Discotic Liquid Crystals of Nanographenes. Self-assembly and molecular dynamics

DIPC Seminars

Prof. George Floudas, Dept. of Physics, University of Ioannina, Greece
Donostia International Physics Center (DIPC).Paseo Manuel de Lardizabal, 4, Donostia
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Discotic Liquid Crystals of Nanographenes. Self-assembly and molecular dynamics Discotic liquid crystals (DLC), consisting of rigid disk-shaped aromatic cores and disordered alkyl substituents tend to organize into columnar supramolecular structures with applications as molecular wires. Their self-assembly is driven by noncovalent intermolecular interactions favoring the π-stacking of aromatic cores and the unfavorable interactions between the cores and the alkyl chains leading to nanophase separation. The role of aliphatic chains is also important as they provide with the required solubility and further impart a rich thermotropic behavior and fast molecular dynamics. X-ray scattering revealed two main columnar structures in HBCs: a liquid crystalline phase (Colh) at higher temperatures composed of columns that are further organized in a hexagonal lattice and a crystalline phase (Cr) at lower temperatures composed of columns of tilted disks (i.e. “herringbone”) in a monoclinic unit cell. The kinetics of phase transformation was investigated by Infrared Spectroscopy and Related Techniques over an extraordinary broad time-window (1-105 s). Identical kinetics were found suggesting that both the core and the alkyl chains simultaneously drive the system from the undercooled Colh to Cr phase. Non-linear phenomena on the phase transformation were also studied. Applications of DLC as nanoscale conductive devices (i.e. molecular wires) rely on the optimal stacking of the aromatic cores that allow for charge carrier mobility along the columnar axis. Herein we report on the effect of molecular structure on the thermodynamics, self-assembly,the hierarchy of dynamics, the kinetics of structure formation and the viscoelastic properties of a class of DLC, the hexa-peri-hexabenzocorenes.