Macroscopically Aligned Ionic Self‐Assembled Perylene‐Surfactant Complexes within a Polymer Matrix

Ionic self‐assembled (ISA) surfactant complexes present a facile concept for self‐assembly of various functional materials. However, no general scheme has been shown to allow their overall alignment beyond local polydomain‐like order. Here we demonstrate that ionic complexes forming a columnar liquid‐crystalline phase in bulk can be aligned within polymer blends upon shearing, taken that the matrix polymers have sufficiently high molecular weight. We use an ISA complex of N,N′‐bis(ethylenetrimethylammonium)perylenediimide/bis(2‐ethylhexyl) phosphate (Pery‐BEHP) blended with different molecular weight polystyrenes (PS). Based on X‐ray scattering studies and transmission electron microscopy the pure Pery‐BEHP complex was found to form a two‐dimensional oblique columnar phase where the perylene units stack within the columns. Blending the complex with PS lead to high aspect ratio Pery‐BEHP aggregates with lateral dimension in the mesoscale, having internal columnar liquid‐crystalline order similar to the pure Pery‐BEHP complex. When the Pery‐BEHP/PS blend was subjected to a shear flow field, the alignment of perylenes can be achieved but requires sufficiently high molecular weight of the polystyrene matrix. The concept also suggests a simple route for macroscopically aligned nanocomposites with conjugated columnar liquid‐crystalline functional additives.     

Electroactive Polymeric Networks Created by Oxidation of Oligothiophene‐Functionalized Perylene Bisimides

A series of fourfold oligothienyl‐functionalized perylene bisimides, N,N′‐bis(2,6‐diisopropylphenyl)‐1,6,7,12‐tetra(4‐(7‐[2,2′]bithien‐5‐yl)‐heptanoyloxyphenoxy)perylene‐3,4:9,10‐tetracarboxylic acid bisimide ( 7a ), N,N′‐bis(2,6‐diisopropylphenyl)‐1,6,7,12‐tetra(4‐(7‐[2,2′;5′,2′′]terthien‐5‐yl)‐heptanoyloxyphenoxy)perylene‐3,4:9,10‐tetracarboxylic acid bisimide ( 7b ), and N,N′‐bis(2,6‐diisopropylphenyl)‐1,6,7,12‐tetra(4‐(7‐(5″‐Methyl‐[2,2′;5′,2″]terthien‐5‐yl))‐heptanoyloxyphenoxy)perylene‐3,4:9,10‐tetracarboxylic acid bisimide ( 7c ), have been synthesized. Oligothienyl and perylene bisimide chromophores in these dyads display their characteristic optical UV/vis absorption properties. Upon excitation of the oligothiophene subunits, fluorescence resonance energy transfer (FRET) occurs to the perylene bisimide core. Cyclic voltammetric studies revealed that the reduction of the perylene bisimide moiety is not affected by the presence of oligothiophenes, showing two waves at around ‐0.7 and ‐1.0 V versus Ag/AgCl, respectively. On the other hand, the oxidation of the oligothienyl moieties leads to oxidative coupling for 7a and 7b , providing electroactive sexithiophene‐ and quaterthiophene‐perylene bisimide networks, respectively. Electrochemical deposition of compounds 7a , b was performed and the films were characterized using cyclic voltammetry and in situ conductance, which reveal remarkable p‐type conductivity. Significantly, two separate regimes of electrical conductance have been observed for the films generated from 7b .     

2,7‐Carbazolenevinylene‐Based Oligomer Thin‐Film Transistors: High Mobility Through Structural Ordering

We have fabricated organic field‐effect transistors based on thin films of 2,7‐carbazole oligomeric semiconductors 1,4‐bis(vinylene‐(N‐hexyl‐2‐carbazole))phenylene (CPC), 1,4‐bis(vinylene‐(N′‐methyl‐7′‐hexyl‐2′‐carbazole))benzene (RCPCR), N‐hexyl‐2,7‐bis(vinylene‐(N‐hexyl‐2‐carbazole))carbazole (CCC), and N‐methyl‐2,7‐bis(vinylene‐(7‐hexyl‐N‐methyl‐2‐carbazole))carbazole (RCCCR). The organic semiconductors are deposited by thermal evaporation on bare and chemically modified silicon dioxide surfaces (SiO₂/Si) held at different temperatures varying from 25 to 200 °C during deposition. The resulting thin films have been characterized using UV‐vis and Fourier‐transform infrared spectroscopies, scanning electron microscopy, and X‐ray diffraction, and the observed top‐contact transistor performances have been correlated with thin‐film properties. We found that these new π‐conjugated oligomers can form highly ordered structures and reach high hole mobilities. Devices using CPC as the active semiconductor have exhibited mobilities as high as 0.3 cm² V^–1 s^–1 with on/off current ratios of up to 10⁷. These features make CPC and 2,7‐carbazolenevinylene‐based oligomers attractive candidates for device applications.     

A Stimuli‐Responsive,Photoluminescent, Anthracene‐Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical Processes

Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable–stable phase transition induced by external stimuli is prepared. A 2,6‐diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6‐diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid‐crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic‐columnar phase transition induced by heating or mechanical shearing for this 2,6‐diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable–stable LC phase transition.     

Size‐Specific Interactions Between Single‐ and Double‐Stranded Oligonucleotides and Cationic Water‐Soluble Oligofluorenes

An improved synthetic approach was developed for the synthesis of 1,4‐bis[9′,9′‐bis(6″‐(N,N,N‐trimethylammonium)‐hexyl)‐fluoren‐2′‐yl]benzene tetrabromide ( 1a ), 1,4‐bis[9′,9′;9″,9″‐tetra(6″′‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″‐bisfluoren‐2′‐yl] benzene octabromide ( 1b ) and 1,4‐bis[9′,9′;9″,9″;9″′,9″′‐hexakis(6″″‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″,7″,2″′‐trifluoren‐2′‐yl] benzene dodecabromide ( 1c ). These molecules provide a size‐specific series of water‐soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy‐transfer measurements were performed with 1a – c and single‐stranded (ss) DNA and double‐stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per‐negative‐charge basis, ssDNA quenches the emission of 1a – c more effectively than dsDNA. Furthermore, we show that the energy‐transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a – c .     

2,5‐Functionalized Spiro‐Bisiloles as Highly Efficient Yellow‐Light Emitters in Electroluminescent Devices

New spiro‐bisilole molecules functionalized with nitrogen‐containing heterocyclic groups including 7‐azaindolyl, indolyl, and 2,2′‐dipyridylamino have been synthesized. These molecules are found to display good chemical and thermal stability. They are luminescent in solution and in the solid state with an emission color ranging from blue–green to yellow, depending on the functional group. In the solid state, they display high photoluminescence quantum efficiency (32–40 %). The electroluminescence properties for one of the new molecules, 2,3,3′,4,4′,5‐hexaphenyl‐2′,5′‐bis(p‐2,2′‐dipyridylaminophenyl)spiro‐bisilole, have been investigated by fabricating single‐layer and double‐layer electroluminescent devices. The double‐layer device, in which N,N′‐bis(1‐naphthyl)‐N,N′‐diphenylbenzidine acts as the hole‐transport layer and the functionalized spiro‐bisilole functions as the emitter (emission wavelength = 566 nm) and the electron‐transport layer, displays a brightness of 8440 cd m^–2 at 9 V with a current efficiency of 1.71 cd A^–1. No evidence of exiplex emission is observed.     

Self‐Assembled Shape‐Memory Fibers of Triblock Liquid‐Crystal Polymers

New thermoplastic liquid‐crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main‐chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape‐memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic–isotropic transition allows drawing thin well‐aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior—reversible contraction of heating and elongation on cooling—has been investigated.     

Photoresponsive Ferroelectric Liquid‐Crystalline Polymers

The photoresponse of ferroelectric smectic side‐chain liquid‐crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans–cis isomerization on the material's phase‐transition temperatures and its ferroelectric properties (spontaneous electric polarization P_S and director tilt angle θ) are analyzed. It turns out that the Curie temperature (transition S_C* to S_A) can be reversibly shifted by up to 17 °C. The molecular mechanism of this “photoferroelectric effect” is studied in detail using time‐resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase.     

Local Probing of Photocurrent and Photoluminescence in a Phase‐Separated Conjugated‐Polymer Blend by Means of Near‐Field Excitation

In this paper scanning near‐field microscopy is used to characterize polymer blends for photovoltaic applications, and fluorescence imaging and photoconductivity are combined to elucidate the spatial distribution and relative efficiency of current generation and photoluminescence in different domains of compositionally heterogeneous films. Focus is placed on a binary system consisting of poly[(9,9‐dioctylfluorene)‐alt‐benzothiadiazole] (F8BT) and poly[(9,9‐dioctylfluorene)‐alt‐(bis(N,N′‐(4‐butylphenyl))‐bis(N,N′‐phenyl‐1,4‐phenylenediamine))] (PFB), spun from xylene solutions, so as to obtain phase separation on micrometer and nanometer length scales. Protruding regions with diameters of about 5 μm in the topography image coincide with regions of high photocurrent (PC) and luminescence; these regions are identified as being F8BT‐rich. A general method to estimate the photoluminescence efficiency in the different domains of phase‐separated blends is proposed. As expected, lack of enhancement of the PC signal at the boundaries between protruding and lower‐lying phases indicate that these microscale boundaries play a small role in the charge generation by exciton splitting. This is consistent with the domains compositional inhomogeneity, and thus with finer phase separation within the domains. We also provide an analysis of the extent to which the metallized probe perturbs the near‐field photocurrent signal by integrating Poisson's equation. Finally, by using a Bethe–Bouwkamp model, the energy absorbed by the polymer film in the different regions is estimated.     

The Directional Peeling Effect of Nanostructured Rigiflex Molds on Liquid‐Crystal Devices: Liquid‐Crystal Alignment and Optical Properties

We report a new strategy, the directional peeling of a rigiflex mold with a nanostructure, to overcome several problems with general patterning techniques for liquid‐crystal (LC) alignment. These include difficulty in generating the pretilt angle and in controlling the LC rising‐up direction, formation of local domains, and weak optical properties. The directional peeling of the rigiflex mold results in pretilt‐angle formation and controls the LC rising‐up direction. In addition, a nanostructure with small spacing aligns the LC with a high order parameter because of a strong confinement effect and suppresses diffraction due to its small spacing. Eventually, the nanostructure achieves improvements in the optical properties. In summary, while recent patterning techniques for LC alignment only solve one problem, the directional peeling of the rigiflex mold with a nanostructure simultaneously overcomes several problems with LC alignment and optical properties.     

Red Phosphorescent Iridium Complex Containing Carbazole‐Functionalized β‐Diketonate for Highly Efficient Nondoped Organic Light‐Emitting Diodes

A novel red phosphorescent iridium complex containing a carbazole‐functionalized β‐diketonate, Ir(DBQ)₂(CBDK) (bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(carbazol‐9‐yl)‐5,5‐dimethylhexane‐2,4‐diketonate)) is designed, synthesized, and characterized. The electrophosphorescence properties of a nondoped device using the title complex as an emitter with a device configuration of indium tin oxide (ITO)/N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐diphenyl‐4,4′‐diamine (NPB; 20 nm)/iridium complex (20 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 5 nm)/tris(8‐hydroxyquinoline) (AlQ; 30 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) are examined. The results show that the nondoped device achieves a maximum lumen efficiency as high as 3.49 lm W^–1. To understand this excellent result observed, two reference complexes Ir(DBQ)₂(acac), where acac is the acetyl acetonate anion, and Ir(DBQ)₂(FBDK), [bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(9‐methyl‐fluoren‐9‐yl)‐6,6‐dimethylheptane‐3,5‐diketonate)], have also been synthesized, and as emitters they were examined under the same device configuration. The maximum lumen efficiency of the former compound is found to be 0.26 lm W^–1 while that for the latter is 0.37 lm W^–1, suggesting that the excellent performance of Ir(DBQ)₂(CBDK) can be attributed mainly to an improved hole‐transporting property that benefits the exciton transport. In addition, a bulky diketonate group separates the emitter centers from each other, which is also important for organic light‐emitting diodes.     

Hybrid Capsules via Self‐Assembly of Thermoresponsive and Interfacially Active Bionanoparticle–Polymer Conjugates

New bionanoparticles have been prepared from horse spleen ferritin by grafting thermoresponsive poly(N‐isopropyl acrylamide) (PNIPAAm) and photo‐crosslinkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide (DMIAAm) from the protein surface. The 72 addressable amino groups on the exterior of HSF were modified with N‐hydroxysuccinimide‐activated 2‐bromo‐isobutyrate to form a macro‐initiator for atom transfer radical polymerization, which was performed in water/DMF solutions at low temperature. The modification of the HSF and the presence of the polymer shell were confirmed by size exclusion chromatography (SEC), sodium dodecyl sulfate‐polyacrylamide gel‐electrophoresis, transmission electron microscopy, and scanning force microscopy. The thermoresponsive behavior of the ferritin‐PNIPAAm conjugates was investigated in solution by UV–vis spectroscopy showing a phase transition in the form of a cloud point around 32 °C. Further, dynamic light scattering revealed an increasing hydrodynamic radius around this transition, indicating aggregation of the particles at elevated temperatures which was confirmed by transmission electron microscopy. Initial experiments show that the particles are highly surface active, much more than the individual components alone, which was demonstrated by pendant‐drop interfacial tension measurements. This leads to the fact that they form stable Pickering emulsions, i.e., emulsion droplets decorated with polymer‐modified bionanoparticles which can be cross‐linked successively. This allows the formation of capsules with thermoresponsiveness for controlled release purposes, e.g., in drug delivery.     

Mesomorphic Organization and Thermochromic Luminescence of Dicyanodistyrylbenzene‐Based Phasmidic Molecular Disks: Uniaxially Aligned Hexagonal Columnar Liquid Crystals at Room Temperature with Enhanced Fluorescence Emission and Semiconductivity

A new dicyanodistyrylbenzene‐based phasmidic molecule, (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(3,4,5‐tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT). GDCS molecules self‐assemble into supramolecular disks consisting of a pair of molecules in a side‐by‐side disposition assisted by secondary bonding interactions of the lateral polar cyano group, which, in turn, constitute the hexagonal columnar LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystalline states, respectively, in contrast to the total absence of fluorescence emission in the isotropic melt state according to the characteristic aggregation‐induced enhanced emission (AIEE) behavior. The AIEE and two‐color luminescence thermochromism of GDCS are attributed to the peculiar intra‐ and intermolecular interactions of dipolar cyanostilbene units. It was found that the intramolecular planarization and restricted molecular motion associated with a specific stacking situation in the liquid/solid crystalline phases are responsible for the AIEE phenomenon. The origin of the two‐color luminescence was elucidated to be due to the interdisk stacking alteration in a given column driven by the specific local dipole coupling between molecular disks. These stacking changes, in turn, resulted in the different degree of excited‐state dimeric coupling to give different emission colors. To understand the complicated photophysical properties of GDCS, temperature‐dependent steady‐state and time‐resolved PL measurements have been comprehensively carried out. Uniaxially aligned and highly fluorescent LC and crystalline microwires of GDCS are fabricated by using the micromolding in capillaries (MIMIC) method. Significantly enhanced electrical conductivity (0.8 × 10^?5 S?cm^?1/3.9 × 10^?5 S?cm^?1) of the aligned LC/crystal microwires were obtained over that of multi‐domain LC sample, because of the almost perfect shear alignment of the LC material achieved in the MIMIC mold.     

Observation of a Chiral Smectic Phase in Azobenzene‐Linked Bolaamphiphiles Containing Free Sugars

Amphiphilic sugars exhibit both lyotropic and thermotropic liquid‐crystalline behavior. Interestingly, in spite of the abundance of chiral centers in amphiphilic sugars, their liquid‐crystalline phases do not exhibit macroscopic chirality. Herein, we report on the first observation of macroscopic chirality in sugar‐based bolaamphiphiles containing free hydroxyl groups. The manifestation of the chiral smectic C* phase in these bolaamphiphiles has been observed to be critically dependent on the presence of the azobenzene moiety and the suitable length of the methylene spacer. These results imply that by suitable selection of linker groups, mesogenic bolaamphiphiles possessing macroscopic chirality can be designed using a variety of naturally available sugar derivatives.     

Organic Thin‐Film Transistors Based on Tolyl‐Substituted Oligothiophenes

Thin films based on the tolyl‐substituted oligothiophenes 5,5′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′‐terthiophene ( 1 ), 5,5′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene ( 2 ) and 5,5′′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′‐quinqethiophene ( 3 ) exhibit hole‐transport behavior in a thin‐film transistor (TFT) configuration, with reasonable mobilities and high current on/off (I_on/I_off) ratios. Powder X‐ray diffraction (PXRD) reveals that these films, grown by vacuum deposition onto the thermally grown silicon oxide surface of a TFT, are highly crystalline, a characteristic that can be attributed to the general tendency of phenyl groups to promote crystallinity. Atomic force microscopy (AFM) reveals that the films grow layer by layer to form large domains, with some basal domain areas approaching 1000 μm². The PXRD and AFM data are consistent with an “end‐on” orientation of the molecules on the oxide substrate. Variable‐temperature current–voltage (I–V) measurements identified the activation regime for hole transport and revealed shallow level traps in thin films of 1 and 2 , and both shallow and deep level traps in thin films of 3 . The activation energies for thin films of 1 , 2 , and 3 were similar, with values of E_a = 121, 100, and 109 meV, respectively. The corresponding trap densities were N_trap/N_v = 0.012, 0.023, and 0.094, where N_trap is the number of trap states and N_v is the number of conduction states. The hole mobilities for the three compounds were similar (μ ? 0.03 cm² V^–1 s^–1), and the I_on/I_off ratios were comparable with the highest values reported for organic TFTs, with films of 2 approaching I_on/I_off = 10⁹ at room temperature.     

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).     

Fully Differential 5‐GHz LC‐Tank VCOs with Improved Phase Noise and Wide Tuning Range

In this paper, we propose two LC voltage‐controlled oscillators (VCOs) that improve both phase noise and tuning range. With both 1/f induced low‐frequency noise and low‐frequency thermal noise around DC or around harmonics suppressed significantly by the employment of a current‐current negative feedback (CCNF) loop, the phase noise in the CCNF LC VCO has been improved by about 10 dB at 6 MHz offset compared to the conventional LC VCO. The phase noise of the CCNF VCO was measured as ?112 dBc/Hz at 6 MHz offset from 5.5 GHz carrier frequency. Also, we present a bandwidth‐enhanced LC VCO whose tuning range has been increased about 250 % by connecting the varactor to the bases of the cross‐coupled pair. The phase noise of the bandwidth‐enhanced LC‐tank VCO has been improved by about 6 dB at 6 MHz offset compared to the conventional LC VCO. The phase noise reduction has been achieved because the DC‐decoupling capacitor Cc prevents the output common‐mode level from modulating the varactor bias point, and the signal power increases in the LC‐tank resonator. The bandwidth‐enhanced LC VCO represents a 12 % bandwidth and phase noise of ?108 dBc/Hz at 6 MHz offset.     

Self‐Assembled Nanowires of Organic n‐Type Semiconductor for Nonvolatile Transistor Memory Devices

Organic nonvolatile transistor‐type memory (ONVM) devices are developed using self‐assembled nanowires of n‐type semiconductor, N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI). The effects of nanowire dimension and silane surface treatment on the memory characteristics are explored. The diameter of the nanowires is reduced by increasing the non‐solvent methanol composition, which led to the enhanced crystallinity and high field‐effect mobility. The BPE‐PTCDI nanowires with small diameters induce high electrical fields and result in a large memory window (the shifting of the threshold voltage, ΔV_th). The ΔV_th value of BPE‐PTCDI nanowire based ONVM device on the bare substrate can reach 51 V, which is significantly larger than that of thin film. The memory window is further enhanced to 78 V with the on/off ratio of 2.1 × 10⁴ and the long retention time (10⁴ s), using a hydrophobic surface (such as trichloro(phenyl)silane‐treated surface). The above results demonstrate that the n‐type semiconducting nanowires have potential applications in high performance non‐volatile transistor memory devices.     

Graphene‐Oxide‐Conjugated Polymer Hybrid Materials for Calmodulin Sensing by Using FRET Strategy

The conformation of calmodulin (CaM) changes from closed configuration to open one, converting to a claviform dumbbell‐shaped biomolecule upon Ca²⁺‐binding. A hybrid probe of graphene oxide (GO) cationic conjugated polymer for detection of the conformation transition of CaM by using FRET technique is demonstrated. The stronger hydrophobic interaction and weaker electrostatic repulsion leads to more CaM adsorption to the surface of GO upon binding with Ca²⁺ than that of CaM in the absence of Ca²⁺ (apoCaM), resulting in much farther proximity between poly[(9,9‐bis(6′‐N,N,N‐trimethy­lammonium)hexyl)‐fluorenylene phenylene dibromide] (PFP) and green fluorescent protein labeled at the N‐terminus of CaM and therefore much weaker FRET efficiency for PFP/Ca²⁺/CaM in comparison with that of PFP/apoCaM in the presence of GO. Notably, the assembly of CaM with GO is quantitatively and reversibly controlled by Ca²⁺ ions.     

A Light‐Blue Phosphorescent Dendrimer for Efficient Solution‐Processed Light‐Emitting Diodes

We describe the preparation of a dendrimer that is solution‐processible and contains 2‐ethylhexyloxy surface groups, biphenyl‐based dendrons, and a fac‐tris[2‐(2,4‐difluorophenyl)pyridyl]iridium(III ) core. The homoleptic complex is highly luminescent and the color of emission is similar to the heteroleptic iridium(III ) complex, bis[2‐(2,4‐difluorophenyl)pyridyl]picolinate iridium(III ) (FIrpic). To avoid the change in emission color that would arise from attaching a conjugated dendron to the ligand, the conjugation between the dendron and the ligand is decoupled by separating them with an ethane linkage. Bilayer devices containing a light‐emitting layer comprised of a 30 wt.‐% blend of the dendrimer in 1,3‐bis(N‐carbazolyl)benzene (mCP) and a 1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene electron‐transport layer have external quantum and power efficiencies, respectively, of 10.4 % and 11 lm W^–1 at 100 cd m^–2 and 6.4 V. These efficiencies are higher than those reported for more complex device structures prepared via evaporation that contain FIrpic blended with mCP as the emitting layer, showing the advantage of using a dendritic structure to control processing and intermolecular interactions. The external quantum efficiency of 10.4 % corresponds to the maximum achievable efficiency based on the photoluminescence quantum yield of the emissive film and the standard out‐coupling of light from the device.