Spin delocalization on curved surface π-system: Corannulene with iminonitroxide

In order to stabilize neutral radicals with curved surface π-system and to evaluate their π-spin structures, we recently reported design and synthesis of an oxoverdazyl derivative with corannulene as the first stable bowl-shaped neutral radical. Spectroscopic and theoretical studies revealed that appreciable amount of π-spin density is delocalized onto the corannulene moiety with most of the π-spin density localized on the oxoverdazyl moiety. In this study, we have designed and synthesized an iminonitroxide derivative with corannulene as a novel bowl-shaped neutral radical with a higher stability than the oxoverdazyl derivative with corannulene. ESR/ENDOR/TRIPLE spectroscopies and density functional theory calculations have shown that the π-spin delocalization onto the corannulene moiety is lower than that of the oxoverdazyl derivative with corannulene in the ground state. A degree of π-conjugation between the corannulene moiety and the iminonitroxide moiety has also been evaluated by UV–Vis measurements.

Graphical abstractCorannulene with iminonitroxide radical has been designed and synthesized as a novel stable bowl-shaped neutral radical. ESR/ENDOR/TRIPLE spectroscopies and density functional theory calculation have shown that appreciable amount of π-spin is delocalized onto the corannulene moiety, although most of the π-spin density is localized on the iminonitroxide moiety.Figure optionsDownload full-size imageDownload as PowerPoint slide