Nanoporous Ultra‐Low‐Dielectric‐Constant Fluoropolymer Films via Selective UV Decomposition of Poly(pentafluorostyrene)‐block‐Poly(methyl methacrylate) Copolymers Prepared Using Atom Transfer Radical Polymerization

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(methyl methacrylate) (PMMA) (PFS‐b‐PMMA) have been synthesized using atom transfer radical polymerization (ATRP). Then, nanoporous fluoropolymer films have been prepared via selective UV decomposition of the PMMA blocks in the PFS‐b‐PMMA copolymer films. The chemical composition and structure of the PFS homopolymers and copolymers have been characterized using nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), and molecular‐weight measurements. The cross‐sectional and surface morphologies of the PFS‐b‐PMMA copolymer films before and after selective UV decomposition of the PMMA blocks have been studied using field‐emission scanning electron microscopy (FESEM). The nanoporous fluoropolymer films with pore sizes in the range 30–50 nm and porosity in the range 15–40 % have been obtained from the PFS‐b‐PMMA copolymers of different PMMA content. Dielectric constants approaching 1.8 have been achieved in the nanoporous fluoropolymer films which contain almost completely decomposed PMMA blocks.     

Confined Ferroelectric Properties in Poly(Vinylidene Fluoride‐co‐Chlorotrifluoroethylene)‐graft‐Polystyrene Graft Copolymers for Electric Energy Storage Applications

Dielectric polymer film capacitors having high energy density, low loss and fast discharge speed are highly desirable for compact and reliable electrical power systems. In this work, we study the confined ferroelectric properties in a series of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐polystyrene [P(VDF‐CTFE)‐g‐PS] graft copolymers, and their potential application as high energy density and low loss capacitor films. Thin films (ca. 20 μm) are prepared by different processing methods, namely, hot‐pressing or solution‐casting followed by mechanical stretching at elevated temperatures. After crystallization‐induced microphase separation, PS side chains are segregated to the periphery of PVDF crystals, forming a confining interfacial layer. Due to the low polarizability of this confining PS‐rich layer at the amorphous–crystalline interface, the compensation polarization is substantially decreased resulting in a novel confined ferroelectric behavior in these graft copolymers. Both dielectric and ferroelectric losses are significantly reduced at the expense of a moderate decrease in discharged energy density. Our study indicates that the best performance is achieved for a P(VDF‐CTFE)‐g‐PS graft copolymer with 34 wt‐% PS; a relatively high discharged energy density of approximately 10 J cm^?3 at 600 MV m^?1, a low dielectric loss (tanδ = 0.006 at 1 kHz), and a low hysteresis loop loss (17.6%) at 550 MV m^?1.     

Self‐Healing Materials via Reversible Crosslinking of Poly(ethylene oxide)‐Block‐Poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) Block Copolymer Films

The application of well‐defined poly(furfuryl glycidyl ether) (PFGE) homopolymers and poly(ethylene oxide)‐b‐poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) block copolymers synthesized by living anionic polymerization as self‐healing materials is demonstrated. This is achieved by thermo‐reversible network formation via (retro) Diels‐Alder chemistry between the furan groups in the side‐chain of the PFGE segments and a bifunctional maleimide crosslinker within drop‐cast polymer films. The process is studied in detail by differential scanning calorimetry (DSC), depth‐sensing indentation, and profilometry. It is shown that such materials are capable of healing complex scratch patterns, also multiple times. Furthermore, microphase separation within PEO‐b‐PFGE block copolymer films is indicated by small angle X‐ray scattering (lamellar morphology with a domain spacing of approximately 19 nm), differential scanning calorimetry, and contact angle measurements.     

Temperature Responsive Solution Partition of Organic–Inorganic Hybrid Poly(N‐isopropylacrylamide)‐Coated Mesoporous Silica Nanospheres

A series of poly(N‐isopropylacrylamide)‐coated mesoporous silica nanoparticle materials (PNiPAm‐MSNs) has been synthesized by a surface‐initiated living radical polymerization with a reversible addition–fragmentation chain transfer (RAFT) reaction. The structure and the degree of polymerization of the PNiPAm‐MSNs has been characterized by a variety of techniques, including nitrogen sorption analysis, ²⁹Si and ¹³C solid‐state NMR spectroscopy, transmission electron microscopy (TEM), and powder X‐ray diffraction (XRD). The thermally induced changes of the surface properties of these polymer‐coated core–shell nanoparticles have been determined by examining their partition activities in a biphasic solution (water/toluene) at different temperatures.     

Highly Porous Crosslinkable PLA‐PNB Block Copolymer Scaffolds

Poly(lactic acid) (PLA)‐block‐poly(norbornene) (PNB) copolymers which bear photocrosslinkable cinnamate side‐chains are synthesized by combining the ring‐opening metathesis polymerization (ROMP) of norbornenes with the ring‐opening polymerization (ROP) of lactides. Highly porous 3D scaffolds with tunable pore sizes ranging from 20 to 300 µm are fabricated through liquid–solid phase separation. Scaffolds with an average pore size around 250 µm, which are under investigation as bone grafting materials, are reproducibly obtained from freeze‐drying 5% w/v benzene solutions of PLA‐b‐PNB copolymers at −10 °C. As a demonstration of the impact of photocrosslinking of cinnamate side‐chains, scaffolds are exposed to UV radiation for 8 h, resulting in a 33% increase in the compressive modulus of the polymeric scaffold. The foams and the methodology described herein represent a new strategy toward polymeric scaffolds with potential for use in regenerative medicine applications.     

Soluble Phenanthrenyl‐Imidazole‐Presenting Regioregular Poly(3‐octylthiophene) Copolymers Having Tunable Bandgaps for Solar Cell Applications

We have used Grignard metathesis polymerization to successfully synthesize a series of regioregular polythiophene copolymers that contain electron‐withdrawing and conjugated phenanthrenyl‐imidazole moieties as side chains. The introduction of the phenanthrenyl‐imidazole moieties onto the side chains of the regioregular polythiophenes increased their conjugation lengths and thermal stabilities and altered their bandgap structures. The bandgap energies, determined from the onset of optical absorption, could be tuned from 1.89 eV to 1.77 eV by controlling the number of phenanthrenyl‐imidazole moieties in the copolymers. Moreover, the observed quenching in the photoluminescence of these copolymers increases with the number of phenanthrenyl‐imidazole moieties in the copolymers, owing to the fast deactivation of the excited state by the electron‐transfer reaction. Both the lowered bandgap and fast charge transfer contribute to the much higher external quantum efficiency of the poly(3‐octylthiophene)‐side‐chain‐tethered phenanthrenyl‐imidazole than that of pure poly(3‐octylthiophene), leading to much higher short circuit current density. In particular, the short circuit current densities of the device containing the copolymer having 80 mol % phenanthrenyl‐imidazole, P82 , improved to 14.2 mA cm^–2 from 8.7 mA cm^–2 for the device of pure poly(3‐octylthiophene), P00 , an increase of 62 %. In addition, the maximum power conversion efficiency improves to 2.80 % for P82 from 1.22 % for P00 (pure P3OT ). Therefore, these results indicate that our polymers are promising polymer photovoltaic materials.     

Synthesis,Morphology, and Properties of Poly(3‐hexylthiophene)‐block‐Poly(vinylphenyl oxadiazole) Donor–Acceptor Rod–Coil Block Copolymers and Their Memory Device Applications

Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT₄₄ ‐b‐ POXD₁₈ /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.     

Threshold Reduction in Polymer Lasers Based on Poly(9,9‐dioctylfluorene) with Statistical Binaphthyl Units

We introduce novel statistical copolymers of poly(9,9‐dioctylfluorene), PFO, which contain various concentrations of 6,6′‐(2,2′‐octyloxy‐1,1′‐binaphthyl) spacer groups. We demonstrate that, owing to the large dihedral angle (> 60°) between neighboring naphthalene units, we could hinder the formation of the highly ordered β‐phase in thin films of the copolymers. In low‐temperature photoluminescence measurements, the typical signature of the PFO β‐phase at 442 nm is no longer observed for copolymers with a binaphthyl concentration of about 12 %. Moreover, the optical properties of the copolymers resembled those of the glassy α‐phase PFO. Second‐order distributed feedback (DFB) lasers based on thin films of the homopolymer PFO showed a minimum lasing threshold of 11.7 μJ cm^–2 (λ_max = 452 nm, excitation at λ = 337 nm with 500 ps pulses). With increasing binaphthyl concentration in the copolymer backbone, the lasing threshold steadily decreased to 3 μJ cm^–2 for a binaphthyl concentration of about 12 %. Therefore, our novel copolymers provide a vast improvement for PFO‐based optoelectronics.     

Microphase‐Separated Donor–Acceptor Diblock Copolymers: Influence of HOMO Energy Levels and Morphology on Polymer Solar Cells

The synthesis of novel semiconducting donor–acceptor (D–A) diblock copolymers by means of nitroxide‐mediated polymerization (NMP) is reported. The copolymers contain functional moieties for hole transport, electron transport, and light absorption. The first block, representing the donor, is made up of either substituted triphenylamines (poly(bis(4‐methoxyphenyl)‐4′‐vinylphenylamine), PvDMTPA) or substituted tetraphenylbenzidines (poly(N,N′‐bis(4‐methoxyphenyl)‐N‐phenyl‐N′‐4‐vinylphenyl‐(1,1′‐biphenyl)‐4,4′‐diamine), PvDMTPD). The second block consists of perylene diimide side groups attached to a polyacrylate backbone (PPerAcr) via a flexible spacer. This block is responsible for absorption in the visible range and for electron‐transport properties. The electrochemical properties of these fully functionalized diblock copolymers, PvDMTPA‐b‐PPerAcr and PvDMTPD‐b‐PPerAcr, are investigated by cyclic voltammetry (CV), and their morphology is investigated by transmission electron microscopy (TEM). All diblock copolymers exhibit microphase‐separated domains in the form of either wire‐ or wormlike structures made of perylene diimide embedded in a hole‐conductor matrix. In single‐active‐layer organic solar cells, PvDMTPD‐b‐PPerAcr reveals a fourfold improvement in power conversion efficiency (η = 0.26 %, short‐circuit current (I_SC) 1.21 mA cm^–2), and PvDMTPA‐b‐PPerAcr a fivefold increased efficiency (η = 0.32 %, I_SC = 1.14 mA cm^–2) compared with its unsubstituted analogue PvTPA‐b‐PPerAcr (η = 0.065 %, I_SC = 0.23 mA cm^–2).     

Solution‐Processible Blue‐Light‐Emitting Polymers Based on Alkoxy‐Substituted Poly(spirobifluorene)

Alkoxy‐substituted poly(spirobifluorene)s and their copolymers with a triphenylamine derivative have been synthesized by Ni(0)‐mediated polymerization. The polymers were well soluble in common organic solvents. Pure blue‐light emissions without the long wavelength emission of poly(fluorene)s have been observed in the fluorescence spectra of polymer thin films. The light emitting diodes with a device configuration of ITO/PEDT:PSS(30 nm)/polymer(60 nm)/LiF(1 nm)/Al(100 nm) have been fabricated. The electroluminescence spectra showed the blue emissions without the long wavelength emission as observed in the fluorescence spectra. The relatively poor electroluminescence quantum yield of the homopolymer (0.017% @ 20 mA/cm²) with color coordinates of (0.16, 0.07) has been improved by the introduction of triphenylamine moiety, and the copolymer with triphenylamine derivative exhibited an electroluminescence quantum yield of 0.15 % at 20 mA/cm² with color coordinates of (0.16, 0.08). Moreover, the introduction of polar side chains to the spirobifluorene moiety enhanced the device performance and led to the quantum yields of 0.6 to 0.7 % at 20 mA/cm², although there was some expense of color purities.     

Ferritin–Polymer Conjugates: Grafting Chemistry and Integration into Nanoscale Assemblies

Controlled free radical polymerization chemistry is used to graft polymer chains to the corona of horse spleen ferritin (HSF) nanocages. Specifically, poly(methacryloyloxyethyl phosphorylcholine) (polyMPC) and poly(PEG methacrylate) (polyPEGMA) chains are grafted onto the nanocages by atom transfer radical polymerization (ATRP), in which the molecular weight of the polymer grafts is controlled by the monomer‐to‐initiator feed ratio. PolyMPC and polyPEGMA‐grafted ferritin show a generally suppressed inclusion into diblock copolymer films relative to native ferritin, and the polymer coating is seen to mask the ferritin nanocages from antibody recognition. The solubility of polyPEGMA‐coated ferritin in organic solvents enables its processing with polystyrene‐block‐poly(ethylene oxide) copolymers, and selective integration into the PEO domains of microphase‐separated copolymer structures.     

Nanostructured Poly(styrene‐b‐butadiene‐b‐styrene) (SBS) Membranes for the Separation of Nitrogen from Natural Gas

The preparation and characterization of new, tailor‐made polymeric membranes using poly(styrene‐b‐butadiene‐b‐styrene) (SBS) triblock copolymers for gas separation are reported. Structural differences in the copolymer membranes, obtained by manipulation of the self‐assembly of the block copolymers in solution, are characterized using atomic force microscopy, transmission electron microscopy, and the transport properties of three gases (CO₂, N₂, and CH₄). The CH₄/N₂ ideal selectivity of 7.2, the highest value ever reported for block copolymers, with CH₄ permeability of 41 Barrer, is obtained with a membrane containing the higher amount of polybutadiene (79 wt%) and characterized by a hexagonal array of columnar polystyrene cylinders normal to the membrane surface. Membranes with such a high separation factor are able to ease the exploitation of natural gas with high N₂ content. The CO₂/N₂ ideal selectivity of 50, coupled with a CO₂ permeability of 289 Barrer, makes SBS a good candidate for the preparation of membranes for the post‐combustion capture of carbon dioxide.     

A High‐k Fluorinated P(VDF‐TrFE)‐g‐PMMA Gate Dielectric for High‐Performance Flexible Field‐Effect Transistors

A newly synthesized high‐k polymeric insulator for use as gate dielectric layer for organic field‐effect transistors (OFETs) obtained by grafting poly(methyl methacrylate) (PMMA) in poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) via atom transfer radical polymerization transfer is reported. This material design concept intents to tune the electrical properties of the gate insulating layer (capacitance, leakage current, breakdown voltage, and operational stability) of the high‐k fluorinated polymer dielectric without a large increase in operating voltage by incorporating an amorphous PMMA as an insulator. By controlling the grafted PMMA percentage, an optimized P(VDF‐TrFE)‐g‐PMMA with 7 mol% grafted PMMA showing reasonably high capacitance (23–30 nF cm^?2) with low voltage operation and negligible current hysteresis is achieved. High‐performance low‐voltage‐operated top‐gate/bottom‐contact OFETs with widely used high mobility polymer semiconductors, poly[[2,5‐bis(2‐octyldodecyl)‐2,3,5,6‐tetrahydro‐3,6‐dioxopyrrolo [3,4‐c]pyrrole‐1,4‐diyl]‐alt‐[[2,2′‐(2,5‐thiophene)bis‐thieno(3,2‐b)thiophene]‐5,5′‐diyl]] (DPPT‐TT), and poly([N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)) are demonstrated here. DPPT‐TT OFETs with P(VDF‐TrFE)‐g‐PMMA gate dielectrics exhibit a reasonably high field‐effect mobility of over 1 cm² V^?1 s^?1 with excellent operational stability.     

Controlled Pattern Formation of Poly[2‐methoxy‐5‐(2′‐ethylhexyloxyl)–1,4‐phenylenevinylene] (MEH–PPV) by Ink‐Jet Printing

A detailed survey on the processing of poly[2‐methoxy‐5‐(2′‐ethylhexyloxyl)–1,4‐phenylenevinylene] (MEH–PPV) solutions via ink‐jet printing and the subsequent characterization of the resulting films is reported. The printability of MEH–PPV dissolved in different solvents, and with varied concentrations, is studied. Limitations of the printability of highly concentrated polymer solutions are overcome by using ultrasonication. The pattern formation of the resulting lines is explained in relation to the contact angle formed by the MEH–PPV solution on the substrate and interchain interactions. A uniform thickness distribution of MEH–PPV films is obtained when toluene is used as the solvent. Further improvement on the surface quality of the lines is achieved by optimizing the printing parameters. The line stability as a function of the print‐head velocity is also studied. Additionally, current–voltage (I–V) characteristics and the morphology of the MEH–PPV films, as determined by atomic force microscopy, are discussed.     

Intramolecular Donor–Acceptor Regioregular Poly(3‐hexylthiophene)s Presenting Octylphenanthrenyl‐Imidazole Moieties Exhibit Enhanced Charge Transfer for Heterojunction Solar Cell Applications

Intramolecular donor–acceptor structures prepared by covalently binding conjugated octylphenanthrenyl‐imidazole moieties onto the side chains of regioregular poly(3‐hexylthiophene)s exhibit lowered bandgaps and enhanced electron transfer compared to the parent polymer, e.g., conjugation of 90 mol% octylphenanthrenyl‐imidazole moieties onto poly(3‐hexylthiophene) chains reduces the optical bandgap from 1.91 to 1.80 eV, and the electron transfer probability is at least twice as high as that of pure poly(3‐hexylthiophene) when blended with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester. The lowered bandgap and the fast charge transfer both contribute to much higher external quantum efficiencies, thus much higher short‐circuit current densities for copolymers presenting octylphenanthrenyl‐imidazole moieties, relative to those of pure poly(3‐hexylthiophene)s. The short‐circuit current density of a device prepared from a copolymer presenting 90 mol% octylphenanthrenyl‐imidazole moieties is 13.7 mA · cm^?2 which is an increase of 65% compared to the 8.3 mA · cm^?2 observable for a device containing pure poly(3‐hexylthiophene). The maximum power conversion efficiency of this particular copolymer is 3.45% which suggest that such copolymers are promising polymeric photovoltaic materials.     

Fluorene‐Based Copolymers for Red‐Light‐Emitting Diodes

The syntheses of new fluorene‐based π‐conjugated copolymers; namely, poly((5,5″‐(3′,4′‐dihexyl‐2,2′;5′,2″‐terthiophene 1′,1′‐dioxide))‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTORT), poly((5,5″″‐(3″,4″‐dihexyl‐2,2′:5′,2′:5″,2‴:5‴,2″″‐quinquethiophene 1″,1″‐dioxide))‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTTORTT), and poly((5,5‐E‐α‐(2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTCNVT), are reported. In the solid state, PFTORT and PFTCNVT present red–orange emission (with a maximum at 610 nm) while PFTTORTT shows a red emission with a maximum at 666 nm. In all cases, electrochemical measurements have revealed p‐ and n‐dopable copolymers. All these copolymers have been successfully tested in simple light‐emitting diodes and show promising results for orange‐ and red‐light‐emitting devices.     

High‐Conductivity Poly(3,4‐ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices

The conductivity of a poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso‐erythritol (1,2,3,4‐tetrahydroxybutane), or 2‐nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded‐coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded‐coil conformations may become dominant in the treated PEDOT:PSS film. This conformational change results in the enhancement of charge‐carrier mobility in the film and leads to an enhanced conductivity. The high‐conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light‐emitting diodes and photovoltaic cells fabricated using such high‐conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode.     

Synthesis of Amphiphilic Copolymers of Poly(ethylene oxide) and Poly(ϵ‐caprolactone) with Different Architectures,and Their Role in the Preparation of Stealthy Nanoparticles

Well‐defined copolymers of biocompatible poly(?‐caprolactone) (PCL) and poly(ethylene oxide) (PEO) are synthesized by two methods. Graft copolymers with a gradient structure are prepared by ring‐opening copolymerization of ?‐caprolactone (?CL) with a PEO macromonomer of the ?CL‐type. The ?CL polymerization is initiated by a PEO macroinitiator to prepare diblock copolymers. These amphiphilic copolymers are used as stabilizers for biodegradable poly(D,L ‐lactide) (PLA) nanoparticles prepared by a nanoprecipitation technique. The effect of the copolymer characteristic features (architecture, composition, and amount) on the nanoparticle formation and structure is investigated. The average size, size distribution, and stability of aqueous suspensions of the nanoparticles is measured by dynamic light scattering. For comparison, an amphiphilic random copolymer, poly(methyl methacrylate‐co‐methacrylic acid) (P(MMA‐co‐MA)), is synthesized. The stealthiness of the nanoparticles is analyzed in relation to the copolymer used as stabilizer. For this purpose, the activation of the complement system by nanoparticles is investigated in vitro using human serum. This activation is much less important whenever the nanoparticles are stabilized by a PEO‐containing copolymer rather than by the P(MMA‐co‐MA) amphiphile. The graft copolymers with a gradient structure and the diblock copolymers with similar macromolecular characteristics (molecular weight and hydrophilicity) are compared on the basis of their capacity to coat PLA nanoparticles and to make them stealthy.     

Luminescent Poly(p‐phenylenevinylene) Hole‐Transport Layers with Adjustable Solubility

The active part of present polymer light‐emitting diodes (PLEDs) consists of only a single layer. Multilayer devices have the advantage that the electron and hole transport can be balanced and that the recombination can be removed from the metallic cathode, leading to higher efficiencies. A major problem for polymer‐based multilayer devices is the solubility of the materials used; a multilayer can not be fabricated when a spin‐cast layer dissolves in the solvent of the subsequent layer. We demonstrate the development of high‐mobility poly(p‐phenylenevinylene) (PPV)‐based hole‐transport layers with tunable solubility by chemical modification. Enhanced charge‐transport properties are achieved by using symmetrically substituted PPVs; copolymers of long and short side chains enable us to tune the solubility without loss of the enhanced charge transport. Dual‐layer PLEDs, in which the holes are efficiently transported via this copolymer towards the luminescent layer, exhibit an enhanced efficiency at high voltages (> 10 V) and a strongly improved robustness against electrical breakdown.     

High‐Efficiency Red Phosphorescent Iridium Dendrimers with Charge‐ Transporting Dendrons: Synthesis and Electroluminescent Properties

A series of 1‐phenylisoquinoline derivatives encapsulated with peripheral arylamines as dendrons are synthesized by using the Ullmann reaction and palladium‐catalyzed aromatic carbon–carbon Suzuki‐coupling reactions. Red‐emitting dendritic iridium complexes (called G1‐1 , G1‐2 , and G2 ) are synthesized using the following derivatives: N,N‐diphenyl‐3′‐isoquinolin‐4‐biphenylaniline, N,N‐di(9,9‐dimethylfluorenyl‐3′‐isoquinolin‐4‐biphenylaniline, N,N‐di(4′‐di(2′‐(9′,9′‐dimethylfluorenyl)amine)biphenyl‐3′‐isoquinolin‐4‐biphenylaniline as the first ligands and 5‐methyl‐3‐(pyridin‐2′‐yl)‐1H‐1,2,4‐triazole as an ancillary ligand. The obtained dendrimers are soluble in common organic solvents, and uniform thin films can be spin‐coated from such solutions. Devices fabricated from dendritic iridium complexes G1‐2 and G2 with a small molecule host are fabricated by spin‐coating from chloroform solution in different device configurations. G1‐2 and G2 show similar device performances with maximum external quantum efficiencies (EQEs) of 12.8 % and 11.8 % (photons/electron) and luminous efficiency of 9.2 cd A^–1 and 8.5 cd A^–1 at 0.1 mA cm^–2, respectively. Devices based on polymer host poly(9,9‐dioctylfluorene)(PFO) (30 % PBD (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl‐1,3,4‐oxadiazole)) show a slightly higher efficiency for G1‐2 , with a maximum EQE of 13.9 % at a much higher current density of 6.4 mA cm^–2 and luminance of 601 cd m^–2.