A Stable All‐Thiophene‐Based Core‐Modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at Different Oxidation States
Yong Ni, Tullimilli Y. Gopalakrishna, Shaofei Wu, Jishan Wu
Abstract
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‐T8 2+ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC‐T8 4+ 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‐T8 2+ ), and they are stable owing to effective spin delocalization.