A Stable All‐thiophene‐based Core‐modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at Different Oxidation States

Abstract

A soluble and stable core-modified [38]octaphyrin, MC-T8, containing eight thiophene rings was synthesized by Yamamoto coupling followed by oxidative dehydrogenation. X-ray crystallographic analysis revealed a nearly planar backbone, and the molecule is globally aromatic with a dominant 38π conjugation pathway. The dication MC-T82+ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC-T84+ becomes aromatic again, with a shallow-bowl-shaped geometry. Both the neutral compound and the dication demonstrated open-shell diradical character with a small singlet–triplet energy gap (−2.70 kcal mol−1 for MC-T8 and −3.78 kcal mol−1 for MC-T82+), and they are stable owing to effective spin delocalization.