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A family of naphthalene diimide (NDI)-based donor (D)-acceptor (A) copolymers with various acene- (benzene (Bz), naphthalene (Np), and pyrene (Py)) and heteroacene-type (selenophene (Se) and thiophene (Th)) donor rings has been designed and synthesized as a means to systematically understand structure–property relationships on the subject of the structural factor and electron-donating capability of the donor portions for applications in organic field-effect transistors (OFETs) based on NDIs. Alongside of two categories dealing with the lack or existence of the heteroatoms in the donor framework, the resulting copolymers can also be classified into ‘thiophene-free’ D–A copolymers (PNDI-Bz, PNDI-Np, PNDI-Py, and PNDI-Se) and thiophene-containing copolymer (PNDI-Th). The results from optical and electronic properties lead to the determination that the empirical electron-donating strength of donor co-units is in the order of Bz < Np < Py < Th < Se. In contrast with the similarity of the LUMO levels (−3.73∼−3....

The development of a versatile method for nitrogen-doping of graphitic structure is an important challenge for many applications, such as energy conversions and storages and electronic devices. Here, we report a simple but efficient method for preparing nitrogen-doped graphene nanoplatelets via wet-chemical reactions. The reaction between monoketone (C═O) in graphene oxide (GO) and monoamine-containing compound produces imine (Shiff base) functionalized GO (iGO). The reaction between α-diketone in GO and 1,2-diamine (ortho-diamine)-containing compound gives stable pyrazine ring functionalized GO (pGO). Subsequent heat-treatments of iGO and pGO result in high-quality, nitrogen-doped graphene nanoplatelets to be designated as hiGO and hpGO, respectively. Of particular interest, hpGO was found to display the n-type field-effect transistor behavior with a charge neutral point (Dirac point) located at around -16 V. Furthermore, hpGO showed hole and electron mobilities as high as 11.5 and 12.4 cm(2)V(-1)s(-1), respectively.

Large-scale FET-type graphene micropattern (GM) nano-biohybrid-based immunosensor (GMNS) is fabricated in a controlled fashion to detect human immunodeficiency virus 2 antibody. Flexible GMNS shows a highly sensitive response and excellent mechanical bendability. The flexible GMNS in fluidic systems also has a stable response. This is the first experimental demonstration of a large-scale flexible fluidic FET-type immunoassay based on GM nano-biohybrids.

We investigated electrical charge transport through individual strands of single-crystalline dipentyl perylene tetracarboxylic diimide (PTCDI-C5) and dioctyl perylene tetracarboxylic diimide (PTCDI...

Systematic creation of polymeric semiconductors from novel building blocks is critical for improving charge transport properties in organic field-effect transistors (OFETs). A series of ultralow-bandgap polymers containing thienoisoindigo (TIIG) as a thiophene analogue of isoindigo (IIG) is synthesized. The UV-Vis absorptions of the TIIG-based polymers (PTIIG-T, PTIIG-Se, and PTIIG-DT) exhibit broad bands covering the visible to near-infrared range of up to 1600 nm. All the polymers exhibit unipolar p-channel operations with regard to gold contacts. PTIIG-DT with centrosymmetric donor exhibits a maximum mobility of 0.20 cm2 V−1 s−1 under gold contacts, which is higher than those of the other polymers containing axisymmetric donors. Intriguingly, OFETs fabricated with aluminum electrodes show ambipolar charge transport with hole and electron mobilities of up to 0.28 (PTIIG-DT) and 0.03 (PTIIG-T) cm2 V−1 s−1, respectively. This is a record value for the hitherto reported TIIG-based OFETs. The finding demonstrates that TIIG-based polymers can potentially function as either unipolar or ambipolar semiconductors without reliance on the degree of electron affinity of the co-monomers.

Organic ambipolar transistor arrays for chemical sensors are prepared on a flexible plastic substrate with a bottom-gate bottom-contact configuration to minimize the damage to the organic semiconductors, for the first time, using a photolithographically patternable polymer semiconductor. Well-balanced ambipolar charge transport is achieved by introducing graphene electrodes because of the reduced contact resistance and energetic barrier for electron transport.

The photoelectronic characteristics of single-crystalline nanowire organic phototransistors (NW-OPTs) are studied using a high-performance n-channel organic semiconductor, N,N′-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI), as the photoactive layer. The optoelectronic performances of the NW-OPTs are analyzed by way of their current–voltage (I–V) characteristics on irradiation at different wavelengths, and comparison with corresponding thin-film organic phototransistors (OPTs). Significant enhancement in the charge-carrier mobility of NW-OPTs is observed upon light irradiation as compared with when performed in the dark. A mobility enhancement is observed when the incident optical power density increases and the wavelength of the light source matches the light-absorption range of the photoactive material. The photoswitching ratio is strongly dependent upon the incident optical power density, whereas the photoresponsivity is more dependent on matching the light-source wavelength with the maximum absorption range of the photoactive material. BPE-PTCDI NW-OPTs exhibit much higher external quantum efficiency (EQE) values (≈7900 times larger) than thin-film OPTs, with a maximum EQE of 263 000%. This is attributed to the intrinsically defect-free single-crystalline nature of the BPE-PTCDI NWs. In addition, an approach is devised to analyze the charge-transport behaviors using charge accumulation/release rates from deep traps under on/off switching of external light sources.

A novel highly π-extended heteroacene with four symmetrically fused thiophene-ring units and solubilizing substituents at the terminal β-positions on the central ring, dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene (DTBDT) was synthesized via intramolecular electrophilic coupling reaction. The α-positions availability in the DTBDT motif enables the preparation of solution-processable DTBDT-based polymers such as PDTBDT, PDTBDT-BT, PDTBDT-DTBT, and PDTBDT-DTDPP. Even with its highly extended acene-like π-framework, all polymers show fairly good environmental stability of their highest occupied molecular orbitals (HOMOs) from −5.21 to −5.59 eV. In the course of our study to assess a profile of semiconductor properties, field-effect transistor performance of the four DTBDT-containing copolymers via solution-process is characterized, and PDTBDT-DTDPP exhibits the best electrical performance with a hole mobility of 1.70 × 10–2 cm2 V–1 s–1. PDTBDT-DTDPP has a relatively smaller charge injection barrier ...

A narrow bandgap polymeric semiconductor, BOC-PTDPP, comprising alkyl substituted diketopyrrolopyrrole (DPP) and tert-butoxycarbonyl (t-BOC)-protected DPP, is synthesized and used in organic field-effect transistors (OFETs). The polymer films are prepared by solution deposition and thermal annealing of precursors featuring thermally labile t-BOC groups. The effects of the thermal cleavage on the molecular packing structure in the polymer thin films are investigated using thermogravimetric analysis (TGA), UV-vis spectroscopy, atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. Upon utilization of solution-shearing process, integrating the ambipolar BOC-PTDPP into transistors shows p-channel dominant characteristics, resulting in hole and electron mobilities as high as 1.32 × 10−2 cm2 V−1 s−1 and 2.63 × 10−3 cm2 V−1 s−1, which are about one order of magnitude higher than those of the drop-cast films. Very intriguingly, the dominant polarity of charge carriers changes from positive to negative after the thermal cleavage of t-BOC groups at 200 °C. The solution-sheared films upon subsequent thermal treatment show superior electron mobility (μe = 4.60 × 10−2 cm2 V−1 s−1), while the hole mobility decreases by one order of magnitude (μh = 4.30 × 10−3 cm2 V−1 s−1). The inverter constructed with the combination of two identical ambipolar OFETs exhibits a gain of ∼10. Reported here for the first time is a viable approach to selectively tune dominant polarity of charge carriers in solution-processed ambipolar OFETs, which highlights the electronically tunable ambipolarity of thermocleavable polymer by simple thermal treatment.

Conjugated polymers, in general, are unstable when exposed to air, solvent, or thermal treatment, and these challenges limit their practical applications. Therefore, it is of great importance to develop new materials or methodologies that can enable organic electronics with air stability, solvent resistance, and thermal stability. Herein, we have developed a simple but powerful approach to achieve solvent-resistant and thermally stable organic electronic devices with a remarkably improved air stability, by introducing an azide cross-linkable group into a conjugated polymer. To demonstrate this concept, we have synthesized polythiophene with azide groups attached to end of the alkyl chain (P3HT-azide). Photo-cross-linking of P3HT-azide copolymers dramatically improves the solvent resistance of the active layer without disrupting the molecular ordering and charge transport. This is the first demonstration of solvent-resistant organic transistors. Furthermore, the bulk-heterojunction organic photovoltaics (B...

High charge carrier mobility solution-processed n-channel organic thin-film transistors (OTFTs) based on core-chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are demonstrated. These OTFTs were prepared through a solution shearing method. Core-chlorination of NDIs not only increases the electron mobilities of OTFTs, but also enhances their air stability, since the chlorination in the NDI core lowers the lowest unoccupied molecular orbital (LUMO) levels. The air-stability of dichlorinated NDI was better than that of the tetrachlorinated NDIs, presumably due to the fact that dichlorinated NDIs have a denser packing of the fluoroalkyl chains and less grain boundaries on the surface, reducing the invasion pathway of ambient oxygen and moisture. The devices of dichlorinated NDIs exhibit good OTFT performance, even after storage in air for one and a half months. Charge transport anisotropy is observed from the dichlorinated NDI. A dichlorinated NDI with −CH2C3F7 side chains reveals high mobilities of up to 0.22 and 0.57 cm2 V−1 s−1 in parallel and perpendicular direction, respectively, with regard to the shearing direction. This mobility anisotropy is related to the grain morphology. In addition, we find that the solution-shearing deposition affects the molecular orientation in the crystalline thin films and lowers the d(001)-spacing (the out-of-plane interlayer spacing), compared to the vapor-deposited thin films. Core-chlorinated NDI derivatives are found to be highly suitable for n-channel active materials in low-cost solution-processed organic electronics.

5-Perfluorophenyl-11-phenyltetracene (FPPT) having both aryl (Ar) and perfluoroaryl (FAr) groups has been designed and synthesized to obtain well-defined π−π stacking structure of the tetracene core. Single-crystal X-ray analyses as well as photoconductivity and hole mobility measurements revealed that this strategy is promising for enhancement of the charge carrier properties.

A scalable synthesis of swallow-tailed quaterrylene diimides (STQDIs) and a method for the solution processing of sparingly soluble quaterrylene diimide (QDI) thin films are described. The pressure-assisted thermal cleavage of swallow tails yields crystalline QDI layers with electron mobility up to 0.088 cm(2) V(-1) s(-1). The developed method opens up a new route toward the solution processing of higher rylene diimides with poor solubility.

Core-chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are synthesized and employed for n-channel organic thin-film transistors (OTFTs). Structural analyses of the single crystals and thin films are performed and their charge-transport behavior is investigated in terms of structure–property relationships. NDIs with two chlorine substituents are shown to exhibit a herringbone structure with a very close π-plane distance (3.3–3.4 A), a large π-stack overlap (slipping angle ca. 62°), and high crystal densities (2.046–2.091 g cm−3). These features result in excellent field-effect mobilities of up to 1.43 cm2 V−1 s−1 with minimal hysteresis and high on–off ratios (ca. 107) in air. This is similar to the highest n-channel mobilities in air reported so far. Despite the repulsive interactions of bulky Cl substituents, tetrachlorinated NDIs adopt a slip-stacked face-to-face packing with an interplanar distance of around 3.4 A, resulting in a high mobility (up to 0.44 cm2 V−1 s−1). The air-stability of dichlorinated NDIs is superior to that of tetrachlorinated NDIs, despite of their higher LUMO levels. This is closely related to the denser packing of the fluorocarbon chains of dichlorinated NDIs, which serves as a kinetic barrier to the diffusion of ambient oxidants. Interestingly, these NDIs show an optimal performance either on bare SiO2 or on octadecyltrimethoxysilane (OTS)-treated SiO2, depending on the carbon number of the fluoroalkyl chains. Their synthetic simplicity and processing versatility combined with their high performance make these semiconductors highly promising for practical applications in flexible electronics.

The appropriate arrangement of organic semiconductors in the solid state is decisive for efficient charge-carrier transport between source and drain electrodes in organic thin-film transistors (OTFTs). However, the still unsolved challenges in crystal engineering mean that there are only few examples where the packing of p-conjugated semiconductors can be controlled by means of rational design concepts to avoid the most common herringbone p-stacking motif (Figure 1a). An outstanding example is provided by the

The effects of the interplay between energetic and kinetic factors on the air stability of n-channel organic thin-film transistors (OTFTs) were studied using two perylene diimide (PDI) compounds with distinctly different lowest unoccupied molecular orbital (LUMO) levels. On the basis of the empirical energy level windows, one compound (N,N′-bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl)-3,4:9,10-tetracarboxylic acid diimide (PDI-F): −3.84 eV) is at the onset region for air stability, whereas the other (N,N′-bis(cyclohexyl)-1,7-dicyano-perylene-3,4:9,10-tetracarboxylic acid diimide (PDI-CN2): −4.33 eV) is in the air-stable region. Charge-transport behaviors under an inert atmosphere and in air were investigated as a function of active layer thickness. Charge transport in air was greatly affected by the active layer thickness for both compounds, an effect that has been overlooked so far. The ambient stability of the air-unstable PDI-F TFTs increased significantly for thicknesses over ∼10 monolayers (ML). Surprisin...

In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments,indicate that additionalsurface parametersmust beidentified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes twodimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3cm 2 V � 1 s � 1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport.

The 1D structure of single-walled carbon nanotubes (SWNTs) leads to unique physical properties, which have been investigated extensively. Numerous applications and device prototypes have been demonstrated; however, most have used SWNTs grown in situ by chemical vapor deposition. This limits throughput and choice of substrate owing to the high growth temperatures involved. Solution-based postsynthesis device fabrication, typically involving purification, solubilization, chemical functionalization, cutting, and/ or controlled assembly of SWNTs, is more desirable because of low cost, scalability to large areas, and compatibility with flexible plastic substrates. Unfortunately, SWNTs are not readily soluble, and chemical functionalization strategies for their solubilization usually alter their electronic properties. Furthermore, to take full advantage of the anisotropic charge-transport properties of SWNTs and to enhance their performance in high-strength composite materials, it is necessary to align them over a large area. Noncovalent functionalization of SWNTs is a particularly attractive avenue for dispersion because it enables modification of material properties without altering the chemical structure of the nanotubes. To date, most high-concentration dispersions (>1mg mL ) have been obtained in aqueous solutions by mixing SWNTs with surfactants, doubleor

The development of solution-processable, high-performance n-channel organic semiconductors is crucial to realizing low-cost, all-organic complementary circuits. Single-crystalline organic semiconductor nano/microwires (NWs/MWs) have great potential as active materials in solution-formed high-performance transistors. However, the technology to integrate these elements into functional networks with controlled alignment and density lags far behind their inorganic counterparts. Here, we report a solution-processing approach to achieve high-performance air-stable n-channel organic transistors (the field-effect mobility (μ) up to 0.24 cm 2 /Vs for MW networks) comprising high mobility, solution-synthesized single-crystalline organic semiconducting MWs (μ as high as 1.4 cm 2 /Vs for individual MWs) and a filtration-and-transfer (FAT) alignment method. The FAT method enables facile control over both alignment and density of MWs. Our approach presents a route toward solution-processed, high-performance organic transistors and could be used for directed assembly of various functional organic and inorganic NWs/MWs.

p-type semiconductors have been studied extensively, research on n-channel semiconducting materials still lags behind these developments. The availability of high-performance n-type materials, in which the majority charge carriers are electrons, is desirable for the fabrication of p-n junctions and complementary circuits. Apart from high electron mobilities, practically useful n-type semiconductors should possess a sufficiently high electron affinity to allow for efficient electron injection from common metal electrodes into these materials. [1d] A major drawback of many compounds described in the literature is the poor stability in devices operated under ambient conditions. The introduction of fluorinated alkyl groups has been shown to lead to improved air-stabilities in various instances, and it has been argued that this stabilization originates in self-segregation of closely-packed fluorocarbon chains that prevents the diffusion of air and moisture into the channel region. [1a,b] Perylene tetracarboxylic acid bisimides (PBIs) are among the most promising and versatile candidates for (opto)electronic applications, because their electronic and optical properties as well as their solid–state packing can be tuned in a wide range. [2] The solid state packing and concomitant properties of PBIs can be tailored by introduction of appropriate substituents either in the imide position or by core substitution in the bay region. Substitution in the 1, 6, 7, and 12 positions of the PBI backbone enforces a considerable twisting of the perylene skeleton out of planarity. [2] The effect of this structural modification on the electrical and charge transport properties of these semiconductors is not yet well understood, though. Whereas intermolecular coupling might be reduced in core-twisted PBIs, this modification might, on the other hand, help to prevent the formation of dimeric pairs that have been envisaged as potential electron traps. [3] To elucidate the effect of successive bay substitution, we describe here the synthesis and a comparison of two novel fluoro-substituted PBI derivatives, PBI-F2 and PBI-F4 (Scheme 1), that combine fluoroalkyl groups in imide position with two or four fluorine atoms in the bay region. [4]

Mechanically robust, flexible and electrically conductive textiles are highly suitable for use in wearable electronic applications. In this study, highly conductive and flexible graphene/Ag hybrid fibers were prepared and used as electrodes for planar and fiber-type transistors. The graphene/Ag hybrid fibers were fabricated by the wet-spinning/drawing of giant graphene oxide and subsequent functionalization with Ag nanoparticles. The graphene/Ag hybrid fibers exhibited record-high electrical conductivity of up to 15,800 S cm−1. As the graphene/Ag hybrid fibers can be easily cut and placed onto flexible substrates by simply gluing or stitching, ion gel-gated planar transistors were fabricated by using the hybrid fibers as source, drain and gate electrodes. Finally, fiber-type transistors were constructed by embedding the graphene/Ag hybrid fiber electrodes onto conventional polyurethane monofilaments, which exhibited excellent flexibility (highly bendable and rollable properties), high electrical performance (μh = 15.6 cm2 V−1 s−1, Ion/Ioff > 104) and outstanding device performance stability (stable after 1,000 cycles of bending tests and being exposed for 30 days to ambient conditions). We believe that our simple methods for the fabrication of graphene/Ag hybrid fiber electrodes for use in fiber-type transistors can potentially be applied to the development all-organic wearable devices.

Replacing or minimizing the use of halogenated organic solvents in the processing and manufacturing of conjugated polymer-based organic electronics has emerged as an important issue due to concerns regarding toxicity, environmental impact, and high cost. To date, however, the processing of well-ordered conjugated polymer nanostructures has been difficult to achieve using environmentally benign solvents. In this work, we report the development of water and alcohol processable nanowires (NWs) with well-defined crystalline nanostructure based on the solution assembly of azide functionalized poly(3-hexylthiophene) (P3HT-azide) and subsequent photo-cross-linking and functionalization of these NWs. The solution-assembled P3HT-azide NWs were successfully cross-linked by exposure to UV light, yielding good thermal and chemical stability. Residual azide units on the photo-cross-linked NWs were then functionalized with alkyne terminated polyethylene glycol (PEG-alkyne) using copper catalyzed azide-alkyne cycloaddition chemistry. PEG functionalization of the cross-linked P3HT-azide NWs allowed for stable dispersion in alcohols and water, while maintaining well-ordered NW structures with electronic properties suitable for the fabrication of organic field effect transistors (OFETs).

Nano-floating gate memory (NFGM) devices are transistor-type memory devices that use nanostructured materials as charge trap sites. They have recently attracted a great deal of attention due to their excellent performance, capability for multilevel programming, and suitability as platforms for integrated circuits. Herein, novel NFGM devices have been fabricated using semiconducting cobalt ferrite (CoFe2O4) nanoparticles (NPs) as charge trap sites and pentacene as a p-type semiconductor. Monodisperse CoFe2O4 NPs with different diameters have been synthesized by thermal decomposition and embedded in NFGM devices. The particle size effects on the memory performance have been investigated in terms of energy levels and particle-particle interactions. CoFe2O4 NP-based memory devices exhibit a large memory window (≈73.84 V), a high read current on/off ratio (read I(on)/I(off)) of ≈2.98 × 10(3), and excellent data retention. Fast switching behaviors are observed due to the exceptional charge trapping/release capability of CoFe2O4 NPs surrounded by the oleate layer, which acts as an alternative tunneling dielectric layer and simplifies the device fabrication process. Furthermore, the NFGM devices show excellent thermal stability, and flexible memory devices fabricated on plastic substrates exhibit remarkable mechanical and electrical stability. This study demonstrates a viable means of fabricating highly flexible, high-performance organic memory devices.

Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96 eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications., There is currently interest in two-dimensional graphene-like materials incorporating heteroatoms. Here, the authors synthesize a solution-processable, holey two-dimensional network with C2N stoichiometry containing evenly distributed holes and nitrogen atoms, and use it to fabricate a field effect transistor.

Poly(acrylonitrile) (PAN) nanotubes with tunable wall thickness were successfully fabricated using a modified vapor deposition polymerization technique. To enhance the uniformity, heptane was employed as a nonreactive solvent. It is revealed that the heptane vapor in the reaction vessel plays an important role for producing nanotubes with tunable and uniform wall thickness. In addition, photoluminescence dyes such as pyrene for blue emission and rhodamine B for red emission were employed as host materials. These dyes were loaded into the inner surface of the PAN nanotubes and effectively encapsulated with a supplemental PAN layer. Confocal laser scanning microscopy images confirmed the successful fabrication of PAN−dye−PAN nanotubes without phase separation of the organic dyes. The photoluminescent analysis demonstrated the effective confinement of pyrene as well as rhodamine B in the PAN layer with a varying concentration of pyrene and rhodamine B as a multi-emission polymer nanotube.

This work was supported by the Brain-Korea 21 Program (Korea Ministry of Education), and the Korea Science and Engineering Foundation through the Hyperstructured Organic Materials Research Center.

Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two-step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) and UV-vis spectroscopies, and electrical-conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer-thick PMMA shell has a lower glass-transition temperature (Tg), and can be effectively annealed to form a conductive-filler network with a high electrical conductivity at a relatively low filler content.

This work was supported by the Brain-Korea 21 Program of the Korean Ministry of Education and the Hyperstructured Organic Materials Research Center supported by the Korean Science and Engineering foundation. We thank Dr. S.-H. Yoon for discussions and acknowledge JEOL Co. for assistance with HRTEM.

Evaporation-induced self-assemblies (EISAs) with various morphologies were selectively fabricated by drying a solution containing polypyrrole nanoparticles. The morphogenesis of EISAs was strongly dependent upon the solvent evaporation rate and the nanoparticle concentration. In the case of fast evaporation, 2-D dendrites or pseudo 1-D dendrites were observed. When the liquid medium evaporated slowly, ring and spherulitic assemblies took place. Multiple rings could be created on a substrate surface under one single drop.

Recent interest in flexible electronics has led to a paradigm shift in consumer electronics, and the emergent development of stretchable and wearable electronics is opening a new spectrum of ubiquitous applications for electronics. Organic electronic materials, such as π-conjugated small molecules and polymers, are highly suitable for use in low-cost wearable electronic devices, and their charge-carrier mobilities have now exceeded that of amorphous silicon. However, their commercialization is minimal, mainly because of weaknesses in terms of operational stability, long-term stability under ambient conditions, and chemical stability related to fabrication processes. Recently, however, many attempts have been made to overcome such instabilities of organic electronic materials. Here, an overview is provided of the strategies developed for environmentally robust organic electronics to overcome the detrimental effects of various critical factors such as oxygen, water, chemicals, heat, and light. Additionally, molecular design approaches to π-conjugated small molecules and polymers that are highly stable under ambient and harsh conditions are explored; such materials will circumvent the need for encapsulation and provide a greater degree of freedom using simple solution-based device-fabrication techniques. Applications that are made possible through these strategies are highlighted.

Phenyl-substituted heteroacene, diphenyl-dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene (DPh-DBTTT), is introduced as a thermally durable high-performance organic semiconductor. The DPh-DBTTT single crystals exhibit hole mobility up to 31.9 cm2 V−1 s−1, and the vacuum-deposited DPh-DBTTT thin-film transistors show a maximum mobility of 6.32 cm2 V−1 s−1. X-ray crystallographic analysis reveals that the small tilting angle between the phenyl substituent and the DBTTT core reduces the reorganization energy dramatically. The structure–property relationships are thoroughly investigated using atomic force microscopy, transmission electron microscopy, and grazing incidence X-ray diffraction analyses, in addition to charge-transport studies. The vacuum-deposited DPh-DBTTT thin-film transistors show superior thermal durability compared to the core DBTTT, which is highly valuable for device processability.

Chiral supramolecular nanostructures with optoelectronic functions are expected to play a central role in many scientific and technological fields but their practical use remains in its infancy. Here, this paper reports photoconductive chiral organic semiconductors (OSCs) based on perylene diimides with the highest electron mobility among the chiral OSCs and investigates the structure and optoelectronic properties of their homochiral and heterochiral supramolecular assemblies from bottom-up self-assembly. Owing to the well-ordered supramolecular packing, the homochiral nanomaterials exhibit superior charge transport with significantly higher photoresponsivity and dissymmetry factor compared with those of their thin film and monomeric equivalents, which enables highly selective detection of circularly polarized light, for the first time, in visible spectral range. Interestingly, the heterochiral nanostructures assembled from co-self-assembly of racemic mixtures show extraordinary chiral self-discrimination phenomenon, where opposite enantiomeric molecules are packed alternately into heterochiral architectures, leading to completely different optoelectrical performances. In addition, the crystal structures of homochiral and heterochiral nanostructures have first been studied by ab initio X-ray powder diffraction analysis. These findings give insights into the structure-chiroptical property relationships of chiral supramolecular self-assemblies and demonstrate the feasibility of supramolecular chirality for high-performance chiroptical sensing.

Liquid-phase sensing of various organic solvents is performed for the first time, using a solvent-resistant organic-transistor platform. Sensors composed of a cross-linked poly(3-hexylthiophene) (P3HT)-azide co-polymer and a calixarene derivative exhibit highly sensitive and selective sensing behavior, owing to the selective binding effects of the liquid analytes with the calixarene-functionalized P3HT-azide, extending the range of their use in practical applications.

Inspired by the outstanding charge-transport characteristics of poly(isoindigo-alt-benzothiadiazole) (PIIG-BT) in our previous study, herein we present two new polymers (PIIG-DTBT and PIIG-DSeBT) involving IIG and BT blocks constructed using five-membered heteroaromatic spacers such as thiophene (T) and selenophene (Se) and investigate the effects of the spacer groups on the optical, electrochemical, and charge-transport properties. As a consequence of the red-shifts induced by the more extended conjugation and enhanced intramolecular charge transfer (ICT), both PIIG-DTBT and PIIG-DSeBT show smaller bandgaps compared to PIIG-BT. Interestingly, the LUMO energy levels (-3.57 eV) for the two polymers are the same, but the HOMO levels (-5.39 and -5.26 eV for PIIG-DTBT and PIIG-DSeBT, respectively) clearly vary as a function of the structural modification of the spacers. In addition to the changes in their optical properties and energy levels induced by the incorporation of the spacers, ambipolar charge transport behaviors with hole and electron mobilities of up to 7.8 × 10(-2) and 3.4 × 10(-2) cm(2) V(-1) s(-1), respectively, are observed for PIIG-DTBT films with highly ordered lamellar packing. This represents the second example of IIG-based polymers exhibiting ambipolar charge transport in OFETs reported to date.

The maximum responsivity of a pure monolayer graphene-based photodetector is currently less than 10 mA W(-1) because of small optical absorption and short recombination lifetime. Here, a graphene hybrid photodetector functionalized with a photoactive ruthenium complex that shows an ultrahigh responsivity of ≈1 × 10(5) A W(-1) and a photoconductive gain of ≈3 × 10(6) under incident optical intensity of the order of sub-milliwatts is reported. This responsivity is two orders of magnitude higher than the precedent best performance of graphene-based photodetectors under a similar incident light intensity. Upon functionalization with a 4-nm-thick ruthenium complex, monolayer graphene-based photodetectors exhibit pronounced n-type doping effect due to electron transfer via the metal-ligand charge transfer (MLCT) from the ruthenium complex to graphene. The ultrahigh responsivity is attributed to the long lifetime and high mobility of the photoexcited charge carriers. This approach is highly promising for improving the responsivity of graphene-based photodetectors.

Two acceptor-acceptor (A-A) type copolymers (PIIG-BT and PIIG-TPD) with backbones composed exclusively of electron-deficient units are designed and synthesized. Both copolymers show unipolar n-type operations. In particular, PIIG-BT shows electron mobility of up to 0.22 cm(2) V(-1) s(-1). This is a record value for n-type copolymers based on lactam cores.

The physical structure of an organic solid is strongly affected by the surface of the underlying substrate. Controlling this interface is an important issue to improve device performance in the organic electronics community. Here we report an approach that utilizes an organic heterointerface to improve the crystallinity and control the morphology of an organic thin film. Pentacene is used as an active layer above, and m-bis(triphenylsilyl)benzene is used as the bottom layer. Sequential evaporations of these materials result in extraordinary morphology with far fewer grain boundaries and myriad nanometre-sized pores. These peculiar structures are formed by difference in molecular interactions between the organic layers and the substrate surface. The pentacene film exhibits high mobility up to 6.3 cm(2) V(-1) s(-1), and the pore-rich structure improves the sensitivity of organic-transistor-based chemical sensors. Our approach opens a new way for the fabrication of nanostructured semiconducting layers towards high-performance organic electronics.

The effects of hyperbranched polymers (HBPs) on the cure behavior of tetrafunctional epoxy resin were investigated using differential scanning calorimetry (DSC) and FT-IR spectroscopy and compared with those of the linear analog. The hydroxyl terminal groups of the HBP initiated the cure reaction through proton donor–acceptor complex. The heat of cure in epoxy/HBP system was higher than that in epoxy/linear polymer system. The activation energy for cure reaction was lower in epoxy/HBP system. When the hydroxyl terminal groups of the HBP were transformed into benzoate groups, the induction time for cure reaction became much longer and the heat of cure was reduced. The isothermal kinetic parameters were obtained from Kamal equation, where the overall reaction order was ca. 1.5. As the cure reaction proceeded, the characteristic peaks of epoxy ring were decreased and H-bonded C O peak was increased. The intensity of the H-bonded C O peak was increased with increasing amount of the HBP.

To understand the possibilities and limitations of the treatment of concentrated nitrate in wastewater, a space-saving biofilm process was introduced to investigate how efficiently concentrated nitrate was utilized in a biofilm process. Lab-scale submerged biofilters stuffed with plastic pall-ring media were developed for the treatment of wastewater containing high nitrate concentration. Two identical biofilters were operated at 2 and 4 hr media HRT in parallel and the concentration of nitrate in the influent was increased stepwise from 50 to 3000 mg-N/L. The concentration of NOx in the effluent was measured at various volumetric loading rates that were proportional to influent nitrate concentrations. There was a critical point for volumetric loading rate (9 kg NO3–N/m3/day) distinguishing the biofilter performances. At the volumetric loading rate below this critical point, the effluent NOx concentration was maintained steadily in spite of the drastic change in the loading rates. However, the effluent NOx concentration severely fluctuated for the small change when the loading rate was higher than the critical point. It was found that the reactor performance was closely related with the biomass concentration (g-dw/ring) in the biofilters.

The effects of terminal groups and composition of hyperbranched polymers (HBPs) on the crystallization behavior of poly(ethylene terephthalate) (PET) in HBP/PET blends were investigated using in situ FT-IR spectroscopy and differential scanning calorimetry. Hyperbranched aliphatic polyester was synthesized from an AB2 type monomer and a B3 type core. The hydroxyl terminal groups of the HBP were transformed into acetate and benzoate groups by organic synthetic methods. The effects of the HBPs were compared with those of linear polyester (LPE) synthesized from an AB type monomer and a B2 type core. A small amount of HBP with hydroxyl groups could greatly reduce the relative crystallinity of PET through hydrogen bonds. HBP with acetate groups showed effects similar to those of LPE. As the composition of LPE was increased, the relative crystallinity of PET was slightly decreased. On the contrary, HBP with benzoate groups played the role of nucleating agent in the blends with PET. The crystallization rate of PET was highest in the blend with 12 wt % HBP. Dynamic viscosity measurements were performed to investigate the role of the HBPs as processing aids.

The synthetic process of hyperbranched aliphatic polyesters based on 2,2-bis(hydroxymethyl)propionic acid (AB2-type monomer) and 2ethyl-2-(hydroxymethyl)-1,3-propanediol (B3-type core) was investigated with in situ Fourier transform infrared (FT-IR) spectroscopic analysis. The experimental parameter was the stoichiometric ratio between monomer and core moiety corresponding to theoretical first, second and third generation. In the theoretical first generation, monomers were directly combined with a core molecule. In the theoretical second and third generation, oligomers derived from the reaction between monomers were gradually combined with a core moiety as the reaction time increased. The microstructure of the main product was surmised from the peak integration of in situ FT-IR spectra, the intensity of each repeating unit on 13 C NMR spectra and the number average molecular weight. q 1999 Elsevier Science Ltd. All rights reserved.

Although state-of-the-art ambipolar polymer semiconductors have been extensively reported in recent years, highperformance ambipolar polymers with tunable dominant polarity are still required to realize on-demand, target-specific, high-performance organic circuitry. Herein, dithienyl-diketopyrrolopyrrole (TDPP)-based polymer semiconductors with engineered side-chains have been synthesized, characterized and employed in ambipolar organic field-effect transistors, in order to achieve controllable and improved electrical properties. Thermally removable tert-butoxycarbonyl (t-BOC) groups and hybrid siloxane-solubilizing groups are introduced as the solubilizing groups, and they are found to enable the tunable dominant polarity and the enhanced ambipolar performance, respectively. Such outstanding performance based on our molecular design strategies makes these ambipolar polymer semiconductors highly promising for low-cost, large-area, and flexible electronics.

Ambipolar polymer semiconductors are highly suited for use in flexible, printable, and large-area electronics as they exhibit both n-type (electron-transporting) and p-type (hole-transporting) operations within a single layer. This allows for cost-effective fabrication of complementary circuits with high noise immunity and operational stability. Currently, the performance of ambipolar polymer semiconductors lags behind that of their unipolar counterparts. Here, we report on the side-chain engineering of conjugated, alternating electron donor-acceptor (D-A) polymers using diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing groups (PTDPPSe-Si) to enhance ambipolar performance. The alkyl spacer length of the hybrid side chains was systematically tuned to boost ambipolar performance. The optimized three-dimensional (3-D) charge transport of PTDPPSe-Si with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm(2) V(-1) s(-1), respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains.