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

In order to stabilize neutral radicals with curved surface pi-system and to evaluate their pi-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 pi-spin density is delocalized onto the corannulene moiety with most of the pi-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 pi-spin delocalization onto the corannulene moiety is lower than that of the oxoverdazyl derivative with corannulene in the ground state. A degree of pi-conjugation between the corannulene moiety and the iminonitroxide moiety has also been evaluated by UV-Vis measurements. (c) 2005 Elsevier Ltd. All rights reserved.