Azatrioxa[8]circulenes: Planar Anti‐Aromatic Cyclooctatetraenes

Abstract

We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.

Electronic structure, aromaticity and spectra of hetero[8]circulenes

“…21,52,53 sym-Tetraselenatetrathia [8]circulene 10 prepared two years later has a similar planar structure. 22,28 Azaoxa [8]circulenes 23,24 prepared by the group of Pittelkow are the latest synthesized heterocirculenes. Among these compounds are azatrioxa [8]circulene 23 11, its dibenzo derivative comprising two naphthalene moieties 23 and diazadioxacirculene 24 12.…”

DFT simulation of the heteroannelated octatetraenes vibronic spectra with the Franck–Condon and Herzberg–Teller approaches including Duschinsky effect

“…In particular, the azaoxa[8]circulenes 4 and 5 absorb intensively in the visible region in the range 380-450 nm. Additionally, they demonstrate a relatively high fluorescence quantum yield [31,32]. In order to explain these features we have calculated vibronic structure for the electronic absorption spectra of azaoxa [8]circulenes 4, 5.…”

“…In our previous studies [28][29][30][31][32][33][34][35][36][37][38][39][40][41] the structure and electronic absorption spectra of the heteroannelated octatetraenes were described in detail but the vibronic effects have been discussed only qualitatively. As a good example of vibronic effects manifestation the electronic absorption spectrum of the tetraoxa [8]circulene 1 (Fig.…”

“…Therefore their structural features, functionalization possibilities and spectral properties are studied extensively in the numerous recent researchers [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”

Structure and Properties of [8]BN-Circulenes: Inorganic Analogues of [8]Circulenes

“…DFT studies 13-17 using B3LYP/6-31G(d) were found reliable in predicting experimental vibrational (IR and Raman) and UV-spectra of such π-extended tetraoxa- [8]circulenes. Also, a wide range of hetero- [8]circulenes (such as tetrathio and tetraseleno 20 , octathio 18, 21 , tetraseleno-tetrathio 21 , azatrioxa 22 and diazadioxa [8]circulene 23 properties with corresponding carbon [8]circulenes. These molecular models of [8]BNcirculenes may be considered as the building blocks of crystalline nanoscale materials.…”