Tetrabenzo[8]circulene: Aromatic Saddles from Negatively Curved Graphene

An aromatic saddle was designed from the hypothetical three-dimensional graphene with the negative Gaussian curvature (Schwarzite P192). Two aromatic saddles, tetrabenzo[8]­circulene (<b>TB8C</b>) and its octamethyl derivative <b>OM-TB8C</b>, were synthesized by the Scholl reaction of cyclic octaphenylene precursors. The structure of <b>TB8C</b> greatly deviates from planarity, and the deep saddle shape was confirmed by single-crystal X-ray crystallography. There are two conformers with the <i>S</i>₄ symmetry, which are twisted compared to the DFT structure (<i>D</i>_2<i>d</i>). The theoretical studies propose that the interconversion of <b>TB8C</b> via the planar transition state (125 kcal mol^–1) is not possible. However, the pseudorotation leads to a low-energy tub-to-tub inversion via the nonplanar transition state (7.3 kcal mol^–1). The ground-state structure of <b>TB8C</b> in solution is quite different from the X-ray structure because of the crystal-packing force and low-energy pseudorotation. <b>OM-TB8C</b> is a good electron donor and works as the p-type semiconductor

Perfluorinated and Half-Fluorinated Rubrenes: Synthesis and Crystal Packing Arrangements

Perfluororubrene (PF-RUB) has been synthesized by cycloaddition of perfluorinated 1,3-diphenylisobenzofuran and 1,4-diphenyl-2,3-didehydronaphthalene followed by reductive deoxygenation. This method was easily applied for the synthesis of half-fluorinated rubrene (F₁₄-RUB). The electrochemical measurements and DFT calculations indicate that perfluorination strongly lowers the HOMO and LUMO energies. Recrystallization and sublimation of PF-RUB gave two different crystals with planar and twisted conformations, respectively. In both cases, perfluorination leads to the formation of short C–F and F–F contacts and completely disrupts face-to-face π interactions. Single crystals of F₁₄-RUB were grown by sublimation, and twisted molecules display the two-dimensional π-stacking with a face-to-face distance of 3.54 Å

Tetrabenzo[8]circulene: Aromatic Saddles from Negatively Curved Graphene

An aromatic saddle was designed from the hypothetical three-dimensional graphene with the negative Gaussian curvature (Schwarzite P192). Two aromatic saddles, tetrabenzo[8]­circulene (<b>TB8C</b>) and its octamethyl derivative <b>OM-TB8C</b>, were synthesized by the Scholl reaction of cyclic octaphenylene precursors. The structure of <b>TB8C</b> greatly deviates from planarity, and the deep saddle shape was confirmed by single-crystal X-ray crystallography. There are two conformers with the <i>S</i>₄ symmetry, which are twisted compared to the DFT structure (<i>D</i>_2<i>d</i>). The theoretical studies propose that the interconversion of <b>TB8C</b> via the planar transition state (125 kcal mol^–1) is not possible. However, the pseudorotation leads to a low-energy tub-to-tub inversion via the nonplanar transition state (7.3 kcal mol^–1). The ground-state structure of <b>TB8C</b> in solution is quite different from the X-ray structure because of the crystal-packing force and low-energy pseudorotation. <b>OM-TB8C</b> is a good electron donor and works as the p-type semiconductor

Tetrabenzo[8]circulene: Aromatic Saddles from Negatively Curved Graphene

An aromatic saddle was designed from the hypothetical three-dimensional graphene with the negative Gaussian curvature (Schwarzite P192). Two aromatic saddles, tetrabenzo[8]­circulene (<b>TB8C</b>) and its octamethyl derivative <b>OM-TB8C</b>, were synthesized by the Scholl reaction of cyclic octaphenylene precursors. The structure of <b>TB8C</b> greatly deviates from planarity, and the deep saddle shape was confirmed by single-crystal X-ray crystallography. There are two conformers with the <i>S</i>₄ symmetry, which are twisted compared to the DFT structure (<i>D</i>_2<i>d</i>). The theoretical studies propose that the interconversion of <b>TB8C</b> via the planar transition state (125 kcal mol^–1) is not possible. However, the pseudorotation leads to a low-energy tub-to-tub inversion via the nonplanar transition state (7.3 kcal mol^–1). The ground-state structure of <b>TB8C</b> in solution is quite different from the X-ray structure because of the crystal-packing force and low-energy pseudorotation. <b>OM-TB8C</b> is a good electron donor and works as the p-type semiconductor

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

Three N-substituted tetracyclo­(2,7-carbazole)­s were synthesized to investigate the inner regions of nanohoops. One compound has a 5,5-dimethylnonane bridge between two neighboring <i>anti</i>-carbazoles, which can be used as covalently bonded “methane probes”. These probes near the ring center are strongly shielded by local ring currents and exhibit a singlet at δ = −2.70 ppm in ¹H NMR. To visualize local and macrocyclic ring currents separately, we drew nucleus-independent chemical shift contour maps of tetracyclo­(9-methyl-2,7-carbazole) and [<i>n</i>]­cycloparaphenylenes (CPPs). Local ring currents make the interior diatropic, and paratropic regions exist only outside the ring. Macrocyclic ring currents in [5]­CPP to [7]­CPP generate deshielding cones, which are typical of antiaromatic [4<i>n</i>]­annulenes

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

Three N-substituted tetracyclo­(2,7-carbazole)­s were synthesized to investigate the inner regions of nanohoops. One compound has a 5,5-dimethylnonane bridge between two neighboring <i>anti</i>-carbazoles, which can be used as covalently bonded “methane probes”. These probes near the ring center are strongly shielded by local ring currents and exhibit a singlet at δ = −2.70 ppm in ¹H NMR. To visualize local and macrocyclic ring currents separately, we drew nucleus-independent chemical shift contour maps of tetracyclo­(9-methyl-2,7-carbazole) and [<i>n</i>]­cycloparaphenylenes (CPPs). Local ring currents make the interior diatropic, and paratropic regions exist only outside the ring. Macrocyclic ring currents in [5]­CPP to [7]­CPP generate deshielding cones, which are typical of antiaromatic [4<i>n</i>]­annulenes