Masahiro Funahashi

High ambipolar carrier mobility in self-organizing terthiophene derivative

Dialkylterthiphene derivatives exhibiting self-organization of molecular alignment were synthesized and their electrical properties were studied. It was found that these materials exhibited very fast electron transport in smectic mesophases as well as hole transport, both of which were independent of electric field and temperature. The mobility for electrons and holes was 5×10−4 cm2/V s in smectic C (SmC) and was increased up to 2×10−3 cm2/V s and even more up to 1×10−2 cm2/V s in accompany with upgrade of molecular alignment from SmC to SmF and from SmF to SmG, respectively. This abrupt increase in the mobility to the extent of about one order of magnitude corresponds to that in 2-phenylnaphthalene derivatives at the phase transition from SmA to SmB and from SmB to SmE whose molecular alignments are in good correlation with those of SmC, SmF, and SmG, respectively.

Fast ambipolar carrier transport in smectic phases of phenylnaphthalene liquid crystal

The carrier transport of a new calamitic liquid crystal, i.e., 2-(4′-octylphenyl)6-dodecyloxynaphthalene (8-PNP-O12) was investigated by the time-of-flight technique. The fast ambipolar electronic conduction was observed in two smectic phases of 8-PNP-O12. The carrier mobilities were determined to be 1.6×10−3 cm2/V⋅s in the lower temperature smectic phase (Sm1) between 79 and 100 °C and to be 2.5×10−4 cm2/V⋅s in the higher temperature phase (Sm2) between 100 and 121 °C, regardless of carrier signs, i.e., electron and hole. The slower ambipolar transport was observed in isotropic phase as well, whose mobility was 8×10−5 cm2/V⋅s. These mobilities were independent of applied electric fields and temperature.

Nanostructured Liquid Crystals Combining Ionic and Electronic Functions

New molecular materials combining ionic and electronic functions have been prepared by using liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid crystals show thermotropic smectic A phases. Nanosegregation of the pi-conjugated mesogens and the ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of 2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic responses are observed for compound 1 without additional electrolyte solution on the application of double-potential steps between 0 and 2.5 V in the smectic A phase at 160 degrees C. In contrast, compound 2 having a tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-organized molecular redox systems can be built by nanosegregated pi-conjugated liquid crystals containing imidazolium moieties with and without electroactive thin layers on the electrodes.

Anomalous high carrier mobility in smectic E phase of a 2-phenylnaphthalene derivative

Ambipolar carrier transport properties in different phases of a liquid-crystalline photoconductor, 2-(4-octylphenyl)–6-n-butoxynaphthalene, were investigated by a time-of-flight technique. Carrier mobilities were increased stepwise when phase transition took place as the temperature decreased. The smectic E phase in the range of 55–125 °C exhibited nondispersive ambipolar carrier transport with an anomalous high carrier mobility of 1.0×10−2 cm2/V s, while the smectic A phase between 125 and 129 °C had similar carrier transport with a smaller mobility of 4×10−4 cm2/V s. In contrast to the crystalline phase, structural defects in the smectic E phase, which were obvious under microscopic observation with polarized illumination, did not deteriorate the carrier transport properties.

An Electrochromic Nanostructured Liquid Crystal Consisting of π-Conjugated and Ionic Moieties

A new electrochromic molecule comprised of pi-conjugated and ionic moieties has been designed and synthesized. It forms a nanosegregated smectic phase in which ion-conductive layers of imidazolium salts are located between hole transport layers of phenylterthiophene moieties. Electrochromism is observed in the bulk liquid crystal state of this compound without an electrolyte solution. In this nanosegregated smectic phase, an electrical double layer is formed rapidly at the electrode. Consequently holes are injected from the electrode, resulting in oxidation of the pi-conjugated moieties.

Electron Transport and Electrochemistry of Mesomorphic Fullerenes with Long-Range Ordered Lamellae

Fullerenes, C60, modified with long alkyl chains form long-range ordered lamellar mesophases permitting a high C60 content. The mesomorphic fullerenes feature reversible electrochemistry and a comparably high electron carrier mobility making them attractive components for fullerene-based soft materials.

Functional Liquid-Crystalline Polymers for Ionic and Electronic Conduction

Liquid-crystalline (LC) polymers that exhibit ionic or electronic conduction are described. Anisotropic and efficient transportation of electrons and ions is expected for these materials. The ordered LC nanostructures of LC polymers having ion- or electron-active moieties are important for efficient anisotropic transport. For electron-conductive materials, we focus on side-chain LC polymers.

Polarized light emission from a calamitic liquid crystalline semiconductor doped with dyes

Liquid crystal cells containing a homogeneously aligned calamitic liquid crystalline semiconductor, 2-(4-octylphenyl)-6-dodecyloxynaphthalene, doped with dyes such as 3-(2-benzothiazolyl)7-diethylaminocoumarin, emitted a visible light when a dc bias was applied. This light emission occurred irrespective of phase, and polarized light emission was well established in the Smectic B phase. The unique features of the calamitic liquid crystalline semiconductors are also discussed from a practical viewpoint.

High electron mobility in a columnar phase of liquid-crystalline perylene tetracarboxylic bisimide bearing oligosiloxane chains

A liquid-crystalline (LC) semiconductor based on perylene tetracarboxylic bisimide (PTCBI) bearing four 1,1,1,3,3-pentamethyldisiloxane chains was synthesized. This LC PTCBI derivative exhibits ordered columnar phases and the low temperature columnar phase is retained below room temperature. The electron mobility in the ordered columnar phase of this compound at room temperature exceeds 0.1 cm2 V−1 s−1. Moreover, this compound is soluble in various organic solvents, except alcohols, and thin films in which the columnar aggregates are aligned parallel to the substrates are produced by spin-coating. In particular, LC thin films in which the columnar stacks are uniaxially oriented can be produced by a friction transfer method.

Nanostructured liquid-crystalline semiconductors – a new approach to soft matter electronics

In contrast to solid-state organic semiconductors, superstructures can be constructed in liquid-crystalline (LC) phases, using chirality, hybridization with nanofibers, and nanosegregation. Chiral LC molecules form LC phases with helical structures. Gelator molecules self-assemble into fibrous aggregates in LC phases to form nanohybrid materials. Liquid crystal molecules consisting of π-conjugated moieties and incompatible functional parts form nanosegregated LC phases. These nanostructured π-conjugated LC materials have the potential to create new soft matter with unique photonic and electronic functions.