonding donor components, allowing for sequestration of small molecule guests in acetonitrile. Upon E→Z photoisomerization of oAzoBox⁴⁺ the guest is expelled from the macrocyclic cavity.

Chaperone-Assisted Formation of Cucurbit[8]uril-Based Molecular Porous Materials with One-Dimensional Channel Structure

Exploiting "chaperone molecule" to navigate the successful assembly energy landscapes has been extensively used in biological systems, whereas in artifical supramolecular systems the "chaperone-assisted" assembly strategy to be used for the synthesis of materials with novel structures or the structures to be hardly prepared by "conventional" methods are still far from realizing the potential functions. In this work, we present a new example of small organic molecule acting as "chaperone molecule" in the facile formation of organic molecular porous materials. This porous material is composed of pure cucurbit[8]uril (CB[8]) macrocycle and possesses a honeycomb-like structure with an isolated and relatively large one-dimensional (1D) nanochannel. Moreover, it has good chemical and thermal stability, and shows a good adsorption capability for large molecule loading. Importantly, with the assistance of chaperone molecules, pure CB[8] could also be recycled even from a complex aqueous solution, demonstrating a powerful purification method of CB[8] from complex systems.

Our Expedition in Linear Neutral Platinum-Acetylide Complexes: The Preparation of Micro/nanostructure Materials, Complicated Topologies, and Dye-Sensitized Solar Cells

During the past few decades, the construction of various kinds of platinum-acetylide complexes has attracted considerable attention, because of their wide applications in photovoltaic cells, non-linear optics, and bio-imaging materials. Among these platinum-acetylide complexes, the linear neutral platinum-acetylide complexes, due to their attractive properties, such as well-defined linear geometry, synthetic accessibility, and intriguing photoproperties, have emerged as a rising star in this field. In this personal account, we will discuss how we entered the field of linear neutral platinum-acetylide chemistry and what we found in this field. The preparation of various types of linear neutral platinum-acetylide complexes and their applications in the areas of micro/nanostructure materials, complicated topologies, and dye-sensitized solar cells will be summarized in this account.

Pyrazine-based donor tectons: synthesis, self-assembly and characterization

Two donor tectons, each bearing a central pyrazine moiety covalently linked to two pyridine units, have been self-assembled with PtII2 acceptor units to yield ionic nanoscalar metallamacrocycles, having a convex hexagonal cavity.

Heterogeneous catalysis of water oxidation supported by a novel metallamacrocycle

Metallamacrocycles 1 and 2 were constructed, and 1 was further explored as a precatalyst for water oxidation, giving a good efficiency.

M2L4 coordination capsules with tunable anticancer activity upon guest encapsulation

Guest encapsulation can modulate the cytotoxicity of anthracene-based nano-capsules and broaden their applications from metallodrugs to biocompatible delivery systems.

Supramolecular hexagonal nano tubes assembled by vanadium diamine complexes with thiogermanates

A supramolecular hexagonal nano tube is characterized, which is assembled by oxo-vanadium thiogermanate in a sulfur–diamine reduction system.

Metallosupramolecular receptors for fullerene binding and release

Different strategies for fullerene separation and purification mediated by supramolecular metallocages are reviewed in this Tutorial.

Engineering an iridium-containing metal–organic molecular capsule for induced-fit geometrical conversion and dual catalysis

Quantitative dynamic capsule–capsule conversion by cooperative binding one carbonate anion and switchable dual catalysis was achieved within an Ir₂Co₃-type capsule.

Reversible Guest Uptake/Release by Redox-Controlled Assembly/Disassembly of a Coordination Cage

Controlling the guest expulsion process from a receptor is of critical importance in various fields. Several coordination cages have been recently designed for this purpose, based on various types of stimuli to induce the guest release. Herein, we report the first example of a redox-triggered process from a coordination cage. The latter integrates a cavity, the panels of which are based on the extended tetrathiafulvalene unit (exTTF). The unique combination of electronic and conformational features of this framework (i.e. high π-donating properties and drastic conformational changes upon oxidation) allows the reversible disassembly/reassembly of the redox-active cavity upon chemical oxidation/reduction, respectively. This cage is able to bind the three-dimensional B12 F12 (2-) anion in a 1:2 host/guest stoichiometry. The reversible redox-triggered disassembly of the cage could also be demonstrated in the case of the host-guest complex, offering a new option for guest-delivering control.

Light driven mesoscale assembly of a coordination polymeric gelator into flowers and stars with distinct properties

Control over the self-assembly process of porous organic-inorganic hybrids often leads to unprecedented polymorphism and properties. Herein we demonstrate how light can be a powerful tool to intervene in the kinetically controlled mesoscale self-assembly of a coordination polymeric gelator. Ultraviolet light induced coordination modulation via photoisomerisation of an azobenzene based dicarboxylate linker followed by aggregation mediated crystal growth resulted in two distinct morphological forms (flowers and stars), which show subtle differences in their physical properties.

Recent advances in the construction of fluorescent metallocycles and metallocages via coordination-driven self-assembly

During the last few years, the construction of fluorescent metallocycles and metallocages has attracted considerable attention because of their wide applications in fluorescence detection of metal ions, anions, or small molecules, mimicking complicated natural photo-processes, and preparing photoelectric devices, etc. This perspective focuses on the recent advances in the construction of a variety of fluorescent metallocycles and metallocages via coordination-driven self-assembly. In addition, the fluorescence properties and the applications of these organometallic architectures have also been discussed.

A novel photo-responsive azobenzene-containing nanoring host for fullerene-guest facile encapsulation and release

Azobenzenes in particular have been proved to have a robust photo-response, in which their configuration can transform between the trans- and cis-form upon UV-visible irradiation. Accordingly, azobenzene-containing molecules are frequently applied in the design of the guests, involving so-called host-guest chemistry. In this paper, a novel photo-responsive nanoring host molecule ([4]AB) has been designed by introducing four azobenzene groups onto the ring, and interactions between the designed nanoring host and fullerenes C60 and C70 guests were investigated at both the M06-L/MIDI! as well as M06-2X/6-31G(d) level of theory. By analyzing the geometric characteristics and host-guest binding energies, it is revealed that the designed [4]AB with diameter ca. 13.4 Å is an ideal host molecule for the encapsulation of guests C60 and C70 fullerene. Meanwhile, inferred from UV-vis-NIR spectroscopy, the guest C60 and C70 could be facilely released from the cavity of the [4]AB via configuration transformation between trans- and cis-form of the host under 474 and 506 nm photo-irradiation, respectively. Frontier orbital features, weak interaction regions, infrared spectroscopy and (1)H NMR spectra have also been theoretically simulated. The present work would provide a new strategy for facile reversible encapsulation and release of fullerene guest by a novel nanoring host.

Guest-induced transformation of a porphyrin-edged Fe(II)4L6 capsule into a Cu(I)Fe(II)2L4 fullerene receptor

The combination of a bent diamino(nickel(II) porphyrin) with 2-formylpyridine and Fe(II) yielded an Fe(II) 4 L6 cage. Upon treatment with the fullerenes C60 or C70 , this cage was found to transform into a new host-guest complex incorporating three Fe(II) centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsaturation at one of the Fe(II) centers as the result of the incommensurate metal-to-ligand ratio, which enabled the preparation of a heterometallic cone-shaped Cu(I) Fe(II) 2 L4 adduct of C60 or C70 .

Chloride triggered reversible switching from a metallosupramolecular [Pd2L4]4+ cage to a [Pd2L2Cl4] metallo-macrocycle with release of endo- and exo-hedrally bound guests

A metallosupramolecular [Pd₂L₄]⁴⁺ cage can be cleanly, and reversibly, converted into a [Pd₂L₂Cl₄] metallo-macrocycle upon addition or removal of chloride ions.

Non-covalent composites of antiaromatic isophlorin–fullerene

Cocrystallates of fullerene C₆₀ and antiaromatic tetraoxa isophlorin exhibit π–π interaction to form non-covalent molecular complex.

Polyaromatic molecular tubes with a subnanometer pore and the guest-induced emission enhancement behavior

New polyaromatic molecular tubes with a subnanometer pore (0.8 nm) can bind one molecule of hydrocarbon guests in water with accompanying guest-induced emission enhancement (up to ∼3 times).

Multipoint recognition of ditopic aromatic guest molecules via Ag-π interactions within a dimetal macrocycle

A macrocyclic host molecule possessing a nanocavity with two Ag(I) centers for guest binding and four anthracene walls has been developed. This dimetal-macrocycle forms stable inclusion complexes with ditopic aromatic guest molecules, [2.2]paracyclophane, and ferrocene, in solution and/or in the solid state through Ag-π interactions within the nanocavity. The binding constants for the inclusion complexes were found to range roughly from 10(4) to 10(9) M(-1). Electrochemical measurement revealed that the oxidized form of the included cationic ferrocene was less stabilized due to the direct binding to the cationic two Ag(I) centers.

Sponge-like molecular cage for purification of fullerenes

Since fullerenes are available in macroscopic quantities from fullerene soot, large efforts have been geared toward designing efficient strategies to obtain highly pure fullerenes, which can be subsequently applied in multiple research fields. Here we present a supramolecular nanocage synthesized by metal-directed self-assembly, which encapsulates fullerenes of different sizes. Direct experimental evidence is provided for the 1:1 encapsulation of C60, C70, C76, C78 and C84, and solid state structures for the host-guest adducts with C60 and C70 have been obtained using X-ray synchrotron radiation. Furthermore, we design a washing-based strategy to exclusively extract pure C60 from a solid sample of cage charged with a mixture of fullerenes. These results showcase an attractive methodology to selectively extract C60 from fullerene mixtures, providing a platform to design tuned cages for selective extraction of higher fullerenes. The solid-phase fullerene encapsulation and liberation represent a twist in host-guest chemistry for molecular nanocage structures.

Molecular architectures of multi-anthracene assemblies

Anthracene, with its molecular panel-like shape and robust photophysical behaviour, is a versatile building block that is widely used to construct attractive and functional molecules and molecular assemblies through covalent and non-covalent linkages. The intrinsic photophysical, photochemical and chemical properties of the embedded anthracenes often interact to engender desirable chemical behaviours and properties in multi-anthracene assemblies. This review article focuses on molecular architectures with linear, cyclic, cage, and capsule shapes, each containing three or more anthracene subunits.

Solvent effects upon guest binding and dynamics of a Fe(II)4L4 cage

Solvent-dependent host-guest chemistry and favoring of otherwise disfavored conformations of large guests has been achieved with an adaptive, self-assembled Fe(II)4L4 coordination cage. Depending on the counterion, this face-capped tetrahedral capsule is soluble either in water or in acetonitrile and shows a solvent-dependent preference for encapsulation of certain classes of guest molecules. Quantitative binding studies were undertaken, revealing that both aromatic and aliphatic guests bind in water, whereas only aliphatic guests bind in acetonitrile. The flexibility of its subcomponent building blocks allows this cage to expand or contract upon guest binding, as studied by VT-NMR, thereby ensuring strong binding of both small and large guests. Upon encapsulation, large guest molecules can adopt conformations which are not thermodynamically favored in the free state. In addition, the chirotopic inner phase of the cage renders enantiotopic guest proton signals diastereotopic in specific cases.

Phosphorus-containing chiral molecule for fullerene recognition based on concave/convex interaction

A C3-symmetric chiral concave molecule having a phosphorus atom at the center was synthesized, and its enantiomers were resolved. The chiral concave shape and absolute structure of the concave molecules were revealed by X-ray analysis. The concave molecule exhibited intense chiroptical properties with a large anisotropy, which was derived from molecular orbitals delocalized to the side chains. In the co-crystal with pristine C60, four of the enantiopure concave molecules perfectly wrapped the surface of C60. MALDI-TOF mass, NMR, and circular dichromism spectra also supported the concave/convex interaction between the concave molecule and fullerene. These results suggest that the phosphorus-containing molecule with a concave shape plays an important role as a chiral host molecule for C60.

An aqueous molecular tube with polyaromatic frameworks capable of binding fluorescent dyes

An aqueous polyaromatic tube binds two molecules of fluorescent dyes in water and the bound dye dimers exhibit unusual excimer-like emissions through efficient host–guest energy transfer.

An aqueous molecular tube composed of polyaromatic frameworks with peripheral hydrophilic groups was prepared. The new tube has a well-defined hydrophobic cavity with a diameter of ∼1 nm and quantitatively binds two molecules of fluorescent coumarin dyes in aqueous solutions. The bound coumarin dimers in a stacked fashion exhibit unusual excimer-like emissions in the confined space through efficient host–guest energy transfer.