A Sterically Congested Nitrogenated Benzodipentaphene with a Double π-Expanded Helicene Structure

Abstract

Herein, we describe a series of three sterically congested nitrogenated benzodipentaphenes, one of which shows a highly distorted aromatic backbone with an unprecedented double π-expanded helicene structure.

Planar and Helical Dinaphthophenazines

“…The high quantum yield for 1-Z is in agreement with those observed on parent double π-expanded helicenes. 10 The lower quantum yield observed for 1-U also agrees with previous reports that describe lower fluorescence quantum yields for twisted systems. 12 2-Z and 2-U showed no fluorescence, which is consistent with a nonemissive intramolecular charge transfer transition (also see the theory section below).…”

“…The structure of 1-U shows large torsion angles along the BCD/B′C′D′ rings (21.5 and 20.7°, respectively, Figure S1 ) that together produce a helix angle of 42.2°. This helical structure and the helix angle value is consistent with the structures and helix angles observed on a parent double π-expanded helicene (40.6°) 10 and with those of a similar family of less-strained π-expanded helicenoids (28°). 13 In the case of the quinone series, dinaphthophenazine 2-Z is not as planar as 1-Z .…”

“…However, the U-shaped isomers, if properly functionalized, can give rise to π-expanded helicenoids. 10 …”

Synthesis, Structures, and Properties of Helically Fused Anthraquinones with Unusually Close Carbonyl‐Carbonyl Contacts

“…The distance between the terminal carbon atoms C7•••C7'' (3.47 Å) is comparable to the sum of the vdW radii of C atoms (3.40 Å). This molecule has two [4]helicene substructures, BÀ E and EÀ H, where the dihedral angles along the inner rims are + 24.5°(BÀ D and FÀ H) and + 22.0°(CÀ E and EÀ G). This magnitude of helical deformation in [3]AQa is larger than that in anthracene analog [3]ANa (10-20°) [1] because of the enhanced steric hindrance by the carbonyl groups.…”

“…We have recently reported multiply fused anthracene [3]ANa as an example of expanded helicene (Figure 1), [1] which has been defined as a helicene with additional linearly fused benzo moieties into angularly fused units. [2,3,4] Compound [3]ANa possesses a helical structure to avoid steric interactions between the terminal aromatic moieties, and the enantiomers of its diphenyl derivative show very high circular dichroism and circularly polarized luminescence activities. [5] Based on this molecular design, we synthesized helical anthracenes with four and five fused anthracene moieties were successfully synthesized as long expanded helicenes, where the interlayer π•••π interactions significantly influenced their photophysical properties.…”