Contorted Polycyclic Aromatic Hydrocarbons with Two Embedded Azulene Units

Abstract

Polycyclic aromatic hydrocarbons (PAHs) that contain both five‐ and seven‐membered rings are rare, and those where these rings are annulated to each other and build azulene units have, to date, mainly been generated in minute amounts on surfaces. Herein, a rational approach to synthesize soluble contorted PAHs containing two embedded azulene units in the bulk is presented. By stepwise detachment of tert‐butyl groups, a series of three azulene embedded PAHs with different degrees of contortion has been made to study the impact of curvature on aromaticity and conjugation. Furthermore, the azulene PAHs showed high fluorescence quantum yields in the NIR regime.

Dicyclohepta[ijkl,uvwx]rubicene with Two Pentagons and Two Heptagons as a Stable and Planar Non‐benzenoid Nanographene

“…DHR can be stored in air at room temperature for more than 6 months without structural change, and its 1 H NMR and MS spectra kept unchanged even if it was heated at 200 °C for 1 hour in the air (see Figure S3, S4). Thus, DHR shows good stability, being similar to PAHs with two embedded azulene units reported by Mastalerz and co‐workers . This makes DHR different from nanographenes with two pentagons and two heptagons reported recently by Müllen and Feng which are not stable in air …”

“…These two expanded conjugated molecules were found to show open‐shell character and low air‐stability because of their unique electronic structures. Very recently, Mastalerz and co‐workers have reported the synthesis of larger contorted and soluble PAHs that contain 15 fused aromatic rings and two embedded azulene moieties . These PAHs were found to be stable and their structures were confirmed unambiguously by single crystal structural analysis.…”

Synthesis of Defective Nanographenes Containing Joined Pentagons and Heptagons

“…Synthesis of contorted nanographenes 62 with two azulene units. [82,83] Scheme 11. Synthesis of planar nonbenzenoid nanographene 67 with two 5-7 pairs.…”

“…On the basis of their previous discovery that Scholl‐type oxidative cyclization of 60a in the presence of DDQ/TfOH or FeCl 3 /CH 3 NO 2 exclusively gave the pentagon‐forming product 61a , [ 82 ] in this work, the modified precursor 60b was prepared to conduct the same highly selective Scholl reaction that enabled the generation of azulene‐embedded nanographenes. [ 83 ] In contrast, treatment of precursor 60b with FeCl 3 /CH 3 NO 2 , even in a large excess of equivalents, afforded only the pentagon‐containing chlorinated product 61b . In the presence of DDQ/TfOH, two pentagons accompanied by two heptagons were formed, resulting in three unexpectedly substitutional products 62 , of which the respective yield was dictated by the concentration of DDQ.…”

NIR‐Absorbing π‐Extended Azulene: Non‐Alternant Isomer of Terrylene Bisimide

“…However, the unique electronic properties of azulene are usually not preserved when embedded into a larger π‐scaffold. The aromaticity of such azulene moieties is typically lost due to structural distortions . But even if planarity prevails, such PAHs usually possess non‐ or anti‐aromatic “formal azulene“ units because of the dominant aromaticity of the surrounding benzenoid rings.…”