Azepine‐ or Azocine‐Embedded Hexabenzocoronene Derivatives as Nitrogen‐Doped Saddle or Saddle‐Helix Nanographenes

Abstract

Two novel nitrogen-doped, hexa-peri-hexabenzocoronene (HBC)-based nanographenes (NGs) 1 and 2 bearing an azepine and an azocine at the fjord region, respectively, were synthesized and characterized. Notably, structure 1 was synthesized by Diels-Alder reaction of cyclic alkene and tetrachlorothiophene-S,S-dioxide, followed by Suzuki-Miyaura cross-coupling and Scholl-type reactions, which represents a modified strategy to construct NGs. The azoheptagon-embedded NG 1 leads to a saddle shape, and the azooctagon-embedded NG 2 exhibits a distorted saddle-helix conformation with the largest torsion angle recorded so far in [5]helicenes. As a result, the different structural topographies for NGs 1 and 2 lead to significant changes in the optical properties including UV absorption and fluorescent emission. Additionally, the 8p-heterocycles azepine and azocine in the NGs 1 and 2 exhibited obvious antiaromatic properties.

N‐Doped Octagon‐Containing HBC as Redox and pH Chiroptical Switch in the NIR

“…Therefore, we carried out its geometrical optimization (DFT‐CAM−B3LYP/6‐31G(d,p)) leading to a highly distorted structure (Scheme 1, bottom left). The saddle curvature induced by the octagonal ring reaches 2.3 Å deep and the maximum dihedral angle described by the helicene (66.4°) is similar to the one observed for the all‐carbon HBC‐ oct ‐[5]helicene (66.8°) previously reported by our research group (Figure 1, bottom left) [7] and the N‐doped HBC‐ oct ‐[5]helicene (67.6°) reported by P. An et al [23] . In addition, the angle between the two planes described by the terminal rings of the [5]helicene of 1 (78.9°, Figure S25) is again in good agreement with the HBC‐ oct ‐[5]helicenes, slightly superior than other related analogues such as Rajca's oct‐[5]helicene (72.4°) [30] or Narita's HBC‐ hept‐[5]helicene (77.3°) [31] and, lower than the actual value of An's aza‐HBC‐ oct ‐[5]helicene (87.4°).…”

“…The synthetic route towards aza‐HBC‐ oct ‐[5]helicene 1 is similar to those previously reported, [7,23] which is based on the Beckmann rearrangement to insert the nitrogen atom and to expand the seven‐membered ring of dibenzosuberenone 2 (Scheme 1). Afterwards, the aza‐hexaphenylbenzene 5 was prepared by Diels‐Alder reaction from the described aza‐cyclobenzooctyne 3 and cyclopentadienone 4 (70 %).…”

“…In another interesting example, reported by M. Melle‐Franco, A. Mateo‐Alonso et al., the octagonal ring stabilizes the helical conformation of a molecular nanoribbons [22] . Recently, the group of P. An et al [23] . has reported the aza‐HBC‐ oct ‐[5]helicene version of our previously reported HBC‐ oct ‐[5]helicene [7] .…”

“…In addition, the angle between the two planes described by the terminal rings of the [5]helicene of 1 (78.9°, Figure S25) is again in good agreement with the HBC‐ oct ‐[5]helicenes, slightly superior than other related analogues such as Rajca's oct‐[5]helicene (72.4°) [30] or Narita's HBC‐ hept‐[5]helicene (77.3°) [31] and, lower than the actual value of An's aza‐HBC‐ oct ‐[5]helicene (87.4°). This difference might be due to the presence of different substituents [23] …”

Synthesizing Strained Azatriseptane Frameworks

“…expanded and nitrogen-doped derivative (Figure 1, top right) shows a clear trend towards increased solubility (as a result of non-planarity) whilst also displaying antiaromaticity and red-shifted absorption as a consequence of the presence of the peripheral nitrogen. [44] With the synthetic challenges that arise by fusing seven-membered rings, only a few examples of higher septane frameworks have been reported besides the synthesis of [7,7]circulene. [45] To the best of our knowledge, that feature three directly fused seven-membered rings.…”