Interfacial Organization of Y-Shaped Rod-Coil Molecules Packed into Cylindrical Nanoarchitectures

The relationship between molecular structure and supramolecular morphology in the self-assembly of rod-coil molecules with oligoether chains

Controlling the morphology of rod-coil molecular aggregates is crucial for studying and obtaining functional materials with exceptional properties. In this paper, we report the construction of rod-coil molecular nanoaggregates with well-defined structures. The rod-coil molecules, labeled 1a-1d, consist of a rod section, composed of phenyl and biphenyl groups, and oligoether chains with 7 and 12 repeating units. The final assembled structures showed either oblique or hexagonal columnar structures, depending on the length of the coils in the bulk state. Interestingly, in water, molecules 1a and 1c self-assemble into scrolled nanofibers and cylindrical micelles. Instead, molecules 1b and 1d, which have methyl groups decorated at the interface of the rod and coil sections, self-organize into helical nanofibers and nanorings, respectively. Thus, controlling the length of the coil chains and inserting lateral methyl groups is an effective strategy to construct precise rod-coil molecular assemblies in the bulk and in aqueous solution.

Chiral assemblies of achiral rigid-flexible molecules at the air/water interface induced by silver(I) coordination

Chiral films are obtained from achiral rigid-flexible molecules. Due to hydrogen bonding and steric constraints, these molecules can self-assemble into chiral assemblies at the air/water interface upon compression. When the molecules are spread on a subphase containing AgNO(3), they form a stable monolayer through coordination with Ag(I) ions, as confirmed by surface pressure-area isotherms, UV/Vis and FTIR spectroscopy, and AFM. More interestingly, macroscopic chirality was detected in the Ag(I)-coordinated films by circular dichroism measurements. The formation mechanisms of the two kinds of chiral films are briefly discussed.

Chiral assembly from achiral rod-coil molecules triggered by compression at the air-water interface

A series of achiral rod-coil molecules consisting of an oligo(p-phenylene) conjugated rod with a poly(ethylene oxide) or poly(propylene oxide) coil laterally attached through an imidazole linkage were synthesized, and their interfacial behaviors were investigated. Compounds 1a and 1b have a similar surface behavior with a shoulder indicating a transformation of rod segments from flat-on to vertical orientation. Interestingly, CD and AFM suggest chiral films are formed when the LB films were deposited after the shoulder. Although compound 1c shows different surface behavior because the PEO chains dissolved into water upon compression, macroscopic chirality was also detected. In contrast, compound 2, based on a reduced conformational rigidity of the aromatic rod segment, does not form chiral assemblies. Combining the data collected, the cooperative interaction of the hydrogen bond between the molecules and pi-pi stacking as well as the steric constraint between the aromatic rod segments are responsible for the macroscopic chirality. Such kind of stacking can be realized through a molecular design and a lateral compression. A deep insight into the relationship between the molecular structure and the chirality was gained.