Biased Bowl-Direction of Monofluorosumanene in the Solid State.

A new curved π-conjugated molecule 1-fluorosumanene (1) was designed and synthesized that possesses one fluorine atom on the benzylic carbon of sumanene. This compound can exhibit bowl inversion in solution, leading to the formation of two diastereomers, 1endo and 1exo, with different dipole moments. Experimental and theoretical investigation revealed an energetical relationship among 1exo, 1endo, and solvent to realize the various endo:exo ratios in the single crystals of 1 depending on the crystallization solvent. Significantly, the molecular dynamics (MD) simulations revealed that 1exo positively worked for the elongation of the stacking structure and the final endo:exo ratio was affected by the relative stability difference between 1endo and 1exo derived by solvation. Such an arrangeable endo:exo ratio of 1 realized the preparation of unique materials showing a different dielectric response from the same molecule 1 just by changing the crystallization solvent.

Acceleration Effect of Bowl-Shaped Structure in Aerobic Oxidation Reaction: Synthesis of Homosumanene ortho-Quinone and Azaacene-Fused Homosumanenes.

An oxidation reaction of hydroxyhomosumanene on silica gel providing homosumanene ortho-quinone and its synthetic application for azaacene-fused homosumanenes is described. Hydroxyhomosumanene is photochemically oxidized by air, when it is coated on silica gel; this aerobic oxidation proceeds faster than that of planar analogues. The difference of such reactivity was attributed to the unusual keto-enol tautomerization due to structural difference between planar and curved π-system. The homosumanene ortho-quinone was used in the synthesis of several azaacene-fused homosumanenes, azaacenohomosumanenes. X-ray diffraction analysis of the single crystals revealed their columnar stacking structures due to the interactions between each bowl. Azaacenohomosumanenes exhibited high electron affinity due to the combination of buckybowl and electron-deficient azaacene moieties.

Synthesis of the C70 Fragment Buckybowl, Homosumanene, and Heterahomosumanenes via Ring-Expansion Reactions from Sumanenone.

Bowl-shaped aromatic molecules, buckybowls, are attractive molecules because of the unique properties derived from their curved-π scaffolds. Doping heteroatoms into buckybowl frameworks is a powerful method to change their structural and electronical properties. Herein, we report the synthesis of C70 fragment buckybowl, homosumanene, and heterahomosumanenes having a lactone moiety and a lactam moiety via three ring-expansion reactions using sumanenone as a common intermediate. X-ray diffraction analysis of the single crystals reveals their columnar packing structure with a shallow bowl-depth. The lactam moiety is readily derivatized to give azahomosumanene derivatives, nitrogen-doped analogues of homosumanene possessing a pyridine ring at the peripheral carbon. The synthetic application of the α-phenyl azahomosumanene as a cyclometalating ligand with platinum also revealed its utility for preparing a metal complex bearing a buckybowl ligand.

Synthesis of C70-fragment buckybowls bearing alkoxy substituents.

Buckybowls bearing a C70 fragment having two alkoxy groups were synthesized and their structural and optical properties were investigated by single crystal X-ray analysis and UV-vis spectroscopy. In the synthesis of dioxole derivative 5b, the regioisomer 5c was also produced. The yield of 5c was increased by increasing the reaction temperature, indicating that the rearrangement might involve the equilibrium between the Pd(IV) intermediates through C-H bond activation.

Formation of a Large Confined Spherical Space with a Small Aperture Using Flexible Hexasubstituted Sumanene.

Two sumanene-based porous coordination networks were successfully prepared by the complexation of hexapyridylsumanene with Zn(NO3)2·6H2O or Cd(NO3)2·4H2O. X-ray single crystal analysis unambiguously revealed that the curved structure of the central sumanene skeleton of the ligand resulted in the formation of a large confined space with a small aperture size. In the Zn2+ network, the beltlike trimer units were connected to each other to form a 1D channel separated by the counteranion to afford isolated spaces. The Cd2+ network formed spherical tetramer units, which also eventually afforded a 1D channel with open windows smaller than the kinetic diameter of helium. The investigation of the structural parameters of the ligand in both networks revealed the unique feature of hexapyridylsumanene, which flexibly changed its bond length and angles depending on the structural requirements for the network formations.

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes.

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.

An Organic Mixed-Valence Ligand for Multistate Redox-Active Coordination Networks.

The multistate redox-active/multi-interactive ligand 5,5',8,8'-tetra(4-pyridyl)-2,2'-(1,4-phenylene)bis-1H-perimidine (H2 TPP) was designed and synthesized. H2 TPP undergoes four one-electron oxidation steps, and was used for the preparation of a multistate redox-active coordination network in a solid-liquid interface reaction using molten Cd2+ salts. The multiple redox states of H2 TPP were confirmed spectroscopically by stepwise four-electron oxidation. Spectroscopic analysis indicated that the mixed-valence states of the ligand are class II on the UV/Vis/NIR timescale and borderline class II/class III on the ESR timescale.

Structural Investigation of Chemiresistive Sensing Mechanism in Redox-Active Porous Coordination Network.

By changing the rate of evaporation, two kinds of crystalline films composed of redox-active porous coordination networks (1 and 2) were selectively prepared on a gold-patterned substrate using a DMF solution of 2,5,8-tri(4-pyridyl)1,3-diazaphenalene and Cd(NO3)2. We found the highly sensitive humidity sensing ability of film 1. Single crystal structures and infrared spectroscopic analyses before and after hydration of a single crystal of 1 revealed the sensing mechanism: exchange of nitrate ions with water on Cd atoms occurred in hydrated conditions to generate a conductive cationic network.

Selective Formation of Conductive Network by Radical-Induced Oxidation.

Cd-based coordination networks having channels were formed selectively by using a redox-active aromatic ligand 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (TPDAP, H(+)1(-)). An electron-conductive network having a π-π stacking columnar structure of TPDAP formed in the presence of a trace amount of TPDAP radical (1(•)). In contrast, a nonconductive network having a dimer unit of H(+)1(-) formed in the absence of 1(•). These results suggest the presence of a unique oxidation mechanism of TPDAP induced by formation of H(+)1(-)-1(•) dimer, which was initiated by a trace amount of 1(•). The dimerization increased HOMO level of H(+)1(-) moiety within the dimer to generate further radicals that could not form when H(+)1(-) was well isolated in CH3OH.

Strain-induced carbon-carbon bond cleavage of bowl-shaped sumanenone.

This study details a highly effective ring-opening reaction that involves acid-mediated carbon-carbon bond cleavage of the buckybowl, sumanenone. The reaction of the bowl-shaped sumanenone with AcOH and TfOH results in the formation of a planar carboxylic acid. The examination of reactivity in comparison to planar analogues, along with theoretical calculations, suggests that the release of curved strain is a crucial factor for the success of this reaction.

Amplification sensing manipulated by a sumanene-based supramolecular polymer as a dynamic allosteric effector.

The synthesis of signal-amplifying chemosensors induced by various triggers is a major challenge for multidisciplinary sciences. In this study, a signal-amplification system that was flexibly manipulated by a dynamic allosteric effector (trigger) was developed. Herein, the focus was on using the behavior of supramolecular polymerization to control the degree of polymerization by changing the concentration of a functional monomer. It was assumed that this control was facilitated by a gradually changing/dynamic allosteric effector. A curved-π buckybowl sumanene and a sumanene-based chemosensor (SC) were employed as the allosteric effector and the molecular binder, respectively. The hetero-supramolecular polymer, (SC·(sumanene)n), facilitated the manipulation of the degree of signal-amplification; this was accomplished by changing the sumanene monomer concentration, which resulted in up to a 62.5-fold amplification of a steroid. The current results and the concept proposed herein provide an alternate method to conventional chemosensors and signal-amplification systems.

Thermodynamic Differentiation of the Two Sides of Azabuckybowl through Complexation with Square Planar Platinum(II).

The precise control of the two faces, concave/convex faces, is an attractive challenge to realizing novel dynamic molecular systems. Herein, we report the synthesis, X-ray crystal structure, and bowl-to-bowl inversion behavior of a platinum complex with azabuckybowl as a monodentate ligand. X-ray crystallography revealed that the azabuckybowl is orthogonally coordinated to the plane containing the Pt center and other ligands. One and two-dimensional NMR studies have also confirmed that this complex was observed as mixtures of two isomers, although the isomeric ratio was highly biased. Theoretical calculations indicate that the difference in thermodynamic stability of these isomers is due to the direction of the concave/convex face of an azabuckybowl ligand.

Derivatization of sumanenetrione through Lewis acid-mediated Suzuki-Miyaura coupling and an unprecedented ring opening.

A series of sumanenetrione derivatives were synthesized through Lewis acid-mediated Suzuki-Miyaura cross-coupling. Their optical properties reflected the significantly strong electron-accepting ability of sumanenetrione. The bowl strain of the 2-hydroxyphenyl derivative brought the ring-opening response adjacent to the substituent even at room temperature without any activation, which generally requires harsh conditions.

Sumanene-stacked supramolecular polymers. Dynamic, solvation-directed control.

In this study, we found that a pristine buckybowl, sumanene, can form solution-state supramolecular polymers. We also demonstrated that sumanene supramolecular polymers can be dynamically controlled by external stimuli, in which solvation plays a significant role. This study not only provides new guidelines for the rational design of supramolecular polymers, particularly for the use of buckybowls, but also presents interesting dynamic behaviors of supramolecular polymerization.

Tuning the dielectric response by co-crystallisation of sumanene and its fluorinated derivative.

A series of co-crystals of 1,1-difluorosumanene (F2-Sum) and sumanene (Sum) were obtained. The co-crystallization successfully tuned their structural and physical properties, especially the dielectric response, without any chemical modifications. X-ray analyses and theoretical calculations revealed the reduction of intermolecular interaction energy due to the presence of F2-Sum.

Triple-stranded metallo-helicates addressable as Lloyd's electron spin qubits.

We have first achieved the synthesis of triple-stranded metallo-helicates composed of 4,4':2',2'':4'',4'''-quaterimidazole (Qim) and Mn(II) or Zn(II) ions, which serve as synthetic electron spin qubits (quantum bits). In the crystal structure, a hydrogen-bonding network through counteranions and/or crystal solvents was constructed by the outward N-H hydrogen-bonding functional groups intrinsic to the imidazole skeleton. Importantly, these helicates showed high stability even in a solution state at room temperature. These salient features of triple helicates of Qim are different from those of reported metallo-helicates. These chemical properties of the Qim-based triple helicates allow us to synthesize magnetically diluted single crystals composed of Mn(II) (S = 5/2) and diamagnetic Zn(II) complexes of Qim in an appropriate Mn(II)/Zn(II) ratio. The magnetically diluted crystals can afford to build up the prototype of electron-spin qubits of Lloyd's one-dimensional periodic system, which gives a practical approach to scalable quantum computers/quantum information processing systems (QCs/QIPSs). The experiments have proven the practical capability of oligo(imidazole)s as a component of Lloyd's system which has nonequivalent g-tensors within the helicate (g-engineering). The helical symmetry plays an important role in giving a prototype of the synthetic spin qubits of the formidable Lloyd model. This result links supramolecular chemistry to the field of QCs/QIPSs.

Control by one drop of solvent: selective preparation of guest release/trap-triggered interconvertible molecular crystals.

Interconvertible molecular crystals 1close and 1open composed of 4-pyridyl-1,3-indanedione dimer 1 were selectively obtained. Thermal removal of solvent molecules in 1open afforded 1close. Further dipping of 1close in a specific solvent reproduced 1open. No crystallinity loss was observed even though both processes involved a drastic change of molecular packing arrangements.

Generation of "Sumanenylidene": A Ground-State Triplet Carbene on a Curved π-Conjugated Periphery.

We have observed the generation of sumanenylidene (2), a divalent, neutral-carbon species at the benzylic position of sumanene (1). We also clarified both experimentally and theoretically that the ground state of compound 2 was a triplet state and that its singlet-triplet energy gap (ΔEST ) was similar to that in fluorenylidene. The curved structure of compound 2 led to slightly better spin delocalization over the two adjacent aromatic rings than in planar systems, because of the unpaired spins on the σ and π orbitals. Synthetic application of the carbene precursor, diazosumanene (5), with a variety of thiocarbonyl compounds revealed its utility for the preparation of tetrasubstituted alkene compounds (e.g., that contain a strongly electron-donating unit) that are directly conjugated to the sumanene (1) moiety.