In-Plane
Aromaticity in Cycloparaphenylene Dications:
A Magnetic Circular Dichroism and Theoretical Study
- Publication date
- Publisher
Abstract
The electronic structures of [8]cycloparaphenylene
dication ([8]CPP<sup>2+</sup>) and radical cation ([8]CPP<sup>•+</sup>) have been investigated by magnetic circular dichroism (MCD) spectroscopy,
which enabled unambiguous discrimination between previously conflicting
assignments of the UV–vis–NIR absorption spectral bands.
Molecular orbital and nucleus-independent chemical shift (NICS) analysis
revealed that [8]CPP<sup>2+</sup> shows in-plane aromaticity with
a (4<i>n</i> + 2) π-electron system (<i>n</i> = 7). This aromaticity appears to be the origin of the unusual stability
of the dication. Theoretical calculations further suggested that not
only [8]CPP<sup>2+</sup> but also all [<i>n</i>]CPP (<i>n</i> = 5–10) dications and dianions exhibit in-plane
aromaticity