Phase Behavior and Liquid Crystalline Ordering of [2]Catenated Molecular Systems

Catenatedmolecule as one type of mechanically interlockedmolecule(MIM) is formed by not only conventional covalent bonds but also mechanicalbonds between molecular rings. The [2]catenane molecule consists oftwo mechanically interlocked macrocycles, which is a typical examplecombining nonconvex molecular rings and mechanical bonds. In thisstudy, coarse-grained molecular dynamics simulation is performed toinvestigate the thermodynamics and phase behavior of [2]catenane fordeepening our understanding of the role of the mechanical bond indetermining the phase behavior of catenated molecular systems. Wedemonstrate that the mechanical bond in [2]catenane destabilizes thepacking between molecular rings and also provides an additional internaldegree-of-freedom for two interlocked macrocycles, which shows anentropy-driven molecular conformation transition from free-rollingto cross-stacking with respect to density increase. The [2]catenanemolecule with a large ring size undergoes a transition from disorderto a smectic layering structure with high free volume. Different fromconventional smectics, the smectic state in [2]catenane with largepore sizes shows cubatic ordering due to the interpenetration of macrocycles.The diffusion behavior of [2]catenane confirms the molecular fluidityin the smectic layer, and interlayer displacement behaves as subdiffusivein the smectic state of [2]catenane.

Automated summary

In this study, coarse-grained molecular dynamics simulation is used to investigate the thermodynamics and phase behavior of [2]catenane. The mechanical bond in [2]catenane not only destabilizes the packing between molecular rings but also provides additional internal degrees of freedom. The [2]catenane molecule undergoes a conformation transition from free-rolling to cross-stacking with respect to density increase, and exhibits a smectic layering structure with high free volume, showing cubatic ordering due to the interpenetration of macrocycles.