Assignment of aromaticity of the classic heterobenzenes by three aromatic criteria

Aromaticity is a key concept in physical organic chemistry. The aromatic order of the classic heterobenzenes was reported in experiment early. However, the unambiguous criteria used to validate the aromaticity of that were controversial or inadequate in theory. In this work, the global aromaticity of the compounds has been studied using the ELF, NICS and ISE. NICS(max)zz was calculated based on the maximum NICS contribution to the out-of-plane zz tensor component. Two types of bonds are observed. The correlations between NICS(max)σzz and NICS(max)πzz with respect to aromaticity are demonstrated, specifically between NICS(max)πzz and ELFπ (cc = 0.98) for π bonds. For σ bonds, the different electron delocalization of σ bonds out of the plane of the ring predicted well the discrepancies between NICS(max)σzz and ELFσ. The σ aromatic order of the classic heterobenzenes (C5H5N > C6H6 > C5H5P > C5H5As > C5H5Bi, C5H5Sb) was proved via the level of electronic delocalization

Indacenodibenzothiophenes: Synthesis, Optoelectronic Properties and Materials Applications of Molecules with Strong Antiaromatic Character

Indeno[1,2-b]fluorenes (IFs), while containing 4n π-electrons, are best described as two aromatic benzene rings fused to a weakly paratropic s-indacene core. In this study, we find that replacement of the outer benzene rings of an IF with benzothiophenes allows the antiaromaticity of the central s-indacene to strongly reassert itself. Herein we report a combined synthetic, computational, structural, and materials study of anti- and syn-indacenodibenzothiophenes (IDBTs). We have developed an efficient and scalable synthesis for preparation of a series of aryl- and ethynyl-substituted IDBTs. NICS-XY scans and ACID calculations reveal an increasingly antiaromatic core from [1,2-b]IF to anti-IDBT, with syn-IDBT being nearly as antiaromatic as the parent s-indacene. As an initial evaluation, the intermolecular electronic couplings and electronic band structure of a diethynyl anti-IDBT derivative reveal the potential for hole and/or electron transport. OFETs constructed using this molecule show the highest hole mobilities yet achieved for a fully conjugated IF derivative