Computational Study of Ground-State Destabilization Effects and Dipole–Dipole Interaction Energies in Amphidynamic Crystals

Ground-state
destabilization is a promising strategy to modulate
rotational barriers in amphidynamic crystals. Density functional theory
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 to 11.7 kcal/mol.
An evaluation of the effects of substituents on dipole–dipole
interaction energies and rotational barriers suggests that it should
be possible to engineer amphidynamic crystals where the dipole–dipole
interaction energy becomes comparable to the rotational barriers.
Notably, while pure dipole–dipole interaction energies reached
values ranging from 0.6 to 2.4 kcal/mol, the inclusion of electronic
and steric effects can alter dipolar orientations to significantly
greater values. We propose that careful selection of polar substituents
with different sizes may help create temperature-responsive materials
with switchable collective polarization.