Biomedical Engineering Reference
In-Depth Information
systems, but also as functional materials for device applications such as
one-dimensional conductors, photoconductors, light-emitting diodes,
photovoltaic solar cells, gas sensors, etc. [69]. In contrast, ionic DLCs have
been given much less attention as organic semiconductors, particularly
because of the uncertainty of localized charges which may act as ionic
impurities, and thus may create obstacles to their performance in elec-
tronic devices. It was also proposed that as localized charges may func-
tion as traps for holes and electrons, their electronic properties may be
disturbed in the presence of ionic environment. But they are extremely
potential candidates that show high ionic and electrical conductivity
with particularly promising behavior such as better alignment on sub-
strates (through spontaneous self-organization of the ionic mesophase)
and compatibility with biological function because of water solubility, and
they may be easily processed by several cost-ef ective techniques (such as
printing and electrostatic layer-by-layer deposition).
In general, ionic interactions tend to stabilize the mesophases formed
by conventional DLCs, due to an ion-ion stacking and electrostatic inter-
actions. h ese additional long-range ionic interactions control the rela-
tive stacking orientations within the columnar mesophase and thus the
molecular dynamics. h ese kinds of ionic DLCs are expected to serve as
novel anisotropic ion-conductors, ordered reaction media or templates for
synthesis of mesoporous nanomaterials and electrolytes in dye-sensitized
solar cells. Most of the reports on ionic DLCs have focused on the synthe-
sis and mesomorphic behavior of several dif erent discotic cores and their
dependence on structural changes. However, there are only a few reports
which described their electronic and other materials properties.
In this part of the chapter, we will focus on the recent studies of ionic
thermotropic DLCs and their potential applications. We have categorized
all ionic discotic compounds based on the type of core structure. In each
core, compounds are subdivided into two main groups: monomeric ionic
DLCs (both charged side chains and charged aromatic core or charged
group directly attached to the discotic core) and oligomeric/polymeric
ionic DLCs. h is will serve as a general overview of ionic DLCs and their
structure-property relationship based on each core.
9.3.1 Classii cation Based on Dif erent Cores
9.3.1.1 Benzene
With the aim of preparing charge transfer complexes containing both donor
and acceptor moieties within the same molecule, Kato and coworkers [70,
