Functional Liquid-Crystalline Polymers for Ionic and Electronic Conduction - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 172

Fig. 22 Molecular structures of LC 2-phenylnaphthalene derivative and hexanediol di-

acryalte

lated between smectic layers, resulting in the stabilization of the smectic thin
films [109]. Yoshimoto et al. reported stabilization of the smectic A and B
phases of 2-phenylnaphthalene derivative 27 doped by hexanediol diacry-
late 28 with photopolymerization (Fig. 22). In this study, carrier mobility
was maintained in the smectic A and B phases when photopolymerization
was carried out in the smectic phases; however, carrier mobility decreased
when the photopolymerization was done in the isotropic phase. In this case,
microscopic segregation of the polymer network formed during the pho-
topolymerization process should play important role [110, 111].
Enhanced photoconductive properties were reported for physical gels of
a liquid-crystalline triphenylene derivative [112].

3.5
Miscellaneous Systems and Related Compounds

Conjugated polymers have become very important materials in organic
electronics since the discovery of electrical conductivity in doped poly-
acetylenes [113]. In a single chain of conjugated polymers, 1D band structure
should be formed under an ideal state. Here, each

-conjugated chain ex-
tends linearly and is planar without defects, resulting in fast carrier transport
along the single chain. However, in actual systems, the single chain is bent
or twisted and carriers have to migrate between many chains and segments
when they drift between electrodes. Therefore, the carrier transport process
in bulk or in thin films of conjugated polymers is mainly controlled by inter-
chain or inter-segment hopping of charge carriers rather than fast carrier
transport within single chains [114].
Comparing with conventional amorphous organic semiconductors [16],
it is characteristic that conjugated polymer films consist of crystal-like do-
mains, in which

π

-conjugated chains are stacked closely, and an amorphous
domain, in which polymer chains are disordered [115]. In crystal-like do-
mains, band-like carrier transport that is similar to that of molecular crystals
should be possible. However, hopping transport influenced by structural dis-
order is the dominant process in the amorphous domains. The total carrier
transport process is dominated mainly by that in amorphous domains, result-
ing in bulk carrier transport characteristics similar to those of amorphous
organic semiconductors.

π