Hajime Shigemitsu

Octadehydrodibenzo[12]annulene‐Based Organogels: Two Methyl Ester Groups Prevent Crystallization and Promote Gelation

Recently, p-conjugated cyclic systems involving benzene rings and acetylene units, the dehydrobenzoannulenes (DBAs), have attracted substantial interest from the viewpoint of acting as building blocks of supramolecular assemblies, along with their optoelectronic functionality, rigid, well-defined molecular structures, and extensively delocalized p electrons. To date, a handful of superstructures based on triangular DBAs have been reported. They include onedimensional (1D) fibrous superstructures in films from Diederich, Nielsen et al. and Iyoda et al., micelles and liquid crystals from Tew et al., and two-dimensionally ordered networks at the liquid–solid interface from Tobe, De Feyter et al. More recently, we also demonstrated that a single crystal composed of one-dimensionally p-stacked DBA exhibited highly anisotropic charge-carrier mobility. However, superstructures of DBAs have not been extensively reported except for the case of crystals, and there has been no report on organogels based on DBAs. One of the reasons for the lack of DBA superstructures is that the affinity interactions between DBA rings are weaker than those of other systems, such as discotic graphene-like molecules, owing to weaker p–p interactions of DBA rings containing sphybridized carbon atoms. Indeed, for gelators, strong and highly directional intermolecular interactions are required. Herein, we describe the construction and structural characterization of an organogel derived from boomerangshaped DBA 1 with methyl ester groups, which was designed according to the strategy detailed below. For construction of organogels, it is generally recognized that gelators have to satisfy the following three requirements: 1) formation of 1D fibrous aggregates through self-complementary and unidirectional intermolecular interactions,

Construction of 1D π‐Stacked Superstructures with Inclusion Channels through Symmetry‐Decreasing Crystallization of Discotic Molecules of C3 Symmetry

Supramolecular architectures that possess both 1D π-stacked columns and inclusion channels were constructed by symmetry-decreasing crystallization of dehydrobenzo[12]annulene (DBA) derivatives with naphthyl arms and C(3) symmetry. The crystallization can be interpreted as i) formation of a two-fold column, ii) layer formation, and iii) lamination of the layer accompanied by guest inclusion.

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. The crystallinity of the SNFs allowed the molecular arrangements in the SNFs to be determined. Therefore the mechanism of construction and correlations between the molecular arrangements and optical and electrical properties could be considered. The results clearly indicate that the properties of the SNFs are affected by the chemical structures and molecular arrangements. Moreover, one of the SNFs exhibits a high charge-carrier mobility (Σμ=0.61 cm(2) V(-1) s(-1)) because of its crystallinity and appropriate molecular arrangement. This systematic experimental study based on a proposed strategy has provided information for improving the electrical properties of SNFs. This strategy will lead to highly functional SNFs.

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.

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.

Preparation of nano- and microstructures through molecular assembly of cyclic oligosaccharides

The shape, size, and size distribution of nano- and microstructures formed by the self-assembly of small molecules are crucial factors that govern their chemical and physical properties. Understanding these factors can reveal the correlations between the supramolecular structure and the emergent properties and may realize innovative new materials. Hence, the formation processes and syntheses of nano- and microstructures consisting of various functional molecules have been actively studied. Herein, we report the bottom-up preparation and functions of nano- and microstructures formed by the self-assembly of cyclodextrins (CDs), which are cyclic oligosaccharides. Reprecipitation and electrospinning methods produce various supramolecular structures based on CDs. The assembly modes of CD molecules and their morphologies remarkably affect the properties and functions of the supramolecular structures. In particular, γ-CD-based supramolecular structures achieve the inclusion of guest molecules dissolved in oils, which is difficult to achieve with a single-CD molecule. Furthermore, cubic γ-CD structures show excellent dispersibility in oils, forming organogels in various oils, and organic solvents at ambient temperature. These studies indicate that the construction and morphological control of self-assembled CD structures can effectively realize the potential function of CD molecules and open new fields in oligosaccharide chemistry and supramolecular chemistry.The bottom-up preparation methods and functions of nano- and microstructures formed by the self-assembly of cyclic oligosaccharides ‘cyclodextrins (CDs)’ are overviewed in this review. Reprecipitation and electrospinning methods produce various supramolecular structures based on CDs. The CD supramolecular structures exhibit a variety of functions such as organogelation and pollutant removal, depending on the morphologies. Additionally, the CD-assembled structures can be used as a template for fabricating hollow polymer structures.