18 Electrochemical Functions of Nanostructured Liquid Crystals …
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formation of electrical double layers, due to the presence of the ion-conductive layers.
Moreover, hole hopping between the π-conjugated units made it possible to oxidize
distant LC molecules from the anode.
18.3 Nanosegregated π-Conjugated Liquid Crystals
18.3.1 Oligosiloxane Moieties as a Side Chain of Liquid
Crystals
As shown in Sect. 18.2, nanosegregation is an effective method to functionalize
LC materials by coupling the electronic transport with the ionic conductivity. An
ionic moiety introduced to the terminal of the alkyl side chain played a significant
role in the nanosegregation process. This fact indicates that not only a design of
π-conjugated functional units but also an engineering of side chains is effective to
create new functional LC materials.
Conventional liquid crystal molecules have rigid core units and flexible alkyl
side chains. One of the driving forces to form smectic or columnar structures is
nanosegregation between core units and alkyl side chains. Other than alkyl side
chains, hydrophilic oligoethylene oxide chains, perfluoroalkyl groups with small
polarizability are recognized to enhance nanosegregation and promote the formation of various superstructures in liquid crystal phases [15, 16]. Moreover, liquid
crystals bearing ionic moieties such as imidazolium groups form ion-conductive
liquid crystals which have one-dimensional columnar, two-dimensional lamellar,
and three-dimensional bicontinuous cubic structures [17–19].
The authors have paid an attention to oligosiloxane chains as a flexible side
chain of functional liquid crystals. Side-chain-type LC polymers consisting of a
polysiloxane backbone and mesogenic side chains have been investigated for the
application to LC elastomers [20]. Polysiloxanes bearing terthiophene side chains
exhibit photoconductivity [21].
On the other hand, ferroelectric liquid crystals bearing pentamethyl-1,3-disiloxane
or heptamethyl-1,3,5-trisiloxane chains at the terminals of alkyl side chains have also
been synthesized. Because of nanosegregation, layer structures are stabilized and they
sometimes indicate de Vries-type phase transition [22]. For rod-like liquid crystal
molecules exhibiting smectic phases, not a few liquid crystals have been designed and
synthesized. However, the advantage of oligosiloxane side chains has not been took
for columnar liquid crystals except for only one example of hexaalokoxytriphenylene
derivative [23].
The perylene bisimide derivatives have been known as red pigments and n-type
semiconductors. Various N-alkylated derivatives have been synthesized; however,
their solubilities in organic solvents are low and it is difficult to produce thin films
for device applications by solution processes. We synthesized perylene bisimide
derivatives bearing oligosiloxane chains at the terminals of alkyl side chains, as
363
formation of electrical double layers, due to the presence of the ion-conductive layers.
Moreover, hole hopping between the π-conjugated units made it possible to oxidize
distant LC molecules from the anode.
18.3 Nanosegregated π-Conjugated Liquid Crystals
18.3.1 Oligosiloxane Moieties as a Side Chain of Liquid
Crystals
As shown in Sect. 18.2, nanosegregation is an effective method to functionalize
LC materials by coupling the electronic transport with the ionic conductivity. An
ionic moiety introduced to the terminal of the alkyl side chain played a significant
role in the nanosegregation process. This fact indicates that not only a design of
π-conjugated functional units but also an engineering of side chains is effective to
create new functional LC materials.
Conventional liquid crystal molecules have rigid core units and flexible alkyl
side chains. One of the driving forces to form smectic or columnar structures is
nanosegregation between core units and alkyl side chains. Other than alkyl side
chains, hydrophilic oligoethylene oxide chains, perfluoroalkyl groups with small
polarizability are recognized to enhance nanosegregation and promote the formation of various superstructures in liquid crystal phases [15, 16]. Moreover, liquid
crystals bearing ionic moieties such as imidazolium groups form ion-conductive
liquid crystals which have one-dimensional columnar, two-dimensional lamellar,
and three-dimensional bicontinuous cubic structures [17–19].
The authors have paid an attention to oligosiloxane chains as a flexible side
chain of functional liquid crystals. Side-chain-type LC polymers consisting of a
polysiloxane backbone and mesogenic side chains have been investigated for the
application to LC elastomers [20]. Polysiloxanes bearing terthiophene side chains
exhibit photoconductivity [21].
On the other hand, ferroelectric liquid crystals bearing pentamethyl-1,3-disiloxane
or heptamethyl-1,3,5-trisiloxane chains at the terminals of alkyl side chains have also
been synthesized. Because of nanosegregation, layer structures are stabilized and they
sometimes indicate de Vries-type phase transition [22]. For rod-like liquid crystal
molecules exhibiting smectic phases, not a few liquid crystals have been designed and
synthesized. However, the advantage of oligosiloxane side chains has not been took
for columnar liquid crystals except for only one example of hexaalokoxytriphenylene
derivative [23].
The perylene bisimide derivatives have been known as red pigments and n-type
semiconductors. Various N-alkylated derivatives have been synthesized; however,
their solubilities in organic solvents are low and it is difficult to produce thin films
for device applications by solution processes. We synthesized perylene bisimide
derivatives bearing oligosiloxane chains at the terminals of alkyl side chains, as