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A concave indolo[3,2,1‐jk]carbazole‐based compound was synthesized and characterized, which was further compared with the property of its planar congener. The results reveal that the change in molecular shape alters the molecular electronic structure, thus leading to the reduced aromaticity and divergent energy levels of frontier molecular orbitals of the concave compound. Moreover, the bowl‐shaped molecule demonstrates a blue‐shift in the UV/Vis absorption and a red‐shift in the weakened fluorescence emission due to the vibration of the concave face. [ABSTRACT FROM AUTHOR]

This Review surveys the experimental and synthetic history of three classic antiaromatic cores: cyclobutadiene, borole, and pentalene. The coverage extends from the bare molecular cores to fused or substituted variants that impart thermodynamic or kinetic stability to the antiaromatic systems. Recent studies to utilize the unusual properties of these antiaromatic cores in the context of advanced electronic materials are discussed. [ABSTRACT FROM AUTHOR]

Relatively scarce literature data on BN/CC isosterism in 4nπ‐electronic systems have prompted us to investigate theoretically the influence of BN pair position within the central butadiene fragment of dibenzo[a,e]pentalene on two fundamental molecular properties: stability and (anti)aromaticity. It was found that stability and aromaticity follow the same trend only for BN‐orientational isomers. The source of different stability of other isomers was examined first by an analysis of bond types and their dissociation energies and then by isomerization energy decomposition analysis and was explained in terms of classical electrostatic interactions, quantum‐mechanical orbital interactions, structural changes and electronic changes (transition from charge‐separated π‐system to the neutral one). (Anti)aromaticity was investigated by using three kinds of indices, HOMA, FLUπ, and NICS(1)zz, which indicated that delocalization at the central pentalene motif is almost unaffected by various BN arrangements, molecular perimeter is slightly affected, while the most affected subunits are five‐membered rings and benzene‐fused five‐membered rings containing only one heteroatom. The BN/CC isosterism is increasingly exploited to tune physical and biochemical properties of organic compounds. Here, we use density functional calculations to explore how BN/CC substitution modifies local, semilocal and global (anti)aromaticity of the 4nπ‐electronic dibenzo[a,e]pentalene and to predict and explain the relative stability of the six isomeric BN‐dibenzo[a,e]pentalenes. [ABSTRACT FROM AUTHOR]

Rylenes are peri-fused naphthalene oligomers and possess a unique electronic structure, which makes them attractive materials as organic dyes and semiconductors. In particular, rylenes beyond terrylene are promising near-infrared dyes with high molar extinction coefficients. Recent studies have demonstrated an unusual open-shell diradical character for long rylene molecules and potential half-metallic properties of polyrylene ribbon. However, the synthesis of long rylenes and polyrylene is a very challenging task, with various strategies directed towards solving the critical molecular aggregation and stability problems having been developed since 1910. In addition, recent research has also shown that quinoidal rylenes have an irresistible tendency to become diradical, and so they constitute a new type of open-shell singlet diradicaloids with magnetic activity. This microreview mainly summarizes the synthesis of long rylene ribbons and quinoidal rylene diradicaloids, together with their unique electronic structures and physical properties. [ABSTRACT FROM AUTHOR]

This is a theoretical (DFT) study of the impact of electronic structural changes, induced by B-N/C-C isosterism, on two basic properties of 4π-electron antiaromatic system, that is, stability and antiaromaticity. The main driving force for the nonplanarity of B2N2 rings is electrostatic energy, and that for a ring with one B-N unit is the relief of Pauli repulsion. The charge-separation instability, inherent for a 1,3-B,N relationship, turns the ground state of the BCNC system to an aromatic triplet, which is less stable than the isomeric BNCC system, mostly because of larger Pauli interactions. The alternating BNBN connectivity is favoured primarily by orbital interaction energy and, secondarily, by better electrostatic attraction. The C--C → B-N substitution weakens the antiaromatic character, except that for a 1,3-B,N relationship, which results in increased antiaromaticity in the closed-shell state relative to that of cyclobutadiene.q [ABSTRACT FROM AUTHOR]