Ferroelastic phase transition and switchable dielectric behavior associated with ordering of molecular motion in a perovskite-like architectured supramolecular cocrystal

An organic supramolecular co-crystal with a perovskite-like architecture, dabco.p-nitrophenol (1, dabco = 1,4-diazabicyclo[2.2.2]octane), which undergoes a reversible ferroelastic phase transition with the Aizu notation of 2/mF (1) over bar at around 128 K (T-c), displays switchable dielectric behaviors triggered by the ordering of molecular rotational motion in the dabco moieties. Its transition dynamic behaviors were investigated by variable-temperature crystal structure analysis, thermal analysis and dielectric measurements. The results reveal that in the high-temperature state, 1 behaves as a molecular rotor, in which the dabco moiety rotates around the N center dot center dot center dot N axis as a rotator, and the neutral p-nitrophenol part acts as a stator jointed through the intermolecular N-H center dot center dot center dot OH-bonds. Below the T-c, the rotational motions of the rotator are frozen and the whole setup becomes much more ordered, corresponding to its low-temperature stable phase. Moreover, study of the deuterated analogue of 1 excludes the possibility of proton movement along N-H center dot center dot center dot O bonds as the microscopic origin of the phase transition. The findings provide a useful strategy to explore a new class of compounds exhibiting distinct switchable dielectric performances for application in the ferroic-related field.