Elucidation of Substituent-Responsive Reactivities via Hierarchical and Asymmetric Assemblies in Crystalline p-Quinodimethane Derivatives.

We propose a mechanism for substituent-responsive reactivities of p-quinodimethane derivatives with four ester groups through their hierarchical and asymmetric assembly modes. Four asymmetric 7,8,8-tris(methoxycarbonyl)-p-quinodimethanes with a 7-positioned ethoxycarbonyl (2 a(H)), 2'-fluoroethoxycarbonyl (2 b(F)), 2'-chloroethoxycarbonyl (2 c(Cl)), or 2'-bromoethoxycarbonyl (2 d(Br)) were synthesized and crystallized. 2 a(H), 2 b(F) and 2 d(Br) afforded only one shape crystal, while 2 c(Cl) did two polymorphic 2 c(Cl)-α and 2 c(Cl)-β.

Aggregation-Induced Singlet Oxygen Generation: Functional Fluorophore and Anthrylphenylene Dyad Self-Assemblies.

The assembly of monomeric building blocks can manifest the display of new properties, including optical, mechanical, and electrochemical functionalities. In this study, we sought to develop a functional fluorophore self-assembly that can generate reactive oxygen species only when aggregated. With an anthrylphenylene (AP) group, negatively charged and neutral fluorescein units form non-fluorescent H-aggregates in aqueous solution because of the weak intermolecular interaction between the anthracene and fluorescein moieties.

Gold-Catalyzed [3+2]/Retro-[3+2]/[3+2] Cycloaddition Cascade Reaction of N-Alkoxyazomethine Ylides.

A novel cascade reaction has been developed for the synthesis of 2,6-methanopyrrolo[1,2-b]isoxazoles based on the gold-catalyzed generation of an N-allyloxyazomethine ylide. This reaction involves sequential [3+2]/retro-[3+2]/[3+2] cycloaddition reactions, thus providing facile access to fused and bridged heterocycles which would be otherwise difficult to prepare using existing synthetic methods. Notably, this reaction allows the efficient construction of three C-C bonds, one C-O bond, one C-N bond and one C-H bond, as well as the cleavage of one C-C bond, one C-O bond and one C-H bond in a single operation.

Photoinduced electron transfer in porous organic salt crystals impregnated with fullerenes.

Porous organic salt (POS) crystals composed of 9-(4-sulfophenyl)anthracene (SPA) and triphenylmethylamine (TPMA) were impregnated with fullerenes (C60 and C70), which were arranged in one dimensional close contact. POS crystals of SPA and TPMA without fullerenes exhibit blue fluorescence due to SPA, whereas the fluorescence was quenched in POS with fullerenes due to electron transfer from the singlet excited state of SPA to fullerenes.

A Series of Layered Assemblies of Hydrogen-Bonded, Hexagonal Networks of C3-Symmetric π-Conjugated Molecules: A Potential Motif of Porous Organic Materials.

Hydrogen-bonded porous organic crystals are promising candidates for functional organic materials due to their easy construction and flexibility arising from reversible bond formation-dissociation. However, it still remains challenging to form porous materials with void spaces that are well-controlled in size, shape, and multiplicity because even well-designed porous frameworks often fail to generate pores within the crystal due to unexpected disruption of hydrogen bonding networks or interpenetration of the frameworks. Herein, we demonstrate that a series of C3-symmetric π-conjugated planar molecules (Tp, T12, T18, and Ex) with three 4,4'-dicarboxy-o-terphenyl moieties in their periphery can form robust hydrogen-bonded hexagonal networks (H-HexNets) with dual or triple pores and that the H-HexNets stack without interpenetration to yield a layered assembly of H-HexNet (LA-H-HexNet) with accessible volumes up to 59%.

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates.

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their components. Therefore, the arrangements in the clusters have been precisely characterized, especially for metal complexes. Contrary to this, characterizations of molecular arrangements in supramolecular clusters composed of organic molecules are limited to a few cases.

Excited-state dynamics of Si-rhodamine and its aggregates: versatile fluorophores for NIR absorption.

Since it was first reported in 2008, great attention has been paid to Si-rhodamine (SiR) because of its far-red to near-infrared (NIR) absorption/fluorescence and suitability for high-resolution in vivo imaging. However, properties of SiR in the excited state have not been reported, even though they are directly related to its fluorescence. In the present study, the properties of SiR monomers in the excited states are thoroughly characterized for the first time.

Polymorphs of layered assemblies of hydrogen-bonded hexagonal networks caused by conformational frustration.

Generation of four polymorphs of 2D-nCOF crystals that are formed through stacking of a hydrogen-bonded, hexagonally-networked framework is revealed for the first time. The structural diversity is caused not from the topology or the stacking manner of the framework but from subtle structural factors such as rotational conformation and location of conformational frustration within the framework.

The unprecedented J-aggregate formation of rhodamine moieties induced by 9-phenylanthracenyl substitution.

We report a substitution of 9-phenylanthracenyl group into rhodamine derivatives that can induce the J-aggregate formation of rhodamine moieties in the aqueous solution upon the addition of a halide ion. From X-ray crystallographic analysis, the dramatic red-shift in the absorption band (i.e.

A C3-symmetric macrocycle-based, hydrogen-bonded, multiporous hexagonal network as a motif of porous molecular crystals.

A C3-symmetric π-conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58%. The frameworks were obtained through non-interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO2 up to 96 cm(3) g(-1) at 195 K under 1 atm.

Amphiphilic inclusion spaces for various guests and regulation of fluorescence intensity of 1,8-bis(4-aminophenyl)anthracene crystals.

A host framework for inclusion of various guest molecules was investigated by preparation of inclusion crystals of 1,8-bis(4-aminophenyl)anthracene (1,8-BAPA) with organic solvents. X-ray crystallographic analysis revealed construction of the same inclusion space incorporating 1,8-BAPA and eight guest molecules including both non-polar (benzene) and polar guests (N,N-dimethylformamide, DMF). Fluorescence efficiencies varied depending on guest molecule polarity; DMF inclusion crystals exhibited the highest fluorescence intensity (ΦF=0.

Characterization of supramolecular hidden chirality of hydrogen-bonded networks by advanced graph set analysis.

Supramolecular hidden chirality of hydrogen-bonded (HB) networks of primary ammonium carboxylates was exposed by advanced graph set analysis from a symmetric viewpoint in topology. The ring-type HB (R-HB) networks are topologically regarded as faces, and therefore exhibit prochirality and positional isomerism due to substituents attached on the faces. To describe the symmetric properties of the faces, additional symbols, Re (right-handed or clockwise), Si (left-handed or anticlockwise), and m (mirror), were proposed.

Engineering switchable rotors in molecular crystals with open porosity.

The first example of a porous molecular crystal containing rotors is presented. The permanently porous crystal architecture is sustained by rotor-bearing molecular rods which are connected through charge-assisted hydrogen bonds. The rotors, as fast as 10(8) Hz at 240 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors at low pressure.

Crystalline supramolecular nanofibers based on dehydrobenzoannulene derivatives.

Supramolecular nanofibers (SNFs) composed of low-molecular-weight π-conjugated molecules exhibit attractive optical and electrical properties and are expected to be the next optoelectronic materials. In this work, five crystalline SNFs have been constructed from three dehydrobenzoannulene (DBA) derivatives. The DBAs were designed to assemble in one dimension in a strategy based on anisotropic crystal growth.

A facile and versatile approach to efficient enhancement of solid-state luminescence by organic-inorganic hybrid salts.

Organic-inorganic hybrid salts based on 1,5-bisaminophenylanthracene were able to overcome aggregation-induced quenching and emit multiple colours of luminescence according to the counter acid employed. Moreover, the emission colour could be reversibly and dynamically changed on absorption and desorption of guest molecules.

Synthesis of dihydrobenzofurans with quaternary carbon center under mild and neutral conditions.

A new method has been developed for the construction of dihydrobenzofurans from O-aryloxime ethers bearing an α-cyano group using a sequential regioselective isomerization/[3,3]-sigmatropic rearrangement/cyclization reaction in MeOH without any catalysts under neutral conditions at ambient temperature. The current transformation provides environmentally benign and atom-economical access to a variety of dihydrobenzofurans containing a quaternary carbon from readily available cyclic and acyclic oxime ethers.

Linkage control between molecular and supramolecular chirality in 2₁-helical hydrogen-bonded networks using achiral components.

Chiral molecules preferentially form one-handed supramolecular assemblies that reflect the absolute configuration of the molecules. Under specific conditions, however, the opposite-handed supramolecular assemblies are also obtained because of flexibility in the bond length and reversibility of non-covalent interactions. The mechanism of the handedness selectivity or switching phenomenon remains ambiguous, and most phenomena are observed by chance.

Indeno[2,1-b]fluorene: a 20-π-electron hydrocarbon with very low-energy light absorption.

Smaller can be better: The first example of meta-quinodimethane embedded in an indenofluorene framework has been synthesized. 10,12-Dimesitylindeno[2,1-b]fluorene exhibits extremely low-energy light absorption, despite the small conjugation space of the molecule, which consists of only 20 π electrons.

Structural transformation between supramolecular nanofibers with drastic change of conductivity by heat and ultrasound.

Transformation with every fiber of its being: Dehydrobenzoannulene derivatives with a boomerang shape, dipole moment, and substituents that make diverse interactions enable the construction of stimuli-responsive nanofibers despite the lack of stimuli-responsive groups in these compounds. Interestingly, the supramolecular nanofibers obtained after ultrasonic treatment displayed an 80% decrease in conductivity as compared to untreated nanofibers. This is the first example of an electronic wire for which the conductivity can be controlled by ultrasound.

Role-allocated combination of two types of hydrogen bonds towards constructing a breathing diamondoid porous organic salt.

A diamondoid porous organic salt (d-POS) composed of 8-hydroxyquinoline-5-sulfonic acid (HQS) and triphenylmethylamine (TPMA) shows reversible structure contraction and expansion ("breathing") in response to guest desorption and adsorption. This flexible structure is designed hierarchically by utilizing two different types of hydrogen bonds. X-ray crystallographic analysis reveals that the two types of hydrogen bonds are formed separately to play respective roles for constructing the d-POS.

Interactions between dehydrobenzo[12]annulene (DBA) and gas molecules: do the preorganized acetylenes work cooperatively?

Intermolecular interactions of the cyclic conjugated molecule (DBA) with hydrogen, nitrogen and carbon dioxide molecules were evaluated by high level ab initio calculations.

Crystal structure of quinine: the effects of vinyl and methoxy groups on molecular assemblies of Cinchona alkaloids cannot be ignored.

Quinine, one of Cinchona alkaloids, has been of great interest from medical, synthetic, and supramolecular viewpoints. However, unaccountably, the guest-free (GF) crystal of quinine containing no solvent or other molecules has not been reported for nearly three decades, although GF crystals of other Cinchona alkaloids, such as quinidine, cinchonidine, and cinchonine, are already known. In this study, we successfully revealed the crystal structure of quinine, which belongs to the P2(1) space group with the cell parameters of a=6.

Supramolecular-tilt-chirality on twofold helical assemblies.

A twofold helix (2(1) helix) is an essential motif in approximately 70% of organic crystals. Although handedness of 2(1) helix has not been discussed from a mathematical viewpoint, we noticed that the handedness can be defined by considering the molecular shape and manner of assembly. Herein we propose the supramolecular-tilt-chirality (STC) method to define the handedness, and illustrate it by way of some examples.