Phase Behavior and Liquid Crystalline Ordering of 2Catenated Molecular Systems

XT Xie and L Wu and H Sun and XZ Yan and XY Zhu, MACROMOLECULES, 56, 6189-6198 (2023).

DOI: 10.1021/acs.macromol.3c00186

Catenatedmolecule as one type of mechanically interlockedmolecule(MIM) is formed by not only conventional covalent bonds but also mechanicalbonds between molecular rings. The 2catenane 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 2catenane fordeepening our understanding of the role of the mechanical bond indetermining the phase behavior of catenated molecular systems. Wedemonstrate that the mechanical bond in 2catenane 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 2catenanemolecule 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 2catenane with largepore sizes shows cubatic ordering due to the interpenetration of macrocycles.The diffusion behavior of 2catenane confirms the molecular fluidityin the smectic layer, and interlayer displacement behaves as subdiffusivein the smectic state of 2catenane.

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