Comparison of Antiaromatic Properties in a Series of Structurally Isomeric Naphthothiophene‐Fused s‐Indacenes

Abstract

Fusion of aromatic subunits to stabilize an antiaromatic core allows the isolation and study of otherwise unstable paratropic systems. A complete study of a series of six naphthothiophene-fused s-indacene isomers is herein described. Additionally, the structural modifications resulted in increased π-π overlap in the solid state, which was further explored through changing the sterically blocking mesityl group to (triisopropylsilyl)ethynyl in three derivatives. The computed antiaromaticity of the six isomers is compared to the observed physical properties, such as NMR chemical shift, UV-vis, and CV data. We find that the calculations predict the most antiaromatic isomer and give a general estimation of the relative degree of paratropicity for the remaining isomers, when compared to the experimental results.

Thermal Equilibrium Between Quinoid/Biradical Forms Enhancing Electrochemical Amphotericity

“…Each of the biradical forms 1 ‐ B , 4 ‐ B , and 5 ‐ B has two units of bis[5‐(4‐methoxyphenyl)2‐thienyl]methyl moiety (as in VI ), which undergoes 1e‐oxidation and reduction to the corresponding cationic and anionic states. For those biradicals, two radical units behave independently upon electron transfer, so that both redox waves in the voltammograms are 2e‐processes (Figure 8 and Table 2) that give the span of the second oxidation and reduction potentials E 2 sum (= E 2 ox − E 2 red ) of 1.35, 1.38, and 1.39 V, respectively, which are record‐small values for reversible 2e‐processes [27–34] . By considering that similar amphotericity is not expected for the corresponding quinoid form ( A ) with much higher E ox and much lower E red , thermal control of the redox properties, especially such amphotericity with the smallest E 2 sum value, is the outstanding feature of Type‐II molecules for developing highly functionalized materials.…”