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Updated: May 22, 2025
Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Polycyclic (anti)aromatic hydrocarbons: interstellar formation and spectroscopic characterization of biphenylene and
Athena R Flint1, Vincent J Esposito2, Ryan C Fortenberry1
1Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, USA. r410@olemiss.edu.
Abstract:
Formation of biphenylene (C6H4)2 and its isomer benzopentalene, C12H8, may act as a consumption route for ortho-benzyne (o-C6H4) in interstellar clouds such as TMC-1. MRCI-F12 and CCSD(T)-F12 potential energy surfaces show that o-C6H4 dimerization is possible through a C2h-symmetry single-bond association to a (C6H4)2 precursor before isomerization to (C6H4)2 and subsequently C12H8. Formation of a bimolecular product set from either species is energetically hindered, allowing (C6H4)2 and C12H8 to stabilize radiatively. To remedy the dearth of spectroscopic data for these species, anharmonic frequencies from explicitly-correlated quartic force fields (QFFs) for o-C6H4 and c-C4H4 are employed to reparameterize the semiempirical method PM6 for use in lower-cost QFFs for (C6H4)2 and C12H8. In both cases, at least one reparameterized PM6-QFF spectrum results in the prominent C-H stretch and symmetric C-H out-of-plane-bend features to be accurately predicted with respect to gas-phase experiment or the B3LYP/N07D anharmonic absorption spectrum. B3LYP/N07D accurately recreates the experimental infrared spectrum of (C6H4)2, showing the utility of this method for spectral prediction of small and midsize polycyclic hydrocarbons on the whole. For larger systems, reparameterized PM6-QFF spectra can reproduce the most important infrared features for a species. B3LYP/N07D cascade emission spectra show that the 730 cm-1 C-H symmetric out-of-plane bending feature dominates the emission spectrum of (C6H4)2, while the spectrum of C12H8 becomes characterized by the collective set of C-H out-of-plane bends. As such, infrared emission spectra of (C6H4)2 will likely be overshadowed by C2H2. Derivatives such as cyanobiphenylene are likely better targets for infrared observation.
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