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  4,7,11,14,18,21-Hexa-tert-butyltribenzodecacyclenyl Radical: A Six-Stage Amphoteric Redox System

 

 

Multi-stage amphoteric redox compounds have been subject to extensive investigation. In these chemistries, phenalenyl structures play an important role to develop amphoteric redox properties. Some closed-shell compounds containing phenalenyl units have shown amphoteric redox properties with a small numerical sum (E1sum) of first oxidation (E1ox) and reduction (E1red) potentials. On the other hand, open-shell compounds are also potential candidates for redox systems. Thus we designed a open-shell compound containing phenalenyl units.

The target compound is a hydrocarbon radical containing three phenalenyl units. This neutral radical was prepared from commercially available decacyclene in ten steps. Cyclic voltammogram of the neutral radical exhibits six reversible redox waves with a small E1sum. This finding indicates that the neutral radical behaves as six-stage amphoteric redox system.

To investigate electronic structures of the redox states, some redox species of the radical were generated from the neutral state and characterized by NMR, ESR, UV-Vis-NIR spectroscopies, and theoretical calculations. The spin and the charges are delocalized over the entire C3 molecule of trication, monoradical dication, neutral radical, and trianion species. On the other hand, monoanion and monoradical dianion species show the localization of the spin and the charges on one phenalenyl unit, which are consistent with the distorted C2 structure caused by the Jahn-Teller effect.

 

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