National Synchrotron Light Source Seminar

Since their discovery, columnar mesophases have become increasingly important in fundamental research and in practical applications1,2 due to their peculiar supramolecular architectures allowing one-dimensional charge transport. Although the most studied columnar phases are formed by disc-shaped molecules, it is now recognized that such phases can also be formed by dendrimers, main- or side-chain polymers with or without mesogenic moieties, phasmids and board-like molecules. The electronic and optical properties of the liquid crystalline (LC) phases strongly depend on the chemical structure of the molecules and the way there are self-assembling at different scales in bulk and at interfaces. In particular, the organization at the mesoscopic scale, spanning from several nanometers to some hundreds of nanometers, must be tailored to control features such as the size and orientation of the LC mono-domains.
The lecture will show and discuss how the influence of the molecular architecture (degree of flexibility of molecules) and specific interactions such as hydrogen bonding can play on the supramolecular organization. We will demonstrate that using hydrogen bonds to “clamp” the molecules along the columns results in the smallest inter-molecular distance (3.18 Å) ever found for columnar mesophases3. In the same time, it would be shown how flexible star-shaped molecules self-assemble to give rise to a unique double helical crystal. An AFM image of such a structure can be seen in fig.1. Interestingly, the growth of the helical crystals can be tailored at the scale of one columnar diameter (2-4 nm) via a monotropic columnar mesophase4. This scale is one order of magnitude smaller than the characteristic size of the block-copolymer morphology. By actively playing with the chemical structure we can identify some of the factors responsible for the structure formation
Ultimately, since the use of columnar phases in opto-electronic devices imply the proper orientation of the