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A Stable All-Thiophene-Based Core-Modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at
Yong Ni1, Tullimilli Y Gopalakrishna1, Shaofei Wu1
1Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore, Singapore.
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.
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