16 research outputs found
Aromatic Saddles Containing Two Heptagons
Soluble derivatives of C<sub>70</sub>H<sub>26</sub> (<b>1a</b>,<b>b</b>) and C<sub>70</sub>H<sub>30</sub> (<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
Ï€-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]Âcirculene
in terms of the average Gauss curvature, but surprisingly much more
rigid than [7]Âcirculene. 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
Ï€-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
Ï€-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]Âcirculene
in terms of the average Gauss curvature, but surprisingly much more
rigid than [7]Âcirculene. 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
Ï€-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
TetrabenzoÂ[7]Âcirculene,
a new member of aromatic saddles, was conveniently
synthesized from 2-(1-naphthoyl)Âbenzoic 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]Âcirculenes. The structures of tetrabenzo[7]Âcirculene and [7]Âcirculene
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]Âcirculene functioned as a p-type semiconductor
in thin-film transistors and cocrystallized with C<sub>60</sub>
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 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>
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 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>
Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes
We herein report an efficient synthesis
of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicene, a new member
of nonplanar cyclopenta-fused
polycyclic aromatic hydrocarbon, and its derivatives. It is found
that the conformation and molecular packing of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes in the solid state can be tuned by
the substituting groups, and the silylethynylated derivatives of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes function as p-type organic
semiconductors in solution-processed thin film transistors with field
effect mobility of up to 1.0 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>
Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes
We herein report an efficient synthesis
of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicene, a new member
of nonplanar cyclopenta-fused
polycyclic aromatic hydrocarbon, and its derivatives. It is found
that the conformation and molecular packing of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes in the solid state can be tuned by
the substituting groups, and the silylethynylated derivatives of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes function as p-type organic
semiconductors in solution-processed thin film transistors with field
effect mobility of up to 1.0 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>
Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[<i>a</i>,<i>m</i>]rubicenes
We herein report an efficient synthesis
of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicene, a new member
of nonplanar cyclopenta-fused
polycyclic aromatic hydrocarbon, and its derivatives. It is found
that the conformation and molecular packing of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes in the solid state can be tuned by
the substituting groups, and the silylethynylated derivatives of dibenzoÂ[<i>a</i>,<i>m</i>]Ârubicenes function as p-type organic
semiconductors in solution-processed thin film transistors with field
effect mobility of up to 1.0 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>