Antiaromatic character of cycloheptatriene-bis-annelated indenofluorene framework mainly originated from heptafulvene segment

Abstract

Fully π-conjugated polycyclic hydrocarbons with antiaromatic character have attracted research attention because of their unique properties such as narrow energy gaps, and thus should find application as optical and electronic materials. Although antiaromatic 16π-electron frameworks can be constructed by the incorporation of multiple seven-membered rings in a fused fashion to install methylenecycloheptatriene (heptafulvene) segments, the development of corresponding benzo[1,2:4,5]di[7]annulene (BDA)-containing π-conjugated systems remains challenging due to the difficulty of their molecular design and synthesis. In this study, we develop an unprecedented chemical structure of cycloheptatriene-bis-annelated indenofluorene, which possesses both BDA and indenofluorene frameworks in a fused fashion. Physical measurements and X-ray analyses, along with theoretical calculations, indicated that antiaromaticity appeared in the BDA framework. By using the conjugated polycyclic hydrocarbon possessing both seven-membered and five-membered rings, this study provides fundamental insight into the strong antiaromatic nature of heptafulvene-based BDA framework.

On-Surface Synthesis of Non-Benzenoid Nanographenes by Oxidative Ring-Closure and Ring-Rearrangement Reactions

“…odd-membered polycycles (pentagons or heptagons), in the honeycomb lattice may have a considerable impact on the physicochemical properties of NGs, arising from local changes in strain and conjugation. [22][23][24][25] Under this scenario, atomically-precise bottom-up approaches have provided in the last decades an appealing playground for the design and investigation of NGs with perfectly defined structures and properties, 24,[26][27][28][29][30][31][32][33][34][35][36] in contrast to the well-known disadvantages such as non-regular edge structures or uncontrollable sizes presented by the top-down approach. 37 In this regard, on-surface chemical reactions have proven to be a versatile tool for the formation of stable molecular graphene structures that cannot be synthesized in solution.…”

Construction of Heptagon‐Containing Molecular Nanocarbons

“…In 2018, Aso and co‐workers reported the synthesis of 123 , a PAH consisting of benzo[1,2:4,5]di[7]annulene (BDA) and indenofluorene subunits (Scheme 31). [104] BDA is a 16π electron system, but possesses non‐aromatic character due to its twisted structure, [21] while indenofluorene possesses 20π electrons and exhibits antiaromatic and biradical character [105] . Tetra‐allylated compound 120 was prepared from the reaction of the corresponding diketone with allylmagnesium bromide.…”

Multi‐Redox Active Carbons and Hydrocarbons: Control of their Redox Properties and Potential Applications

“…To date, various multi‐redox active C x H y molecules have been explored. These include, but are not limited to, nanographenes, [16–24] radicaloids (mostly based on diindenoarenes), [25–34] macrocycles, [35–39] fullerene fragments (including buckybowls), [40–45] nanographene‐buckybowl hybrids, [46] pentalene derivatives, [47] ethynylenes, [48] spiro‐compounds, [14] cumulenes, [49] other C x H y molecules with either the azulene, [50] barrelene, [51] fluoranthene, [52] fluorene, [53] diphenalene, [54] phenylene, [55] or Schwarzite framework, [56] and hydrofullerenes [57–61] . The redox properties of dissolved C x H y molecules are summarized in Table 1, where C x H y molecules that show at least six redox reactions (Scheme 1) are listed.…”

“…The addition of functional groups to the periphery of C x H y molecules is a common solution to this limitation. Bulky substituents, such as tert ‐butyl groups and long alkyl chains, are often used to increase the solubility of C x H y molecules [21,47] . However, these substituents usually have larger molecular weights than non‐hydrocarbon‐based ones.…”