Diazadioxa[8]circulenes: Planar Antiaromatic Cyclooctatetraenes

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Benzoannelated aza-, oxa- and azaoxa[8]circulenes as promising blue organic emitters

In the present study, we studied the synergetic effect of benzoannelation and NH/O-substitution for enhancing the absorption intensity in a series of novel designed benzoannelated aza- and oxa[8]circulenes.

Structure and spectroscopic characterization of tetrathia- and tetraselena[8]circulenes as a new class of polyaromatic heterocycles

The FTIR, Raman and UV-vis spectra of the recently synthesized tetrathia[8]circulene and tetraselena[8]circulene compounds have been measured and interpreted in details by the density functional theory (DFT) calculations taking into account the molecular symmetry constrains. The structural and electronic features of the studied compounds have also been discussed in connection with the observed spectroscopic characteristics. Particularly, we have found that despite a slightly non-planar conformation the neutral tetrathia[8]circulene and tetraselena[8]circulene molecules demonstrate bifacial aromatic/antiaromatic nature. The inner octatetraene core is characterized by the presence of paratropic ("antiaromatic") ring currents, whereas the outer macrocycle constructed of benzene, thiophene or selenophene rings possesses the strong magnetically-induced diatropic ("aromatic") ring current. This fact suggests the general electronic and magnetic similarity of the tetrathia- and tetraselena[8]circulenes with the strictly planar isoelectronic tetraoxa[8]circulene and related azaoxa-derivatives discussed earlier. However, the vibrational and UV-vis absorption spectra of the studied circulenes are rather different from those of the parent tetraoxa[8]circulene which indicates a clear manifestation of the symmetry selection rules.

Synthesis of a Tetrabenzotetraaza[8]circulene by a "Fold-In" Oxidative Fusion Reaction

Tetrabenzotetraaza[8]circulene (1) has been synthesized in good yield by a "fold-in" oxidative fusion reaction of a 1,2-phenylene-bridged cyclic tetrapyrrole. X-ray diffraction analysis of 1 has revealed a planar square structure with a central cyclooctatetraene (COT) core that shows little alternation of the bond lengths. Despite these structural features, 1 shows aromatic-like character, such as sharp absorption bands, high fluorescence quantum yields (Φ(F)=0.55 in THF), and a single exponential fluorescence decay with τ(F)=3.8 ns. These observations indicate a dominant contribution of an [8]radialene-like π conjugation and hence aromatic character of the local aromatic segments in 1.

Synthesis and properties of unsymmetrical azatrioxa[8]circulenes

Synthesis and properties are reported for a series of unsymmetrical antiaromatic azatrioxa[8]circulenes.

Design of novel tetra-hetero[8]circulenes: a theoretical study of electronic structure and charge transport characteristics

Tetra-hetero[8]circulenes were theoretically designed and emerged as good candidates for ambipolar organic semiconductors.

Diversity-oriented synthesis of tetrathia[8]circulenes by sequential C–H borylation and annulation

We have succeeded in the diversity-oriented synthesis of tetrathia[8]circulenes by sequential C–H borylation and annulation from cyclic tetrathiophene.

Stability and properties of 2D porous nanosheets based on tetraoxa[8]circulene analogues

Two-dimensional porous nanosheets based on tetraoxa[8]circulene and its analogue are theoretically studied using first principles calculations focusing on their thermal stability and mechanical, electronic, optical and thermoelectric properties. It is found that the nanosheets composed of tetraoxa[8]circulene (TO8C) and tetraaza[8]circulene (TA8C) are thermodynamically and kinetically stable. Both sheets show anisotropic Young's moduli corresponding to tetragonal symmetry. However, due to their porosity, the Young's moduli of both sheets are much smaller than that of graphene. Electronic structure calculations indicate that both TO8C and TA8C nanosheets are direct semiconductors with a band gap of 1.92 eV and 1.83 eV respectively, and they can adsorb strongly visible light and exhibit a huge Seebeck coefficient. Thus they can be promising candidates for solar and thermoelectric applications.

Design of nanoscaled materials based on tetraoxa[8]circulene

Nanotubes and two-dimensional sheet-like compounds containing tetraoxa[8]circulene core units are theoretically predicted. The large cavities with a diameter of 6 Å in the 2D sheets could be useful for hydrogen storage. The designed compounds are predicted to adsorb strongly in the visible region and to be a promising material for nanophotonics because of their electron-donor properties (p-type semiconductors).

Aromaticity of the planar hetero[8]circulenes and their doubly charged ions: NICS and GIMIC characterization

All hetero[8]circulenes represent nonaromatic species because the paratropic internal currents (red colour) substantially cancel out the diatropic contribution on the outside edge (blue colour).

The art of the possible: computational design of the 1D and 2D materials based on the tetraoxa[8]circulene monomer

Single-wall nanotube based on tetraoxa[8]circulene monomer.