Modifying the liquid crystalline chessboard tiling : soft reticular self-assembly of side-chain fluorinated polyphiles

Abstract

Development of new functional materials requires the understanding of the fundamental rules of complex superstructure formation in self-assembling systems. Here we report new liquid crystalline honeycombs based on reticular self-assembly of bolapolyphilic rods with two mutually incompatible and branched side-chains, one a semiperfluorinated, the other one a non-fluorinated alkyl chain, all derived from the chessboard tiling by cell deformation due to distinct modes of tilting of π-conjugated rods within or out of the crystallographic plane. Among them the new square + rhomb tiling and a stretched rectangular “chessboard” tiling, both with alternatingly filled prismatic cells, are constructed. Out of plane tilting leads to cell shrinking and cell deformation. Nonfluorinated polyaromatic cores allow a continuously changing tilt, retaining the square cells by simultaneously tilting all molecules, associated with an inversion of the birefringence via an optically isotropic state. In contrast, fluorinated cores with different discrete face-to-face stacking modes can assume only discrete tilt angles, which provides rectangular cells with only two walls being tilted. The system offers even more phases including single-color cells with sparingly packed “voids” and a three-color rhomb tiling with additional mixed cells. The research uncovers basic rules of reticular self-assembly by formation of soft multi-functional liquid-crystalline materials.