Guest molecule dynamics and ferroelectric transition in a clathrate compound

Low molecular weight glass formers encapsulated within clathrate structures offer a singular testground to study the intricate interplay of confined molecular motion and ferroelectric properties. Using broadband dielectric spectroscopy (BDS), we investigate the dynamic behavior of 1-propyl-1H-imidazole within a supramolecular enclosure formed by duad semicage p-tert-butylcalix[4]arene. Unlike the bulk liquid, where the dielectric spectrum is dominated by the structural relaxation, the clathrates paraelectric phase reveals two distinct molecular relaxation processes. Aided by quantum chemical calculations, the slow process is assigned to head-to-tail reorientations of the guest molecule, while the faster process arises from intramolecular fluctuations of the imidazole ring. These dynamics freeze as the system transitions to the ferroelectric state via a second-order phase change that has been characterized by photopyroelectric calorimetry.