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

Who: Prof. George Floudas, Dept. of Physics, University of Ioannina, Greece

Place: Donostia International Physics Center (DIPC).Paseo Manuel de Lardizabal, 4, Donostia

Date: Wednesday, 21 May 2014, 16:30

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 ?-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.

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