Synthesis and Properties of Twisted and Helical Azulene Oligomers and Azulene‐Based Polycyclic Hydrocarbons

Abstract

The construction of 1,2‐position‐connected azulene oligomers was achieved. In the crystal packing structure of the terazulene, two molecules of (Ra)‐ and (Sa)‐configurations formed a pair. Variable temperature NMR measurements and theoretical calculations of the quaterazulene suggest that the helical and syn‐type structure with terminal azulene overlap is more stable. Two kinds of fused terazulenes (1,2′′‐closed and 1,8′′‐closed) were also synthesized by intramolecular Pd‐catalyzed C−H/C−Br arylation of the terazulene moieties. X‐ray structure analysis of 1,2′′‐closed terazulene revealed a planar structure, while an analysis of 1,8′′‐closed terazulene performed on a C60 co‐crystal revealed a curved structure forming a 1 : 1 complex covering the co‐crystal. Nucleus‐independent chemical shift (NICS) calculations carried out for the central seven‐membered ring of 1,8′′‐closed terazulene showed a positive value, suggesting anti‐aromatic properties.

Syntheses of Azulene Embedded Polycyclic Compounds

“…The helical azulene dimer displays an efficient π-conjugation, and the authors believe that the newly created seven-membered ring could be considered as an equivalent "cycloheptatrienyl anion having the antiaromatic character" and proposed the resonance structures 71A-71.C shown in Scheme 71. Interesting steric behavior in reactions between different azulene compounds was also observed by Tsuchiya et al and is described in Scheme 72 [101]. 1,2′-Biazulene bromination and Suzuki-Miyaura coupling with boronic ester 8.1 provide the twisted azulene trimer 72.1, which was then used in two syntheses.…”

“…Interesting steric behavior in reactions between different azulene compounds was also observed by Tsuchiya et al and is described in Scheme 72 [101]. 1,2 ′ -Biazulene bromination and Suzuki-Miyaura coupling with boronic ester 8.1 provide the twisted azulene trimer 72.1, which was then used in two syntheses.…”

Intense absorption of azulene realized by molecular orbital inversion

“…1a), and it is also known as a redox-active molecule compared to naphthalene, anthracene, pyrene and so on. [11][12][13][14][15] In this context, holetransporting materials with a two-dimensionally expanded p-system around the azulene core for efficient perovskite solar cells have also recently attracted interest. 21,22 In addition, 1,3-bis(diarylamino)azulene 1 (Scheme 1a) is reported to exhibit high electron-donating properties.…”

“…1b). [11][12][13][14][15] Hence, it is conceivable that the electronic structure of azulene changes significantly depending on the positions where the diarylamino groups are introduced.…”

“…8 These substituted acenes are also attracting attention because of their ability to absorb visible light, which enables them to be used as photoreduction catalysts. 9,10 Furthermore, azulene [11][12][13][14][15][16][17][18][19][20] is a structural isomer of naphthalene, with relatively high HOMO and low LUMO energy levels due to its unique polarisation structure (Fig. 1a), and it is also known as a redox-active molecule compared to naphthalene, anthracene, pyrene and so on.…”