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We prepared crosslinked azobenzene main-chain liquid-crystalline polymers (MCLCPs), in which the exchange of crosslinks can be brought about by transesterification reactions. The exchangeab...

We prepared 2 types of crosslinked liquid-crystalline polymers (CLCPs) (polyacrylates) with the same side-chain length but a different position of an azobenzene moiety in the side chain. We...

Poly(4-vinylpyridine) (P4VP) brushes were grafted onto a substrate via Cu(0)-mediated atom transfer radical polymerization and 1-pyrenebutyric acid (PBA) was incorporated into the brushes t...

We developed a novel block copolymer composed of poly(ethylene oxide) (PEO) and polymethacrylate functionalized with liquid–cryst-alline oligothiophene by using the atom transfer radical polymeriza...

Crosslinked liquid-crystalline polymers (CLCPs) containing azobenzene moieties show reversible macroscopic deformation upon irradiation with light. The deformation of CLCPs strongly depends on alig...

We prepared crosslinked azotolane liquid-crystalline polymer (LCP) films doped with a stilbene derivative (two-photon chromophore) utilizing an interpenetrating polymer network (IPN) structure. The IPN films bend toward the light source upon irradiation with femtosecond laser pulses at 600 nm, which can excite the stilbene derivative by two-photon absorption. The bending speed of the IPN films increases with the square of the laser pulse intensity, which is compelling evidence for the two-photon processes.

We have synthesized a photo-crosslinkable polythiophene copolymer functionalized with a cinnamate moiety to improve the stability of organic photovoltaic (OPV) cells. The active layer of OPV cells is generally bulk heterojunction (BHJ) that consists of two or more organic semiconductors. When BHJ forms a micro-phase-separated structure with a blend of two organic materials, its structure inclines to change into a macro-phase-separated one after some time. To stabilize the BHJ morphology, we used a crosslinkable polymer containing a cinnamate moiety. The copolymer film became insoluble after UV irradiation because of [2+2] dimerization of the cinnamate groups.

We synthesized polymers containing a liquid-crystalline (LC) oligothiophene moiety in the side chain. This oligothiophene shows LC behavior between 101°C and 194°C in its original form, while when incorporated into the side chains of a polymer, the resultant polymer showed a nematic phase in a much wider temperature range. Thin films of these polymers showed nano-phase-separated structures with domain sizes of 15–40 nm upon annealing.

Crosslinked liquid-crystalline polymers (CLCPs) show unique behavior of deforming macroscopically when stimulated with heat, electricity and light. However, they cannot be remolded and reshaped once prepared. Here, we designed crosslinked polysiloxane with side chain mesogens that contain exchangeable crosslinking points based on transesterification between phenyl benzoates and hydroxy groups. After the formation of a polymer network, a base catalyst was introduced into the CLCP. When heated at 80°C, a piece of the CLCP was reshaped into a film and separate pieces of the CLCP were fused together, indicating that the CLCP is remoldable.

We prepared photomobile polymer materials composed of crosslinked azobenzene liquid-crystalline polymers (LCPs) and methacrylates with interpenetrating polymer network (IPN) structures, and explored their photoresponsive behavior. The IPN films exhibited reversible bending upon photoirradiation. In addition, the durability of the IPN films was much higher than that of the pristine crosslinked azobenzene LCP films.

Various fabrication methods of photomobile polymer materials containing photochromic moieties have been developed to improve their photoresponsive and mechanical properties. Here, we newly prepared photomobile polymer materials with interpenetrating polymer network (IPN) structures. The IPN films, which are composed of azobenzene liquid crystalline polymer (LCP) and polymethacrylates, showed reversible bending behavior upon exposure to UV and visible light. Bending speed of the IPN films became higher with decreasing glass-transition temperature of polymethacrylate components. The IPN film containing poly(dodecyl methacrylate) showed faster bending than the pristine azobenzene LCP film.

Organic light-emitting diodes (OLEDs) based on conjugated polymers exhibiting polarized emission have attracted much attention because of their potential as backlights for conventional liquid crystal (LC) displays and 3-D displays. We have reported a new series of LC polymers based on donor-acceptor architecture containing an oxadiazole (OXD) and several amine moieties in the same side chain, which exhibit bipolar character with a wide energy band gap. In this study, to develop phosphorescent OLEDs with polarized emission, we synthesized a platinum complex, Pt(4-decyloxy)salen, with emitting property, and fabricated the device consisting of Pt complex as a guest and LC polymers as a host material. The Pt complex exhibited high thermal stability, good solubility and an emission peak at 530 nm in dichloromethane. To obtain electroluminescense from the Pt complex, we fabricated ITO/rubbed PEDOT:PSS/Pt(4-decyloxy)salen:host polymer/MgAg devices. The devices emitted a yellowish green light, which was dominated...

Organic light-emitting diodes (OLEDs) based on chromophore-containing liquid crystals (LCs) can emit polarized light due to self-assembly of mesogenic chromophores. The stability of LC phases in LC polymers with a mesogenic group in the main chain is higher than that in the polymers containing a mesogenic group in the side chain. In this study, a novel family of polyesters containing a carbazole moiety as a hole-transporting unit and an oxadiazole (OXD) moiety as an electron-transporting unit in the main chain, P10-DOXDCz and P16-DOXDCz, were designed and synthesized. These polyesters were prepared by transesterification of N-hexyl-3,6-di[2-([1,3,4]oxadiazol-5-yl)-4-methylbenzoate]carbazole and 1,10-decanediol or 1,16-hexadecanediol at 220 °C for 20 h. They showed a nematic phase. Both P10-DOXDCz and P16-DOXDCz emitted intense blue fluorescence with a maximum at 439 nm and 450 nm in thin films, respectively, and their fluorescence quantum yields were 0.74 and 0.81 in solution, respectively. Both compounds...

Crosslinked azobenzene liquid-crystalline polymer films have been prepared by in-situ photopolymerization, and their photoinduced changes in birefringence and stress on macroscopic motion were investigated. Upon exposure to UV light, the film bent toward an actinic light source along the rubbing direction, and the bent film also reverted to the initial flat state after exposure to visible light at room temperature. Moreover, the birefringence simultaneously decreased and the stress was generated upon UV irradiation. These results indicate that the molecular alignment in the film becomes disordered by trans-cis photoisomerization of the azobenzene moieties and the resultant contraction of the film generates the stress.

We prepared crosslinked azobenzene liquid-crystalline polymer brushes on flexible polymer films by surface-initiated atom transfer radical polymerization and a subsequent crosslinking reaction. Reversible isomerization of azobenzene moieties was observed in the crosslinked films upon irradiation with UV and visible light. Upon exposure to linearly polarized UV light, the films bent slightly along the polarization direction of light toward an actinic light source. After turning off the UV light, the films maintained the bent shape, and then reverted to the initial form by irradiation with visible light. We have successfully developed a novel photomobile material with crosslinked azobenzene liquid-crystalline polymer brushes.

We proposed a new approach to fabricate bilayer films with a crosslinked azobenzene liquid-crystalline (LC) polymer. The polyethylene (PE) substrates were coated with linear azobenzene LC polymers, and then the azobenzene layers were crosslinked by irradiation with electron beams (EBs). In the EB-irradiated films with ordered azobenzene moieties, exposure to UV light caused trans-cis isomerization and the change in alignment of azobenzene moieties. Bending of the bilayer films could be induced toward an actinic light source when they were irradiated from the side of the azobenzene layer, while they bent away from the actinic light source upon UV irradiation from the side of the PE layer. In both cases, the bent films reverted to the initial flat state by turning off the light, which could be repeated at room temperature.

Crosslinked liquid-crystalline polymer films with a different content of an azobenzene moiety were prepared by in-situ photopolymerization, and their photoresponsive behavior was investigated. Observation of the films by polarized absorption spectroscopy and polarizing optical microscopy has revealed that the azobenzene moieties are aligned along the rubbing direction in the films. Upon irradiation with UV light, a film with 5 mol% of the azobenzene bent toward an actinic light source along the rubbing direction. The bent film reverted completely to the initial state upon irradiation with visible light. On the other hand, films with 3 and 1 mol% of the azobenzene showed no obvious bending by continuous irradiation with UV light. The bent film also reverted to the flat state upon continuous irradiation with UV light.

A telechelic poly(N-isopropylacrylamide) (PNIPAM) with azobenzene end-groups (telechelic Az-PNIPAM) was prepared by reversible addition-fragmentation chain transfer (RAFT) free radical polymerization of NIPAM. This polymer self-assembles in cold water forming nanoparticles with a hydrodynamic radius (R H) of 8 nm and an aggregation number of 29 chains. The thermoresponsive behavior of Az-PNIPAM in water was investigated by turbidimetry and light scattering. In addition, the photoresponsive behavior of aqueous Az-PNIPAM was investigated by monitoring the changes with temperature of the solution and transmittance at 650 nm before and after irradiation at 366 nm.

Blue-emitting polymers based on a donor-acceptor architecture composed of oxadiazole and carbazole moieties containing various substituted groups in the same side chain were used as a host polymer in phosphorescent polymer light-emitting diodes (PhPLEDs). The polymer containing N-methylcarbazole showed a liquid-crystalline (LC) phase above its glass transition temperature but the other polymer containing N-ethylhexylcarbazole exhibited an amorphous phase. The single-layer PLEDs using these polymers exhibited blue emission with peaks from 430 to 440 nm. To examine the LC polymer (LCP) and the amorphous polymer as host materials, we fabricated simple devices using Ir(ppy)3 and (btp)2lr(acac) as phosphorescent dopants at various doping concentrations. The device composed of lTO/PEDOT-PSS/2 wt% of (btp)2Ir(acac) doped into LCP/MgAg showed intense red light (0.67, 0.32) with the luminance efficiency of 4.7 cd/A. The luminance efficiency of the PhPLEDs using the LCP was higher than that of the PhPLEDs using the...

Two azobenzene-containing block copolymers with an oxyethylene (P1) or an alkyl (P2) spacer in the side chain were prepared by atom transfer radical polymerization (ATRP). Neither of the block copolymers with a low azobenzene content showed a liquid-crystalline phase. However, their glass transition temperatures (T gs) were lowered by introducing flexible spacers. In particular, T g was lowered by about 30°C in P1. Their photoalignment and holographic behavior was investigated at various temperatures in thin films. Rapid changes in refractive index were induced in the P1 films upon irradiation at a temperature below T g. But the photoinduced birefringence in the P1 film was lower than that in the P2 films. Similar results were obtained in holographic recording. The azobenzene-containing block copolymer with the oxyethylene spacer (P1) used in this study has potential application for dynamic hologram.

Laminated films composed of a flexible plastic sheet and a crosslinked azobenzene liquid-crystalline polymer (CLCP) layer with different initial alignment of azobenzene mesogens were prepared by thermal compression bonding of a CLCP film and an unstretched low-density polyethylene (PE) film with an adhesion layer. In both laminated films with a homogeneous alignment of mesogens and a homeotropic one, large movements could be induced by irradiation with UV light at room temperature. A partly laminated film with homogeneous CLCP bent from both ends of the whole film, while one with homeotropic CLCP bent up from the center of the film toward the light source. These results indicate that we enable plastic films with no photoresponsive property to move flexibly upon photoirradiation just by laminating the CLCP layers partly, and the photoinduced motions of the laminated films are completely dependent on the alignment direction of the mesogens in the CLCP layers. In addition, it was found that the maximum stres...

A block copolymer containing an azobenzene (Az) moiety in the side chain was prepared by atom transfer radical polymerization (ATRP). For comparison, a random copolymer with a similar Az content was also designed. Their photoresponsive and holographic behavior was investigated in thin films. The block copolymer film showed microphase separation with cylinder microdomains after annealing, which was then irradiated at 366 nm. It was found that trans-cis photoisomerization in the block copolymer film was slower than that in the random copolymer film. This may be due to the restricted motion of the Az moieties in the Az blocks. The photoinduced birefringence (Δn) of the block copolymer film was higher than that of the random copolymer film upon irradiation with a linearly polarized beam. In holographic recording, similar results were obtained. A block copolymer with 22-mol% Az showed a liquid-crystalline (LC) phase, while a random copolymer with 24-mol% Az exhibited no LC phase. The block copolymer showed an ...

Fabrication of a microlens array film was explored by means of photoinduced reorientation of dye-doped polymerizable liquid crystals (LCs). LC monomer/photoinitiator mixtures doped with a small amount of an oligothiophene derivative were irradiated with a 488-nm beam from an Ar+ laser. Then the sample cell was periodically moved. After these two processes were repeated for a few tens times, remaining photoinitiators were quenched by irradiation with UV light. Observation of the cells with a polarizing optical microscope revealed that the molecular alignment of LCs induced by the Ar+ laser beam remained unchanged after the beam was turned off and a microlens array with a square-lattice type was obtained. This indicates that formation of the microlens and photopolymerization of the LC monomers are brought about simultaneously in a small area. The fabricated microlens has polarization selectivity that reflects molecular alignment. The focal length of the microlens arrays could be changed by controlling the i...

To precisely control the first-order diffraction efficiency of holographic gratings recorded in an amphiphilic diblock liquid-crystalline copolymer P40A37, effect of recording time on grating formation and enhancement was studied systematically. Several parameters such as surface relief, the first-order diffraction efficiency, the maximum transmittance under an optical polarizing microscope and order parameters of grating samples were evaluated before and after annealing. Then the enhancement coefficient with recording time was estimated. The best enhancement effect was obtained at 10-s recording upon nano-scaled phase separation. By precisely adjusting the recording time, the diffraction efficiency of holographic gratings in P40A37 can be finely controlled from 0.13% to 10%.

Plastic films coated with crosslinked liquid-crystalline polymer (CLCP) layers containing azobenzene moieties (plastic/CLCP bilayer films) were prepared by thermal polymerization of mixtures of an azobenzene monomer and a crosslinker placed between a plastic film and a glass substrate. When the glass substrate was untreated, the obtained bilayer film bent slightly away from the UV light source when irradiated on the CLCP layer side. This bending direction was the same as that of a hybridly aligned CLCP film. When the glass substrate was coated with a rubbed polyimide to strengthen the homogeneous alignment of the azobenzene moieties of the CLCP surface layer, the obtained bilayer film bent toward the irradiation direction of the incident UV light. It was the same as a homogeneously aligned CLCP film and the degree of bending was larger than that of the untreated sample. This means that the photoinduced bending behavior of the plastic/CLCP bilayer films strongly depends on the alignment of the azobenzene m...

Three azobenzene acrylate monomers containing alkyl spacers of different length were synthesized. Thermodynamic and mesomorphic properties of the monomers were measured by differential scanning calorimetry and polarizing optical microscopy. A crosslinker with the undecyl spacer was also synthesized to prepare crosslinked liquid-crystalline polymer films by photopolymerization. Polarized UV spectra and polarizing optical micrographs demonstrated that the mesogens are aligned homogeneously in the films. Low glass transition temperature of the films enabled them to bend near room temperature upon UV irradiation. Besides, the films generally bent away from the light source before they at last bent towards the light irradiation.

After being pre-treated upon irradiation of unpolarized light at 366 nm, an azobenzene-containing liquid-crystalline polymer film was photoinduced alignment by one linearly polarized laser beam at 488 nm, leading to a large birefringence of 0.21. Then holographic gratings were recorded in the pre-irradiated polymer films by interference of two coherent laser beams. Little surface relief was obtained by the holographic recording process, indicating that a refractive-index grating paid most of contributions to the diffraction efficiency. Because the cooperative motion of the azobenzene mesogens were eliminated in the cis-azobenzene-rich isotropic film by the pre-irradiation, multi-processes of the refractive-index gratings were successfully achieved. The obtained grating structures were clearly shown in the polarizing optical microscopic pictures, which were also verified by their diffraction patterns. The azobenzene-containing liquid-crystalline polymer used in this study has potential application in high-...

An amphiphilic diblock liquid-crystalline copolymer consisting of poly(ethylene oxide) (PEO) and polymethacrylate containing an azobenzene moiety in the side chain was prepared by atom transfer radical polymerization (ATRP). The specifically-designed chemical constitution and the low molecular-weight polydispersity enable the block copolymer to form a regular microphase-separated nanostructure self-assembled in its bulk films, in which a hexagonal packing of the PEO cylinders normal to the substrates was dispersed in a continuous phase of azobenzene mesogens with out-of-plane alignment. Then a commerically available rubbing technique was first used to control the microphase-separated domains in the copolymer films. By introducing novel supramolecular cooperative motions between ordered azobenzene mesogens and PEO microphase domains, macroscopic array of PEO nanocylinders was regularlly formed along the rubbing direction. Both the dotted and parrallel stripe patterns of PEO nanocylinders were successfully ...

Input and output grating couplers with a grating period of 1.3 µm were fabricated in an azobenzene liquid-crystalline polymer film by holography. When a He-Ne laser beam at 633 nm was incident to the input grating, the beam was coupled, propagated in the polymer film, and then was taken out from the output grating. The coupling efficiency of the input and output coupler was estimated as about 1.1% in TE mode. Upon irradiation of the film with UV light to cause trans-cis photoisomerization of the azobenzene moiety, the intensity of the output beam was repeatedly changed.

Liquid-crystalline polymers containing an oxadiazole moiety as an electron-transporting unit and a carbazole moiety as a hole-transporting unit in the same side chain were designed and synthesized to investigate electroluminescent (EL) properties. The synthesized polymers showed high fluorescence quantum efficiency. Furthermore, it was found that the luminescent polymers possessed bipolar carrier-transporting property. The single-layer organic light-emitting diode was fabricated to demonstrate EL emission. The device, ITO glass/the polymer/MgAg, exhibited intense blue emission with a maximum brightness of 30 cd/m2 at 30 V.

The change in transmittance of a 1.55-μm laser beam was investigated by a photochemical phase transition of an azobenzene liquid-crystalline polymer. Effects of the intensity of actinic light and temperature on the photoresponsive behavior were explored using laser beams at 633 nm and 1.55 μm. It was found that the intensity of the actinic light or temperature affected on the response, regardless of the wavelength of the probe beam.

We have synthesized two types of azobenzene liquid-crystalline polymers with a tolane moiety exhibiting high birefringence: one is the copolymer having an azobenzene moiety and a 3-ring tolane group in the side chain (PA-3T) and the other is the polymer containing a long mesogen core, in which the azobenzene group is directly connected to the tolane moiety (P3AT). The values of 0.35 and 0.39 in birefringence were obtained in PA-3T and P3AT, respectively. When the film was irradiated with a writing beam at 488 nm, the change in birefringence was efficiently induced with P3AT compared with PA-3T.

Optical switching of a 1.55-μm laser beam was explored by means of photochemical phase transition of polymer and low-molecular-weight azobenzene liquid crystals (LCs). It was observed that the 1.55-μm laser beam could be repeatedly switched by turning on and off the actinic light, and a large change in refractive index was induced in the azobenzene LCs at the near infrared region. It was also found that controlling the thickness of LCs could enhance the change in the transmittance of the 1.55-μm laser.

A series of poly(alkyl methacrylate)s having azobenzene and cyanobiphenyl moieties were synthesized and their optical properties were characterized. The effect of content of the photosensitive unit and the length of alkyl chain of a transparent unit on the photoresponsive alignment behavior was investigated. The azobenzene monomer (photoresponsive unit), the cyanobiphenyl monomer (mesogenic unit), and the alkyl methacrylate monomers with methyl, ethyl, n-butyl, hexyl or lauryl group (transparent unit) were copolymerized to yield transparent polymer films. Upon irradiation of LPL at 488 nm, a uniaxial optical anisotropy was generated due to the molecular alignment. The photoinduced alignment behavior was strongly dependent on the alkyl chain length and the intensity of the actinic light.

The azobenzene liquid-crystalline gel (LCG) films with macroscopic uniaxial alignment were prepared to investigate photoresponsive behavior. By polarizing microscopy, fiber-like structures aligned in one direction were observed. Furthermore, with a confocal laser scanning microscope (CLSM), it was confirmed that the fiber-like structures were formed even in the bulk of the LCGs. When the LCG films were irradiated with UV light below Tg, changes in the microscopic surface morphology were observed, while no appreciable macroscopic change was observed. On the other hand, when the LCGs were plasticized by suspending in solvents or heating above Tg, the LCG films showed macroscopic changes (e.g. bending) upon UV light irradiation. The bending and unbending could be repeated just by changing the wavelength of the irradiation light. It was suggested that the bending is induced by an absorption gradient which produces a volume difference between the front surface area and the bulk of the gel films.

Unique characteristics were observed in phase-type gratings which were formed in polymer liquid crystal (PLC) films. We have investigated the formation and the properties of the holographic gratings recorded in PLCs with azobenzene moieties (photoresponsive unit). Two types of PLCs were examined: homopolymers of azobenzene monomers (PALC) and copolymers with a tolane moiety (mesogenic unit with a high birefringence) in the side chain. The diffraction efficiency (η) was enhanced in the LC phase. We obtained the value of η of 31% while it was less than 1% in a glassy state in the Raman-Nath regime. This difference may be due to the modulation of refractive index (Δn) based on alignment change of mesogens in the PLC film. In addition, we attempted the holographic image storage of three-dimensional (3-D) objects in the PLC film. The 3-D object was reconstructed with high resolution (>5,000 lines/mm).

Several kinds of symmetric and asymmetric phenylene-thienylene co-oligomers substituted with alkyl, alkoxy, ester or cyano groups in the ends were newly synthesized. Liquid-crystalline (LC) properties of these compounds were evaluated by differential scanning calorimetry and polarizing optical microscopy. It was found that all the compounds showed an LC phase. The photoinduced reorientation behavior of the dye-doped nematic LCs was investigated upon exposure to an Ar+ laser beam at 488 nm. The change in refractive index was estimated to be larger than 0.1. It was revealed that the dyes synthesized act as an efficient trigger for the photoinduced reorientation.

The use of a crosslinked azobenzene liquid-crystalline polymer (CALP) system for micro-integrated actuators becomes especially attractive. CALPs can deform along the alignment direction of mesogens upon irradiation of UV/visible light owing to photochemical phase transition. In this study, to improve the bending speed, CALP films with a homogenous alignment on one surface and a homeotropic alignment on the opposite surface (hybrid alignment) were prepared and their bending behavior was investigated. The films showed photoinduced bending whose direction was determined by the surface alignment treatment, and the bending speed was greatly enhanced upon irradiation from both surfaces of the film at the same time.

A novel liquid-crystalline polymer (LCP) containing an azobenzene group directly connected to a tolane moiety (azotolane moiety) was synthesized. The LCP showed a nematic phase in a broad temperature range (> 200°C). Trans-cis photoisomerization and cis-trans thermal isomerization occurred even though the LCP contains a long azotolane moiety. The homogeneously aligned film of the LCP exhibited an extremely large value of Δn (0.70 at 633 nm). Upon irradiation with a pumping beam in the LC phase, a large change in Δn was induced due to destruction of the homogeneous alignment of the azotolane moieties.

We report the synthesis and physical properties of crosslinked liquid-crystalline polymer (CLCP) fibers consisting of a liquid-crystalline monomer and an acrylate monomer with a hydroxyl group that acts as a reactive site for crosslinking. By differential scanning calorimetry, the CLCP fibers showed a glass transition temperature around 60°C. Polarizing optical microscopy revealed that we obtained fibers with high orientation of mesogens along the fiber axis. The CLCP fibers showed deformations induced by heated the fiber to an isotropic phase.