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Refractive-index modulation by change in alignment of liquid crystals (LCs) has been explored: order to disorder phase transition of LCs by photochemical reactions of photoresponsive molecules, order to order alignment change of LCs in the LC phases induced by photochemical reactions. In the order to disorder phase transition of LCs, the refractive index can be changed very quickly while the change in the refractive index is smaller than those induced by the order to order alignment change of LC molecules. In-plane (2 D) and out-of-plane (3 D) alignment change of LCs have been studied. With the out-of-plane alignment change of LC molecules, refractive-index modulation not only to linearly polarized light but also to unpolarized light can be achieved. The alignment change of LCs without photochemical processes is also discussed.

Photochemical phase transition of polymer liquid crystals (LCs) with hydoxyazobenzene moieties has been studied. By irradiation with the laser pulse at 355 nm, photochemical LC-isotropic (I) phase transition of the polymer LCs was induced in microsecond timescale. When the irradiated sample was kept in the dark, the initial LC phase recovered thermally. The response time of the I-LC phase transition was 300 ms in hydoxyazobenzene LCs. while it was 1.5 s in O-alkyl analogues. In the cis-trans isomerization process in hydroxyazoben zenes, the hydrazone was produced by proton transfer, and this tautomer is converted into trans-azobenzenes. In the thermal cis-trans isomerization, hydroxyazobenzenes prefer this two-step mechanism to the one-step mechanism because the activation energy of this mechanism is lower than that of the one-step mechanism. Thus, the thermal isomerization occurred effectively, and the recovery of the LC phase took place quickly in the present polymer LC system The results obtained here suggest an approach to accelerate the thermal recovery of the LC phase.

The unique optoelectric feature of structurally simple surfactants was presented. Phosphonium salts as a novel class of thermotropic liquid crystals were used to explore the spatial arrangement of ions in multilayer self-assemblies based on the surfactant complexes. Through the evaluation of second-order nonlinear optical property of the phosphonium self-assemblies, it was revealed that the phosphonium thin film assemblies can be regarded as a polar thin film consisting of two-dimensional ionic layers with noncentrosymmetric atomic arrangement. Such spontaneous formation of the in-plane polar structure was assumed to originate from the variety of bonding manner (i.e., the characteristic electronic structure) of phosphorus atom. Furthermore, it was also found that the macroscopic polar order is enhanced by application of an external electric field.

The direction of molecular switching, i.e., the sign of the electro-optic response, in ferroelectric liquid crystals depends on the polarity of the applied electric field as well as on the sign of the spontaneous polarization. Light-induced switching of the molecules by ultraviolet light was found in a photochromic ferroelectric liquid crystal at fixed field polarity. A high contrast image was recorded whose contrast could easily be inverted by reversing the field polarity. Moreover, in the presence of bistable boundary conditions, the optically recorded image can be stored after removal of the electric field. The effect of light-assisted switching in the photochromic ferroelectric liquid crystal seems to be promising for applications such as optical recording, all-optical switches, and image storage.

Propene polymerization was conducted at 0 °C by [t-BuNSiMe2Flu]TiMe2 combined with B(C6F5)3, MAO, or the MAO which had been dried in a vacuum and washed with hexane before use. The effect of cocata...

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‐...

Films were formed by coating hydroxypropyl cellulose (HPC) or ethyl cellulose (EC) with different kinds of solvents at high coating speeds and thin coating thicknesses. These films were used as alignment layers for liquid crystals. Atomic force microscopy (AFM) and polarizing optical microscopy (POM) were used to identify the banded texture structure of the films. The alignments of a nematic liquid crystal 5CB droplet on those films were observed by POM. Further, a novel cycle disclination line was recorded and studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2770–2774, 2001

Polar order in the phosphonium liquid crystal thin films, which are composed of two-dimensional ion-pair-based domains separated by the insulating hydrocarbon layers, was probed by second harmonic generation (SHG) analysis. Despite the ordinary amphiphilic self-assemblies containing no pi-electron moieties, the solid-state thin films retaining a smectic layer structure showed clearly an SHG activity, while the disordered films without the layer structure were not active at all for the SHG. It was found that the multilayer structure plays a crucial role for the SHG from the phosphonium thin films and the ionic layers act as an SHG-active site. The most significant characteristic of this system is to possess an ability to control SHG intensity electrically. The efficiency of the SHG process in the thin-film assemblies was enhanced by applying an external electric field parallel to the layer plane. Furthermore, through evaluation of thermal stability of the sample films, it was revealed that the SHG signals were detected only in the solid-state temperature range and the disappearance of the SHG occurs earlier than the solid-to-liquid crystalline phase transition. These results demonstrated that the origin of polar order in the phosphonium thin films is due to in-plane noncentrosymmetric arrangement (ferroelectric ordering) of ion pairs as an electric dipole, that is, dipole symmetry in an ionic layer.

This paper deals with two series of novel side-group liquid crystalline polymers containing coumarin (2H-1-benzopyran-2-one) moieties. Several kinds of polymethacrylates of Series I (Fig. 1) containing a 7-benzoyloxycoumarin unit in the side group with or without substituent at 3 or 4 position of coumarin ring were prepared, in order to study the influence of spacers, tail groups and the positions of the tail groups on their liquid crystalline properties. Three polymethacrylates (Series II, Fig. 1) containing a phenyl 7-octyloxycoumarin-3-carboxylate unit, which consisted of a turned ester group between the aromatic rings in the central unit of side group as compared to Series I, were also prepared. The investigation of the thermal behavior of the two series indicated that the structure of the side-group significantly affected the liquid crystalline properties of the polymers. It was found that the polymers in Series I with substituents at the 3 position of the coumarin ring exhibited mesophase with a wide temperature range, whereas the polymers with substituents at the 4 position showed no mesophase. In addition, each polymer of Series I tended to exhibit a glassy state, whereas each polymer of Series II tended to exhibit a crystalline state. This would be due to the different interactions of side groups of the polymers in Series I and II. It was also revealed that the UV-Vis absorption and fluorescence spectra were influenced by their mesogenic structures and chromophore aggregations. Furthermore, the preliminary results about the emission spectra suggested that the annealing of the polymer film had a great influence on its fluorescence property.

We attempted formation of holographic gratings in an optically isotropic state of polymer azobenzene liquid-crystal films. On irradiation of writing beams at 488 nm, first-order diffraction beams of a probe beam at 633 nm were immediately observed even though the films exhibited the optically isotropic state. The diffraction beams quickly disappeared by turning off the writing beams. The first-order diffraction efficiency was affected by polarization of the writing beams. When unpolarized light was employed as the writing beams, diffraction beams were hardly observed. On the other hand, the highest diffraction efficiency was obtained with the linearly polarized writing beams. It is speculated that photoinduced alignment of azobenzene moieties in bright fringes of the interference pattern would be responsible for the grating formation. Furthermore, it was found that rubbing treatment slightly enhanced the diffraction efficiency. By turning on and off the writing beams, dynamic control of the diffraction be...

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.

Liquid crystals (LCs) show an anisotropic nature in various aspects of optical and electronic properties. This anisotropy enables LC materials to be used as active media in display devices. Birefringence, an anisotropy in optical properties of LCs, is especially useful from the viewpoint of changing refractive indices of LC materials. If alignment of LCs can be changed by light, a large change in refractive index can be induced by light. This is the principle of LC photonics, in which optical signals are processed with the aid of LC materials. In this article, various approaches are described to change the alignment of the LC molecules: 1) photochemically induced phase transition of LCs by photochromic reactions is an order to disorder transition and can be brought about in a time scale of micro- to nanosecond; 2) reorientation of LC molecules by means of linearly polarized light is a change in alignment of LC molecules that occurs within the LC phases and induces a large change in refractive index, but n...

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...

Optical switching and image storage have been examined by means of photochromic polymer liquid crystals (LCs). The photoisomerization of photochromic moieties, which act as a photoresponsive switch, induced the LC-to-isotropic phase transition and the change in alignment of LCs, and they resulted in optical switching and image storage.

Photoinduced alignment in a polymer liquid crystal prepared from 6-{1-[4-(2-cyano-4-nitrophenylazo)phenyl]piperazino}hexyl acrylate and 4'-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl was investigated for the first time on irradiation with a polarized He-Ne laser beam at 633 nm. The azobenzene moieties as well as the inert cyanobiphenyl mesogenic units were aligned with the molecular long axis perpendicular to the polarization direction of the irradiation light. Alignment induced on short irradiation was reversible, while that induced under prolonged irradiation was irreversible due to the occurrence of crosslinking which might be caused by photoinduced decomposition of the azobenzene moieties during the photoirradiation process.

The unique features of the phosphonium salts as functional materials are reviewed, with emphasis being placed on the comparison between the phosphonium salts and the commonly available quaternary ammonium salts, which have the same structure, differing only in the positively-charged heteroatom. The antimicrobial activity of onium salts with different long-chain segments is described with special reference to structure–activity relationships. The unexpected relationship between the antibacterial activity and the aggregation behavior in aqueous solution (i.e. lyotropic liquid-crystalline properties) was revealed through systematic studies on the antibacterial activity of the phosphonium salts as a novel class of cationic biocides. Furthermore, it is shown that the phosphonium salts can act as thermotropic liquid crystals in spite of the fact that they are amphiphiles without a rigid core.

Nichtlineare optische Eigenschaften weist die smektische Phase einfacher Dialkylphosphoniumsalze auf. Die Molekule bilden Schichten, in denen die Ionenpaare durch isolierende Alkylummantelungen getrennt sind, wodurch es zu einer spontanen Polarisierung (Ps) kommt (siehe schematische Darstellung). Auf der Grundlage dieser Materialien werden derzeit neuartige elektrische und elektrooptische Komponenten entwickelt.

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.

Phase-type gratings formed by photochemical phase transitions of a polymer azobenzene liquid crystal have been characterized. The sensitivity of the material was improved by a factor of 23 in the liquid-crystalline phase owing to effective induction of the photochemical phase transition in the bright fringes of the interference pattern. A mechanism for grating formation in films based on dynamics both in grating formation and for the photochemical phase transition has been proposed. Observation of the grating structure with a polarizing optical microscope confirmed that the isotropic phase induced photochemically was arranged at well defined separations. The polymer azobenzene liquid crystal showed a storage capability of >100 Mbits cm−2 which corresponds to a resolution of 1000 lines mm−1. We also attempted holographic image storage using a photomask as an object.

The composition of a crosslinked azobenzene liquid-crystalline polymer and a flexible polymer film can provide a variety of simple devices that can walk in one direction like an ‘inchworm’ and move like a ‘robotic arm’ induced by light.

We have demonstrated reversible change in transmittance of composite films, which are composed of an isotropic (I) polymer matrix and a host nematic (N) liquid crystal (LC) containing donor–acceptor type azobenzene LCs (AzoLCs) as photoresponsive molecules, by means of reversible phase transition in the LC domain. The composite films were prepared by in situ thermal polymerization-induced phase separation (PIPS) method from their homogeneous mixtures. Photoisomerization of AzoLCs was induced within the polymer network, and the resultant effect brought about isothermal change in transmittance. The photoinduced reversible and repeatable changes between opaque light scattering and clear transparent states were achieved effectively by irradiation with a monochromatic light at 366 nm. These changes are attributed to photochemical N–I phase transition and rapid thermal I–N phase transition in the host LC domain based on reversible change in molecular sharp of the guest AzoLCs. The optical effects were influenced by such factors as temperature of the composite films in the initial state and photoisomerization ability of the guest AzoLCs. The composite films acted as an optical switching material without polarizers.

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.

Titanium and zirconium complexes with a pyridine diamide ligand, [2,6-(RNCH 2 ) 2 NC 5 H 3 ] 2- (PDMP; R = 2,6-dimethylphenyl) have been synthesized and their catalytic behaviors investigated for ethylene polymerization. It was found that the zirconium complexes, [PDMP]ZrCl 2 (7) and [PDMP][ZrCl 3 x THF] 2 (8), gave higher activities than the titanium complexes, [PDMP]TiCl 2 (5) and [PDMP][TiCl 3 ] 2 (6). The bimetallic complexes (6, 8) gave higher activities than the corresponding monometallic complexes (5, 7). The titanium complexes gave polymers with higher molecular weight (M w ) than the zirconium complexes. The molecular weight distribution (M w /M n ) of the polymers obtained from the pyridine diamide complexes were much broader than that of the normal metallocene catalysts.

Polymerizations of propene, 1-butene and 1-hexene were conducted with a mixture of rac- and meso-[dimethylsilylenebis(2-methylindenyl)]zirconium dichloride (1) combined with methylaluminoxane (MAO), triethylaluminium (AlEt 3 ))/triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) or triisobutylaluminium (AliBu 3 )/2 as a cocatalyst. The polymerization profiles of propene with rac-1 and meso-1 were determined from the rate of overall propene consumption and the fractions of isotactic and atactic polymers which were sampled during polymerization. An induction time to reach the maximum R p (rate of polymerization) followed by gradual decay was observed in the case of using the systems rac-, meso-1-MAO and rac-1-AliBu 3 /2. Besides, a rapid drop of R p from the initial value was found when using AlEt 3 /2. Molecular weights of the isotactic and atactic polymers sampled do not change during polymerization, and it is suggested that the change of [C * ] (number of active centers) is reflected in the profiles of R p . The rate ratio of rac-1 to meso-1 (R p (rac)/R p (meso)) in propene and 1-butene polymerizations decreases in the following order: AlEt 3 /2 > AliBu 3 /2 > MAO. In the case of 1-hexene polymerization, the highest R p (rac)/R p (meso) value was obtained. This result indicates that the coordination of 1-hexene to the sterically hindered site of meso-1 is difficult compared with propene and 1-butene.

Polymerization of 1,7-octadiene was conducted with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1), syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2) and aspecific bis(cyclopentadienyl)zirconium dichloride (3) metallocene catalysts combined with methylaluminoxane. The microstructure of the poly(1,7-octadiene)s produced was characterized by means of 'H NMR, 13 C NMR and DEPT (distortionless enhancement by polarization transfer) spectroscopy. A portion of monomeric units in poly(1,7-octadiene)s is saturated as a result of cycloaddition. The fraction of the saturated units (cyclization selectivity) decreases in the following order: 1 > 3 > 2. The effect of polymerization temperature was studied, and the cyclization selectivity was found to decrease with lowering the polymerization temperature. The monomer concentration affects the microstructure of poly(1,7-octadiene), and the cyclization selectivity is drastically decreased with increasing monomer concentration.

Monocyclopentadienyl compounds, CpMCl3 (M = Ti, Zr) supported on activated MgCl2 were used for the polymerizations of ethylene in the presence of methylaluminoxane (MAO) or a common alkylaluminium as a cocatalyst. By supporting CpMCl3 on MgCl2, the catalyst activity was increased drastically to show high activity similar to MgCl2-supported TiCl4 catalysts. The activity of the CpZrCl3 /MgCl2 catalyst was higher than that of the CpTiCl3/MgCl2 one. Both catalysts gave polymers with high molecular weight (Mw) and broad molecular weight distribution (Mw/Mn) in comparison with the corresponding soluble half-metallocene catalysts.

Pyruvic acid (3) was found to be arylated chemoselectively at the a-ketocarbonyl carbon in P2O5-MsOH affording decarbonylative α,α-diarylated products 5, decarbonylative a-monoarylated compounds 6, or non-decarbonylative α,α-diarylated adducts 7 depending on the reactivity of arenes (4a-g), in contrast to Lewis acid-catalyzed reaction of its acid chloride (2).

Photoinduced nematic (N)-to-isotropic (I) and thermal I–N phase transition behaviour of liquid crystals (LCs) with donor–acceptor azobenzenes was investigated. Photoirradiation of mixtures of the azobenzenes and host LC resulted in N–I phase transition due to trans–cis photoisomerisation of the azobenzenes, and the N phase recovered when the irradiated sample was kept in the dark because of thermal cis–trans back-isomerisation. Time-resolved measurements with a laser pulse (355 or 532 nm; 10 ns fwhm) revealed that the photoinduced N–I phase transition took place within 200–300 µs in all samples. The rate of the thermal I–N phase transition was affected strongly by the strength of the donor and the acceptor. The response time of the thermal I–N phase transition corresponded closely to the lifetime of the cis isomer of the azobenzenes, hence we can conclude that the rate-determining step of the thermal recovery of the N phase was the cis–trans isomerisation process. The time necessary for the thermal I–N phase transition decreased with increasing donor and acceptor strength, because the thermal cis–trans isomerisation of the azobenzene with a stronger donor–acceptor pair became faster. The N phase recovered within 500 ms in the mixture of the azobenzene (with tertiary amine as the donor and nitro group as the acceptor) and host LC at 37°C.

The formation of real-time holographic gratings was investigated in an azobenzene polymer liquid crystal (PLC) possessing a siloxane spacer in the side chain. Irradiation of thin films of the PLCs created a phase grating which is ascribed to periodic induction of the nematic-to-isotropic (N–I) phase transition due to photochemical trans–cis isomerization of the azobenzene moiety (photochemical phase transition). It was found that the N–I phase transition temperature of the PLC with the siloxane spacer was lower than that of the PLC without the siloxane spacer owing to flexibility of the siloxane units. This property resulted in a decrease in the irradiation temperature, leading to effective induction of the photochemical N–I phase transition by suppression of thermal cis–trans back-isomerization of the azobenzene moiety. Thus formation of the grating in the PLC having the siloxane spacer could be achieved by low intensity of the interference light compared to that in conventional PLCs including only alkyl spacers. Moreover, a grating with narrower fringe spacing could be created by depression of propagation of perturbation due to trans–cis photoisomerization of the azobenzene moiety in the LC phase.

The synthesis, optical and electrical properties of azobenzene-substituted polythiophene derivatives at the 3-position are reported: one without flexible spacer (PT0) and the other with a hexamethylene spacer (PT6). Photoirradiation of PT6 at 366 nm caused trans-cis isomerization of the azobenzene moiety and this photochromic reaction induced a change in conductivity of the thin film of PT6: the conductivity was 1.1×10 –7 S cm –1 before irradiation and 8.3×10 –7 S cm –1 after photoirradiation. After annealing, the conductivity of the film returned to the initial value. The conductivity of a compound without the azobenzene moiety, α-terthienyl (αT3), showed no change on photoirradiation at 366 nm.

Freestanding crosslinked liquid-crystalline polymer films obtained by self-assembly through intermolecular hydrogen bonding showed photoinduced bending and unbending. The structural change at the microscopic level, caused by trans–cisphotoisomerization of the azobenzene moieties at the hydrogen-bonded crosslinks, is successfully converted into a macroscopic deformation in the liquid-crystalline polymer films.

To explore the effect of orientation of monomers and polymerization procedure on polymerization behavior, thermal polymerization and photopolymerization of vinyl monomers having a biphenyl structure were conducted at various temperatures. It was found that the initial rate of polymerization and conversion increased with temperature despite phases of the monomer. It was also observed that Arrhenius plots for the initial rates of photopolymerization fell on a straight line, while those of thermal polymerization changed the slope at the smecticisotropic or nematic-isotropic phase transition temperature. The number-average molecular weight of the polymer produced in the thermal polymerization in the smectic phase was higher than that in the isotropic phase, whereas that of the polymer obtained by photopolymerization in the smectic phase was lower than that in the isotropic phase. These results suggest that polymerization behavior is affected by the initiation method in the polymerization of liquid-cr...

The orientational behavior for a series of side-chain liquid-crystalline polysiloxanes incorporating azo chromophores, i.e., poly(3-{4-[(4-nitrophenyl)azo]phenyl]oxycarbonyl}propylmethylsiloxane)-co-(3-carboxypropylmethylsiloxane) (P1), poly {3-[(6-{[4-[(4-nitrophenyl)azo]phenyl]oxy}hexyl)oxycarbonyl]propylmethylsiloxane}-co-(3-carboxypropylmethylsiloxane) (P2), and poly{3-[(11-{[4-[(4-nitrophenyl)azo]phenyl]oxy}undecyl)oxycarbonyl]propylmethylsiloxane}-co-(3-carboxypropylmethylsiloxane) (P3) were investigated by UV-Vis and polarized FTIR-ATR spectroscopy as well as X-ray diffraction measurement using their thin films. P1 exhibited highly-ordered smectic and nematic phases as the mesophases. On the other hand, P2 and P3 showed only smectic C phase. The mesogenic chromophores of these polymers in smectic phases and the once-annealed solid were spontaneously aligned nearly normal to a substrate surface. In the case of P1, the tilt angle of the mesogenic chromophores in the nematic phase was found t...

Four non-bridged dimethylzirconocene complexes. i.e., bis(η 5 -cyclopentadienyl )dimethylzirconium (1), (η 5 -cyclopentadienyl) (η-fluorenyl)dimethylzirconium (2), bis(η 3 -indenyl)dimethylzirconium (3) and (η 5 -cyclopentadienyl)(η 5 -pentamethylcyclopentadienyl)dimethylzirconium (4) were synthesized and used as a catalyst for the methyl methacrylate polymerization combined with triphenylmethyl tetrakis(pentafluorophenyl)borate in the presence of ZnEt 2 or Al(i-Bu) 3 . The catalyst activity strongly depends on the zirconocene compound and decreases in the order 2 > 1 >> 3 4. The polymerization proceeds in a living manner when 1 and 2 are used combined with ZnEt 2 . On the other hand, stereoregularities of the resulting polymers are independent of the zirconocene compound, and syndiotactic-rich polymers are formed by a chain-end controlled mechanism.

The alignment behavior of nematic liquid crystal (LC) on the surface of four types of polyimide (PI) films, three aromatic PIs and a PI with an alicyclic dianhydride, exposed to linearly polarized light of long wavelength (366 nm) was investigated by polarizing microscopy. It was found that the alignment of the LC was induced by all of the exposed PIs and the alignment direction of the LC was perpendicular to the polarization direction of the linearly polarized light. The degree of uniformity of LC alignment increased with increasing exposure energy incident on PI films. To produce the uniform alignment state, the PI with an alicyclic dianhydride had to be exposed to higher energy than aromatic PIs. Ultraviolet (UV) -visible spectroscopy indicated that the absorbance changes of the aromatic PIs were much smaller than that of the PI with an alicyclic dianhydride when uniform alignment of the LC was caused. Furthermore, both UV-visible and infrared spectroscopy showed the change in the absorbance of the aromatic PI with a diphenyl ether diamine was still very small even though it was exposed to linearly polarized light with a large dose. These results demonstrate that the aromatic PIs are more favorable as a photosensitive alignment layer and the uniform alignment of the LC can be induced without significant destruction of the chemical structure of PI with a diphenyl ether diamine.

Photoinduced alignment behavior in a series of polymer liquid crystals containing different azobenzene moieties in the side chain was investigated. With increase of the strength of donor and acceptor at 4 and 4‘ positions of the azobenzene groups, the possibility of an alignment change in the polymer liquid crystals having the same methacrylic backbone decreased due to the slightly increased enthalpic stability of the mesophase and the significantly decreased concentration of cis-azobenzene, although the cis−trans isomerization rate increased. However, a high alignment efficiency was observed in polymer liquid crystal ACB-ABA6, which contained strong donor−acceptor pairs in the azobenzene moiety and exhibited low stability of mesophase, since both the rate of cis−trans isomerization and the mobility of mesogens are favorable for alignment change. Three different relaxation processes were observed in the aligned polymer liquid crystals.

Polymerization of propene was conducted by [t-BuNSiMe2Flu]TiMe2-based catalysts at −50 °C in the presence of trioctylaluminum. When B(C6F5)3 was used as a cocatalyst, polymer yield monotonically increased with increasing polymerization time. The polypropene obtained showed narrow molecular weight distribution, and the number average molecular weight of the polymer linearly increased against the polymer yield. In addition, the number of polymer chains, which was approximately a half the number of Ti used, was almost constant during the polymerization. The living nature of the [t-BuNSiMe2Flu]TiMe2 catalyst depended on polymerization temperature and cocatalyst. Deactivation occurred at 0 °C or even at −50 °C when Ph3CB(C6F5)4 was used in place of B(C6F5)3. 13C NMR analysis of the polymer indicated that the living polymerization proceeded highly regiospecifically via 1,2-insertion to give syndiotactic-rich polymer. Polymerization of 1-hexene with [t-BuNSiMe2Flu]TiMe2/B(C6F5)3 also proceeded in a living manner...

Polymer/liquid crystal (LC) composite films possessing an azobenzene LC as a photoresponsive molecule (AzoCFs) were prepared by the thermal polymerization-induced phase separation method. The composite films (AzoCFs) showed a strong light-scattering state after polymerization, and their optical properties were strongly affected by the compositional ratio of the liquid crystals in the composite film. Change in the transmittance between a light-scattering and a transparent state could be induced isothermally by photoirradiation. Upon irradiation at 366 nm, AzoCFs changed from the light-scattering state to the transparent state. This is ascribed to nematic (N)−isotropic (I) phase transition due to trans−cis isomerization of the azobenzene molecules in the LC domains within the polymer matrix. Furthermore, restoration of the initial state could be achieved by visible-light irradiation (>420 nm), resulting from the I−N phase transition induced by cis−trans back-isomerization of the azobenzene guest molecules.

Polydomain films of liquid crystalline polymer (MACB-AB6) with low content (6 mol %) of azobenzene units were prepared and irradiated with linearly polarized light at 366 nm, thus inducing an alignment of the photochromic side groups as well as the nonphotoactive mesogens, the cyanobiphenyl groups. An induced order parameter, S, was obtained from polarized UV and IR spectroscopy, and it increased with increase in temperature at first and then decreased due to phase transition. The effect of light intensity on the alignment behavior has been investigated in detail. Alignment change can take place even for a low intensity (0.7 mW/cm2) of irradiation light. Irradiation light at high intensity induced alignment as well as a phase transition at relatively low temperature. A higher saturation order parameter and faster achievement of the order parameter were obtained, since a higher concentration of cis-azobenzene was produced when the film was exposed to polarized light with a higher intensity. This is due to ...

The excited-state S 2 dynamics of an azobenzene derivative, trans-BMAB, was investigated in solution by femtosecond transient absorption and picosecond single-photon timing fluorescence spectroscopies. The fluorescence was observed at 400 nm with a lifetime ∼250 fs. The S 1 state with an absorption maximum at 410–415 nm was formed with a time constant of ∼250 fs from the S 2 state followed by relaxation with a lifetime of ∼2.3 ps in n -hexane. The stimulated emission from the S 2 state overlapped with the femtosecond transient absorption spectra just after excitation, which was confirmed by polarization absorption spectroscopy.

Optical switching behavior of polymer azobenzene liquid crystal (LC) was investigated by the use of reflection-mode analysis. Intensity of reflected light from the interface between glass substrate...

Photochemical phase transition behavior of polymer azobenzene liquid crystals (LCs) was explored by transmission-mode analysis and reflection-mode analysis. Four samples with different structures were used, which show LC behavior in the trans form but no LC phase in the cis isomer. Attention was focused on the effect of the position of the mesogenic azobenzene moiety in the flexible side chain on the photochemical phase transition behavior. Photoirradiation of a thin film of the azobenzene LCs (∼200 nm) in the trans form resulted in the disappearance of the LC phase due to trans-cis photoisomerization of each mesogen. and the LC phase recovered quickly when the irradiated sample was kept in the dark because of thermal cis-trans back-isomerization. In all polymers, the photochemical LC to isotropic (I) phase transition was induced in 100∼200 us on laser pulse irradiation. In the sample with an azobenzene located apart from the main chain of the polymer by a spacer, the LC-I phase transition took p...