An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical |
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Authors: | Tullimilli Y. Gopalakrishna Dr. J. Sreedhar Reddy Prof. Dr. Venkataramanarao G. Anand |
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Affiliation: | Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune–411008, Maharashtra (India) |
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Abstract: | Ever since the discovery of the trityl radical, isolation of a stable and neutral organic radical has been a synthetic challenge. A (4n+1)π open‐shell configuration is one such possible neutral radical but an unusual state between aromatic (4n+2)π and antiaromatic (4n)π electronic circuits. The synthesis and characterization of an air‐ and water‐stable neutral 25π pentathiophene macrocyclic radical is now described. It undergoes reversible one‐electron oxidation to a 24π antiaromatic cation and reduction to a 26π aromatic anion, thus confirming its amphoteric behavior. Structural determination by single‐crystal X‐ray diffraction studies revealed a planar configuration for the neutral radical, antiaromatic cation, and aromatic anion. In the solution state, the cation shows the highest upfield chemical shift ever observed for a 4nπ system, while the anion adhered to aromatic nature. Computational studies revealed the delocalized nature of the unpaired electron as confirmed by EPR spectroscopy. |
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Keywords: | electron transfer macrocycles polythiophenes porphyrinoids radicals |
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