Corannulene and its complex with water: a tiny cup of water

We report the results of a broadband rotational spectroscopic study of corannulene, $C_{20}H_{10}$, all of its singly substituted $^{13}$C isotopologues, and a complex of corannulene with one molecule of water. Corannulene is a polycyclic aromatic hydrocarbon (PAH) with a curved structure that results in a large dipole moment. Observation of $^{13}C$ isotopic species in natural abundance allowed us to precisely determine the molecular structure of corannulene. The differences between the experimental C–C bond lengths correlate to the double-bond character predicted using Kekule's resonance structures. In the case of $C_{20}H_{10}–H_2O$, the water molecule is found to reside inside the bowl-like structure of corannulene. Our experimental and theoretical results indicate that the water molecule rotates freely around its $C_2$ axis and that dispersion interactions are the dominant contribution to the binding