Synthesis and Late-Stage Diversification of BN-Embedded Dibenzocorannulenes as Efficient Fluorescence Organic Light-Emitting Diode Emitters

We report the synthesis and late-stage diversification of a new class of hetero-buckybowl, BN-embedded dibenzocorannulenes (B₂ N₂ -DBCs). The synthesis is achieved via one-shot halogenative borylation, comprising the nitrogen-directed haloboration of alkyne and an intramolecular bora-Friedel-Crafts reaction, which provides BN-embedded dibenzocorannulene possessing two bromo substituents (B₂ N₂ -DBC-Br). B₂ N₂ -DBC-Br undergoes diversification via coupling reactions to provide a variety of arylated derivatives (B₂ N₂ -DBC-R), exhibiting strong blue fluorescence. An organic light-emitting diode (OLED) employing one of the derivatives as an emitter exhibited a high external quantum efficiency of 6.6 % and long operational lifetime of 907 h at an initial luminance of 1000 cd m^-2 , indicating the significant potential for the development of efficient and stable hetero-buckybowl-based OLED materials.

Synthesis of a Negatively Curved Nanocarbon Molecule with an Octagonal Omphalos via Design-of-Experiments Optimizations Supplemented by Machine Learning

A saddle-shaped nanocarbon molecule was synthesized, which revealed the existence of negative Gauss curvatures on a >3-nm molecular structure possessing 192 π-electrons. The synthesis was facilitated by a protocol developed with Design-of-Experiments optimizations and machine-learning predictions, and spectroscopy and crystallography were used to reveal the saddle-shaped structure of the molecule. Solution-phase analyses showed the presence of dimeric assembly, and crystallographic analyses revealed the stacked dimeric structures. The stacked crystal structure was scrutinized by various methods, including Gauss curvatures derived from the discrete surface theory of geometry, to reveal the important role of the molecular Gauss curvature in dimeric assembly.

Activation of positive cooperativity by size-mismatch assembly via inclination of guests in a single-site receptor

A halogenated bowl-shaped guest, corannulene, was encapsulated in a cylindrical host, [4]cyclochrysenylene, to form a bowl-in-tube complex, which mimicked supramolecular complexes between bowl guests and carbon nanotubes. As was the case with carbon nanotubes, the cylindrical space of [4]cyclochrysenylene trapped multiple corannulene molecules in an array, and 1:2 complexes were commonly obtained with the corannulene guests with various halogen substituents (F, Cl, Br and I). Careful statistical analyses of isothermal titration calorimetry titration data succeeded in revealing the stoichiometry, and the molecular structures of the 1:2 complexes were further clarified by X-ray crystallographic analyses. Two fluorinated corannulene guests were stacked perpendicular to the cylinder axis, while two chlorinated guests were stacked with inclined orientations. The structural difference resulted in a large difference in the cooperativity of the two-stage association in solution: fluorinated corannulene guests showed negative cooperativity for the 1:2 complexation, and the other, larger halogenated corannulene guests showed positive cooperativity.

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.

Bowl-Shaped Pentagon- and Heptagon-Embedded Nanographene Containing a Central Pyrrolo[3,2-b]pyrrole Core

A bowl-shaped nitrogen-doped nanographene composed of a pyrrolo[3,2-b]pyrrole core substituted with six arene rings circularly bonded with one another has been prepared via a concise synthetic strategy encompassing the multicomponent tetraarylpyrrolopyrrole (TAPP) synthesis, the Scholl reaction, and intramolecular direct arylation. This synthesis represents the first case of programmed sequential intramolecular direct arylation reactions utilizing the different reactivity of C-Br and C-Cl bonds. The target compound contains two central pentagons confined between two adjacent heptagons-the inverse Stone-Thrower-Wales topology. The presence of both five- and seven-membered rings in the final structure is responsible for interesting properties such as a perpendicularly aligned dipole moment, absorption and fluorescence in the orange-red region, weak emission originating from the charge-transfer character of a low-energy absorption band, and a high lying HOMO. In the solid state slipped convex-to-convex π-π stacking dominates.

Synthesis of a Hemispherical Geodesic Phenine Framework by a Polygon Assembling Strategy

A synthetic strategy to construct large geodesic structures of phenine (1,3,5-trisubstituted benzene) was devised. In this strategy, five pentagons were assembled on an omphalos pentagon, and bridging peripheral pentagons furnished five additional hexagons. Thirty phenine units were synthetically assembled to afford a large C₂₂₀ H₁₈₀ molecule with a phenine framework isoreticular to a hemispherical, bisected segment of C₆₀ . Although a hemispherical structure of the phenine framework was suggested by solution-phase NMR spectra, crystallographic analysis revealed an oval-like deformation of the molecular shape. In-depth structural analyses, including theoretical calculations, showed that structural fluctuations observed as variations in the biaryl torsion angles allowed structural deformations and, at the same time, that the dynamic fluctuations resulted in the spectroscopic observation of a hemisphere as a time-averaged structure.

Bowl Inversion in an Exo-type Supramolecule in the Solid State

Bowl inversion is a unique property of buckybowls. The polarity and assembly configuration of buckybowls are reversed after bowl inversion. So far, this unique phenomenon has been studied in solution and on surface, but not in solid state due to spatial constraint. Now a series of exo-type supramolecular assemblies of trithiasumanene and nanographene are investigated. Tuning the electron density of the nanogaphene component was found to directly affect the binding constant of the complex. Reversible bowl inversion in the solid state was then successfully achieved by subjecting the trithiasumanene-nanographene assembly with the weakest binding strength to repeated heating-cooling cycles, which was unambiguously observed by single crystal X-ray diffraction.