# Host–Guest Interactions in the C59N•⊂[10]CPP Supramolecular Radical

## TL;DR

This study explores the interaction between an azafullerene radical and a nanoring structure using EPR and DFT to understand their supramolecular complex.

## Contribution

The study reveals weak but significant host-guest interactions in a supramolecular radical using ESEEM and DFT.

## Key findings

- EPR measurements identified two spin components in C59N•⊂[10]CPP monomers and oligomers.
- ESEEM data showed strong coupling to the 14N atom near the radical carbon in azafullerene.
- Calculated hyperfine coupling constants aligned well with experimental results, confirming structural insights.

## Abstract

A remarkable stability
of a supramolecular radical comprising
an
azafullerene (C59N•) radical sterically
protected by a [10]cycloparaphenylene ([10]CPP) nanoring, C59N•⊂[10]CPP, has recently been observed by
various experimental probes. In order to investigate the host–guest
interaction in these supramolecular complexes, we carried out electron
paramagnetic resonance (EPR) measurements, theoretically supported
by density functional theory (DFT) calculations. The continuous wave
(CW) EPR spectrum shows the presence of two active spin components:
C59N•⊂[10]CPP monomers that can
in certain cases polymerize into oligomeric radicals. Two- and three-pulse
electron spin echo envelope modulation (ESEEM) measurements allow
for determination of experimental hyperfine coupling constants for 13C and 1H atoms and also show the strong coupling
to the 14N atom adjacent to the radical C of the azafullerene.
These experimental hyperfine coupling constants reasonably agree with
those calculated for the DFT optimized supramolecular structures.
The results are consistent with a small spin delocalization from the
guest (C59N•) to the host ([10]CPP),
thereby explaining weak but non-negligible interaction between them.
Our study demonstrates that ESEEM experiments in alliance with DFT
computations can offer valuable insights into the radical host–guest
structures.