Exfoliatable Layered 2D Honeycomb Crystals of Host-guest Complexes Networked by CH-π Hydrogen Bonds.

Studies of graphene show that robust chemical bonds such as covalent bonds with trigonal-planar atoms afford layered atomic 2D crystals possessing unique properties. Although layered molecular crystals are of interest to diversify elements and structures of 2D materials, the structural diversity of molecules as well as weak intermolecular interactions inevitably makes the design to be one-off and individual. We herein report a versatile method to assemble layered molecular crystals. By developing a D3-symmetry host at vertices to form a honeycomb layer, a diverse range of layered 2D host-guest crystals were obtained. Substituents on the host, elements/structures of the guest, the stereochemistry of the host and types of intercalants were diversified, which should allow for 6×32×3×2 combinations for structural diversification.

Bayesian Inference for Model Analyses of Supramolecular Complexes: A Case Study with Nanocarbon Hosts.

A 126 π-electron nanobowl molecule, phenine tridehydrosumanene, was synthesized in 12 steps through the development of a polygon cyclization strategy that assembled the polygonal precursors by Ni-mediated macrocyclization. The bowl-shaped structure accommodated C70 as a guest at the concave site, and the ball-in-bowl structure was determined by X-ray crystallography. The host-guest equilibrium in solution was studied with titration experiments using isothermal calorimetry, which provided an interesting test case for studying the host-guest stoichiometry. Bayesian inference was introduced for stoichiometric analyses of the equilibrium, and a procedure to estimate the volume of prior probability in the parameter space was developed. The Bayesian procedure functioned as Occam's razor and provided quantitative support for a specific stoichiometry. The method was examined with five host-guest examples comprising nanocarbon hosts, which suggested the versatility of Bayesian inference for studies of supramolecular complexes.

Stoichiometry validation of supramolecular complexes with a hydrocarbon cage host by van 't Hoff analyses.

Defining chemical processes with equations is the first important step in characterizing equilibria for the assembly of supramolecular complexes, and the stoichiometry of the assembled components must be defined to generate the equation. Recently, this subject has attracted renewed interest, and statistical and/or information-theoretic measures were introduced to examine the validities of the equilibrium models used during curve fitting analyses of titration. The present study shows that these measures may not always be appropriate for credibility examinations and that further reformation of the protocols used to determine the overall stoichiometry is necessary. Hydrocarbon cage hosts and their chloroform complexes formed via weak CH-π hydrogen bonds were studied, which allowed us to introduce van 't Hoff analyses for effective validation of the stoichiometries of supramolecular complexes. This study shows that the stoichiometries of supramolecular complexes should be carefully examined by adopting multiple measures with different origins.

Facile Synthesis and Chiral Resolution of Expanded Helicenes with up to 35 cata-Fused Benzene Rings.

Expanded helicenes are expected to show enhanced chiroptical properties as compared to the classical helicenes but the synthesis is very challenging. Herein, we report the facile synthesis of a series of expanded helicenes Hn (n=1-4) containing 11, 19, 27 and 35 cata-fused benzene rings through Suzuki coupling-based oligomerization followed by Bi(OTf)3 -mediated regioselective cyclization of vinyl ethers. Their structures were determined by X-ray crystallographic analysis. Enantiopure H2, H3, and H4 can be isolated by chiral HPLC and they all exhibit strong chiroptical responses with high absorption dissymmetry factor (|gabs |) values (0.020 for H2, 0.021 for H3, and 0.021-0.024 for H4).

Phenine design for nanocarbon molecules.

With the name "phenine" given to 1,3,5-trisubstituted benzene for a fundamental trigonal planar unit to weave nanometer-sized networks, a series of curved nanocarbon molecules have been designed and synthesized. Since the 6π-phenine units were amenable to modern biaryl coupling reactions mediated by transition metals, concise syntheses of >400π-nanocarbon molecules were readily achieved. In addition, the phenine design allowed for installing of heteroatoms and/or transition metals doped at specific positions of the large π-systems of the nanocarbon molecules. Fundamental tools were also developed to specify and describe the locations of defects/dopants, quantify pyramidalizations of trigonal panels and estimate molecular Gauss curvatures of the discrete surface. Unique features of phenine nanocarbons, such as stereoisomerism, entropy-driven molecular assembly and effects of dopants on electronic/magnetic characteristics, were revealed during the first half-decade of investigations.

A minimal cage of a diamond twin with chirality.

A network of tetrahedral vertices can fill three-dimensional (3D) spaces in a beautiful and isotropic manner, which is found as diamonds with sp3-hybridized carbon atoms. Although a network of trigonal vertices (i.e., another form of carbon atoms with sp2-hybridization) naturally results in a lower-dimensional two-dimensional network of graphenes, an isotropic 3D arrangement of trigonal vertices has been of theoretical and mathematical interest, which has materialized as a proposal of a "diamond twin." We herein report the synthesis and optical resolution of a minimal cage of a chiral diamond-twin network. With triangular phenine units at 14 vertices, triply fused decagonal rings were assembled by forming 15 biaryl edges via coupling. A unique chirality of the network has been disclosed with the minimal cage, which may stimulate explorations of chiral carbonaceous materials.

Target-oriented design of helical nanotube molecules for rolled incommensurate bilayers.

Incommensurate double-wall carbon nanotubes give rise to unique stereochemistry originating from twisted stacks of hexagon arrays. However, atomic-level studies on such unique systems have rarely been performed, even though syntheses of molecular segments of carbon nanotubes have been extensively explored. The design of cylindrical molecules with chirality, particularly, in pairs provides synthetic challenges, because relationships between diameters specified with chiral indices and structures of arylene panels have not been investigated in a systematic manner. Here we show that a molecular version of incommensurate double-wall carbon nanotubes can be designed through the development of an atlas for the top-down design of cylindrical molecules. A large-bore cylindrical molecule with a diameter of 1.77 nm was synthesized using a readily available pigment and encapsulated a small-bore cylindrical molecule with a diameter of 1.04 nm. The large- and small-bore molecules possessed helicity in atomic arrangements, and their coaxial assembly proceeded in nonstereoselective manner to give both heterohelical and homohelical combinations.

Manipulations of Chiroptical Properties in Belt-Persistent Cycloarylenes via Desymmetrization with Heteroatom Doping.

A desymmetrization strategy has been devised in the design of molecular cylinders to maximize the dissymmetry factor relevant to circularly polarized light. Although the highest dissymmetry factor of organic molecules was previously achieved with a chiral belt-persistent cycloarylene having magnetic and electric transition dipole moments in parallel, we noticed that an unbalanced magnitude of two moments was detrimental for higher dissymmetry factors. In this study, a molecular cylinder was desymmetrized by arraying doped and undoped panels via stereoselective cross-coupling macrocyclization. The desymmetrization succeeded in balancing two moments by reducing the electric transition moment at the global minimum but failed to maximize the dissymmetry factor. Structural studies revealed that the dissymmetry factor is sensitive to subtle structural fluctuations, while the rotatory strength is not affected. This study is important for the development of chiroptical materials.

Finite phenine nanotubes with periodic vacancy defects.

Discrete graphitic carbon compounds serve as tunable models for the properties of extended macromolecular structures such as nanotubes. Here, we report synthesis and characterization of a cylindrical C304H264 molecule composed of 40 benzene (phenine) units mutually bonded at the 1, 3, and 5 positions. The concise nine-step synthesis featuring successive borylations and couplings proceeded with an average yield for each benzene-benzene bond formation of 91%. The molecular structure of the nanometer-sized cylinder with periodic vacancy defects was confirmed spectroscopically and crystallographically. The nanoporous nature of the compound further enabled inclusion of multiple fullerene guests. Computations suggest that fusing many such cylinders could produce carbon nanotubes with electronic properties modulated by the periodic vacancy defects.