# Diketo[n]CPPs as chiral and shape-adaptive fullerene hosts and precursors to DBP[n]CPPs

## TL;DR

Researchers synthesized chiral nanohoops that bind fullerenes efficiently and show high fluorescence, which could be useful in optoelectronic materials.

## Contribution

The synthesis of chiral diketo[n]CPPs and their fullerene binding properties are newly demonstrated.

## Key findings

- Diketo[8]CPP and diketo[9]CPP have high fluorescence quantum yields of 87% and 92%, respectively.
- Diketo[n]CPPs bind fullerenes C60 and C70 with similar binding constants (5 × 10⁴ to 7 × 10⁴ M⁻¹).
- ESI-MS and collision experiments confirmed the formation and stability of host–guest complexes with fullerenes.

## Abstract

Conjugated nanohoops, such as [n]cycloparaphenylenes ([n]CPPs) and derivatives, exhibit unique structural and optoelectronic properties, making them promising candidates for applications in optoelectronic materials, and as hosts for supramolecular chemistry. Using π-systems unsymmetric to rotation or incorporating chiral units can furnish chiral nanohoops. We herein present the synthesis and characterization of diketo[8]- and diketo[9]CPPs, along with their corresponding dibenzo[a,e]pentalene (DBP) derivatives, DBP[8]- and DBP[9]CPP. Due to the central chirality of the diketone-units, these nanohoops are chiral without the possibility of racemization through rotation and show distinct chiroptical properties. The diketo[n]CPPs possess high fluorescence quantum yields of 87% (n = 8) and 92% (n = 9). The shape-adaptive properties of diketo[n]CPPs, facilitated by the tunable kink angle of the diketo unit, enable efficient host–guest interactions with fullerenes. Fluorescence titration revealed a similar binding constant for both fullerenes C60 and C70 (5 × 104 to 7 × 104 M−1 in toluene), corroborated by DFT calculations that illustrate adaptive changes in nanohoop geometry upon fullerene complexation. ESI-MS is employed to generate ionized [1 : 1] host–guest complexes of diketo[9]CPP and DBP[9]CPP with C60 and C70 as guests. The relative stabilities of these complexes are evaluated in energy-resolved collision experiments.

Diketo[8]CPP and diketo[9]CPP are chiral conjugated nanohoops with high photoluminescence quantum yields and shape-adaptive fullerene binding.