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In a narrow temperature window in going from the isotropic to highly chiral orders, cholesteric liquid crystals exhibit so-called blue phases, consisting of different morphologies of long, space-filling double twisted cylinders. Those of cubic spatial symmetry have attracted considerable attention in recent years as templates for soft photonic materials. The latter often requires the creation of monodomains of predefined orientation and size, but their engineering is complicated by a lack of comprehensive understanding of how blue phases nucleate and transform into each other at a submicrometer length scale. In this work, we accomplish this by intercepting nucleation processes at intermediate stages with fast cross-linking of a stabilizing polymer matrix. We reveal using transmission electron microscopy, synchrotron small-angle X-ray diffraction, and angle-resolved microspectroscopy that the grid of double-twisted cylinders undergoes highly coordinated, diffusionless transformations. In light of our findings, the implementation of several applications is discussed, such as temperature-switchable QR codes, micro-area lasing, and fabrication of blue phase liquid crystals with large domain sizes., The arrangements of defect lines in liquid crystal blue phases provide promising templates for photonic crystals. Here Liu et al. investigate in detail how inter-phase transitions proceed, by intercepting nucleation with on-demand cross linking of a supporting polymer matrix.

A new class of polymer materials has been developed that can convert light energy directly into mechanical work, and show a variety of three-dimensional movements simply from exposure to light. These polymer materials can be fabricated into any shape and size using photolithographic methods and it is expected they will be developed for various applications. In this paper recent progress of this interesting class of polymer material is reviewed.

Group 4 [η1:η3-tert- butyl(dimethylfluorenylsilyl)amido]dimethyl complexes [t-BuNSiMe 2Flu]MMe2 (M = Ti, 1; Zr, 2; Hf, 3) were synthesized in a one-pot synthesis starting from the ligand, MeLi and MCl4 (M = Ti, Zr, Hf), respectively. The structures of these complexes were determined by X-ray crystallography and the results obtained revealed that the fluorenyl ligand coordinates to center metal in a η3-manner irrespective of center metal employed. Propylene polymerization was conducted at 0 or 20 °C in toluene by 1-3 combined with dried methylaluminoxane (MAO), which was prepared from the toluene solutions of MAO by removing free trialkylaluminiums, and HNMe2PhB(C6F5)4 in the presence of triisobutylaluminium. The 1-dried MAO system gave the polymer with syndiotactic triad (rr) of 63 0x1.e2fc8p-891t 0 °C, whereas 2 and 3 did not give any polymer in the same conditions. The 2-dried MAO system gave the polymer with the highest syndiotacticity (rr = 97%) at 20 °C, although the activity was low. The 3-dried MAO system did not give any polymer even at 20 °C. When HNMe2PhB(C6F5)4 was used in place of dried MAO at 20 °C, 1 gave almost atactic polymer, while 2 and 3 gave highly syndiotactic one (rr > 90%). These results indicate that the catalytic performance strongly depended on the center metal of the ansa- fluorenylamidodimethyl complexes as well as cocatalysts employed.

Steady-state and transient photocurrent measurements were carried out to study the charge carrier transport properties of polymer liquid crystal (LC) containing oxadiazole (OXD) and amine moieties in the same side chain. The steady-state photocurrent measurement with asymmetric electrodes of ITO and Al and a short penetration depth of the illumination light indicated that both electrons and holes can be transported in this film. The transient hole photocurrent observed by time-of-flight (TOF) experiments was dispersive at room temperature. The hole drift mobility significantly depended on temperature and electric field and was determined to be 6.1 x 10(-8) cm2/Vs at a field of 9.1 x 10(5) V/cm. According to the disorder formalism, the Gaussian width of the density of states was determined to be 170 meV for holes. Despite the indication of possible electron transport in this film, we could not determine the electron mobility by TOF experiments due to strong dispersive photocurrent. We discuss the present charge transport properties of the film in relation to a large dipole attributed to an electrical push-pull structure of p-dimethylaminophenyl-substitited OXD moiety in polymer LC and its electroluminescent properties.

Recent progress in alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions has been reviewed by dividing the modulation methods into two types: phase transitions (order–disorder change) and change of liquid crystal directors (order–order change). First, photochemical phase transitions and alignment changes of liquid crystals in guest/host mixtures and polymers are summarized. Then, alignment control of liquid crystals by linearly polarized light and photoactive surface layers is discussed. Finally, recent applications of alignment change and photochemical phase transitions of liquid crystals in holographic technology and photomechanical effects are introduced. In addition, future possible applications for a variety of practical devices, such as display devices, optical switching and reversible optical image storage, are mentioned.

Liquid-crystalline gels and elastomers were prepared by polymerization of mixtures containing azobenzene monomers and cross linkers with azobenzene moieties. Oriented liquid-crystalline gels and elastomer films were found to undergo anisotropic bending and unbending behavior only along the rubbing direction, when exposed to alternate irradiation of unpolarized UV and visible light. In the case of polydomain liquid-crystalline elastomer films, the bending and unbending were induced exactly along the polarization direction of incident linearly polarized light. By altering the polarization direction of light, a single film could be bent repeatedly and precisely along any chosen direction.

1,3-Butadiene polymerization was conducted at 0 °C with cobalt dichloride (CoCl2) activated by different cocatalysts: MAO (methylaluminoxane), dried-MAO (substantially free of trimethylaluminum), MMAO (triisobutylaluminum-modified methylaluminoxane), dried-MMAO (substantially free of trialkylaluminum) and TMA (trimethylaluminum). MAO and MMAO were effective cocatalysts for 1,3-butadiene polymerization. CoCl2 activated with MAO showed slowly-initiated living polymerization which has been reported previously, whereas, that with MMAO showed deactivation. Neither dried-MAO nor dried-MMAO, TMA activated the catalyst, whereas dried-MAO-TMA (mixtures of dried-MAO and TMA) and dried-MMAO-TMA (mixtures of dried-MMAO and TMA) allowed the polymerization. These results indicated that trialkylaluminums were necessary with MAOs for generating the active species. Dried-MAO-TMA caused frequent chain transfer reactions, whereas dried-MMAO-TMA showed the living like polymerization not only with slow initiation but with slow propagation also, suggesting that the nature of the active species was strongly dependent on the structure of alkylaluminums and MAOs. The microstructure of the resulting polymers analyzed by 1 H and 13 C NMR was cis-1,4 (98–97%); the percentage slightly decreased in the following order: MAO>dried-MAO>MMAO>dried-MMAO, accompanied by the increase of trans-1,4 and 1,2-inserted units.

The recent highlights in the photoinduced modulation of the liquid-crystalline (LC) alignment and their applications to photonics are reviewed. The molecular alignment of LCs can be controlled by either the photochemical process or the photophysical process and we can change the birefringence as well as refractive index of the material by the modulation of the LC alignment. The photoresponsive LCs show very quick response to stimulus light: the response time is ∼200 ns. Furthermore, the extremely large refractive index modulation (Δ n =∼10 −1 ) can be also induced. The photoresponsive LCs, therefore, are potential materials for holographic recording and other photonic device.

Propene polymerization was carried out by Cp ∗ Ti(CH 2 Ph) 3 , [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 combined with dried or SiO 2 -supported methylaluminoxane (MAO). The dried MAO system generally showed higher activity and gave higher molecular weight polypropenes than the SiO 2 -supported MAO system. The decrease in the activity by changing the cocatalyst from dried MAO to SiO 2 -supported MAO was, however, more significant in the cases of [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 . The molecular weight distribution of the produced polymers indicated that uniform active species were formed from Cp ∗ Ti(CH 2 Ph) 3 regardless of the cocatalyst employed while the active species derived from [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 combined with SiO 2 -supported MAO were inhomogeneous. The microstructure of the produced polymers were independent of the cocatalyst used, and [ t -BuNSiMe 2 Flu]TiMe 2 catalysts produced syndiotactic polypropenes with less regioirregular structure. The Cp ∗ Ti(CH 2 Ph) 3 /SiO 2 -supported MAO system showed a steady polymerization rate with frequent chain transfer at 0 °C while the [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 /SiO 2 -supported MAO system produced the polypropenes with long chain lifetime accompanied by slow deactivation at 0 °C.

By using the depth selective imaging method, we studied the UV induced change in a photomobile liquid crystalline polymer film. With 1 μm depth resolution, each slice inside the film was selectively observed. A network-like structure mixed with the ordered and disordered regions of molecules in the middle of the film, and a rubbed polymer layer at the bottom of the film were observed. In each slice of the film, the phase change induced by UV light was observed strongly dependent on the director direction, which indicates the ordering change of the liquid crystalline molecules in the director direction. It took several tens of seconds for the ordering change caused by the collaborative interaction between the molecules. Furthermore, it was suggested that the UV induced change travelled from the bottom layer to the middle layer on the micron order.

Mechanical properties of flexible films, for example surface strain of largely bending films, are key to design of stretchable electronic devices, wearable biointegrated devices and soft microactuators/robots. However, existing methods are mainly based on strain-gauge measurements that require miniaturized array sensors, lead wires and complicated calibrations. Here we introduce a facile method, based on surface-labelled gratings, for two-dimensional evaluation of surface strains in largely bending films. With this technique, we demonstrate that soft-matter mechanics can be distinct from the mechanics of hard materials. In particular, liquid-crystalline elastomers may undergo unconventional bending in three dimensions, in which both the inner and outer surfaces of the bending film are compressed. We also show that this method can be applied to amorphous elastomeric films, which highlights the general importance of this new mechanical evaluation tool in designing soft-matter-based electronic/photonic as well as biointegrated materials.

Photo-induced molecular motion in a liquid crystal polymer film including azobenzene was studied by the heterodyne transient grating method. The film was confined in a liquid crystal cell, where it is a photomobile film under free-standing conditions. By observation of the refractive index change induced by a laser pulse, contraction of the film was observed on the order of several hundreds of nanoseconds, and the subsequent reorientation and molecular rotation dynamics were observed from a few microseconds to a hundred milliseconds. Finally, the cis isomer of azobenzene was thermally returned back to the trans isomer in about ten seconds because the film could not be bent in the liquid crystal cell. Since the contraction, reorientation and molecular rotation took place before the cis to trans back-transformation, these processes correspond to the preliminary molecular motion preceding the macroscopic bending of the film.

Formation of intensity gratings was studied with two s‐polarized (s+s) configuration in polymer liquid crystals (PLCs) containing a photochromic moiety (azobenzene) and a mesogenic unit (tolane, T‐...

Propene polymerization was conducted by [η3:η1-tert-butyl(dimethylfluorenylsilyl)amido]dimethyltitanium combined with B(C6F5)3 or methylaluminoxane (MAO) as a cocatalyst in the presence or absence of various trialkylaluminums: Me3Al, Et3Al, iBu3Al (triisobutylaluminum) and Oct3Al (trioctylaluminum). In the case of living polymerization with B(C6F5)3 at −50°C, addition of Oct3Al and Et3Al increased the propagation rate. Et3Al also acted as a chain transfer reagent and selectively gave Al-terminated polymers, while Oct3Al induced chain transfer reaction only in high concentration. Little polymer was obtained in the presence of Me3Al or iBu3Al. When MAO was used as a cocatalyst, polymerization did not proceed at −50°C. The MAO system, however, showed high activity at 40°C and selectively gave low molecular weight polymers terminated with Al–C bonds. Contrary to the low temperature polymerization with B(C6F5)3 at −50°C, the polymer yield was enhanced by the addition of Me3Al and iBu3Al, while the molecular weight was reduced by Me3Al and enlarged by iBu3Al. On the other hand, Et3Al and Oct3Al significantly decreased both the polymer yield and the molecular weight under these conditions. It was found that additive effects of trialkylaluminums were strongly dependent on polymerization temperature as well as on the structure of the alkyl group.

All-optical switching of selectively reflected colors based on isomerization of an azobenzene (Azo) and subsequent change in transmittance was investigated in cholesteric liquid crystals (LCs) whic...

In P(2)O(5)-MsOH, or related acidic media, benzoylformic acid (1) undergoes three types of di- or mono-alpha-arylation reactions with or without decarbonylation ((1) decarbonylative alpha, alpha-diarylation, yielding triarylmethanols 6, (2) decarbonylative alpha-monoarylation, giving benzophenone derivatives 7, and (3) alpha,alpha-diarylation without decarbonylation, affording diarylated carboxylic acids 5) and one simple decarbonylation, without arylation, to form benzoic acid (8), instead of the conventional Friedel-Crafts acylation type reaction. The product ratios are governed by the capability of the acidic medium to form mixed anhydrides with carboxylic acids and the ability of the arenes to accept electrophiles.

Ethylene polymerization was conducted with bis(cyclopentadienyl)zirconium dichloride (1) and rac-dimethylsilylenebis(indenyl)zirconium dichloride (2) combined with trialkylaluminum (AlR3; R=methyl (Me), ethyl (Et), isobutyl (iBu))/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) or tris(pentafluorophenyl)borane (B(C6F5)3) to study the effect of cocatalysts on polymerization rate (Rp). When AlMe3 was used, no activity or very low activity was observed with both zirconocenes regardless of the borane compounds used. The replacement of AlMe3 to AlEt3 or AliBu3 with 1–AlR3/Ph3CB(C6F5)4 caused polymerization and induction time was observed to reach the maximum Rp. Especially in the case of using AlEt3, it took about 30 min to show the activity. When B(C6F5)3 was used, AlEt3 was not effective but AliBu3 gave the highest activity among all the combinations of AlR3 and the borane compounds. In the case of polymerization with 2 using Ph3CB(C6F5)4, high activity was observed with both AlEt3 and AliBu3 without any induction period. When B(C6F5)3 was used instead of Ph3CB(C6F5)4, very low activity was observed with AlEt3. On the other hand, high activity was observed with AliBu3, and the maximum Rp was found at the beginning of the polymerization. The effect of AlR3 on the formation of active species was discussed based on these results.

Modulation of light by light as stimulus has been explored by the use of liquid-crystalline (LC) materials with photosensitive moieties. Azobenzene derivatives with monomeric and polymeric forms were prepared, which show nematic (N) LC behavior in the trans form and no LC phase in the cis isomer. Photoirradiation of a very thin film of the liquid-crystalline azobenzene derivatives (∼200 nm) in the trans form resulted in the disappearance of the N phase because of trans−cis photoisomerization of each mesogen, and the N phase recovered quickly when the irradiated sample was kept in the dark in the whole temperature range where the azobenzene LCs showed the N phase because of cis−trans thermal isomerization. Time-resolved measurements by the use of a laser pulse (355 nm, 10 ns fwhm) revealed that the N-to-isotropic (I) phase transition took place in 200 μs in both monomeric and polymeric systems. This response is at least 1 order of magnitude faster than the response of nematic LCs previously reported.1,2 In...

Various phosphonium salts possessing single or double alkyl chains of various lengths (C10 to C18) were prepared as cationic biocides, and their antimicrobial activities against 11 typical strains of microorganisms including methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. The phosphonium salts with long alkyl chains were found to show high levels of antimicrobial activity. Their activities depended strongly on the molecular structure, and a correlation between antimicrobial activity and molecular structure was observed. In the alkyltrimethylphosphonium salts, the bactericidal activity against S. aureus and Escherichia coli increased with increasing alkyl chain length, and the compound with the longest alkyl chain (C18) killed all the bacterial cells (ca. 10(7) cells per ml) within 30 min of contact at concentrations of 2.8 and 28 microM, respectively. In contrast, the bactericidal activity of dialkyldimethylphosphonium salts was found to decrease as the chain length of the substituents increased. It is significant that the phosphonium biocide containing double decyl groups exhibited the broadest spectrum of activity against microorganisms tested and showed the greatest bacteriostatic activity against MRSA (MIC = 0.78 micrograms/ml). Furthermore, we systematically investigated differences in bactericidal activity between the phosphonium salts and commonly available ammonium salts with the same hydrophobic structure. It was observed that the phosphonium salts showed an advantage over the corresponding ammonium salts in bactericidal activity and killing rate. For example, tetradecyltrimethyl- and didecyldimethylphosphonium chlorides killed all S. aureus organisms (ca. 10(7) cells per ml) within 60 and 30 min of exposure at 28 and 2.8 microM, respectively, while tetradecyltrimethyl- and didecyldimethylammonium chlorides which are representative of the existing cationic disinfectants did not kill all the bacteria even at the longest exposure time (120 min).

Superelasticity — a form of elasticity that involves a phase transition — has been observed for the first time in a pure organic crystal. The material could find applications in microfluidics.

Photochemical phase transition of polymer liquid crystals (PLCs) was explored for PLCs with mesogenic side-chain phenylbenzoate and cyanobiphenyl. The photochemical phase transition was triggered by photochemical reaction of photoresponsive molecules incorporated physically or covalently into PLCs as a result of lowering of phase transition temperature of the mixtures below the irradiation temperature. Factors affecting the photochemical phase transition are discussed and resolution of stored image was examined.

Interaction of a polymeric in-chain quaternary ammonium salt with phospholipid bilayer membranes was studied by time-resolved fluorescence spectroscopy with the aid of a picosecond time-rcorrelated single photon counting system (instrument response function, 70 ps FWHM). Particular attention was paid to a phenomenon of polycation-induced fluidization of the membranes, which was well evaluated by time-resolved fluorescence anisotropy measurements. The fluorescence anisotropy, r ( t ), of 1,6-diphenyl-1,3,5-hexatriene (DPH) embedded in the membranes was analyzed based on the wobbling-in-cone model. Strong interaction was observed between the polycation and a negatively charged phosphatidic acid membrane as demonstrated by a large decrease of residual polarization value on adding the polycation to the acidic phospholipid dispersion. This means that the cone angle of the wobbling-in-cone motion of the DPH molecule increases by the addition of the polycaton, indicative of the polycation-induced fluidization of the acidic membrane. On the other hand, r ( t ) of DPH embedded in a zwitterionic phosphatidylcholine membrane was not affected significantly by the addition of the polycation, which is presumably due to non-binding of the polycation to the zwitterionic membrane. Our results clearly indicate that the polycationic disinfectant interacts strongly with negatively charged membranes, inducing fluidization of the membranes.

ansa-Indenylamidodimethyltitanium complex ([t-BuNSiMe2Ind] TiMe2: 1) was synthesized by one-pot reactions starting from the ligand, MeLi and TiCl4. The structure of 1 was determined by X-ray crystallography and the results obtained revealed that the indenyl ligand coordinate to titanium in an η4-tendency. Propylene polymerization was conducted with 1 in toluene or heptane as solvent at 0°C in the presence of dried methylaluminoxane (MAO) or dried modified MAO (MMAO), which was prepared from the toluene solutions of MAO or MMAO by removing free trialkylaluminium contained. Polymerization behavior was investigated from the consumption rate of propylene in a semi-batch system. The dried MAO/toluene system showed the highest activity without any deactivation. The produced polymer in the dried MAO/toluene system had the highest molecular weight and narrowest molecular weight distribution. The number-average molecular weight of the polymer increased almost linearly with increasing polymerization time accompanied by narrowing molecular weight distribution from 1.42 to 1.37 and the number of polymer chains was almost constant. Thus, it was found that quasi-living polymerization of propylene proceeded. The 13C NMR measurement indicated that 1-dried MAO/toluene produced poly(propylene) with isotactic triad of 40%.0

Several kinds of photodeformable polymer systems containing azobenzenes, capable of generating photomechanical effects, are reviewed. In polymer amorphous systems including monolayers, gels and solid films, trans-cis photoisomerization of the azobenzene moieties accompanied by geometrical and dipolar changes caused contraction and expansion of the systems. Recently, polymer liquid-crystalline elastomers containing azobenzenes, a novel system able to produce the photomechanical effects, have been developed to achieve fast and large photoinduced deformations. It is interesting that not only photoinduced contraction but also photoinduced bending have been achieved. These deformations are ascribed to the subtle variation in microscopic ordering during the photochemical phase transition of the polymer liquid-crystalline elastomers. This new photomechanical system is potential for application in driving micromachines and nanomachines without the aid of batteries, motors and gears.

Polymer solutions and solids that contain light-sensitive molecules can undergo photo-contraction, whereby light energy is converted into mechanical energy. Here we show that a single film of a liquid-crystal network containing an azobenzene chromophore can be repeatedly and precisely bent along any chosen direction by using linearly polarized light. This striking photomechanical effect results from a photoselective volume contraction and may be useful in the development of high-speed actuators for microscale or nanoscale applications, for example in microrobots in medicine or optical microtweezers.

LIQUID crystals have been used extensively as active media in display devices such as full-colour television screens. These devices are generally based on changes in the arrangement of the liquidcrystal molecules induced by electric fields, which change their optical properties1. Ferroelectric liquid crystals2,3 exhibit spontaneous polarization and therefore show a faster response to changes in the applied field. Switching of this field causes a reversal in the direction of polarization2–;5. Here we report polarization switching in ferroelectric liquid crystals driven by a photochemical process. The liquid-crystal films are doped with a photochromic compound which undergoes trans–cis isomerization on irradiation. Photoisomerization induces a change in the switching potential of the host liquid-crystal film, and thereby causes switching at the irradiated sites. The process is fast, stable, reversible and repeatable, and should be exploitable in device applications.

Liquid crystals are promising materials for optical switching and image storage because of their high resolution and sensitivity. Azobenzene liquid crystals (LCs) have been developed, in which azobenzene moieties play roles as both mesogens and photosensitive chromophores. Azobenzene LC films showed a nematic phase in trans isomers and no LC phase in cis isomers. Trans-cis photoisomerization of azobenzene with a laser pulse resulted in a nematic-to-isotropic phase transition with a rapid optical response of 200 microseconds.

A mild and regioselective C−H substitution reaction of thiazole by the catalysis of the palladium/copper system is found to proceed in the presence of tetrabutylammonium fluoride under mild conditions. Applying the new reaction, we synthesized various 2,5-diarylthiazoles that exhibit light-emitting and liquid crystalline characteristics in good yields. The color of light emission is tunable by the introduction of the substituent. Differently substituted 2,5-diarylthiazoles are found to exhibit a stable liquid crystal phase in a wide temperature range.

Miniaturizing a simple photomechanical system could expand its range of applications. Polymer solutions and solids that contain light-sensitive molecules can undergo photo-contraction, whereby light energy is converted into mechanical energy1,2,3,4,5,6,7,8. Here we show that a single film of a liquid-crystal network containing an azobenzene chromophore can be repeatedly and precisely bent along any chosen direction by using linearly polarized light. This striking photomechanical effect results from a photoselective volume contraction and may be useful in the development of high-speed actuators for microscale or nanoscale applications, for example in microrobots in medicine or optical microtweezers.