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The arrangement of discotic hexa-peri-hexabenzocoronenes (HBCs) into columnar helical superstructures has been investigated in relation to their molecular architecture. The supramolecular structure of two hexaphenyl-substituted HBC derivatives, differing only in the chiral/achiral nature of the attached alkyl side chains, was studied by circular dichroism and temperature-dependent wide-angle X-ray diffraction on oriented filaments. A structural model in agreement with the experimental observations was developed on the basis of accompanying quantum-chemical calculations. The helical organization along the self-assembled columnar structures was induced by the steric requirements of the bulky phenyl rings near the aromatic core, i.e., by their rotation out-of-plane with respect to the aromatic core. On the other hand, a uniform handedness of the twist was generated by chiral alkyl substituents. At higher temperatures the degree of helical organization decreases due to lateral and longitudinal dynamics of the discotic molecules. Annealing at ambient conditions improved the long-range arrangement of the discs along the columnar structures. This reorganization indicated a self-healing of the plastic material which is desirable for application of discotics as active layers in electronic devices. The helical packing resulted in a considerable stability of the mesophase up to 500 degrees C, which has not been reported for a discotic so far.

In this study, the microstructure and oxidation behaviour of soot from the raw exhaust of a Euro IV test heavy duty ( HD) diesel engine is investigated and compared to that of spark discharge soot and hexabenzocoronene (HBC, C42H18). We find a microstructure -controlled reactivity toward oxidation of all three samples in 5% O2 in N2. The spark discharge soot with its fine primary particles and fullerenoid structure has an onset temperature of 423 K for combustion, while the hexabenzocoronene with its well-ordered crystallites has a high onset temperature of 773 K. Due to an improved combustion process in the Euro IV HD diesel engine, the soot emitted consists of more fullerenoid-like or onion-like particles agglomerated in a chain-like secondary structure. The onset temperature of the Euro IV HD engine soot combustion is 573 K. Oxidat ion of the three samples produces only CO2 and H2O. The different H2O production profiles can be assigned to the functionalised surface of the samples and depend on the soot structures and preparation route.

Phenylenes are non-benzenoid conjugated -electron systems composed of 6and 4-membered rings, in which no two 6-membered rings are adjacent, and each 4-membered ring is adjacent to two 6-membered rings. The chemistry of phenylenes is in rapid expansion, mainly due to the work of Peter Vollhardt and his research group; for details see the recent papers1,2 and the review.3 To every phenylene it is possible to associate a catacondensed benzenoid system, obtained so that the 4-membered rings of the phenylene are “squeezed off”. This benzenoid system was named4 the hexagonal squeeze of the respective phenylene. The construction of hexagonal squeezes should be evident from the examples depicted in Fig. 1. In the following, a phenylene and its hexagonal squeeze will be denoted by PH and HS, respectively, They possess equal number of hexagons, denoted by h. In the last few years we established a number of nontrivial relations between the topological properties of phenylenes and their hexagonal squeezes.4–12 In the present paper one more such connection is reported. In1984NarumiandKatayama13put forwardanovel toplogical indexSdefinedas

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A magnetic field has been utilized for producing highly oriented films of a substituted hexabenzocoronene (HBC). Optical microscopy studies revealed large area HBC monodomains that covered the entire film, while wide-angle X-ray measurements showed that the HBC molecules are aligned with their planes along the applied field. On the basis of this method, solution-processed field-effect transistors (FET) have been constructed with charge carrier mobilities of up to 10(-3) cm2/V.s, which are significantly enhanced with respect to the unaligned material. Exceptionally high mobility anisotropies of 25-75 for current flow parallel and perpendicular to the alignment direction have been measured as a function of the channel length. Atomic force microscopy performed on the FET structures reveals fibril superstructures that are oriented perpendicularly to the magnetic field direction, consisting of molecular columns with a slippage angle of 40 degrees between the molecules. For channel lengths larger than 2.5 mum, the fibrils are smaller than the electrode spacing, which adversely affects the device performance.

Branched hydrocarbon propellers (9 and 12) were prepared by stepwise palladium-catalyzed Hagihara-Sonogashira coupling reactions and Diels-Alder cycloadditions and submitted to oxidative cyclodehydrogenation by FeCl 3 to afford two new giant graphite disks 2 and 3 with 3-fold symmetry in high yield. One of the precursors, the polyphenylene dendrimer 9 containing 150 carbon atoms, was crystallographically characterized. The poorly soluble graphite disks were characterized by isotope-resolved MALDI-TOF mass spectroscopy, and their electronic and vibrational properties were investigated by solid-state UV-vis and Raman spectroscopy. The effect of molecular size and geometry on their properties was discussed. The molecule 2 represents the largest, 3-fold-symmetric all-benzenoid graphite disk, and the five-membered rings in molecule 3 open the opportunity to synthesize large bowl-shaped PAHs.