Photophysical and theoretical investigations of the [8]cycloparaphenylene radical cation and its charge-resonance dimer

Abstract

Treatment of [8]cycloparaphenylene (CPP) with the oxidant triethyloxonium hexachloroantimonate afforded an isolable radical cation of the parent carbon nanohoop. The photophysical properties of [8]CPP˙⁺SbCl₆⁻ were investigated, showing the presence of two absorptions at 535 nm and 1115 nm. Time-dependent density functional theory (DFT) calculations were used to examine these optical absorptions, revealing a delocalized, quinoidal carbon nanohoop. Upon mixing with neutral [8]cycloparaphenylene, the formation of an unusually strong charge-resonance complex ([8]CPP₂)˙⁺ was observed. Spectroscopic and computational studies were indicative of extensive intermolecular charge delocalization between the two carbon nanohoops as well.