Anion‐ and Spacer‐Directed Host–Guest Complexes of Bipyridine with Pyrogallol[4]arene

New oval‐shaped capsular and bilayer‐type hydrogen‐bonded arrangements of C‐propyl‐ol‐pyrogallol[4]arene (PgC3‐OH) with bipyridine‐type spacer complexes are reported here. These complexes are engineered by virtue of derivatization of C‐alkyl tails of pyrogallol[4]arene and the use of divergent spacer ligands. Complexes of PgC3‐OH, PgC3‐OH with bpy (4,4′‐bipyridine) and PgC3‐OH with bpa (1,2‐bis(4‐pyridyl)acetylene) have bilayer type arrangements; however, the use of hydrogen chloride causes protonation of bpy molecule, which is then entrapped flat within an offset oval‐shaped dimeric hydrogen‐bonded PgC3‐OH nanocapsule. The presence of chloride anion in the crystal lattice controls the geometry of the resultant nanoassembly.     

Mechanism of Macroscopic Motion of Oleate Helical Assemblies: Cooperative Deprotonation of Carboxyl Groups Triggered by Photoisomerization of Azobenzene Derivatives

Macroscopic and spatially ordered motions of self‐assemblies composed of oleic acid and a small amount of an azobenzene derivative, induced by azobenzene photoisomerization, was previously reported. However, the mechanism of the generation of submillimeter‐scale motions by the nanosized structural transition of azobenzene was not clarified. Herein, an underlying mechanism of the motions is proposed in which deprotonation of carboxyl groups in cooperation with azobenzene photoisomerization causes a morphological transition of the self‐assembly, which in turn results in macroscopic forceful dynamics. The photoinduced deprotonation was investigated by potentiometric pH titration and FTIR spectroscopy. The concept of hierarchical molecular interaction generating macroscale function is expected to promote the next stage of supramolecular chemistry.     

Intramolecular van der Waals Interactions Challenge Anion Binding in perthio-Bambusurils

Bambusurils (BUs) are known to be rigid cavitands that feature an extended, jigger-like conformation, and the BU[6]s strongly bind anions within their hydrophobic cavity. These features are not necessarily shared by the family of perthio-BUs. This study reveals that perthio-BUs assume a compact conformation and perthio-BU[6]s are poor anion binders, crystallizing as anion-free species from solutions containing halide salts. Computational studies show that the equatorial sulfur atoms compete against guest anions for binding with the glycoluril methine groups via strong van der Waals (vdW) attractive interactions. These competitive contacts not only account for the diminished anion-binding of perthio-BUs, but also explain their compact conformation. The semithio- and perthio-BU[4]s form linear coordination polymers with Hg^II in the solid-state regardless of their intrinsic molecular conformation. The strong involvement of sulfur atoms in intramolecular interactions differentiates the equatorial from the axial (peripheral) heteroatoms, thus offering chemoselective and regioselective transformations.     

Computational Study of van der Waals Complexes between Borylenes and Hydrocarbons

The addition of borylenes (RB) to prototypical carbon?carbon multiple bonds (ethyne, ethene) and the insertion into a C?H bond of methane involves weakly bound van der Waals complexes of the reaction partners according to computational chemistry methods. Geometries of all complexes were optimized using spin‐component scaled second‐order Møller–Plesset perturbation theory (SCS‐MP2) in combination with a quadruple‐ζ (def2‐QZVP) basis set. Energies were further refined using the coupled‐cluster (CCSD(T)) method in combination with basis sets up to quadruple‐ζ quality (def2‐QZVP and aug‐cc‐pVTZ). All of the complexes of borylenes studied correspond to shallow minima on their potential‐energy surfaces. Borylene complexes with ethyne are the most stable and those with methane are the least stable ones. Aminoborylene complexes BNHR with ethyne and ethene are stabilized mainly by NH ??? π interactions. Symmetry‐adapted perturbation theory (SAPT) was performed to analyze the nature of the interaction between borylene molecules and hydrocarbons. Most of the ethyne complexes are dominated by electrostatic interactions, whereas for most of the ethene and all of the methane complexes the interaction is mainly dispersive.     

Photocontrollable self-assembly

The incorporation of photoswitching molecules into molecular building blocks creates the possibility of photoresponsive self-assemblies in which the self-assembled architecture or self-assembling process can be controlled by external light stimulus. Among the photoswitching molecules, azobenzene has been used most widely by virtue of the large photoinduced changes in its molecular geometry and physical properties. This article reviews how azobenzene can be effectively used to construct the self-assemblies in which supramolecular structure and formation/dissociation can be altered by light.     

Tunable Supramolecular Assembly and Photoswitchable Conversion of Cyclodextrin/Diphenylalanine-Based 1D and 2D Nanostructures

A photocontrolled, interconvertible supramolecular 2D-nanosheet/1D-nanotube system was constructed through the supramolecular assembly of adamantanyl-modified diphenylalanine with azobenzene-bridged bis(β-cyclodextrin). The nanosheet exhibited a greater fluorescence enhancement effect than the nanotube. Significantly, these nanosheets and nanotubes could interconvert via the photocontrolled trans/cis isomerization of azobenzene linkers in bis(β-cyclodextrin), and this photo-switchable one-dimensional/two-dimensional morphological interconversion was reversible and recyclable. This enables convenient routes to highly ordered nanostructures with various morphologies and dimensions that can be controlled by external stimuli.     

Augmented van der Waals equations of state: SAFT-VR versus Yukawa based van der Waals equation

Performance of the SAFT-VR equation of state developed for the hard sphere based simple fluids, namely the square-well, Sutherland and Yukawa fluids, is examined by comparing its results with simulation data and an augmented van der Waals (vdW) equation based on a Yukawa (Y) reference. Its shown that both for the equilibrium vapor-liquid data and data along selected isotherms in the liquid and supercritical fluid phases the vdW(Y) equation provides better results, particularly when going to lower temperatures.     

Supramolecular Fullerene Polymers and Networks Directed by Molecular Recognition between Calix[5]arene and C60

A biscalix[5]arene–C₆₀ supramolecular structure was utilized for the development of supramolecular fullerene polymers. Di‐ and tritopic hosts were developed to generate the linear and network supramolecular polymers through the complexation of a dumbbell‐shaped fullerene. The molecular association between the hosts and the fullerene were carefully studied by using ¹H NMR, UV/Vis absorption, and fluorescence spectroscopy. The formation of the supramolecular fullerene polymers and networks was confirmed by diffusion‐ordered ¹H NMR spectroscopy (DOSY) and solution viscometry. Upon concentrating the mixtures of di‐ or tritopic hosts and dumbbell‐shaped fullerene in the range of 1.0–10 mmol L^?1, the diffusion coefficients of the complexes decreased, and the solution viscosities increased, suggesting that large polymeric assemblies were formed in solution. Scanning electron microscopy (SEM) was used to image the supramolecular fullerene polymers and networks. Atomic force microscopy (AFM) provided insight into the morphology of the supramolecular polymers. A mixture of the homoditopic host and the fullerene resulted in fibers with a height of (1.4±0.1) nm and a width of (5.0±0.8) nm. Interdigitation of the alkyl side chains provided secondary interchain interactions that facilitated supramolecular organization. The homotritopic host generated the supramolecular networks with the dumbbell‐shaped fullerene. Honeycomb sheet‐like structures with many voids were found. The growth of the supramolecular polymers is evidently governed by the shape, dimension, and directionality of the monomers.