Search for: All records

Abstract A single‐crystal X‐ray study of a fullerene‐imidazole adduct at nine temperatures (80 K≤T≤480 K), accompanied by energy calculations, strongly suggested thermal motion of the C₆₀moiety with respect to the imidazolium heterocycle. Analysis of the anisotropic displacement parameters, calculations of frequencies, and the refinement of disorder models for the crystal at four temperatures (230 K≤T≤380 K) lead to the conclusion that the rotator is moving at all temperatures. The rotation barrier is low, with one preferred crystallographic site and several other energy minima. 

Ground state destabilization is a promising strategy to modulate rotational barriers in amphidynamic crystals. DFT studies of polar phenylenes installed as rotators in pillared-paddle wheel metal-organic frameworks were performed to investigate the effects of ground state destabilization on their rotational dynamics. We found that as the steric size of phenylene substituents increases the ground state destabilization effect is also increased. Specifically, a significant destabilization of the ground state energy occurred as the size of the substituents increased, with values ranging from 2 kcal/mol to 11.7 kcal/mol. An evalua-tion of the effects of substituents on dipole-dipole interaction energies and rotational barriers suggest that it should be possi-ble to engineer amphidynamic crystals where the dipole-dipole interaction energy becomes comparable to the rotational barri-ers. Notably, dipole-dipole interaction energies reached values ranging from 0.6 kcal/mol to 2.4 kcal/mol. We propose that careful selection of polar substituents with different size may help create temperature-responsive materials with switchable collective polarization.