Abstract
Zeolites represent inorganic solid-state materials with porous structures of fascinating complexity. Recently, significant progress was made by reticular synthesis of related organic solid-state materials, such as metal-organic or covalent organic frameworks. Herein we go a step further and report the first example of a fluid honeycomb mimicking a zeolitic framework. In this unique self-assembled liquid crystalline structure, transverse-lying π-conjugated rod-like molecules form pentagonal channels, encircling larger octagonal channels, a structural motif also found in some zeolites. Additional bundles of coaxial molecules penetrate the centres of the larger channels, unreachable by chains attached to the honeycomb framework. This creates a unique fluid hybrid structure combining positive and negative anisotropies, providing the potential for tuning the directionality of anisotropic optical, electrical and magnetic properties. This work also demonstrates a new approach to complex soft-matter self-assembly, by using frustration between space filling and the entropic penalty of chain extension.
Highlights
Zeolites are well-known inorganic solid-state materials with well-defined porous framework structures, used for gas storage, separation and catalytic applications[1,2]
The honeycomb channels are filled with flexible chains laterally attached to the aromatic rods
As shown in previous work, the volume of the flexible chains relative to the rod length determines the size and shape of the channel cross-section, which range from triangular to hexagonal and beyond[9,10,11]
Summary
Zeolites are well-known inorganic solid-state materials with well-defined porous framework structures, used for gas storage, separation and catalytic applications[1,2]. The cross-sectional shape of the channels is mainly determined by geometric rules, whereas the hydrogen bonding, the segregation of polar from apolar units and rigid from flexible segments, as well as anisotropic interactions between the rod-like cores, contribute to the stabilization of the periodic honeycomb structures Putting it crudely, the periodic tiling in the xy plane ensures low energy, the disorder along z axis secures relatively high entropy. Do we get soft honeycombs with largely disparate cells (pentagonal and octagonal), but the imposed frustration results in an unprecedented type of LC where mesogens orient both perpendicular and parallel to the director axis These complex superstructures are the result of a newly adopted strategy by introducing entropy controlled packing frustration to the previously developed concept of LC honeycombs
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