Stacked antiaromaticity in the π‐congested space between the aromatic rings in the anthracene dimer

Abstract

Substance containing two π-congested aromatic systems are attractive targets in synthetic studies as well as efforts designed to explore the unique properties that originate from π-congestion. Since the time of the computational studies by Schleyer and Warner, the concept of stacked aromaticity created by the encounter of two antiaromatic rings has received much attention. A structure containing π-congestion between two antiaromatic norcorrole rings was prepared by Shinokubo et. al. In contrast, questions about what happens when two aromatic rings are closely stacked have remained unanswered. Specifically, the electronic consequences of stacking of two aromatic π-conjugated systems have not been fully evaluated. To the best of our knowledge, only one computational study has been performed by Herges, the results of which suggest that [2.2]paracyclophane, possessing short distance (<3.00 Å) between two aromatic ring planes, has a paratropic ring current between two the benzene rings. This observation is consistent with the conclusion that stacked antiaromaticity exists within the π-congested space between aromatic rings. Herein, we investigated the stacked antiaromaticity of highly -congested anthracene dimers using anthracenophane, which possesses a short inter-plane carbon-carbon distance of ca. 2.80 Å. The absorption spectrum of this substance contains a weak broad band from 450 to 550 nm that is attributed from HOMO-LUMO transition. These properties exist in planar cyclooctatetraene derivatives that having 8π-electron antiaromaticity. The results of nucleus-independent chemical shift and anisotropy of the induced current density calculations indicate that relatively weak antiaromatic character exists between the central six-membered rings of the two anthracene moieties in anthracenophane. In addition, an attempt to enhance the stacked antiaromaticity of anthracenophane using pressure to enhance π-congestion was unsuccessful.

Gauging the Aromatic, Antiaromatic, and Nonaromatic Character of the Dications and Dianions Derived from Fused Carbocyclic and Heterocyclic Compoundsǂ

“…[25] Molecular structures were fully optimized without imposing symmetry constraints by DFT computations at the B3LYP/aug-cc-pVTZ level. [26] The good performance of the B3LYP functional in benchmark studies justifies its extensive use and several recent reports confirm its reliability in aromaticity related applications on ground and excited states (see for example References [2,3,5,6,10,11,15,16,21,24] and references therein). The restricted and unrestricted procedures were applied for singlet and triplet electronic states respectively.…”

“…The ongoing interest in this topic is evidenced by the remarkable number of recent articles involving experimental and/or theoretical studies (selected examples are cited in this work). [1][2][3][4][5][6][7][8][9][10][11] A major contributing factor in the revival of interest in aromaticity is the application of polycyclic aromatic hydrocarbons (PAHs) or polyarenes in materials science, particularly in the area of organic electronics. [11,12] Modulation of their molecular properties, in particular the highest occupied molecular orbital (HOMO)lowest unoccupied molecular orbital (LUMO) energy gap (ΔE HÀ L ), is critical for the design of organic optoelectronic devices, [12][13][14][15][16] and conductive materials.…”

“…Aromaticity is a pivotal concept in organic chemistry that continues to be an active field of research for both fundamental and applied purposes. The ongoing interest in this topic is evidenced by the remarkable number of recent articles involving experimental and/or theoretical studies (selected examples are cited in this work) [1–11] . A major contributing factor in the revival of interest in aromaticity is the application of polycyclic aromatic hydrocarbons (PAHs) or polyarenes in materials science, particularly in the area of organic electronics [11,12] .…”

Hückel Molecular Orbital Analysis for Stability and Instability of Stacked Aromatic and Stacked Antiaromatic Systems

“…Such an extension of the notion of aromaticity has led to an extension of the scope of chemical graph theory. , Chemistry stimulates mathematics and mathematics stimulates chemistry back. In recent years, yet another aromaticity concept, stacked aromaticity or stacked-ring aromaticity and its opposite, stacked antiaromaticity, have begun to attract attention. − …”

Excited‐state aromaticity and antiaromaticity special issue

“…In their minireview, Krishnan et al [ 9 ] discuss the aromatic character of singlet‐state excimers and through‐space aromaticity of triplet‐state excimers of [ n ]acenes. Nishiuchi et al [ 10 ] discuss the concept of stacked antiaromaticity created in the π ‐congested space between the two central aromatic rings in an anthracene dimer (a benzannelated anthracenophane) during the dimerization process.…”