Minimalist columnar liquid crystals: influence of fluorination on the mesogenic behavior of tetramethoxytriphenylene derivatives†

Conventional columnar liquid crystals are almost invariably functionalized with multiple long aliphatic tails. In contrast, the molecule 1,2,3,4-tetrafluoro-6,7,10,11-tetramethoxytriphenylene is unusual as it has a broad columnar mesophase despite the fact that it has only four minimal-length methoxy tails distributed equally in two rings. Here, the full set of analogous tetramethoxytriphenylene molecules with zero to four fluorine atoms in the remaining ring are synthesized using photocyclodehydrofluorination (PCDHF) or a modified Scholl process for the final ring closure reaction, and their mesogenic properties are examined. Six out of the ten target molecules were found to be mesogenic. We found that a minimum of two fluorine substituents are required to form the mesophase, and one of them must be at the 1-position. These extremely short-tailed columnar liquid crystals possess a relatively simple molecular structure and can serve as model systems for understanding the interactions that are fundamental to the formation of a columnar mesophase, its properties and potential applications.