Porphyrin/Quinoidal-Bithiophene-Based Macrocycles and Their Dications: Template-Free Synthesis and Global Aromaticity |
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Authors: | Dr Longbin Ren Dr Tullimilli Y Gopalakrishna Dr In-Hyeok Park Yi Han Prof Jishan Wu |
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Institution: | Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore, Singapore |
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Abstract: | We report the template-free synthesis and characterization of a new type of porphyrin/quinoidal-bithiophene-based conjugated macrocycle. X-ray crystallographic analysis of the dimer ( 2MC ) revealed a cyclophane-like geometry with large dihedral angles between the porphyrin and the neighboring thiophene rings, and NMR measurements and theoretical calculations confirmed a localized aromatic character of the porphyrin/thiophene rings and quinoidal character of the bithiophene linkers. Restricted rotation of the thiophene rings linked to the porphyrin unit was observed by variable-temperature NMR measurements. The dication ( 2MC2+ ) adopts a chair-shaped conformation to facilitate π-electron delocalization around the whole macrocycle. As a result, the molecule is globally aromatic, with a dominant 54 π conjugation pathway. The trimer ( 3MC ) also shows localized aromatic character of porphyrin rings and conformational flexibility, but its dication ( 3MC2+ ) is rigid and globally aromatic with a dominant 82 π conjugation pathway. |
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Keywords: | Globale Aromatizität Makrocyclen Porphyrine Chinoide Thiophen |
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