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Herein, the structure of an o-xylene C60monoadduct (OXCMA) having high electron mobility in solution-processed devices was studied by single-crystal X-ray analysis. The crystal of OXCMA showed a well-aligned three-dimensional network of the C60moiety without inclusion of solvent molecules. Density functional theory (DFT) methods and hopping modeling were employed to calculate the charge carrier mobility of OXCMA with good agreement with the experimental mobility.The crystal structure of an o-xylene C60monoadduct (OXCMA) showed a well-aligned three-dimensional network without inclusion of solvent molecules. DFT methods and hopping modeling were employed to calculate the charge carrier mobility of OXCMA with good agreement with the experimental mobility.

A series of [5]carbohelicene derivatives substituted by electron-withdrawing maleimide and electron-donating methoxy, such as maleimide-substituted [5]carbohelicene (HeliIm) and methoxy-substituted HeliIm (MeO-HeliIm), were newly designed and synthesized to examine the electrochemical properties, excited-state dynamic and circularly polarized luminescence (CPL). First, electrochemical measurements and DFT calculations of [5]carbohelicene derivatives were performed by comparing with the structural isomers: picene derivatives. Introduction of an electron-withdrawing maleimide group onto a [5]carbohelicene core contributes to the stabilized LUMO state in HeliIm as compared to that of [5]carbohelicene (Heli), whereas the energy level of HOMO state in MeO-HeliIm increases by introducing electron-donating methoxy (MeO) groups onto a HeliIm skeleton. The HOMO–LUMO gap of MeO-HeliIm is smaller than those of HeliIm and Heli, which is similar to the steady-state spectroscopic measurements. The absolute fluorescence quantum yield (ΦFL) of HeliIm (0.37) largely increased as compared to [5]carbohelicene, Heli (0.04), whereas ΦFLof MeO-HeliIm (0.22) was slightly smaller than that of HeliIm. Theses photophysical processes including intersystem crossing are successfully explained by the kinetic discussions. Since [5]carbohelicene derivatives show the chirality, measurements of circular dichroism (CD) and circularly polarized luminescence (CPL) were successfully performed. In particular, HeliIm and MeO-HeliIm have provide excellent circularly polarized luminescence (CPL) and the values of the anisotropy factor glumwere estimated to be ∼2.4 × 10–3and ∼2.3 × 10–3, relatively. This is the first observation of CPL in [5]carbohelicene derivatives.

Tetrasulfone[9]helicene (PTSH) was newly synthesized to improve and evaluate its fluorescence and excited-state dynamics through a single-step oxidation reaction of tetrathia[9]helicene (PTTH). In electrochemical measurements, the reduction potential of PTSH was shifted in a positive direction by approximately 1.0 V when compared to that of PTTH because of its electron-accepting sulfone units. The results of the electrochemical measurements agree with the energy levels calculated by density functional theory (DFT) methods and steady-state spectroscopic measurements. Furthermore, a significant enhancement of the absolute fluorescence quantum yield (ΦFL) was achieved. The absolute fluorescence quantum yield of PTSH attained 0.27, which is approximately 10 times larger than that of PTTH (ΦFL= 0.03). Such an enhancement of ΦFLcan be successfully explained by the corresponding kinetic comparison. The reason is mainly the increased energy gap ΔESTbetween the lowest singlet (S1) and triplet (T1) excited states. Finally, excellent circularly polarized luminescence of PTSH was also observed. The value of the anisotropy factor gCPLwas estimated to be 8.3 × 10–4in PTSH.

A new 1,2-dialkylquinoxaline-fused [7]carbohelicene ([7]Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused [7]carbohelicene ([7]Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, [7]Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of [7]Hl-NAIQx were significantly red-shifted compared to those of [7]Hl-Qx and [7]carbohelicene ([7]Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (ΦFL) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (ΦFL= 0.02). Such a large enhancement of the fluorescence of [7]Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor glum(normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10–3. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.

A series of benzo[ghi]perylene and coronene derivatives substituted by electron-withdrawing imide and ester groups were systematically synthesized considering (i) number of imide and ester groups, (ii) five- and six-membered imide groups, and (iii) the peripheral positions. The spectroscopic, electrochemical, and photophysical properties of these molecules were investigated in full detail by steady-state and time-resolved spectroscopy, cyclic voltammetry, quantum yield measurements of fluorescence and intersystem crossing, electron spin resonance (ESR), and density functional theory calculations. The synthetic introduction of proper substituents on the polycyclic aromatic hydrocarbon ring therefore enables us to successfully control the electrochemical and photophysical behaviors. The steady-state absorption and fluorescence spectra also become red-shifted and broadened as compared to those of reference unsubstituted benzo[ghi]perylene and coronene. Regarding the electrochemistry, with an increase in the number of imide groups, the reduction potentials are significantly shifted to the positive direction, which indicates the large enhancement of electron-accepting properties. Then, absorption spectra of mono- and diradical anions of coronenetetraimide (Cor(Im)4), which were generated by the electrochemical reduction, extended to the near-infrared region (up to ∼1000 nm). The ESR measurements of one-electron reduced species of Cor(Im)4demonstrate that more spin is relatively localized on the nitrogen atom in six-membered imide than that in five-membered imide. Finally, systematic comparison of quantum yields and rate constants of the excited-state dynamics also reveals that the intersystem crossing pathway was accelerated in both benzo[ghi]peryleneimide and coroneneimide derivatives, whereas the fluorescence property was dependent on the number of substituents and structural symmetry. This is in sharp contrast to the high quantum yield (ca. ∼1) of fluorescence of perylenediimides.

Solution processing of polymer semiconductors provides a new paradigm for large‐area electronics manufacturing on flexible substrates, but it also severely restricts the realization of interesting advanced device architectures, such as lateral heterostructures with defined interfaces, which are easily accessible with inorganic materials using photolithography. This is because polymer semiconductors degrade, swell, or dissolve during conventional photoresist processing. Here a versatile, high‐resolution photolithographic method is demonstrated for patterning of polymer semiconductors and exemplify this with high‐performance p‐type and n‐type field‐effect transistors (FETs) in both bottom‐ and top‐gate architectures, as well as ambipolar light‐emitting field‐effect transistors (LEFETs), in which the recombination zone can be pinned at a photolithographically defined lateral heterojunction between two semiconducting polymers. The technique therefore enables the realization of a broad range of novel device architectures while retaining optimum materials performance.

In this work we demonstrate two building blocks of a scalable manufacturing technology for nanoscale electronic devices based on direct-write printing: an architecture for high-yield printing of electrode gaps with 100 nm dimension and a low-temperature silver complex ink for integration of organic materials with high conductivity metal interconnects. We use single printed droplets that are made to dewet slowly from each other to allow reliable, high yield patterning even in the presence of certain surface defects.

Distyrylbenzene(DSB) derivatives, trimer of phenylenevinylene, with cyano and alkoxy groups grew epitaxially on the friction-transferred poly(tetrafluoroethylene) (PTFE) layer. DSBs/PTFE double layers indicated the remarkable anisotropic feature in absorption and emission properties.

Ionic liquids (ILs) are attractive materials for fabricating unique hybrid devices based on electronics and electrochemistry; thus, IL-gated transistors and organic light-emitting devices of light-emitting electrochemical cells (LECs) are investigated for future low-voltage and high-performance devices. In LECs, voltage application induces the formation of electrochemically doped p-n homojunctions owing to ion rearrangements in composites of semiconductors and electrolytes, and achieves electron-hole recombination for light emission at the homojunctions. In this work, we applied this concept of IL-induced electrochemical doping to the fabrication of GaN-based light-emitting devices. We found that voltage application to the layered IL/GaN structure accumulated electrons on the GaN surface owing to ion rearrangements and improved the conductivity of GaN. The ion rearrangement also enabled holes to be injected by the strong electric field of electric double layers on hole injection contacts. This simultaneous injection of holes and electrons into GaN mediated by ions achieves light emission at a low voltage of around 3.4 V. The light emission from the simple IL/GaN structure indicates the usefulness of an electrochemical technique in generating light emission with great ease of fabrication.

Light-emitting devices based on electrolytes, such as light-emitting electrochemical cells (LECs) and electric double-layer transistors (EDLTs), are solution-processable devices with a very simple structure. Therefore, it is necessary to apply this device structure into highly fluorescent organic materials for future printed applications. However, owing to compatibility problems between electrolytes and organic crystals, electrolyte-based single-crystal light-emitting devices have not yet been demonstrated. Here, we report on light-emitting devices based on organic single crystals and electrolytes. As the fluorescent materials, a,o-bis(biphenylyl)terthiophene (BP3T) and 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals were selected. Using ionic liquids as electrolytes, we observed clear light emission from BP3T LECs and rubrene EDLTs.

Uniaxially oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) films were prepared on rubbed polyimide substrates and applied to emitting layers of light-emitting electrochemical cells (LECs). The layered structure of the uniaxially oriented F8T2 film and ionic liquid electrolytes enabled us to demonstrate LEC operations with high anisotropic characteristics both in emission and charge transport. Polarized electroluminescence (EL) from electrochemically induced p-n junctions in the uniaxially oriented F8T2 was obtained. The dichroic ratios of EL were the same as those of photoluminescence, suggesting that the doping process into the oriented F8T2 did not interrupt the polymer ordering. This indicates the usefulness of the layered structure of the polymer/electrolyte for the fabrication of LECs based on highly oriented polymer films. In addition, uniaxially oriented F8T2 was found to show reduced threshold energy in optically pumped amplified spontaneous emission. These demonstrations suggest the advantage of uniaxially oriented polymer-based LECs for potential application in future electrically pumped lasers.

Light-emitting field-effect transistors (LEFET) based on poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV) were prepared with asymmetric electrodes of a Au/Cr source and an Al drain on a SiO2gate insulator (600 nm) through twice of photolithography and lift-off techniques. The light emission was observed when the gate voltages increased above -40 V at the drain voltage of -100 V. The luminous efficiency of the devices was significantly improved comparing to those with conventional electrodes of Au/Cr.

A photolithographic patterning technique of perfluoropolymers was developed for the micropatterning of solution-processed organic semiconductors. We found that a small amount of fluorosurfactant additives in photoresist solutions enabled preparation of the spin-coated films even on the dewetting surfaces of perfluoropolymers. Subsequent photolithography and dry/wet etching achieved excellent patterning of perfluoropolymers, which provided a high contrast of wettability in microscale on the substrate. The dewetting patterns were applied for isolating solution-processed organic thin-film transistor arrays for a 100 ppi active-matrix display by selective dewetting. The isolation of the semiconducting layers achieved significant improvement in the current on/off ratio with a high mobility of >1 cm2V?1s?1.

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