1,2,3,4-Tetrafluorobiphenylene: A Prototype Janus-Headed Scaffold for Ambipolar Materials.

The title compound was synthesized by Ullmann cross-coupling in low yield as the first representative of [n]phenylene containing hydrocarbon and fluorocarbon rings. Stille/Suzuki-Miyaura cross-coupling reactions, as well as substitution of fluorine in suitable starting compounds, failed to give the same product. The geometric and electronic structures of the title compound were studied by X-ray diffraction, cyclic voltammetry and density functional theory calculations, together with Hirshfeld surface and reduced density gradient analyses. The crystal structure features head-to-tail π-stacking and other fluorine-related secondary bonding interactions. From the nucleus-independent chemical shifts descriptor, the four-membered ring of the title compound is antiaromatic, and the six-membered rings are aromatic. The Janus molecule is highly polarized; and the six-membered fluoro- and hydrocarbon rings are Lewis π-acidic and π-basic, respectively. The electrochemically-generated radical cation of the title compound is long-lived as characterized by electron paramagnetic resonance, whereas the radical anion is unstable in solution. The title compound reveals electrical properties of an insulator. On expanding its molecular scaffold towards partially fluorinated [n]phenylenes (n≥2), the properties presumably can be transformed into those of semiconductors. In this context, the title compound is suggested as a prototype scaffold for ambipolar materials for organic electronics and spintronics.

Defect induced photoluminescence and triboluminescence in layered CaLaAl3O7.

In this work, a layered melilite structure, CaLaAl3O7, was synthesized and observed to have obvious luminescence behaviors under the stimuli of ultraviolet light and rubbing, which were called photoluminescence and triboluminescence, respectively. Considering the wide bandgap of CaLaAl3O7 and its specific crystal structure, the observed luminescence should be attributed to intrinsic defects. Both the photoluminescence and triboluminescence of CaLaAl3O7 show a strong dependence on the synthesis atmosphere, suggesting that they should be related to the oxygen vacancy. It is attractive to find that the triboluminescence of CaLaAl3O7 shows a distinct spectral characteristic compared to its photoluminescence. Further computational results suggest that the applied mechanical stimuli on the CaLaAl3O7 cell could promote the formation of the vacancies of oxygen and calcium, responsible for the spectral differences.

The first example of the stereoselective synthesis and crystal structure of a spirobicycloquinazolinone based on (-)-fenchone and anthranilamide.

The possibility of a single-stage solvent-free stereoselective synthesis of a spirocyclic compound from the natural bicyclic monoterpenoid (-)-fenchone and anthranilamide has been shown for the first time. The molecular and crystal structure of (1R,2S,4S)-1,3,3-trimethyl-1'H-spiro[bicyclo[2.2.1]heptane-2,2'-quinazolin]-4'(3'H)-one, C17H22N2O, was established by X-ray diffraction though the chirality was assumed via the known reactant connectivity and 1H and 13C NMR spectroscopy. It has shown that in the molecule, for steric reasons, there is an elongation of the Me2C-C(N)N bond to 1.603 (5) Å. The formation of dimers via N-H...O=C hydrogen bonds with an interaction energy of 93.30 kJ mol-1 and through cavities (33.7% of the unit-cell volume) was established in the packing of the molecules. There are no π-stacking interactions in the structure.

Crystal packing control of a trifluoromethyl-substituted furan/phenylene co-oligomer.

Furan/phenylene co-oligomer single crystals are considered as future materials for organic optoelectronics. Here, the effects of trifluoromethyl substituents on the crystallization, structure and optical properties of furan/phenylene co-oligomer 1,4-bis{5-[4-(trifluoromethyl)phenyl]furan-2-yl}benzene are studied systematically. The solution growth methods and physical vapor transport result in the formation of three polymorphs depending on the growth method and the solvent. Single-crystal X-ray analysis reveals the crystal structures to correspond to H-, J- or mixed aggregates. All obtained crystals exhibit high photoluminescence efficiency and have optical properties which strongly depend on the crystal packing. Variable-temperature X-ray powder diffraction analysis shows the thermal transition of two forms (H- and J-aggregates) into a third one (mixed aggregate). Terminal trifluoromethyl groups induce weak intermolecular interactions which control the crystal packing and optical properties of co-oligomer single crystals.

A quantitative topological descriptor for linear co-oligomer fusion.

A purely topological descriptor for the quantitative classification of fully or partially fused linear quasi-one dimensional centre-symmetric molecules is proposed. The index also makes it possible to quantitatively correlate optoelectronic properties with the molecular topology without involving an explicit calculation of the molecular electronic structure.