Aromatic Saddles Containing Two Heptagons

Soluble derivatives of C₇₀H₂₆ (<b>1a</b>,<b>b</b>) and C₇₀H₃₀ (<b>2a</b>,<b>b</b>), two new saddle-shaped polycyclic arenes containing two heptagons, were successfully synthesized from saddle-shaped diketones (<b>3a</b>,<b>b</b>), whose carbonyl groups are the key in the reactions to extend the polycyclic π-framework. As found from the crystal structures, the polycyclic backbone of <b>1b</b> has a deep saddle shape, while that of <b>2b</b> is even more distorted because of the existence of two [4]-helicene moieties. On the basis of crystal structures, local aromaticity and nonplanarity of individual rings in the saddle-shaped π-backbone were analyzed, and were found to follow Clar’s rule in general. It was found that <b>1b</b> and <b>3b</b> behaved as p-type semiconductors in solution-processed thin film transistors while the amorphous films of <b>2b</b> appeared insulating

Highly Electron-Deficient Hexaazapentacenes and Their Dihydro Precursors

Novel silylethynylated <i>N</i>-heteropentacenes that have three adjacent pyrazine rings at the center of a pentacene backbone are reported. These hexaazapentacenes exhibit a record low energy level of lowest unoccupied molecular orbital (LUMO) for <i>N</i>-heteropentacenes and thus are able to oxidize dihydroanthracene to anthracene. Their synthetic precursors are the corresponding dihydrohexaazapentacenes, which exhibit interesting H-bonding

Curved Polycyclic Aromatic Molecules That Are π‑Isoelectronic to Hexabenzocoronene

Reported here are two types of curved π-molecules that are π-isoelectronic to planar hexabenzocoronene (HBC) but are forced out of planarity either by an embedded seven-membered ring or by atom crowding at the fjord region. Embedding a heptagon in HBC leads to a novel saddle-shaped molecule <b>1</b>, whose π-backbone is slightly less curved than the previously reported [7]­circulene in terms of the average Gauss curvature, but surprisingly much more rigid than [7]­circulene. Overcrowded fjord regions in novel derivatives of hexabenzoperylene (HBP) <b>2a</b>,<b>b</b> lead to both chiral twisted and antifolded conformers. The successful synthesis of <b>1</b> and <b>2a</b>,<b>b</b> is related to introducing alkoxyl groups to unprecedented positions of hexaphenylbenzenes. It is found that the red twisted isomer of <b>2b</b> isomerizes at elevated temperature to the yellow <i>anti</i>-folded conformer. This finding along with the study on the thermodynamics and kinetics of the thermal isomerization has improved the early understandings on the conformation of HBP. In the crystals, <b>1</b> lacks π–π interactions between neighboring molecules, while twisted-<b>2a</b> exhibits both face-to-face and edge-to-face π–π interactions. Twisted-<b>2b</b> is found to function as a p-type semiconductor in thin film transistors, but the thin films of <b>1</b> appear insulating presumably due to lacking π–π interactions. By exploring three different types of curvatures in <b>1</b> and the two isomers of <b>2b</b>, this study has revealed that the curvature of π-face plays a role in determining the frontier molecular orbital energy levels and π–π interactions and thus needs to be considered when one designs new organic semiconductors

Curved Polycyclic Aromatic Molecules That Are π‑Isoelectronic to Hexabenzocoronene

Reported here are two types of curved π-molecules that are π-isoelectronic to planar hexabenzocoronene (HBC) but are forced out of planarity either by an embedded seven-membered ring or by atom crowding at the fjord region. Embedding a heptagon in HBC leads to a novel saddle-shaped molecule <b>1</b>, whose π-backbone is slightly less curved than the previously reported [7]­circulene in terms of the average Gauss curvature, but surprisingly much more rigid than [7]­circulene. Overcrowded fjord regions in novel derivatives of hexabenzoperylene (HBP) <b>2a</b>,<b>b</b> lead to both chiral twisted and antifolded conformers. The successful synthesis of <b>1</b> and <b>2a</b>,<b>b</b> is related to introducing alkoxyl groups to unprecedented positions of hexaphenylbenzenes. It is found that the red twisted isomer of <b>2b</b> isomerizes at elevated temperature to the yellow <i>anti</i>-folded conformer. This finding along with the study on the thermodynamics and kinetics of the thermal isomerization has improved the early understandings on the conformation of HBP. In the crystals, <b>1</b> lacks π–π interactions between neighboring molecules, while twisted-<b>2a</b> exhibits both face-to-face and edge-to-face π–π interactions. Twisted-<b>2b</b> is found to function as a p-type semiconductor in thin film transistors, but the thin films of <b>1</b> appear insulating presumably due to lacking π–π interactions. By exploring three different types of curvatures in <b>1</b> and the two isomers of <b>2b</b>, this study has revealed that the curvature of π-face plays a role in determining the frontier molecular orbital energy levels and π–π interactions and thus needs to be considered when one designs new organic semiconductors

Synthesis, Structure, and Properties of Tetrabenzo[7]circulene

Tetrabenzo­[7]­circulene, a new member of aromatic saddles, was conveniently synthesized from 2-(1-naphthoyl)­benzoic acid with the seven-membered ring constructed at an early stage of the synthesis. This method, upon minor modification, was also useful for synthesis of thiophene-annulated [7]­circulenes. The structures of tetrabenzo[7]­circulene and [7]­circulene were compared in terms of symmetry, flexibility, and curvature on the basis of DFT calculations and X-ray crystallography. It was also found that tetrabenzo[7]­circulene functioned as a p-type semiconductor in thin-film transistors and cocrystallized with C₆₀

Hydrogen-Bonded Dihydrotetraazapentacenes

Three new members of <i>N</i>-heteropentacenes explored herein have adjacent pyrazine and dihydropyrazine rings at one end of the pentacene backbone. Interesting findings from this study include self-complementary N–H···N H-bonds in the solid state, solvent-dependent UV–vis absorption caused by H-bonding, and new <i>p</i>-type organic semiconductors with field effect mobility up to 0.7 cm² V^–1 s^–1

Hydrogen-Bonded Dihydrotetraazapentacenes

Three new members of <i>N</i>-heteropentacenes explored herein have adjacent pyrazine and dihydropyrazine rings at one end of the pentacene backbone. Interesting findings from this study include self-complementary N–H···N H-bonds in the solid state, solvent-dependent UV–vis absorption caused by H-bonding, and new <i>p</i>-type organic semiconductors with field effect mobility up to 0.7 cm² V^–1 s^–1

Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes

We herein report an efficient synthesis of dibenzo­[<i>a</i>,<i>m</i>]­rubicene, a new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its derivatives. It is found that the conformation and molecular packing of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes in the solid state can be tuned by the substituting groups, and the silylethynylated derivatives of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes function as p-type organic semiconductors in solution-processed thin film transistors with field effect mobility of up to 1.0 cm² V^–1 s^–1

Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes

We herein report an efficient synthesis of dibenzo­[<i>a</i>,<i>m</i>]­rubicene, a new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its derivatives. It is found that the conformation and molecular packing of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes in the solid state can be tuned by the substituting groups, and the silylethynylated derivatives of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes function as p-type organic semiconductors in solution-processed thin film transistors with field effect mobility of up to 1.0 cm² V^–1 s^–1

Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes

We herein report an efficient synthesis of dibenzo­[<i>a</i>,<i>m</i>]­rubicene, a new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its derivatives. It is found that the conformation and molecular packing of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes in the solid state can be tuned by the substituting groups, and the silylethynylated derivatives of dibenzo­[<i>a</i>,<i>m</i>]­rubicenes function as p-type organic semiconductors in solution-processed thin film transistors with field effect mobility of up to 1.0 cm² V^–1 s^–1