Synergistic Effects of Steric Hindrance, Dipole Interactions, and External Mechanical Force on Modulating Rotor Dynamics in Pillar-Layered Metal–Organic Frameworks

The introduction of polar rotors is a potential strategy for improving the functionality and tunability of pillar-layered metal–organic frameworks (PLMOFs). However, the complexity due to electromechanical coupling hinders the in-depth understanding of rotor dynamics in polar PLMOFs. In this article, we employed ab initio molecular dynamics (AIMD) combined with well-tempered metadynamics (WT-MTD) to systematically investigate the rotational behavior of rotors in polar PLMOFs, with a focus on the synergistic effects of steric hindrance, dipole interactions, and external mechanical force. By comparing the relative energy of polar Cu₂(fbdc)₂(dabco) and nonpolar Cu₂(bdc)₂(dabco) under external mechanical force, we found that the longer-range dipole interactions alter the rotor’s conformation and reduce the steric hindrance between the rotor and the framework. This leads to a lower rotational barrier and a more monotonic energy profile. Furthermore, the dipole–dipole interactions between adjacent rotors enhance the rotor’s sensitivity and flexibility through redistribution of charge density and deformation of the rotor, which may be critical for reducing the rotational barrier under external mechanical force. Based on these findings, we propose a mechanical strategy utilizing interlayer stress in a designed MOF-on-MOF structure for modulating polar rotor dynamics, which provides a useful method for developing PLMOF functional materials with tunable rotational properties.