This work describes as ynthetica pproachw here an on-planar aromatic heterocyclic [7]helicene is compressedt oy ield ah etero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic[ 8]circulenec ontaining three differenth eteroatoms. The synthetic pathway proceeds via at he flattened dehydro-hetero[7]helicene, which is partially ah elicene and partially ac irculene:i ti s non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleusi ndependent chemical shift (NICS) calculations. The planarizationf rom ah elically p-conjugated[ 7]helicene to af ully planar heterocyclic [8]circulene significantly alterst he spectroscopicp roperties of the molecules.P ost-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the opticals pectrum (400-700 nm).
The self-recombination reactions of 4-aminophenyl cations and parent phenyl cations, each in ground triplet states, are studied within the framework of density functional theory. Only the total zero spin (singlet state) is chosen, as the quintet and triplet counterparts are nonreactive in these systems. The recombination products are the benzidine and biphenyl doubly charged cations. These species are unexpectedly stable. The transition state of the 4-aminophenyl cations reaction is located at the distance of about 4.0 Å between the ipso-carbon atoms. The activation barrier is predominantly formed by electrostatic repulsion between two cations and is estimated to be 27.6 kcal mol 21 [B3LYP/6-3111G(d,p)]. Similar results are obtained for the phenyl cations recombination. The general importance of the participation of other aryl cations in analogous organic reactions is discussed. V C 2013 Wiley Periodicals, Inc.
A new ambient-pressure metastable single-bonded 3D nitrogen allotrope (TrigN) of trigonal symmetry (space group R3[combining macron]) was calculated using density functional theory (DFT). A comprehensive characterization of this material, comprising thermodynamic, elastic, and spectral (vibrational, UV-vis absorption, and nuclear magnetic resonance) properties, was performed. Using high-throughput band structure calculation, the TrigN phase was characterized as an insulator with an indirect band gap of 2.977 eV. Phonon dispersion calculations justified that this structure is vibrationally stable at ambient pressure. The calculated Raman activities at the Γ-point demonstrated a rich pattern, whereas no relatively intense transitions were observed in its IR absorption spectrum. The TrigN material is almost transparent to visible light as well as to ultraviolet A and B. The main absorption peaks appeared within the range of 50-200 nm. The electron arrangement of the nitrogen nuclei in the studied nitrogen allotrope is much denser compared to that of the molecular nitrogen, which is in agreement with the calculated magnetic shielding tensor values. Robust mechanical stability is revealed from the elastic constants calculation. Due to strong anisotropy, the values of the Young's moduli vary from 281 to 786 GPa. A huge amount of internal energy is enclosed in the TrigN material. Upon decomposition to molecular nitrogen, the energy release is expected to be 11.01 kJ g compared to the value of 10.22 kJ g for the cubic gauche form of nitrogen. The TrigN allotrope possesses unique detonation characteristics with a detonation pressure of 146.06 GPa and velocity of 15.86 km s.
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