A Pyrrole-Fused Nanographene and its Edge-Perchlorinated Derivative Featuring a Corannulene Core and Five N-doped Heptagons

Abstract

A pyrrole-fused analogue of warped nanographene, designated as deca-nitrogen doped ′WNG′ (azaWNG), was synthesized through the annular fusion of decapyrroylcorannulene. The resulting azaWNG exhibited extremely limited solubility in common organic solvents and was characterized solely by mass spectrometry. Theoretical calculations revealed that azaWNG has a sunflower-like molecular structure with electron-deficient corannulene as the core and electron-rich pyrrole as the petals, demonstrating a significantly narrower energy gap compared to all-carbon WNG. To improve its solubility and facilitate precise structural characterization, iodine monochloride was utilized for edge-perchlorination of azaWNG, enabling successful separation and purification of chlorinated azaWNG in solution phase. X-ray crystallography analysis unequivocally confirmed that edge-perchlorinated azaWNG contains 5 heptagons and 11 pentagons embedded within the warped π skeleton. Cyclic voltammetry measurements indicated that the first oxidation potential of azaWNG is −0.59 V, representing the lowest value reported for any previously studied aza-nanographene. Consequently, azaWNG can be readily oxidized by AgPF₆ or even atmospheric oxygen to yield stable oxidation states, as corroborated by UV/Visible absorption spectroscopy; this behavior is attributed to the fusion of ten pyrroles around corannulene. This work marks the first instance of nitrogen doping in WNG (C₈₀H₃₀), underscoring the significant modification to electronic structure induced by such doping.