While liquid crystals (LCs) possess diverse structures, they are often oversimplified as requiring a “hard” ring/core component and a “soft” acyclic/tail component as well as some sufficient degree of spacial anisotropy (rods/calamitic or disks/discotic). Small molecule rod-like calamitic LCs without tails are well known but small molecule disc-like LCs without tails are extremely rare. The technical goal of this project is to design, prepare and characterize simple aromatic molecules with no tails that display discotic/columnar behavior. Such materials are potentially important as organic semiconductor materials.

We have prepared triphenylene compounds with careful control of fluorination and other substitution. These molecules were prepared using a series of organometallic C-C bond forming reactions and a final photochemical photocyclodehydrofluorination (PCDHF) reaction; specifically developed for the controlled preparation of selectively fluorinated polynuclear aromatics. New materials have been routinely characterized by standard chemical/physical techniques (NMR, GC-MS, DSC, POM). A subset of materials identified as potentially discotic are subjected to further additional characterization methods (TOF, XRD).

This approach has led to the discovery of a growing class of tail-free triphenylene discotic materials. We are in the process of systematically modifying the structure of the triphenylenes (varying the number, identity and location of small substituents) in order to understand the underlying molecular features required to deliver discotic behavior in the absence of soft segments. As we continue to identify the specific molecular and intermolecular contributions involved we can then selectively turn them on and off to deliver a well-controlled set of phase transitions including columnar phases.