Cyclic Tetraindoles With a Cyclooctatetraene Core: Controlling Planarity and Antiaromatic Character via N ‐Alkylation

Cyclooctatetraene (COT), a representative 4n π‐electronic system, typically exhibits nonaromatic character in highly twisted structures, but planarization significantly alters its electronic properties, increasing antiaromaticity. Therefore, investigations on the structure‐property relationships of COT derivatives are essential for the development of future functional materials. In this study, we have developed a series of cyclic tetraindoles possessing a central COT ring. The degree of molecular distortion can be controlled by N ‐alkylation. Specifically, substitution of the N ‐butyl groups increased the distortion, while the structural fixation by ethylene linkers enhanced its planarity. As planarity increased, a noticeable red‐shift in the absorption wavelength, a decrease in oxidation potential, and a reduction in the HOMO‐LUMO gap were observed. These results can be attributed to the more effective conjugation of the COT ring with increased planarity, which led to an enhancement of the antiaromaticity.