18 Electrochemical Functions of Nanostructured Liquid Crystals …
361
18.2 Electrochromism in Ionic π-Conjugated Liquid
Crystals
In conventional electrochromism of organic materials, an organic thin film is dipped
in an electrolyte solution, and a DC bias is applied to the thin film. Ionic species
penetrate into the film, and an electrical double layer is produced at the interface
between the organic layer and the electrode. Positive or negative charges are injected
to the organic layer by the electric field formed at the interface, and consequently,
colored cationic or anionic species are produced [9].
For a high-speed electrochromic process, fast ion diffusion in the thin films and
efficient charge transfer from the electrode to the organic layer are indispensable.
Moreover, effective charge carrier transport should make it possible to involve the
active molecules separated from the electrode [12].
For this purpose, we designed nanosegregated LC mixed conductors; the
molecules consist of an electro- and redox-active π-conjugated unit as well as an
ionic moiety, as shown in Fig. 18.1. A phenylterthiophene moiety was adopted as a πconjugated unit, and an imidazolium moiety was introduced at the terminal position
of the alkyl side chain [13, 14].
These compounds exhibit a smectic A (SmA) phase at elevated temperatures.
Figure 18.2a shows an X-ray diffraction pattern of the SmA phase of compound 3
and schematic illustration for the structure of the SmA phase. The X-ray diffraction pattern in the SmA phase suggested an anti-parallel arrangement of the LC
molecules. Hole-transporting sublayers made from phenylterthiophene units as well
as ion-conductive sublayers consisting of imidazolium cations and counter-anions
are integrated alternately in the SmA phase, as shown in Fig. 18.2b.
Compound 3 was capillary filled into a LC cell consisting of two ITO-coated
glass plates at the temperature of the isotropic liquid phase, and the sample was
cooled to 100 °C. The sample changed to the SmA phase. When a DC bias was
Fig. 18.1 Molecular structures of LC phenylterthiophene derivatives bearing imidazolium moieties.
The abbreviations ‘Cryst.’, ‘SmA’, and ‘Iso’ are crystal, smectic A, and isotropic phases, respectively
361
18.2 Electrochromism in Ionic π-Conjugated Liquid
Crystals
In conventional electrochromism of organic materials, an organic thin film is dipped
in an electrolyte solution, and a DC bias is applied to the thin film. Ionic species
penetrate into the film, and an electrical double layer is produced at the interface
between the organic layer and the electrode. Positive or negative charges are injected
to the organic layer by the electric field formed at the interface, and consequently,
colored cationic or anionic species are produced [9].
For a high-speed electrochromic process, fast ion diffusion in the thin films and
efficient charge transfer from the electrode to the organic layer are indispensable.
Moreover, effective charge carrier transport should make it possible to involve the
active molecules separated from the electrode [12].
For this purpose, we designed nanosegregated LC mixed conductors; the
molecules consist of an electro- and redox-active π-conjugated unit as well as an
ionic moiety, as shown in Fig. 18.1. A phenylterthiophene moiety was adopted as a πconjugated unit, and an imidazolium moiety was introduced at the terminal position
of the alkyl side chain [13, 14].
These compounds exhibit a smectic A (SmA) phase at elevated temperatures.
Figure 18.2a shows an X-ray diffraction pattern of the SmA phase of compound 3
and schematic illustration for the structure of the SmA phase. The X-ray diffraction pattern in the SmA phase suggested an anti-parallel arrangement of the LC
molecules. Hole-transporting sublayers made from phenylterthiophene units as well
as ion-conductive sublayers consisting of imidazolium cations and counter-anions
are integrated alternately in the SmA phase, as shown in Fig. 18.2b.
Compound 3 was capillary filled into a LC cell consisting of two ITO-coated
glass plates at the temperature of the isotropic liquid phase, and the sample was
cooled to 100 °C. The sample changed to the SmA phase. When a DC bias was
Fig. 18.1 Molecular structures of LC phenylterthiophene derivatives bearing imidazolium moieties.
The abbreviations ‘Cryst.’, ‘SmA’, and ‘Iso’ are crystal, smectic A, and isotropic phases, respectively