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Copper(I) thiocyanate (CuSCN) is known as a wide bandgap p-type semiconductor and recently demonstrated its high ability as a hole-transporting material in thin film devices such as dye-sensitized and perovskite solar cells [1]. However, in fact little is known for its intrinsic physical properties such as bandgap, band positions, optical transparency, carrier density and mobility. We have established methods to electrodeposit well-crystallized CuSCN thin films in various forms. Although the electrochemistry is fairly simple as limited by diffusion of 1 : 1 complex between Cu2+ and SCN- ions ([Cu(SCN)]+), the [Cu2+] : [SCN-] ratio, its absolute concentration and solvent can significantly alter the morphology and crystal orientation of resulting CuSCN [2]. Hybridization with various cationic organic dyes has also been achieved to furnish nanostructures and even transition from rhombohedral β to orthorhombic α form [3]. These unique features of the electrodeposition technique let us anticipate possibilities to tailor-tune physical properties of CuSCN to match the demands for the device applications. Moreover, electrodeposited CuSCN doesn’t hinder its use in flexible electronics unlike many other inorganic materials, since the process is done at room temperature. In this study, we have carried out electrodeposition of CuSCN to vary its morphology and crystal orientation by tuning the bath composition and studied their band structure to explore the room for tuning its physical properties. Morphologies of CuSCN thin films electrodeposited from stoichiometric (REF), Cu-rich and SCN-rich baths are compared in Figs. 1 a-c. While the REF sample has an open structure made of relatively large bulky particles, the Cu-rich sample is dense, made of tiny grains. XRD patterns have found almost random crystal orientation for the former and a high degree of preference of the latter to orient the c-axis of β-CuSCN perpendicular to the substrate. On the other hand, the one from the SCN-rich bath is made of elongated platelets (Fig. 1 b) and strongly oriented to lay down the c-axis in parallel with the substrate. As expected from the morphology, the Cu-rich film is highly transparent, whereas the other two are opaque due to light scattering (Table 1). Tauc plot for indirect transition indicated a systematic increase of bandgap from 3.58 to 3.64 eV on increasing the Cu2+ content. More significant difference was found for their work function (WF) measured by photoelectron yield spectroscopy (PYS). The threshold energy moved downwards from 5.31 to 5.66 eV vs. VAC from Cu-rich to SCN-rich film. The result indicates a high level of p-type doping in the presence of excess SCN-, probably due to increased concentration of Cu2+ as stabilized by SCN- bound to it. Enhanced photoluminescence has also been found for the electrodeposited CuSCN thin film especially for the SCN-rich sample, as compared to commercial CuSCN powder. Thus, electrodeposition has turned out to allow fine-tuning of physical properties of CuSCN for device applications. [1] Vinod E. Madhavan et al., ACS Energy Lett. 2016, 1, 1112−1117. [2] Lina Sun et al., Physics Procedia, 2011, 14, 12-24. [3] Yuki Tsuda et al., Chem., 2017, 148, 845-854. Figure 1

Photochemical conversion of a dry gel coating comprising zinc acetate and monoethanolamine (MEA) into a highly compact and transparent thin film of zinc oxide nanocrystals (ZnO NCs) is shown to pro...

Hybrid thin films of crystalline CuSCN and 4-(N,N-dimethylamino)-4′-(N′-methyl)stilbazolium (DAS) in three distinctively different nanostructures were obtained by electrochemical self-assembly from a single pot containing all the chemical ingredients. Their optical properties for UV–vis-NIR absorption, photoluminescence (PL), and PL excitation spectra were examined between 77 and 298 K, in comparison with solution and solid powder of DAS tosylate (DAST). Unlike all other dyes we tested before, PL of DAS was not quenched but rather enhanced when hybridized with CuSCN. DAST exhibited a strong exciton–phonon coupling to weaken, broaden, and red shift PL at room temperature, so that it inversely is strongly enhanced, sharpened, and blue-shifted at 77 K. The PL of the same dye in the hybrid thin film, however, shows a slight red shift and only a moderate enhancement at reduced temperatures due to strong exciton stabilization in dielectric environment of CuSCN and concerted PL by energy transfer from CuSCN to DAS luminophore, making it a unique nearly temperature-independent luminescent material.

Copper(I) thiocyanate (CuSCN) is known as a wide bandgap p-type semiconductor and recently demonstrated its high ability as a hole-transporting material in perovskite solar cells and light emitting diodes. Its thin film is usually fabricated by simple solution coating and drying [1]. In fact, little is known for physical properties of CuSCN, such as bandgap, band positions, optical transparency, carrier density and mobility. We have established methods to electrodeposit well-crystallized CuSCN thin films in various forms. Although the electrochemistry is fairly simple as limited by diffusion of 1 : 1 complex between Cu2+ and SCN- ions ([Cu(SCN)]+), the [Cu2+] : [SCN-] ratio, its absolute concentration and solvent can significantly alter the morphology and crystal orientation of resulting CuSCN [2]. These unique features of the electrodeposition technique let us anticipate possibilities to tailor-tune physical properties of CuSCN to match the demands for device applications. In this study, we have carried out electrodeposition of CuSCN to vary its morphology and crystal orientation by tuning the bath composition and studied their band structure to explore the room for tuning its physical properties for thin film diodes and hybrid electroluminescence devices. Morphologies of CuSCN thin films electrodeposited from stoichiometric (REF), Cu-rich and SCN-rich baths are shown in Figs. 1 a-c. While the REF sample has an open structure made of relatively large bulky particles, the Cu-rich sample is dense, made of tiny grains to expose their hexagonally shaped top. On the other hand, the one from the SCN-rich bath show rectangular sides of the grains (Fig. 1 a) and strongly oriented to lay down the c-axis in parallel with the substrate. XRD patterns have found almost parallel orientation for the SCN-rich and a high degree of preference of the Cu rich to orient the c-axis of β-CuSCN perpendicular to the substrate. Although all these films indicate nearly the same energy gap of about 3.6 eV estimated by Tauc plot, significant difference was found for their work function (WF) measured by photoelectron yield spectroscopy (PYS) (Fig. 2). The threshold energy moved downwards from 5.23 to 5.66 eV vs. VAC from Cu-rich to SCN-rich film. The result indicates a high level of p-type doping in the presence of excess SCN-, probably due to increased concentration of Cu2+ as stabilized by SCN- bound to it. Simple devices as ITO / electrodeposited CuSCN / Aluminium were fabricated to examine their diode behaviour. While all of the devices employing the electrodeposited CuSCN thin films showed good rectifications in the J-V curves, the onset voltage determined that to observe 5 mA/cm2 moved from 1.21 to 2.57 V (ITO being positive) from Cu-rich to SCN-rich samples to confirm tunability of the device property by conditions of the electrodeposition. Successful operation of organic light emitting diode was also achieved by employing the electrodeposited CuSCN as a hole-injection layer. The device employing the electrodeposited CuSCN achieved a smaller turn-on voltage than that with spin-coated CuSCN in the I-V-L measurements. [1] Vinod E. Madhavan et al., ACS Energy Lett. 2016, 1, 1112−1117. [2] Lina Sun et al., Physics Procedia, 2011, 14, 12-24. Figure 1

Dilution of spin-coating solution of UV-curable polydimethylsiloxane (PDMS) precursor with decamethylcyclopentasiloxane (D5) is able to reduce thickness of the resulting PDMS layer to ca. 100 nm without changing its quality to allow partial photochemical conversion to dense, crack- and pinhole-free inorganic SiOx upon its exposure to vacuum UV (VUV) light with a high photon energy (λ = 172 nm, Eph = 7.2 eV) within 3 min to achieve a facile formation of a PDMS/SiOx double layer. The process of conversion of PDMS to SiOx is clearly understood as monitored by multiple analytical methods used in this study. Since D5 does not attack the materials used for organic light emitting diodes (OLEDs) and the whole process is carried out without water, O2 and at room temperature, this newly developed all solution-based processing is ideally suited to fabrication of thin film encapsulation (TFE) that can be integrated in roll-to-roll (R2R) manufacturing of flexible thin film organic electronics devices. Preliminary test on the standardized OLED devices confirms the effectiveness of the solution-processed PDMS/SiOx alternating multiple layer as the TFE to extend their lifetime by 6 times under air and relative humidity of 50%.

Electrochemical self-assembly of CuSCN/4-(N,N-dimethylamino)-4'-(N'-methyl)stilbazolium (DAS) hybrid thin films has been carried out on systematic variation of bulk concentrations of [Cu(SCN)]+, DAS tosylate (DAST) and changing their flux density by angular speed of rotation of the rotating disk electrode. Switching of DAS loading mechanism dependent on the DAST concentration in the bath has been verified and quantified. The switching occurs at the concentration ratio of the precursors DAST/[Cu(SCN)]+ = ca. 1/31, molar ratio of the product DAS/CuSCN = ca. 1/48, below which the loading becomes diffusion limited for DAS to be occluded in the CuSCN grains, whereas surface reaction for formation of complex between CuSCN and DAS begins to limit the DAS loading when the relative concentration of DAST exceeds this border, resulting in a phase-separated precipitation of CuSCN and (DAS)(SCN) aggregate in unique nanostructures.

Rationale Organic light-emitting diode (OLED) products based on display applications have become popular in the past 10 years, and new products are being commercialized with rapid frequency. Despite the many advantages of OLEDs, these devices still have a problem concerning lifetime. To gain an understanding of the degradation process, the authors have investigated the molecular information for deteriorated OLED devices using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Methods TOF-SIMS depth profiling is an indispensable method for evaluating OLED devices. However, the depth profiles of OLEDs are generally difficult due to the mass interference among organic compounds, including degradation products. In this study, the tandem mass spectrometry (MS/MS) depth profiling method was used to characterize OLED devices. Results After degradation, defects comprised of small hydrocarbons were observed. Within the defect area, the diffusion of all OLED compounds was also observed. It is supposed that the source of the small hydrocarbons derives from decomposition of the OLED compounds and/or contaminants at the ITO interface. Conclusions The true compound distributions have been determined using MS/MS depth profiling methods. The results suggest that luminance decay is mainly due to the decomposition and diffusion of OLED compounds, and that OLED decomposition may be accelerated by adventitious hydrocarbons present at the ITO surface.

Organic light-emitting diodes (OLEDs) are promised to replace the existing displays and lightings in terms of the quality of light. One of the most exciting features of organic electronics is that they can be made flexible. However, flexible OLED encapsulation is actually one of the major challenges because they are very sensitive to oxygen and moisture. Thin-film encapsulation (TFE) prepared by vacuum-deposition processes (ALD, CVD) have high barrier properties, but low throughput and high cost. For the significant cost reduction, all solution-processed roll to roll (R2R) production of OLEDs need to be established. Among the technologies needed, that for the thin-film encapsulation (TFE) imposes the highest challenge, because thin films with a very high level of barrier performance needs to be fabricated onto a complete organic device, so that solvents to attack the materials and high temperature treatments need to be strictly avoided. In this work, organic/inorganic multilayer encapsulation structures based on one step solution-processed alternating polysiloxane and silica layer are presented in Fig. 1(A), in which organic layers are spin-coated, followed by polymer crosslinking reaction, and finally subjected to photochemical conversion of the surface into dense silica barrier layers under exposure to vacuum ultraviolet（VUV) light. The whole process is very simple and fast to perform at room temperature, and the coating solution is successfully developed not to destroy the pre-formed organic emitting layer. Transmission electron microscopic (TEM) image shows successful fabrication of multi-stacks of organic/SiOx hybrid alternating layers (Fig. 1(B)). The thickness of ~ 100 nm was achieved per coating. The performance of such multilayer as thin-film encapsulation (TFE) of an OLED device has also been investigated as shown in Fig. 1 (C). The preliminary life time to reach 90% of the initial luminance (5000 cd/m2) was 73 hours for the OLED encapsulated with 450 nm TFE, about 6 times extended compared to that of the bare device. Figure 1

Nanostructured hybrid thin films of crystalline CuSCN and fluorescent cationic dyes; Rhodamine B (RB), Nile Blue A (NB) and 4-(N,N-dimethylamino)-4'-(N'-methyl)stilbazolium (DAS) were obtained by electrochemical self-assembly from a single pot containing all the chemical ingredients. Concerted functionalities achieved by the intimate interaction between CuSCN and dye was studied for photoluminescence (PL) behavior between 77 and 298 K. PL from RB and NB was totally quenched when they were hybridized with CuSCN, due to hole transfer from the dye excited state to the valence band of CuSCN, potentially indicating their use as light absorber in solar cells and photodiodes. On the contrary, that of DAS was not quenched despite of its favorable HOMO position for the hole transfer. Crystalline DAS salt with tosylate (DAST) exhibited a strong exciton-phonon coupling to weaken, broaden and red-shift PL at room temperature, so that it inversely is strongly enhanced, sharpened and blue-shifted at 77 K. The PL of the same chromophore in the hybrid thin film, however, shows a slight red-shift and only moderate enhancement at reduced temperature, due to exciton stabilization and energy transfer from CuSCN to DAS luminophore, making it a unique nearly temperature-independent luminescent material.

A 3.2-in flexible color display, with a resolution of 50 ppi and composed of bottom-emission multiphoton organic light-emitting diodes (OLEDs) and inkjet-printed organic thin-film transistors (OTFTs) with a bottom-gate/bottom-contact structure on a color filter, was developed. The device could successfully display color videos while being bent, and achieved a maximum luminance of 125 cd/m2 with white light emission. The gate dielectrics of the OTFTs used on the backplane were bilayers of cardo polymer and Parylene, and the material used for the organic semiconductors was dithieno [2,3-d;2’,3’-d’]benzo[1,2-b;4,5-b’]dithiophene blended with polystyrene in tetralin solvent, which was coated using inkjet printing to sufficiently fill the banks composed of a fluorine-based polymer. OTFTs with a channel length of 5 $\mu \text{m}$ were created using the above process, and the structure achieved a high mobility of 1.2 $\mathrm {cm}^{{{2}}}/({\mathrm{ V}}\cdot \text{s}$ ), making it suitable for flexible color OLED displays. The mobility was about three times as high as that obtained using solution shearing methods.

Highly efficient organic light-emitting diodes are in urgent demand in applications of new generation full-color displays and solid-state lighting sources. The limitation of device performance is greatly affected by extrinsic and intrinsic elements of the light out-coupling process. By elaborately designing emitters as sticklike molecules, horizontal orientation ratios in the range of 86–93% were realized to intrinsically increase the out-coupling factor of electroluminescence devices. These elongated compounds are inclined to lie parallel to substrate in vacuum-deposited thin solid films and regularize their transition dipole moments in a major degree. As consequences of such desirable molecule arrangement, remarkable external quantum efficiencies near 21% for pure blue devices, close to 30% for sky-blue devices, and over 35% for greenish blue devices were respectively achieved. A compatible strategy on devising high-performance emitters for organic electroluminescence is advocated herein.

Solution processing of thin film encapsulation (TFE) has been a long anticipated technology to bridge the big idea of flexible organic electronics to become real world values, since only small-sized flexible devices are currently achieved with expensive multilayered TFE by complex vacuum processing. Highly demanding conditions are to carry out the process under inert gas, at a low temperature, and without aggressive chemicals to avoid damages to the organic materials. Here we show for the first time a solution-processed TFE to totally equal the level of conventional glass-cap encapsulation to achieve a "ready-to-be-used" stability of an organic light emitting diode (OLED). A seamless organic/inorganic multilayer in a structure such as polydimethylsiloxane (PDMS)/SiO

Zinc oxide (ZnO), as a wide band gap (3.37 eV) semiconductor, are useful materials for wide range of applications in thin-film transistor (TFT), photovoltaics, photocatalysts, sensors, and so on. Large exciton binding energy (60 meV) at room temperature (RT) makes ZnO a promising luminescent material especially in optoelectronic devices such as UV lasers and light emitting diodes (LED). Among them, ZnO nanocrystals (quantum dots) has attracted increasing attention because their optical properties can be tuned by varying the crystal size. However, its nanoscale crystallites tend to aggregate to undergo Ostwald ripening due to their high surface energy. To stabilize them, surface modification are usually necessary. At the same time, the whole processes for nanocrystal synthesis and film fabrication become complicated. Here, we report a simple novel photochemical gel conversion approach for one-step preparation of ZnO thin films with an average nanocrystals in about 2-3 nm size (inset in Fig. 1a), by employing vacuum ultraviolet (VUV) light irradiation in dry N2. Systematic characterization is performed to understand the surface chemistry and the optical properties of ZnO nanocrystals. Thus obtained ZnO films show unique absorption peak at 294 nm (4.2 eV) (Fig. 1a) and strong tunable photoluminescence in the range of 386-496 nm when expose to UV light, from violet, blue to bluish-green upon increasing time of VUV irradiation (Fig. 1b). Clearly blue-shifted absorption peaks of the VUV treated samples are indicative of quantum-confinement effect, as contrasted to the broad character of the annealed film, which originates from band structure of bulky ZnO. The extension of VUV time only results in increase of absorbance, with no change of the peak wavelength, indicating population increase but no crystal growth by Ostwald ripening during the VUV irradiation. Therefore, the color change of the emitted light should be associated with the change of defect state distribution, rather than the size effect. However, such photoluminescence from defects was fairly strong to be clearly recognized by naked eyes, so that the university logo could be patterned by photomasking VUV to be seen under black light was demonstrated (inset in Fig. 1b). Figure 1

Whether they are inorganic or organic, the key words for creation of new functional materials should be (1) solution, (2) low temperature, and (3) rare-element-free for sustainable development. As a leading example, we explore electrochemical self-assembly (ESA) of inorganic / organic hybrid thin films. In addition to the interests to study evolution of unique hybrid structures, concerted new functionalities are anticipated due to intimate interaction between the inorganic and organic constituents. Herein, we report ESA of CuSCN / 4-(N,N-dimethylamino)-4’-(N’-methyl)stilbazolium (DAS) hybrid thin films and its concerted photoluminescence (PL) behavior [1]. Hybrid thin films of crystalline CuSCN/DAS in three distinctively different nanostructures were obtained by ESA from a single pot containing all the chemical ingredients. Adsorption of DAS during the electrochemical precipitation of CuSCN result in significant change of film morphology, crystal structure and its orientation, as DAS “occluded” into crystal grains of β-CuSCN, DAS phase separated nano-“haircomb” shape β-CuSCN, and DAS phase-separated in nano-“scale” shape α-CuSCN, by simply increasing DAST concentration in the bath [2]. Their optical properties for UV-vis-NIR absorption, photoluminescence (PL), and PL excitation (PLE) spectra were examined between 77 and 298 K, in comparison with solution and solid powder of DAS tosylate (DAST). While all the fluorescent dyes we previously found to hybridize with CuSCN underwent quenching due to hole injection from dye excited state to the valence band of CuSCN, DAS presented the first and only example to exhibit PL when combined with CuSCN [3]. DAST exhibited a strong exciton-phonon coupling to weaken, broaden, and red shift PL at room temperature, so that it inversely is strongly enhanced, sharpened, and blue-shifted at 77 K. However, the PL of the same dye in the hybrid thin film shows a slight red shift and not much intensified. Dielectric environment as well as ordered alignment of DAS greatly stabilize exciton against thermalization loss by suppressing twisted intramolecular charge transfer (TICT) and exciton-phonon coupling. The smallest temperature dependence, thus to be interpreted as the strongest exciton stabilization, was found for the “haircomb” β-CuSCN/DAS hybrid. The PLE spectra of the “scale” α-CuSCN/DAS hybrid show a prominent sharp peak at 380 nm and another double-peak between 400 and 450 nm by cooling temperature. The former corresponds to the band-edge absorption of CuSCN, while the latter being similar to the LMCT absorption of [Cu(SCN)]+ complex. It has been confirmed that those peaks in PLE spectra indicate the contribution of CuSCN thin film without DAS for the generation of PL. These contributions of the light absorption by CuSCN to the PL from DAS clearly indicate energy transfer from CuSCN to DAS as a concerted PL mechanism. Concerted PL by energy transfer from CuSCN to DAS has also been found to occur efficiently, especially for the “scale” α-CuSCN/DAS with the largest contact area due to interpenetrating hybrid nanostructure in the smallest domain size. Those hybrid thin film having the concerted PL mechanism (Fig. 1) can possibly make these materials useful as LEDs. [1] K. Uda et al., ACS Omega, 2019, 4 (2), 4056-4062. [2] Y. Tsuda et al., Chem., 2017, 148, 845-854. [3] K. Uda et al., ECS Trans., 2019, 88, 323-333. Figure 1

Visible-light-induced two-electron oxidation of water to form hydrogen peroxide (H2O2) was investigated in a photovoltaic cell (PVC) composed of an ITO electrode coated by tetrakis-(4-carboxylphenyl) porphyrinatogermanium(IV) (1)-adsorbed titanium oxide (TiO2) particles as an anode (1/TiO2/ITO) and a Pt electrode as a cathode in an aqueous solution containing an electrolyte. The short-circuit photocurrent was observed under irradiation of the 1/TiO2/ITO anode with the light of 550 nm under aerated conditions. Simultaneously, H2O2 was detected only in the anode chamber. After irradiation for 6 h, the turnover number (TON) and the faradaic efficiency for the formation of H2O2 were estimated to be 9.0 and 92%, respectively. The action spectrum for the formation of H2O2 was well consistent with the absorption spectrum of 1. These findings indicate that H2O2 is produced by the excitation of 1 on the anode through a quantitative process with the obtained faradaic current. It was concluded that water acted as an electron donor on the anode, while molecular oxygen acted as an electron acceptor under aerated conditions, and several different types of ions also acted as an electron acceptor under argon atmosphere on the cathode. It is suggested that the photooxidation of water to form H2O2 was initiated by a photoinduced electron transfer from the excited singlet state of 1 to TiO2 to generate the porphyrin radical cation (1+ ), which underwent a proton dissociation from the hydroxo axial ligand to give a Ge-oxyl complex as a key intermediate for a two-electron activation of water to form hydrogen peroxide.

An active matrix backplane based on solution-processed organic thin-film transistors (OTFTs) has been developed for flexible displays having multiphoton organic light-emitting diodes (OLEDs). The OTFT device has a bottom-gate/bottom-contact type structure consisting of a polyethylene naphthalate-based flexible substrate covered with patterned gate electrodes and a gate dielectric of UV-cured cardo-polymer. Teflon AF was used for a hydrophobic bank structure that defines active regions of the OTFTs, and the organic semiconductor was coated by solution shearing. The OTFT backplane fabricated here had $384 \times 128$ pixels at a resolution of 300 dpi; images and video were successfully displayed on the resulting flexible multiphoton-emission OLED display.

Metal oxides such as TiO2, ZnO, SnO2 are useful in many of energy devices because of their high chemical stability, n-type semiconductivity and photoelectrochemical properties. Various methods of solution processing of their thin films are known, such as chemical bath deposition, electrodeposition and sol-gel reactions. Typically, high temperatures need to be applied for crystallization to achieve good properties. The need of high temperature however limits the choice of substrates to heat-resistant materials. Also, crystallization often results in pinholes and cracks to damage the performance of devices. We have developed an alternative sol-gel method to obtain ultra-smooth thin films of various metal oxides at room temperature, by employing photochemical decomposition of coated precursor by vacuum ultraviolet (VUV) light irradiation. The method is compatible with conductive plastic film substrates, so that multiple applications in thin film devices such as transparent conductive layer, light emitter, buffer layer in solar cells and thin-film encapsulation (TFE) as an example shown in Fig. 1 can be envisioned. Figure 1

The substitution of the bulky substituents, such as the triphenylsilyl groups, on the 9,10-positions of anthracene produced a remarkable increase in Φ f , and the substituents controlled the intermolecular stacking by diminishing the electroplex formation and inter- and intra-molecular photochemical reactions. Organic light-emitting diode (OLED) devices composed of these anthracene derivatives showed highly pure blue electroluminescence (EL).

Recent developments in the field of π-conjugated polymers have led to considerable improvements in the performance of solution-processed organic light-emitting devices (OLEDs). However, further improving efficiency is still required to compete with other traditional light sources. Here we demonstrate efficient solution-processed multilayer OLEDs using small molecules. On the basis of estimates from a solvent resistance test of small host molecules, we demonstrate that covalent dimerization or trimerization instead of polymerization can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power efficiencies of 36, 52 and 34 lm W(-1) at 100 cd m(-2) for solution-processed blue, green and white OLEDs, respectively, with stable electroluminescence spectra under varying current density. We also show that the composition at the resulting interface of solution-processed layers is a critical factor in determining device performance.

Phosphorescent emitters are extremely important for efficient organic light-emitting diodes (OLEDs), which attract significant attention. Phosphorescent emitters, which have a high phosphorescence quantum yield at room temperature, typically contain a heavy metal such as iridium and have been reported to emit blue, green and red light. In particular, the blue cyclometalated complexes with high efficiency and high stability are being developed. In this review, we focus on blue cyclometalated complexes. Recent progress of computational analysis necessary to design a cyclometalated complex is introduced. The prediction of the radiative transition is indispensable to get an emissive cyclometalated complex. We summarize four methods to control phosphorescence peak of the cyclometalated complex: (i) substituent effect on ligands, (ii) effects of ancillary ligands on heteroleptic complexes, (iii) design of the ligand skeleton, and (iv) selection of the central metal. It is considered that novel ligand skeletons would be important to achieve both a high efficiency and long lifetime in the blue OLEDs. Moreover, the combination of an emitter and a host is important as well as the emitter itself. According to the dependences on the combination of an emitter and a host, the control of exciton density of the triplet is necessary to achieve both a high efficiency and a long lifetime, because the annihilations of the triplet state cause exciton quenching and material deterioration.

Hydrogen evolution coupled with the photochemical oxygenation of cyclohexene with water was observed in the system sensitized by Sn(IV)–porphyrin adsorbed on Pt loaded TiO2 nano-particles in aqueous acetonitrile solution upon visible light irradiation.

We have significantly improved the emission efficiency in an organic light-emitting device (OLED) based on iridium (III)bis[(4,6-di-fluoropheny)-pyridinato-N,C2′]picolinate (FIrpic). To improve the efficiency, 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl, which has a high triplet energy, was used as the carrier-transporting host for the emissive layer. The FIrpic-based OLED exhibited a maximum external quantum efficiency of 10.4%, corresponding to a current efficiency of 20.4 cd/A, and a maximum power efficiency of 10.5 lm/W. The efficiency was drastically improved compared to that of a previously reported FIrpic-based OLED. This result indicates that triplet energy is efficiently confined on FIrpic molecules, resulting in the high efficiency.

π-Conjugated copolymers composed of 9,9-didodecylfluorene and boron quinolate were synthesized by an efficient chelating reaction of quinolinol-based polyfluorene derivative, as a polymeric ligand, with arylborane compounds such as triphenylborane (BPh3) or fluorobis(pentafluorophenyl)borane diethyl etherate ((C6F5)BF·OEt2). The polymeric ligand was prepared from the deprotection reaction of boron tribromide and benzyloxyquinoline-based polyfluorene, which was produced via the efficient Suzuki cross-coupling reaction of 5,7-dibromo-8-benzylquinoline and 9,9-didodecylfluorene-2,7-diboronic acid in the presence of 2-(2′,6′-dimethoxybiphenyl)dicyclohexylphosphine (S-Phos) and palladium(II) acetate. Their optical properties were studied by UV-vis absorption and photoluminescence spectroscopies. The absorption and PL spectra of the obtained polymers were red-shifted in comparison with those of the polymeric ligand due to the decrease of the LUMO level by the formation of boron complexes, explained by theoretical calculations of the model compounds using the density-functional theory (DFT) method. The molar extinction coefficients and emission maxima of boron-chelating polymers were analogous values to those of (κ2-(N,O)-5,7-bis(9,9-dihexylfluoren-2-yl)-8-quinolinolate)diphenylborane (BFluorene2q). Furthermore, the electron mobilities of the polymers were determined from the space-charge limited current (SCLC) with electron-only device structure of ITO/Ca/polymer/LiF/Al. As a result, the mobilities for the polymers (3.9 or 2.0 × 10−5 cm2 V−1 s−1) were reasonably close to the value (7.9 × 10−5 cm2 V−1 s−1) calculated from the Alq3-fabricated device.