[1,4]Diazocine-Embedded Electron-Rich Nanographenes with Cooperatively Dynamic Skeletons

Abstract

Curved nanographenes (NGs) are emerging as promising candidates for organic optoelectronics, supramolecular materials, and biological applications. Here we report a distinctive type of curved NGs bearing a [1,4]­diazocine core that is fused with four pentagonal rings. This is formed by Scholl-type cyclization of two adjacent carbazole moieties through an unusual diradical cation mechanism followed by C–H arylation. Owing to the strain in the unique 5–5–8–5–5-membered ring skeleton, the resulting NG adopts an interesting concave–convex cooperatively dynamic structure. By peripheral π-extension, a helicene moiety with fixed helical chirality can be further mounted to modulate the vibration of the concave–convex structure, through which the distant bay region of the curved NG inherits the chirality of the helicene moiety in a reversed fashion. The [1,4]­diazocine-embedded NGs show typical electron-rich characteristics and form charge transfer complexes with tunable emissions with a series of electron acceptors. The relatively protruding armchair edge also allows the fusion of three NGs into a C 2 symmetric triple diaza[7]­helicene which reveals a subtle balance of fixed and dynamic chirality.

π‐Extended Diaza[7]helicenes with Dual Negatively Curved Heptagons: Extensive Synthesis and Spontaneous Resolution into Strippable Homochiral Lamellae with Helical Symmetry

“…Double saddle‐shaped structures were also observed for 2 , which were wider and deeper than that of 1 a (Figure 6a). Such C 2 ‐symmetric homochiral triple helicene was apparently different from the previously reported triple helicenes in which C 3 / D 3 ‐symmetry for homochiral conformers [27] and C 2 ‐symmetry for heterochiral structures [10g,14] were normally observed. The mean torsion angle of the inner rim (29.4°) of the diaza[7]helicene moiety was comparable with that of 1 a (30.1°).…”

“…Meanwhile, the incorporation of carbazole moieties would facilitate the simultaneous accomplishment of nitrogen‐doping, creation of polycyclic skeleton, and provision of reactive sites. However, practical attempts showed that the octagonal cyclization of the two carbazole moieties was preferred over the heptagonal cyclization of the adjacent phenyl and carbazole moieties under Scholl reaction condition (Scheme S1) [14] . Thus, we switched to a non‐oxidative cyclization route involving the Pd‐catalyzed C−H arylation [15] of chlorinated oligoarylene‐carbazole precursors 4 a – 4 e (Figure 1a).…”

“…However, practical attempts showed that the octagonal cyclization of the two carbazole moieties was preferred over the heptagonal cyclization of the adjacent phenyl and carbazole moieties under Scholl reaction condition (Scheme S1). [14] Thus, we switched to a non-oxidative cyclization route involving the Pd-catalyzed CÀ H arylation [15] of chlorinated oligoarylene-carbazole precursors 4 a-4 e (Figure 1a). Precursors 3 a and 3 b were synthesized by nucleophilic aromatic substitution of 1,4-dibromo-2,3difluorobenzene with two equivalents of carbazole derivatives.…”

An eight-membered ring formed by the Scholl reaction of o-quateraryls

“…In contrast, geometry optimization of the radical-cation intermediate, 13 , could not reach a local energy minimum. 34 These calculations indicate that the formation of an eight-membered ring is favourable in the arenium cation pathway, with a lower energy barrier than for the formation of a six-membered ring. On the other hand, the radical cation pathway does not allow the formation of an eight-membered ring.…”

Topology-Directed Synthesis of Helical Phosphoniums with High Diradical Character and Polar-Dependent Electron Transfer

“…[28][29][30][31][32][33][34] Helicenes, the ortho-fused superstructures, have an intrinsic folded spiral superposition of PAHs. 36,37 The topology tailoring in helicenes endows an accessional possibility of stable radical incubation, 34,35,38 circularly polarized luminescence (CPL), 14,39,40 and chiralityinduced spin selectivity (CISS). 41,42 The traditional carbon [n]helicenes with high diradical character and dynamic luminescence switchability is hardly accessible due to resonance delocalization and monotonous electron transfer inherency (e.g.…”