A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators†

Comprehensive Summary As an extended model of conventional molecular rotors, a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here. The supramolecular self-assembly of 18-crown-6 host and two rotator-containing ion-pair guests affords a three-in-one cocrystal, (2-NH3-iBuOH)(18-crown-6)[ZnBr3(H2O)], in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators. On the basis of the variable-temperature single-crystal X-ray diffraction, variable-temperature/frequency dielectric response, density functional theory calculations, and molecular dynamics simulations, it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature, and more importantly, could be controlled by a reversible polar-to-polar structural phase transition, i.e., from a single-(polar rotator) state at low-temperature phase to a mixed-dual-(polar rotator) state in the vicinity of transition, and to an unusual synchronized-dual-(polar rotator) state at high-temperature phase.

Automated summary

This research presents a novel crystalline molecular rotor with two discrete polar rotators. Experimental results show that these rotators experience an enhanced rotation with increasing temperature, and can be controlled by a reversible polar-to-polar structural phase transition.