Diketo[n]CPPs as Chiral and Shape-adaptive Fullerene Hosts and Precursors to DBP[n]CPPs

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]CPP, 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 property of diketo[n]CPPs, facilitated by the tunable angle of the diketo unit, enables efficient host-guest interactions with fullerenes. Fluorescence titration revealed similar binding constant for both fullerenes C60 and C70 (5 × 10^4 – 7 × 10^4 M^−1 in toluene), corroborated by DFT calculations that illustrate adaptive changes in nanohoop geometry upon fullerene complexation