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Dependence of retardation dispersion on the chemical structure of H-shaped reactive molecules.

To develop highly sensitive updatable hologram materials, an azobenzene monomer was synthesized herein that supports effective photoisomerization under visible green beam irradiation. Furthermore, an acetylene group was introduced via Sonogashira coupling for higher birefringence. Polymerization was performed on the synthesized azobenzene monomer and on the methyl methacrylate (MMA) monomer, which serves as the skeleton of the film. The structures of all molecules were characterized by nuclear magnetic resonance (NMR) spectroscopy, and UV-Visible absorption spectroscopy was performed to analyze their optical properties. The holographic writing and rewriting capabilities of the newly synthesized azobenzene side-chain polymer were characterized by using a green laser as a writing beam, which showed that a high diffraction efficiency was reliably achievable under low-energy laser irradiation when evaluated with a four-wave-mixing optical scheme. In this study, high birefringent acetylene group containing azobenzene-based polymers were synthesized as materials for rewritable green-laser holograms, and their properties were evaluated. Birefringence change of polymer, which has an absorption wavelength suitable for green laser (532 nm), is 0.018. The diffraction efficiency of polymer was 72% under low-energy irradiation (7 J/cm2). These results show that the hologram recording material made in this study with high birefringent azobenzene are stable, without undergoing decomposition even when repeated recording and rewriting were performed.

Photorefractive materials are capable of reversibly changing their index of refraction upon illumination. That property allows them to dynamically record holograms, which is a key function for developing an updateable holographic 3D display. The transition from inorganic photorefractive crystals to organic polymers meant that large display screens could be made. However, one essential figure of merit that needed to be worked out first was the sensitivity of the material that enables to record bright images in a short amount of time. In this review article, we describe how polymer engineering was able to overcome the problem of the material sensitivity. We highlight the importance of understanding the energy levels of the different species in order to optimize the efficiency and recording speed. We then discuss different photorefractive compounds and the reason for their particular figures of merit. Finally, we consider the technical choices taken to obtain an updateable 3D display using photorefractive polymer. By leveraging the unique properties of this holographic recording material, full color holograms were demonstrated, as well as refreshing rate of 100 hogels/second.

We herein report the preparation of a soluble polyimide from a photoreactive diamine and a phenolic diamine, to which electro-optic (EO) properties were imparted by the introduction of an EO chromophore (Disperse Red 1) into the phenolic group of the polyimide. Following poling at 1 MV/cm and 210 °C, the polyimide was irradiated with UV light (280–310 nm) to form a photo-crosslinking network. The EO coefficient of the polyimide-containing EO device was 27.7 p.m./V at 1.3 μm, and this value was maintained at ≥90%, even after annealing at 150 °C for 500 h. Our results indicated that the thermal and chemical stabilities of the EO polyamide were remarkably increased due to the photo-crosslinking reaction.

We have synthesized a thermally curable polymeric gate insulator (TFVOB-PVP) through the modification of the well-known poly(4-vinylphenol) (PVP) polymer using a 4-(1,2,2-trifluorovinyloxy)...

We obtained preferential in-plane molecular orientation and charge-transport anisotropy in pentacene thin-film transistors (TFTs) on conventional SiO 2 /Si substrates. The nanoscale SiO 2 grooves with depths of 1–3 nm were prepared by a simple scratching process with diamond powder to create a new type of alignment template for inducing the aligned growth of pentacene with in-plane anisotropy. Results of atomic force microscopy and grazing-incidence X-ray diffraction showed that the nanogrooved SiO 2 structure could control the alignment and growth mode of pentacene, and it remarkably decreased the grain size of the pentacene crystals. The charge-carrier mobility along the parallel axis of the nanogrooved structure (0.392 ± 0.039 cm 2 /(V·s)) was more than four-fold higher than that perpendicular to the alignment (0.104 ± 0.048 cm 2 /(V·s)). In addition, we investigated the effect of nanogrooved SiO 2 's surface roughness on the electrical properties of the pentacene TFT and found out that the surface roughness of SiO 2 dielectric layer was more crucial factor on the device performance compared to the preferential alignment of the pentacene molecule.

We developed a facile method for treating polyimide-based organic gate insulator (OGI) surfaces with self-assembled monolayers (SAMs) by introducing metal-oxide interlayers, called the metal-oxide assisted SAM treatment (MAST). To create sites for surface modification with SAM materials on polyimide-based OGI (KPI) surfaces, the metal-oxide interlayer, here amorphous alumina (α-Al2O3), was deposited on the KPI gate insulator using spin-coating via a rapid sol–gel reaction, providing an excellent template for the formation of a high-quality SAM with phosphonic acid anchor groups. The SAM of octadecylphosphonic acid (ODPA) was successfully treated by spin-coating onto the α-Al2O3-deposited KPI film. After the surface treatment by ODPA/α-Al2O3, the surface energy of the KPI thin film was remarkably decreased and the molecular compatibility of the film with an organic semiconductor (OSC), 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), was increased. Ph-BTBT-C10 molecules were uniformly deposited on the treated gate insulator surface and grown with high crystallinity, as confirmed by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. The mobility of Ph-BTBT-C10 thin-film transistors (TFTs) was approximately doubled, from 0.56 ± 0.05 cm2 V−1 s−1 to 1.26 ± 0.06 cm2 V−1 s−1, after the surface treatment. The surface treatment of α-Al2O3 and ODPA significantly decreased the threshold voltage from −21.2 V to −8.3 V by reducing the trap sites in the OGI and improving the interfacial properties with the OSC. We suggest that the MAST method for OGIs can be applied to various OGI materials lacking reactive sites using SAMs. It may provide a new platform for the surface treatment of OGIs, similar to that of conventional SiO2 gate insulators.

Cholesteric liquid crystals (CLCs) possess a photonic bandgap owing to the helical arrangement of molecules. The CLCs reflect circularly-polarized light of a specific handedness and wavelength, exhibiting colors. The wavelength of the selective reflection, or the structural color, can be easily controlled by varying the concentration of a chiral dopant. Although this unique optical property renders CLCs promising for various applications, their fluidity severely limits the ease of processing and their structural stability. To overcome this limitation, we designed CLC microparticles (CLC-MPs) via photopolymerization of reactive mesogens (RMs) in CLC droplets. Using capillary microfluidic devices, highly uniform emulsion drops of CLC-RM mixtures were prepared in aqueous phase drops, which were then exposed to ultraviolet (UV) irradiation to obtain solid microparticles. The diameter of the CLC-MPs can be precisely controlled by either manipulating the flow rates of the dispersed and continuous phases or varying the diameter of the capillary orifice in the microfluidic devices. The wavelength of reflection and the handedness of the helical structure are selected via the composition of the dispersed phase. The photo-polymerization of RMs leads to the formation of a three-dimensional rigid network, thereby yielding CLC-MPs with high mechanical stability. The CLC-MPs could be further assembled to form two-dimensional hexagonal arrays on flat surfaces or deposited in pre-defined trenches or holes via mechanical rubbing. Moreover, two distinct CLC-MPs with opposite handedness can be patterned to show different color graphics depending on the selection of handedness of circularly-polarized light, which are appealing for anti-forgery patches.

The electrical performance of organic field-effect transistors (OFETs) depends on the quality of thin-film organic semiconductors, which is significantly affected by solution-processing conditions and additional processes. We investigated the effects of post-thermal annealing on the thin-film morphologies of liquid crystalline organic semiconductors on polyimide gate insulator surface and the FET performances of the films. The active material selected for the OFETs was 2-decyl-7-phenyl-[1]benzothieno[3,2 -b ][1]benzothiophene (Ph-BTBT-C 10 ), which shows a highly ordered smectic E (SmE) mesophase and polycrystalline thin films feature very high mobility. We aimed to produce well defined molecular orientation and crystal structure in thin-film Ph-BTBT-C 10 on polyimide gate insulator not typical SiO 2 gate insulator via thermal annealing process. Uniform bilayer- or monolayer-structured polycrystalline thin films were obtained on polymer gate insulator after thermal annealing at a SmE (over 148 °C) and SmA (over 213 °C) liquid crystalline phase temperature, respectively. The OFET using bilayer-structured thin film showed high performance with a mobility of 2.27 cm 2 /V s.

In this study, graphite nanoplatelets (GNPs), known as a thermally conductive and anisotropic carbon material, was used with polyvinyl alcohol (PVA) as matrix, which is a hydrophilic and biodegradable polymer. In order to expect enhanced thermal conductivity, silver nanoparticle-decorated graphite nanoplatelets (Ag-GNPs) were fabricated by adding silver acetate as a precursor using ‘mix-and-heat’ method. Polyvinyl alcohol composite films containing pristine GNPs and Ag-GNPs were prepared using solution casting method. The prepared composite films were uniaxially stretched to induce the filler alignment along the stretching direction as well as the strain-induced crystallization in polymer chains. The effects of the particle size of GNPs, the silver nanoparticle on the surface of GNPs, and the stretching ratios on the thermal conductivity of the composite films were investigated.

In order to develop a green laser rewritable hologram material, azobenzene monomers and polymers were synthesized and holographic properties such as diffraction efficiency, rewritability were measured. As a result, it has been found that even if repeated recording and rewriting are performed, the recoding medium is maintained in a stable state and we confirmed that G#-5/95, which has an absorption wavelength more suitable for green laser (532 nm), has higher diffraction efficiency than G-5/95.

In this paper, we report the fabrication of a polyimide/polyvinyl alcohol (PVA) bilayer gate insulator for low-voltage organic thin-film transistors (TFTs). The introduction of a PVA layer to form a bilayer structure improves the dielectric and insulating properties of the gate insulator. Organic TFTs with 150 nm-thick polyimide and PVA gate insulators were inactive at low operation voltages below 5 V. Conversely, organic TFTs with 150 nm-thick polyimide/PVA bilayer gate insulators exhibited excellent device performances. Our results suggest that the introduction of a PVA layer with a high dielectric constant could be a simple and efficient way to improve the device performance of low-voltage organic TFTs.

The development of high performance and large area photoresponsive materials for hologram have been one of the great challenges in order to realize holographic 3D display technology which needs no special eyewear. Desirable hologram materials should provide the high diffraction efficiency, fast response, high resolution, stable and reversible storage, low-energy consuming in the recording and reading processes as well as easy mass production. Azobenzene-containing polymers has been recognized as one of the promising candidate materials for holography because they can modulate effectively due to the photosensitivity and reversibility of azo moieties. In addition, polymer systems have several advantages such as simple fabrication, flexibility, thermal stability, and large scale production. It has been reported that highly birefringent azotolan-containing liquid crystalline polymer (LCP) film can induce a large change in refractive index upon exposure to actinic light. Analogously, we prepared new photochromic polymers based on the polymerisable liquid crystalline acrylate monomers (RMs) containing azo and highly birefringent diphenyldiacetylen (DPDA) mesogenic units connected directly. Evaluation of new polymers for rewritable hologram media will be discussed.

New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δn) values of 0.32–0.40.

We report here a low-temperature-annealed alumina/polyimide gate insulator with excellent electrical insulating properties for solution-processed ZnO TFTs. In this study, 150 nm-thick polyimide and 20 nm-thick alumina thin films were deposited by a simple spin-coating followed by a 200 °C-annealing process. With the deposition of the alumina interlayer, the surface of the polyimide film was successfully modified. We prepared ZnO TFTs annealed at 230 °C to investigate the potential of the prepared gate insulator. The field-effect mobility and the on/off current ratio of solution-processed ZnO TFTs with an alumina/polyimide gate insulator were 0.11 cm 2 /V s and 1.8 × 10 5 , respectively, whereas a ZnO TFT with a polyimide gate insulator was inactive. The alumina interlayer introduced here might provide a compatible interface for the ZnO semiconductor.

We prepared a poly(imide-benzoxazole) gate insulator for solution-processed flexible metal oxide thin-film transistors (TFTs). The electrical insulating property of the poly(imide-benzoxazole) gate insulator is maintained up to at least 350 °C. The 350 °C-annealed indium-zinc oxide (IZO) TFT with the poly(imide-bezoxazole) gate insulator showed excellent TFT performance with the field-effect mobility of 9.2 cm2 V−1 s−1 and the on/off current ratio of 1.5 × 106. A flexible IZO TFT with the poly(imide-bezoxazole) gate insulator was also fabricated directly on a flexible Kapton substrate. The flexible IZO TFT with the poly(imide-bezoxazole) gate insulator could be operated during bending. Before bending, the mobility and on/off current ratio were 4.1 cm2 V−1 s−1 and 4.7 × 105, respectively. During bending with a radius of 10 mm, the mobility was maintained and the on/off current ratio was slightly decreased to 3.2 × 105.

Highly ordered organic semiconductor micropatterns of the liquid-crystalline small molecule 2,7-didecylbenzothienobenzothiophene (C10 -BTBT) are fabricated using a simple method based on template-assisted self-assembly (TASA). The liquid crystallinity of C10 -BTBT allows solvent-free fabrication of high-performance printed organic field-effect transistors (OFETs).

Surface properties of gate insulators strongly affect the device performance of organic thin-film transistors (OTFTs). To improve the performance of OTFTs, we have developed photo-sensitive polyimide gate insulator with fluorine groups. The polyimide gate insulator film could be easily patterned by selective UV exposure without any photoinitiator. The polyimide gate insulator film, fabricated at 130 °C, has a dielectric constant of 2.8 at 10 kHz, and leakage current density of −10 A/cm 2 while biased from 0 to 90 V. To investigate the potential of the polyimide with fluorine groups as a gate insulator, we fabricated C 10 -BTBT TFTs. The field-effect mobility and the on/off current ratio of the TFTs were measured to be 0.76 ± 0.09 cm 2 /V s and >10 6 , respectively.

We report a facile and cost-effective photo-patterning process to obtain patterned source and drain electrodes in organic thin-film transistors (OTFTs). Instead of conventional photoresist, photo-sensitive polyimide (PSPI) was used in the photo-patterning process. PSPI with cinnamate moieties could be crosslinked by UV-light exposure without any photoinitiator. After the photo-patterning process of this work, gold/PSPI bilayer electrodes were easily prepared and they were used as source and drain electrodes of the pentacene OTFT. The field effect carrier mobility, threshold voltage and on/off current ratio of the pentacene OTFT with the gold/PSPI bilayer electrodes were 0.067 cm 2 /V s, −5.3 V and 1.4 × 10 4 , respectively.

The surface property of a polyimide gate insulator was successfully modified with an n-octadecyl side-chain. Alkyl chain-grafted poly(amic acid), the polyimide precursor, was synthesized using the diamine comonomer with an alkyl side-chain. By adding a base catalyst to the poly(amic acid) coating solution, the imidization temperature of the spin-coated film could be reduced to 200 °C. The 350 nm-thick polyimide film had a dielectric constant of 3.3 at 10 kHz and a leakage current density of less than 8.7 × 10(-10) A cm(-2), while biased from 0 to 100 V. To investigate the potential of the alkyl chain-grafted polyimide film as a gate insulator for solution-processed organic thin-film transistors (TFTs), we fabricated C(10)-BTBT TFTs. C(10)-BTBT was deposited on the alkyl chain-grafted polyimide gate insulator by spin-coating, forming a well-ordered crystal structure. The field-effect mobility and the on/off current ratio of the TFT device were measured to be 0.20-0.56 cm(2) V(-1) s(-1) and10(5), respectively.

Triphenylene (TP)-based liquid crystals, a category of discotic liquid crystals (DLCs), are easy to synthesise, thermally stable and can undergo self-assembly. A new DLC compound, 2,7,10-tris[4-(6-acryloyloxyhexyloxy)benzoate]-3,6,11-tris[(4-hexylphenyl)ethynyl]-triphenylene, was obtained with a 49% yield using catechol as a starting material and features acetylene groups on its TP core. This material can form films with high birefringence through its cross-linkable acrylate ends. Here, we synthesised this new compound and characterised it using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. The thermal behaviour was also investigated using differential scanning calorimetry and polarised optical microscopy. This new asymmetric TP-based DLC compound exhibited a nematic liquid-crystalline phase between −20 and 170°C and formed an optical anisotropic film with a high birefringence (Δn = 0.21–0.25).

We have developed photo-sensitive, low-temperature processable, soluble polyimide (PSPI) gate insulator with excellent resistance to the photo-patterning process. The PSPI was synthesized through one-step condensation polymerization of monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) and 3,5-diaminobenzyl cinnamate (DABC). PSPI thin film, fabricated at 160 °C, has a dielectric constant of 3.3 at 10 kHz, and leakage current density of −10 A/cm 2 , while biased from 0 to 100 V. PSPI could be easily patterned by selective UV-light exposure and dipping into γ-butyrolactone. To investigate the potential of the polyimide as the photo-patternable gate insulator, we fabricated pentacene OTFTs and confirmed the PSPI’s resistance to the photo-patterning process. The photo-patternable polyimide shows promise as gate dielectrics for OTFTs.

We modified the surface of a polyvinyl alcohol (PVA) layer by self assembly monolayer technique using a fluorine substituted silane compound (1H,1H,2H,2H-perfluorooctyl-trichlorosilane: FTS) to protect a pentacene thin-film transistor (TFT) from O2 and H2O. Surface modified PVA showed very low surface energy with water contact angle of 106.2 degrees. Surface treatment of PVA layer on pentacene TFT device was done in toluene solvent and we did not observe any damage to the PVA layer or pentacene TFT devices during surface modification process. Pentacene TFT with surface modified PVA passivation layer exhibited very stable TFT operation with almost no field effect mobility drop or threshold voltage shift up to 400 hrs. The performance of unpassivated OTFTs exponentially degraded and almost failed in 290 hrs. We propose that modified PVA layer can be used as a good passivation layer for oxygen and water in OTFT.

We have synthesised a series of new reactive mesogens with photopolymerisable di-acrylates and their corresponding non-reactive analogues based on the π-conjugated aromatic core, fluorene (F)-di-[thiophene (T)-benzene (B)], using the Stille and Suzuki coupling reaction. The effect of lateral alkyl chains on the 9-position of the central fluorene moiety as well as α, ω- side alkyl chains attached to the π-conjugated aromatic core on the mesomorphism was investigated by utilising differential scanning calorimetry (DSC) and polarising optical microscopy (POM). A wide angle X-ray scattering (WAXS) study at the various temperatures was also carried out to reveal phase structures. Photopolymerisable di-acrylates connected directly to the rigid aromatic core showed higher phase transition temperatures, probably due to the induced dipole moment in comparison with those of a non-reactive methyl–ether counterpart.

We introduce a photo-curable polyimide-based gate insulator for organic thin-film transistors (OTFTs) that allows low-temperature and solution-based processing and provide low leakage current density and high field-effect mobility in devices. Organic gate insulator (PI-TTE) was prepared from a blend of 75.2 wt% hydroxyl group containing polyimide (PI) and 23.8 wt% trimethylolpropane triglycidyl ether as the crosslinker, 0.5 wt% benzoyl peroxide, and 0.5 wt% triphenylsulfonium triflate as the photoacid generator (PAG). PI-TTE showed extremely low leakage current density as 2.33 × 10−10 A/cm2 at 3.3 MV/cm and exhibited a very stable capacitance (96.74 pF/mm2) and it is unchangeable up to 600 hrs. Pentacene TFT using PI-TTE as a gate dielectric showed a field effect mobility as 0.203 cm2/Vs and an on/off ratio of 1.55 × 105 with almost no hysteresis.

We present a technique to record refreshable holographic stereograms continuously. We eliminated the translation stage that shifts the recording beams back and forth and replaced it with an uninterrupted transparent belt holding holographic lenses. The belt is driven along a perimeter, shifting the lens laterally in front of a photorefractive screen without reversing direction. The holographic lenses focus the object beam onto holographic pixels and are permanently recorded in a thin photopolymer. The photopolymer material is flexible enough for the lenses to follow the curvature of the belt when it goes around the tensioning rollers. The hogel data are uploaded sequentially onto a spatial light modulator to form the object beam. The rotation of the belt in one single direction allows for a continuous operation and a much faster recording speed than with a translation stage that needs to reverse direction at the end of its travel span.

This report discusses the preparation and the unusual mesomorphism of three homologues of photopolymerisable triphenylene ether compounds. These homologues showed ‘a cold crystallisation’ on heating differential scanning calorimetry curves, and this phenomenon is attenuated with increase methylene units, spacers between the triphenylene core and the terminal photopolymerisable acrylate group. Classical textures of hexagonal columnar (Colh) mesophase were observed by polarising optical microscopy for all three photopolymerisable mesophase compounds described here. Also described is the mesomorphism of their intermediates, hydroxylalkoxytriphenylenes. In some cases, the discotic columnar hexagonal mesophases were confirmed by wide angle X-ray scattering techniques.

High dielectric constant (k) metal oxides such as hafnium oxide (HfO2) have gained significant interest due to their applications in microelectronics. In order to study and control the surface properties of hafnium oxide, self-assembled monolayers (SAMs) of four different long aliphatic molecules with binding groups of phosphonic acid, carboxylic acid, and catechol were formed and characterized. Surface modification was performed to improve the interface between metal oxide and top deposited materials as well as to create suitable dielectric properties, that is, leakage current and capacitance densities, which are important in organic thin film transistors. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle goniometry, atomic force microscopy (AFM), and simple metal-HfO2-SAM-metal devices were used to characterize the surfaces before and after SAM modification on sol-gel processed hafnium oxide. The alkylphosphonic acid provided the best monolayer formation on sol-gel processed hafnium oxide to generate a well-packed, ultrathin dielectric exhibiting a low leakage current density of 2x10(-8) A/cm2 at an applied voltage of -2.0 V and high capacitance density of 0.55 microF/cm2 at 10 kHz. Dialkylcatechol showed similar characteristics and the potential for using the catechol SAMs to modify HfO2 surfaces. In addition, the integration of this alkylphosphonic acid SAM/hafnium oxide hybrid dielectric into pentacene-based thin film transistors yields low-voltage operation within 1.5 V and improved performance over bare hafnium oxide.

One of the most challenging tasks in fabricating multilayer polymer light-emitting diodes (PLEDs) is to develop robust hole-transporting materials that possess matched energy level with indium tin oxide (ITO) anode and the highest occupied molecular orbital (HOMO) of light-emitting polymers to facilitate efficient hole injection and transport. In this article, a series of thermally cross-linkable 4,4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA) derivatives have been synthesized to explore their function as efficient hole-transporting materials for blue-emitting electrophorphorescent devices. In particular, their excellent solvent resistance enables them to be used in the double hole-transporting layer (HTL) device configuration to facilitate cascade hole injection. The effects of cross-linking temperature and the functional group on the compatibility between two HTLs are investigated through optical and atomic force microscopy. When vinylbenzyl ether is used as the cross-linking group for TCTA, it shows t...

A series of novel hole-transporting materials (HTMs) bearing thermally cross-linkable styryl groups have been synthesized and characterized. These HTMs could be in situ cross-linked under mild thermal polymerization without any initiator. The cross-linking temperatures (150–180 °C) for these HTMs are substantially lower than that typically used for curing perfluorocyclobutane (PFCB)-based HTMs (230 °C). After cross-linking, the resultant HTMs form robust, smooth, and solvent-resistant networks, which enables the subsequent spin-coating of emissive layer (EML). The HTMs based on an ether linkage connecting triarylamine dimers exhibited better hole-transporting ability compared to their corresponding monotriarylamine compounds due to higher content and closer distance of the hole-transporting units. Most importantly, the milder cross-linking condition for these HTMs allows the commonly used conducting polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), to be incorporated as the b...

One of the most challenging tasks encountered in developing highly efficient electro-optic (EO) devices is to find a material system that possesses all desirable properties such as large EO coefficients, good thermal and mechanical stability, and low optical loss. In order to meet this stringent requirement, we have developed a series of crosslinkable EO dendrimers using the standardized AJL8-type chromophore as the center core and the furyl- and anthryl-containing dendrons as the periphery. Upon adding a trismaleimide (TMI) dienophile, these dendrimers could be in-situ crosslinked via the Diels-Alder cycloaddition and efficiently poled under a high electric field. Through this dynamic process, the spatially voided and π-electron-rich surrounding of the chromophore core changes into a dense and more aliphatic network, with the dipolar chromophore embedded and aligned inside. The resultant materials exhibit large EO coefficients (63-99 pm V -1 at 1.31 μm), excellent temporal stability (the original r 33 values remain unchanged at 100 °C for more than 500 h), and blue-shifted near-IR absorption. With these combined desirable properties, a poled EOD2/TMI film could be processed through multiple lithographic and etching steps to fabricate a racetrack-shaped micro-ring resonator. By coupling this ring resonator with a side-polished optical fiber, a novel broadband electric-field sensor with high sensitivity of 100 mV m -1 at 550 MHz was successfully demonstrated.

Organic and polymer light-emitting diodes (LEDs) have been the subject of intensive investigation in recent years because of their potential as emissive elements for flat-panel displays and white-light sources for general lighting. As dualinjection devices, multilayer structures with discrete hole-injection layers (HILs) and/or hole-transport layers (HTLs), light-emitting layers (EMLs), and electron-transport layers (ETLs) are necessary for high efficiency, where these layers can be optimized, respectively, according to their functions. [1–3] For LEDs based on small molecules, it is rather straightforward to adopt this multilayer strategy via layer-bylayer vacuum deposition. However, for polymer-based LEDs, where solution-based casting or spin-coating is the basic way to form films, it is very challenging to form multilayer structures, because of solvent erosion of previously deposited layers during spin-coating. [4] To overcome this problem, a

Three dendron−linear diblock copolymers with a polyene-type nonlinear optical (NLO) chromophore incorporated in the dendron segment and polystyrene as the linear block were synthesized to investigate the effect of nanostructures on electrooptic (EO) properties. These block copolymers form nanostructures with a periodicity between 36 and 44 nm, which can be characterized using atomic force microscopy (AFM). High EO coefficients (r33) up to 64 pm/V can be achieved in these materials that only have relatively low chromophore concentrations (the highest one is 18 wt %). The resulting poled copolymers also showed good temporal stability. More than 81% of the original r33 value can be retained after being isothermally heated at 85 °C for more than 500 h. On the contrary, the results from the guest−host systems (the chromophore was dispersed into polystyrene) only exhibited lower r33 values and very poor thermal stability (less than 30% of the original r33 values remained after 120 h at 85 °C). These results cle...

Poled electro-optic (EO) polymers have enabled many advances in the exploration of high-speed and broadband information technologies. Polymer based EO devices have been demonstrated to have large bandwidths (over 110 GHz), low driving voltages, and sustain their performance in a flexible form or under extreme environmental conditions. For optical circuits, EO polymers can be easily integrated with striplineor ring-structured waveguides made of sol–gels, low-loss fluorinated polymers, silicon slots, conducting oxides, and photonic crystals. Recently, EO polymers have also been utilized for the generation/detection of a gap-free pulsed THz system with a bandwidth up to ca. 12 THz. Large numbers of discrete photonic components need to be inserted into integrated systems of telecommunication and silicon microphotonics, especially where an extreme amount of data is required to travel in a very small space. Therein lies the great challenge for polymer-based EO technologies: to have thermally stable EO coefficients (r33) of around 500 pm V at wavelengths of 1.31 or 1.55 lm. Currently, the most commonly used materials for polymeric EO devices are based on poled polymers with r33 values around 50–80 pm V at wavelengths of 1.31 or 1.55 lm. In these materials, dipolar nonlinear optical (NLO) chromophores have been doped or incorporated at a level of ca. 20– 25 wt % to reach their maximum r33 values. [5–10] Beyond such a moderate loading of chromophores, strong intermolecular electrostatic interactions severely limit the poling-induced polar order and cause phase-separation problems between chromophores and polymers. To further improve EO activity, research efforts have focused on developing shape-engineered chromophores with high molecular optical nonlinearities (lb), where lb is a product of first hyperpolarizability and the dipole moment of the NLO chromophore, and increasing order within the matrices by controlling the nanoscale architecture of macromolecules. In our recent study we have demonstrated, using Diels–Alder (DA) “click chemistry” to post-functionalize NLO chromophores onto polymers, that high chromophore loading levels (up to 35 wt %) and large r33 values (up to 110 pm V) could be achieved in in situ generated side-chain dendronized NLO polymers with non-reacted chromophores as guest dopants. This opens a new avenue to explore optimal host–guest combinations and to develop an efficient way to control lattice hardening in these hybrid polymers. The ultimate goal is to simultaneously achieve very large EO activity, good thermal stability, high optical transparency, and excellent mechanical properties within the same material via molecular design and facile processing. In this paper, we report a novel method to disperse a highly efficient secondary chromophore into in situ crosslinked NLO polymer networks, leading to both enhanced EO activity (> 260 pm V at 1.31 lm) and alignment stability at 85 °C. In photorefractive (PR) polymers and liquid-crystal (LC) systems, binary chromophore mixtures have been shown to elevate the loading density of small dipolar dyes without causing phase separation. We have extended this further by incorporating highly polarizable NLO chromophores into these binary systems. In addition, DA click chemistry has also been employed to improve the physical properties of these materials. This combined effort demonstrates that binary mixtures of large-bl chromophores can be loaded into side-chain NLO matrices and efficiently poled to give EO activities higher than the summed value of two added chromophores. These systems can also be mildly cured to ensure a thermally stable EO response. The EO polymers studied in this work exist as a three-component host–guest system (Fig. 1). The host polymer is a copolymer, poly[(methyl methacrylate)-co-(9-anthracenyl methyl methacrylate)] (PMMA-AMA), with around 10 mol % of the anthracenyl moiety. To this host, AJC146 was added together with compound 1a, 1b, or 1c as binary guest chromoC O M M U N IC A TI O N S

We have designed and developed novel lanthanide(III)-cored supramolecular systems with light-harvesting dendritic arrays for advanced photonics applications such as planar waveguide amplifiers, plastic lasers, and light-emitting diodes. The supramolecular ligands, such as naphthalenes and metalloporphyrins, were specially designed and synthesized in order to provide enough coordination sites to form stable lanthanide(III)-chelated complexes. The energy levels of the supramolecular ligands were tailored to maintain the effective energy transfer process from supramolecular ligands to lanthanide(III) ions for getting a higher optical amplification gain. Also, efficient energy transfer pathways for the sensitization of lanthanide ions by supramolecular ligands were investigated, for the first time to the best our knowledge. Furthermore, to enhance the optophysical properties of novel supramolecular systems, aryl ether-functionalized dendrons as photon antennas have been incorporated into lanthanide-cored supramolecular systems, yielding novel lanthanide-cored dendritic materials with efficient site-isolation effect.

Functionalized azacryptands containing resorcinol derivatives such as orcinol (5-methylresorcinol), 3,5-dihydroxybenzoic acid (5-carboxyresorcinol), and methyl 3,5-dihydroxybenzoate (5-methoxycarbonylresorcinol) were synthesized by one-pot synthesis in the presence of potassium carbonate with moderately good yields for advanced photonic materials, such as optical amplifying and light-emitting materials, for the first time to our knowledge.

We have investigated the development of lanthanide-cored supramolecular complexes containing porphyrins to circumvent the solubility problem and improve the optical amplification property. The new synthetic methodology has been developed and accomplished through the ligand-exchange model reaction using ErCl3 to optimize its synthetic condition. First, we designed and synthesized the model compounds to investigate coordination property between the ligand and the lanthanide ion. In addition, with these synthetic results, lanthanide-cored supramolecular complexes based on porphyrins were synthesized and characterized. Highly coordinated lanthanide-cored model complexes (at least 8 to 10 coordination) showed the strong near infrared emission at 1525 nm, corresponding to the characteristic 4I13/2→ 4I15/2 transition of trivalent erbium ions.

We have developed novel lanthanide-cored supramolecular systems with highly efficient light-harvesting dendritic arrays for integrated planar waveguide-typed amplifiers. Er3+ ions were encapsulated by the supramolecular ligands, such as porphyrins and macrobicyclics. The supramolecular ligands have been designed and synthesized to provide enough coordination sites for the formation of stable Er(III)-chelated complexes. For getting a higher optical amplification gain, also, the energy levels of the supramolecular ligands were tailored to maintain the effective energy transfer process from supramolecular ligands to erbium(III) ions. Furthermore, to maximize the light-harvesting effect, new aryl ether-functionalized dendrons as photon antennas have been incorporated into lanthanide-cored supramolecular systems. In this paper, molecular design, synthesis and luminescent properties of novel lanthanidecored integrated supramolecular systems with highly efficient light-harvesting dendritic arrays will be discussed.

E-mail: jwka@krict.re.krReceived November 16, 2011, Accepted November 23, 2011Key Words : Calix[4]pyrrole, Fluorescence probes, Calix[2]pyreno[2]pyrrole, TNTThe elevated selectivity and sensitivity for specific analytesare the core requirements for an ideal chemical probes. Asignal induced by guest binding must be sensitive enough sothat accurate real time monitoring could be satisfactorilyachieved.

In this paper, we report synthesis and characterization of alkylated fullerene derivatives for solution-processable organic thin film transistors and solar cells. Their physical, thermal, and semiconducting properties have been studied. Organic thin-film transistors fabricated from C60TH-Oc exhibit electron mobilities as high as 3.2 x 10(-2) cm2 V(-1) s(-1) with 32 V of a threshold voltage. The best power conversion efficiency (PCE) was observed in a layered structure P3HT:C60TH-Oc (PCE = 0.44%), which was a twice value of P3HT:C60TH-Dd (PCE = 0.23%).