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Funding: S. W. thanks the China Scholarship Council (201906250199). A. K. G. is grateful to the Royal Society for Newton International Fellowship NF171163. EZ-C and IDWS acknowledge support from EPSRC (EP/L017008, EP/P010482/1). We are also grateful for financial support from the University of St Andrews Restarting Research Funding Scheme (SARRF) which is funded through the Scottish Funding Council grant reference SFC/AN/08/020. EZ-C is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089). We would also like to thank the Leverhulme Trust (RPG-2016-047) for financial support. Herein, we demonstrate how judicious selection of donor decorating a central multi-resonant thermally activated delayed fluorescence (MR-TADF) core based on DiKTa can lead to very high-performance OLEDs. Decorating the DiKTa core with triphenylamine (TPA) and diphenylamine (DPA), 3TPA-DiKTa and 3DPA-DiKTa exhibit bright, narrowband green and red emission in doped films, respectively. The OLEDs based on these emitters showed record-high performance with maximum external quantum efficiencies (EQEmax) for this family of emitters, with a EQEmax of 30.8% for 3TPA-DiKTa at λEL of 551 nm and 16.7% for 3DPA-DiKTa at λEL of 613 nm. The efficiency roll-off in the OLEDs was improved significantly by using 4CzIPN as an assistant dopant in hyperfluorescence (HF) devices. The outstanding device performance has been attributed to preferential horizontal orientation of the transition dipole moments of 3TPA-DiKTa and 3DPA-DiKTa. Publisher PDF

S.W. thanks the China Scholarship Council (201906250199). EZ-C and IDWS acknowledge support from EPSRC (EP/L017008, EP/P010482/1). We are also grateful for financial support from the University of St Andrews Restarting Research Funding Scheme (SARRF) which is funded through the Scottish Funding Council grant reference SFC/AN/08/020. EZ-C is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089). We would also like to thank the Leverhulme Trust (RPG-2016-047) for financial support. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement No 838885 (NarrowbandSSL). S.M.S. acknowledges support from the Marie Skłodowska-Curie Individual Fellowship. Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement n1117545. Y.O. acknowledges funding by the Fonds de la Recherche Scientifique-FNRS under Grant n° F.4534.21 (MIS-IMAGINE). D.B. is a FNRS Research Director. Strategies to tune the emission of multiresonant thermally activated delayed fluorescence (MR-TADF) emitters remain rare. Here, we explore the effect of donor substitution about a MR-TADF core on the emission energy and the nature of the excited state. We decorate different numbers and types of electron-donors about a central MR-TADF core, DiKTa. Depending on the identity and number of donor groups, the excited state either remains short-range charge transfer (SRCT) and thus characteristic of an MR-TADF emitter or becomes a long-range charge transfer (LRCT) that is typically observed in donor–acceptor TADF emitters. The impact is that in three examples that emit from a SRCT state, Cz-DiKTa, Cz-Ph-DiKTa, and 3Cz-DiKTa, the emission remains narrow, while in four examples that emit via a LRCT state, TMCz-DiKTa, DMAC-DiKTa, 3TMCz-DiKTa, and 3DMAC-DiKTa, the emission broadens significantly. Through this strategy, the organic light-emitting diodes fabricated with the three MR-TADF emitters show maximum electroluminescence emission wavelengths, λEL, of 511, 492, and 547 nm with moderate full width at half-maxima (fwhm) of 62, 61, and 54 nm, respectively. Importantly, each of these devices show high maximum external quantum efficiencies (EQEmax) of 24.4, 23.0, and 24.4%, which are among the highest reported with ketone-based MR-TADF emitters. OLEDs with D–A type emitters, DMAC-DiKTa and TMCz-DiKTa, also show high efficiencies, with EQEmax of 23.8 and 20.2%, but accompanied by broad emission at λEL of 549 and 527 nm, respectively. Notably, the DMAC-DiKTa-based OLED shows very small efficiency roll-off, and its EQE remains 18.5% at 1000 cd m–2. Therefore, this work demonstrates that manipulating the nature and numbers of donor groups decorating a central MR-TADF core is a promising strategy for both red-shifting the emission and improving the performance of the OLEDs. Publisher PDF

Organic optoelectronic devices combine high-performance, simple fabrication and distinctive form factors. They are widely integrated in smart devices and wearables as flexible, high pixel density organic light emitting diode (OLED) displays, and may be scaled to large area by roll-to-roll printing for lightweight solar power systems. Exceptionally thin and flexible organic devices may enable future integrated bioelectronics and security features. However, as a result of their low charge mobility, these are generally thought to be slow devices with microsecond response times, thereby limiting their full scope of potential applications. By investigating the factors limiting their bandwidth and overcoming them, we demonstrate here exceptionally fast OLEDs with bandwidths in the hundreds of MHz range. This opens up a wide range of potential applications in spectroscopy, communications, sensing and optical ranging. As an illustration of this, we have demonstrated visible light communication using OLEDs with data rates exceeding 1 gigabit per second., Organic LEDs (OLEDs) have generally been considered to be slow devices. Through engineering the structure and materials of OLEDs, the authors achieve a breakthrough in the high-speed operation of OLEDs and demonstrate a 1 Gbps optical wireless link using the OLEDs.

Examples of multi-resonant thermally activated delayed fluorescence (MR-TADF) emitters that emit at longer wavelengths remain rare. To reach that goal, we decorate different numbers and types of electron-donors about a central MR-TADF core, DiKTa. Depending on the identity and number of donor groups, the excited state either remains short range charge transfer (SRCT) and thus characteristic of an MR-TADF emitter or becomes a long-range charge transfer (CT) that is typically observed in donor-acceptor TADF emitters. The impact is that in three examples, Cz-DiKTa, Cz-Ph-DiKTa and 3Cz -DiKTa, which emit from a SRCT state, the emission remains narrow, while in four examples, TMCz-DiKTa, DMAC-DiKTa, 3TMCz-DiKTa and 3DMAC-DiKTa, which emit via a CT state, the emission broadens significantly. Through this strategy, the organic light-emitting diodes fabricated with the three MR-TADF emitters show maximum electroluminescence emission wavelengths, EL, of 511, 492 and 547 nm with moderate full-width at half maxima (FWHM) of 62, 61 and 54 nm, respectively. Importantly, each of these devices show high maximum external quantum efficiencies (EQEmax) of 24.4%, 23.0% and 24.4%, which are amongst the highest reported with ketone-based MR-TADF emitters. OLEDs with D-A type emitters, DMAC-DiKTa and TMCz-DiKTa, also show high efficiencies, with EQEmax of 23.8% and 20.2%, but accompanied by broad emission at EL of 549 and 527 nm, respectively. Noteworthy is that the DMAC-DiKTa-based OLED shows very small efficiency roll-off, and its EQE remains 18.5% at 1000 cd m-2. Therefore, this work demonstrates that manipulating the nature and numbers of donor groups decorating a central MR-TADF core is a promising strategy for both red-shifting the emission and improving the performance of the OLEDs.

Bacterial infection and the growth of antibiotic resistance is a serious problem that leads to patient suffering, death and increased costs of healthcare. To address this problem, we propose using flexible organic light-emitting diodes (OLEDs) as light sources for photodynamic therapy (PDT) to kill bacteria. PDT involves the use of light and a photosensitizer to generate reactive oxygen species that kill neighbouring cells. We have developed flexible top-emitting OLEDs with the ability to tune the emission peak from 669 to 737 nm to match the photosensitizer, together with high irradiance, low driving voltage, long operational lifetime and adequate shelf-life. These features enable OLEDs to be the ideal candidate for ambulatory PDT light sources. A detailed study of OLED–PDT for killing Staphylococcus aureus was performed. The results show that our OLEDs in combination with the photosensitizer methylene blue, can kill more than 99% of bacteria. This indicates a huge potential for using OLEDs to treat bacterial infections. Flexible OLED technology is becoming increasingly mature and is ready to open new directions in antimicrobial photodynamic therapy. An international team led by Prof Ifor Samuel from University of St Andrews, UK presents a comprehensive study to show that flexible organic light-emitting diodes (OLEDs) are ideal light sources to be used in photodynamic therapy to kill bacteria. They design the OLED device structure to enable large area, high uniformity, low driving voltage, long operational lifetime, adequate shelf-life and colour tunability and address all the requirements of photodynamic therapy. Actual biological experiments show killing rates of more than 99% for S. aureus bacteria. The approach clearly demonstrates the huge potential of OLEDs for treatment of bacterial infections and future wearable healthcare devices.

OLEDs are attractive and distinctive light sources because of they are very thin, emit over an area and can be flexible. These features also make them very interesting for medical applications as compact, lightweight sources can enable ambulatory treatment. In photodynamic therapy (PDT), light in combination with a photosensitiser leads to the generation of reactive oxygen species that can kill nearby cells. We report the development of improved OLEDs for PDT. In particular, we show their use for antimicrobial PDT i.e. for killing bacteria, parasites and fungi in vitro.

OLEDs and other organic optoelectronic devices combine many attractive features. However, they are generally thought to be slow, limiting their range of possible applications. We demonstrate that by careful study of the factors limiting their bandwidth, and appropriate design in terms of device size, operating field and emitter lifetime exceptionally fast OLEDs can be made with modulation bandwidths up to 245 MHz, opening up new potential applications in communications, spectroscopy, sensing and ranging. In particular, we demonstrate visible light communication in which a single OLED transmits data at a rate exceeding 1 gigabit per second.

Organic semiconductors are an important class of optoelectronic material that are widely studied because of the scope for tuning their properties by tuning their chemical structure, and simple fabrication to make flexible films and devices. Although most effort has focused on developing displays and lighting from these materials, their distinctive properties also make them of interest for visible light communications (VLCs). This article explains how their properties make them suitable for VLC and reviews the main uses that have been explored. On the transmitter side, record white VLC communication has been achieved by using organic semiconductors as colour converters, while direct modulation of organic light-emitting diodes is also possible and could be of interest for display-to-display communication. On the receiver side, organic solar cells can be used to harvest power and data simultaneously, and fluorescent antennas enable fast and sensitive receivers with large field of view. This article is part of the theme issue ‘Optical wireless communication’.

Unraveling the quantitative properties of the spatio-temporal cortical responses to microstimulation is of essential importance for designing intracortical neural prostheses. Despite the millisecond-order precision of neuronal spiking and synaptic signaling in the cortex, the circuit response dynamics at such temporal resolution has been investigated to a limited extent. In the present, cortical neural responses to repetitive microstimulation pulses were examined in the mouse cerebral slices by means of the voltage-sensitive dye imaging. The amplitude of the population spikes induced directly by the stimulus pulses successively decreased when the inter-pulse interval of the stimuli was 5 msec, but not 20 msec. This was similar between the experiments in that the stimulation was applied to either the layer II/III or IV. These results suggested that the refractory period of spiking at the population level is one of limiting conditions for designing efficient frequency for repetitive pulse stimulation.

Funding: Royal Society (Grant Number(s): IE160703); Engineering and Physical Sciences Research Council (Grant Number(s): EP/L015110/1). Conventional fluorescence sensing equipment for disease detection is expensive and bulky, restricting access of patients to accurate diagnosis. Organic light-emitting diodes (OLEDs) have the potential to enable compact fluorescence sensing compatible with point-of-care (POC) testing. However, the limited brightness and broad emission spectra of OLEDs can be a challenge for achieving good sensitivity. Here, co-host microcavity OLEDs with narrowed spectra, high conductivity, and high brightness are developed for fluorescence sensing. The OLEDs are driven in pulsed mode for achieving higher brightness and stable light output. To sense the presence of single-stranded DNA (ssDNA), two complementary ssDNA labelled with Cyanine dyes – Cy3 (ssDNA-Cy3) or Cy5 (ssDNA-Cy5) are used to form a Förster resonance energy transfer (FRET) pair when the DNA hybridized. The dye-labelled DNA is then excited by the OLED at the Cy3 excitation wavelength, and the fluorescence is detected at the emission wavelength of Cy5. As a result, the device shows a very high sensitivity that can detect as low as 1 × 10−9 m of ssDNA-Cy5 in fetal bovine serum (FBS). This work shows a simple approach to highly sensitive fluorescence sensing with OLED light sources that is promising for use in POC diagnostics. Publisher PDF

Funding: Leverhulme Trust (RPG-2017-231), the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA NESD program (N66001-17-C-4012) and the RS Macdonald Charitable Trust. C.M. acknowledges funding from the European Commission through a Marie Skłodowska Curie individual fellowship (703387). A.M. acknowledges funding through an individual fellowship of the Deutsche Forschungsgemeinschaft (404587082). Y.D. acknowledges support from the Chinese Scholarship Council (CSC). L.T. acknowledges studentship funding through the EPSRC CM-CDT (EP/L015110/1). M.S. acknowledges funding by the Royal Society (Dorothy Hodgkin Fellowship, DH160102). Fluorescence imaging is an indispensable tool in biology, with applications ranging from single‐cell to whole‐animal studies and with live mapping of neuronal activity currently receiving particular attention. To enable fluorescence imaging at cellular scale in freely moving animals, miniaturized microscopes and lensless imagers are developed that can be implanted in a minimally invasive fashion; but the rigidity, size, and potential toxicity of the involved light sources remain a challenge. Here, narrowband organic light‐emitting diodes (OLEDs) are developed and used for fluorescence imaging of live cells and for mapping of neuronal activity in Drosophila melanogaster via genetically encoded Ca2+ indicators. In order to avoid spectral overlap with fluorescence from the sample, distributed Bragg reflectors are integrated onto the OLEDs to block their long‐wavelength emission tail, which enables an image contrast comparable to conventional, much bulkier mercury light sources. As OLEDs can be fabricated on mechanically flexible substrates and structured into arrays of cell‐sized pixels, this work opens a new pathway for the development of implantable light sources that enable functional imaging and sensing in freely moving animals. Postprint

In response to cellular stresses, activating transcriptional factor 4 (ATF4) regulates the expression of both stress-relieving genes and apoptosis-inducing genes, eliciting cell fate determination. Since pharmacological activation of ATF4 exerts potent anti-tumor effects, modulators of ATF4 activation may have potential in cancer therapy. We herein attempted to identify small molecules that activate ATF4. A cell-based screening to monitor TRB3 promoter activation was performed using crude drugs used in traditional Japanese Kampo medicine. We found that an extract from Sophora flavescens roots exhibited potent TRB3 promoter activation. The activity-guided fractionation revealed that kurarinone was identified as the active ingredient. Intriguingly, ATF4 activation in response to kurarinone required PKR-like endoplasmic reticulum kinase (PERK). Moreover, kurarinone induced the cyclin-dependent kinase inhibitor p21 as well as cytostasis in cancer cells. Importantly, the cytostatic effect of kurarinone was reduced by pharmacological inhibition of PERK. These results indicate that kurarinone triggers ATF4 activation through PERK and exerts cytostatic effects on cancer cells. Taken together, our results suggest that modulation of the PERK-ATF4 pathway with kurarinone has potential as a cancer treatment.

Record-high 200 Mbps transmission using an OLED with a 31 MHz 3 dB bandwidth using a 3-tap feedforward equaliser is achieved, demonstrating the potential of such devices for use in low-cost polymer optical fiber links.

The transient current and electroluminescent characteristics of p - i - n organic light-emitting diodes driven using short voltage pulses with various amplitudes and pulse widths were investigated to understand high current behavior (>10 A/cm 2 ). Even under short voltage pulse operation, Joule heating was found to strongly affect the transient characteristics and lead to temperature rises estimated to be over 100 K in the high current density region (>400 A/cm 2 ). This results in a large increase in both current density and EL intensity within the pulse width. In addition, the Joule heating was found to have an effect on the external quantum efficiency. However its contribution was found to be limited compared with the other quenching mechanism, singlet-polaron quenching.

To quantify the rise in device temperature caused by Joule heating during short voltage-pulse excitation at high current densities (>10 A/cm2), the device temperatures of unipolar organic conductors were measured using electrical testing methods. For a maximum voltage amplitude of 59 V at a current density of ∼300 A/cm2, temperature rose over 145 °C within a pulse duration of 5 μs in an N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD)-based single-carrier organic conductor. This result is in reasonable agreement with numerically calculated values. These findings indicate that suppressing the effects of Joule heating by carefully adjusting pulse width, substrate and organic materials, and device configuration is important to achieve further carrier injection in the ultra-high current density region (>1 kA/cm2).

Highly fluorescent non-volatile fluidic fluorene derivatives functionalized with siloxane chains were synthesized and used in monolithic solvent-free liquid organic semiconductor distributed feedback lasers. The photoluminescence quantum yield values, the amplified spontaneous emission thresholds and the ambipolar charge carrier mobilities demonstrate that this class of materials is extremely promising for organic fluidic light-emitting and lasing devices.

We report on the use of oxygen as triplet quencher to reduce singlet-triplet annihilation in light-emitting organic solid films and solvent-free molecular semiconducting liquids. For this purpose, a fluorescent heptafluorene derivative is dispersed either in a wide bandgap 4,4′-Bis (N-carbazolyl)-1,1′-biphenyl (CBP) host or in a solvent-free liquid matrix based on 9-(2-ethylhexyl)carbazole (EHCz). To introduce oxygen in the samples, a modified cold isostatic pressure technique is used in the case of spin-coated CBP blends while oxygen is bubbled in the liquids. The influence of the oxygenation on their photophysical and amplified spontaneous emission properties is examined. Both solid blend films and liquids showed before and after the introduction of oxygen a photoluminescence quantum yield higher than 80% and an amplified spontaneous emission threshold lower than 0.4 μJ/cm 2. While oxygen does not quench significantly the singlet excitons in these systems, singlet-triplet annihilation is strongly reduced in solid thin films and nearly suppressed in the liquid layers. This study demonstrates that liquid organic semiconductors are promising candidates for optically pumped continuous wave lasers and provides important insights for a more effective triplet management in organic semiconductor lasers.

This research was financially supported by the EPSRC NSF‐CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA‐NESD programme (N66001‐17‐C‐4012), and the Leverhulme Trust (RPG‐2017‐231). Y.L.D. acknowledges a stipend from the Chinese Scholarship Council (CSC). C.M. acknowledges funding by the European Commission through a Marie Skłodowska Curie Individual Fellowship (703387). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). Organic light‐emitting diodes (OLEDs) can emit light over much larger areas than their inorganic counterparts, offer mechanical flexibility, and can be readily integrated on various substrates and backplanes. However, the amount of light they emit per unit area is typically lower and the required operating voltage is higher, which can be a limitation for emerging applications of OLEDs, e.g., in outdoor and high‐dynamic‐range displays, biomedical devices, or visible‐light communication. Here, high‐luminance, blue‐emitting (λpeak = 464 nm), fluorescent p–i–n OLEDs are developed by combining three strategies: First, the thickness of the intrinsic layers in the device is decreased to reduce internal voltage loss. Second, different electron‐blocking layer materials are tested to recover efficiency losses resulting from this thickness reduction. Third, the geometry of the anode contact is optimized, which leads to a substantial reduction in the in‐plane resistive voltage losses. The OLEDs retain a maximum external quantum efficiency of 4.4% as expected for an optimized fluorescent device and reach a luminance of 132 000 cd m−2 and an optical power density of 2.4 mW mm−2 at 5 V, a nearly eightfold improvement compared to the original reference device. Postprint

Visible light communications (VLC) have attracted considerable interest in recent years due to an increasing need for data communication links in home and enterprise environments. Organic light-emitting diodes (OLEDs) are widely used in display applications owing to their high brightness, high quality colour-rending capability and low cost. As a result, they are attractive candidates for the implementation of ultra-low cost visible light optical links in free-space and guided-wave communications. However, OLEDs need to exhibit a bandwidth of at least ~MHz to be able to support the modest data rates (~Mbps) required in these applications. Although fluorescent OLEDs typically exhibit shorter photon lifetimes than inorganic LEDs, the bandwidth performance of the large size OLEDs used in display applications are limited by their electrical characteristics. In this work, we present a detailed physical simulation that describes well the performance of fast OLED devices that exhibit significant -3 dB bandwidths (f 3dB ) of 44 MHz obtained for a 0.12 mm2 device. It is demonstrated that the reduction of the device size results in a significant bandwidth improvement due primarily to a reduction in parasitic capacitance of the devices, though this is counteracted by carrier dynamic effects. The model provides an insight into the basic physical properties of the OLED and may be used for optimisation of future generations of OLED devices.

This research was financially supported by the EPSRC NSF - CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA-NESD program (N66001-17-C-4012) and by the EPSRC CDT Capital Equipment funding stream (EP/L017008/1). C.- M.K. acknowledges support from Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). C.M. acknowledges funding by the European Commission through a Marie Skłodowska Curie Individual Fellowship (703387). Y.D., W.L., and M.W. acknowledge stipends from the Chinese Scholarship Council (CSC). I.D.W.S. acknowledges support from a Royal Society Wolfson research merit award. 4,7‐Diphenyl‐1,10‐phenanthroline (BPhen) is widely used to create the electron transport layer (ETL) in organic light‐emitting diodes (OLEDs) because of its high electron mobility and good compatibility with alkali metal n‐dopants. However, the morphology of these ETLs is easily altered by heating due to the relatively low glass transition temperature (Tg) of BPhen and this change often reduces the performance of OLEDs. Here, an enhancement in the thermal stability of OLEDs when doping their BPhen‐based ETLs with cesium (Cs) is reported. To investigate the role of the Cs dopant in the BPhen matrix, the crystallization features of Cs‐doped BPhen films with different doping concentrations are examined. Next, the electrical and optical properties of blue fluorescent and red phosphorescent OLEDs containing Cs‐doped BPhen ETLs are characterized after annealing the OLEDs at temperatures up to 100 °C. Cs plays a critical role in inhibiting the undesired crystallization of BPhen films, which enhances the thermal stability of OLEDs beyond the Tg of neat BPhen. Finally, highly stable BPhen‐based OLEDs encapsulated via atomic layer deposition at 80 °C are demonstrated. This work may lead to a new strategy for enhancing the intrinsic thermal durability of organic devices and their compatibility with thermally demanding processes. Postprint

Organic light-emitting diodes (OLEDs) have reached a huge market as technology for small displays, e.g. in smartphones, and are entering the larger display and solid-state lighting markets as well. In parallel to these commercial successes, the OLED technology is adapted to a multitude of promising new applications, such as in optogenetics and medical therapy. However, it is still challenging to ensure good stability in applications that require high brightness (or high optical power density), in part due to the resulting resistive heating. Increased temperature can lead to a change in morphology of one or several organic layers, e.g. via crystallization of organic molecules, which then reduces electrical and optical performance and likely results in rapid device failure. Aside from an intrinsic resistive heating, heating can also be due to environmental effects during operation or fabrication and encapsulation of devices. For instance, atomic layer deposition (ALD) is a promising technique to form thin, yet highly protective encapsulation layers. However, state-of-the-art ALD processes require relatively high temperature during deposition (< 80 °C). 4,7-diphenyl-1,10-phenanthroline (BPhen) has been widely used as electron transporting layer (ETL) due its high electron mobility, particularly in an organic matrix-dopant system. However, it is well known that thin films of BPhen tend to recrystallize spontaneously. Annealing accelerates crystallization even further due to the relatively low glass transition temperature (Tg) of BPhen (62 °C). A straightforward way to enhance the device thermal stability is to make use of a high Tg material, yet materials have to be carefully adopted to provide appropriate functionality in OLEDs. In this contribution, we report the improvement of the thermal stability of OLEDs with BPhen based electron transport layers (ETLs) by cesium (Cs) doping. To verify the role of the Cs dopant in the BPhen matrix, recrystallization features of Cs-doped BPhen films with different doping concentrations were investigated using optical microscopy and atomic force microscopy. We also examined the photophysical properties of the films, i.e. photoluminescence (PL) and absorption. PL spectra exhibit monotonic red-shifts and broadening as the Cs doping concentration increases. This presumably indicates formation of metal complexes via interaction between the 1,10-phenanthroline group of BPhen molecules and the Cs ions. It was found that Cs plays a critical role, not only in inhibiting undesired recrystallization of BPhen molecules in a thin-film, but also in allowing BPhen layers to be thermally stable beyond the Tg of neat BPhen. Next, the electrical and optical properties of blue and red OLEDs that contain BPhen layers with different Cs-doping concentrations as ETL were characterized after annealing at temperatures between 60 and 100 °C. We find that higher doping concentrations lead to a marked increase in thermal device stability (quantified by current density and luminance at a fixed voltage). Making use of this observation, we successfully encapsulated BPhen based OLEDs with thin-film oxide layers using ALD. The results shown in this work may be transferable to other material systems and can thus provide a useful guideline to enhance the intrinsic thermal durability of organic devices and to render them compatible with processes involving thermal treatment.

The quenching of singlet excitons by injected charge carriers in molecules that display thermally activated delayed fluorescence (TADF) was investigated using time-resolved transient photoluminescence (PL) techniques. Injected electrons did not affect the excitons; however, injected holes caused significant quenching. Using a rate-equation analysis, the hole-induced exciton quenching rate was determined to be between 10–11 and 10–12 cm3 s–1. Interestingly, the TADF emission component was enhanced in the presence of injected holes, plausibly due to a reduction of the singlet-exciton energy level.

Organic semiconductor laser operating in the quasi-CW regime at 80 MHz and under 30 ms long pulse photoexcitation is demonstrated., The demonstration of continuous-wave lasing from organic semiconductor films is highly desirable for practical applications in the areas of spectroscopy, data communication, and sensing, but it still remains a challenging objective. We report low-threshold surface-emitting organic distributed feedback lasers operating in the quasi–continuous-wave regime at 80 MHz as well as under long-pulse photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield, and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve a low lasing threshold. A simple encapsulation technique greatly reduced the laser-induced thermal degradation and suppressed the ablation of the gain medium otherwise taking place under intense continuous-wave photoexcitation. Overall, this study provides evidence that the development of a continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture.

The alternating current (AC) responses of double-injection and double-insulated organic light-emitting diodes (OLEDs) were investigated and compared. To reveal the electroluminescent (EL) processes in these devices, the AC voltage and frequency dependence of the EL intensity and capacitive current were studied in the time domain with a focus on phase difference analysis. It was found that the voltage-dependent transit time and frequency-dependent carrier distribution were important for the AC-driven performance of the double-injection OLEDs. In contrast, although the double-insulated OLEDs shared some similarities with the double-injection OLEDs, they had some unique characteristics, which were the absence of resistive current and phase shift of EL profiles. It was revealed that the EL in the double-insulated OLEDs was driven by the displacement current generated by the ionization of the doped layers, which, however, formed space charge regions and undermined the EL emission. The space charge redistributed the electric field across the devices after the initiation of EL, making the EL maintain for a limited time interval. This effect was significant under low frequency and high AC voltage. Comparing the phase difference between both devices, it was indicated that the space charge effect was responsible for the observed EL phase shift and the asymmetric EL profiles at low frequency and high AC voltage in the double-insulated OLEDs. The proposed model was also of help to understand the EL saturation phenomena with AC frequency and voltage in those devices.

In response to cellular stresses, activating transcriptional factor 4 (ATF4) regulates the expression of both stress-relieving genes and apoptosis-inducing genes, eliciting cell fate determination. Since pharmacological activation of ATF4 exerts potent anti-tumor effects, modulators of ATF4 activation may have potential in cancer therapy. We herein attempted to identify small molecules that activate ATF4. A cell-based screening to monitor TRB3 promoter activation was performed using crude drugs used in traditional Japanese Kampo medicine. We found that an extract from Sophora flavescens roots exhibited potent TRB3 promoter activation. The activity-guided fractionation revealed that kurarinone was identified as the active ingredient. Intriguingly, ATF4 activation in response to kurarinone required PKR-like endoplasmic reticulum kinase (PERK). Moreover, kurarinone induced the cyclin-dependent kinase inhibitor p21 as well as cytostasis in cancer cells. Importantly, the cytostatic effect of kurarinone was reduced by pharmacological inhibition of PERK. These results indicate that kurarinone triggers ATF4 activation through PERK and exerts cytostatic effects on cancer cells. Taken together, our results suggest that modulation of the PERK-ATF4 pathway with kurarinone has potential as a cancer treatment.

Since the discovery of organic solid-state lasers, great efforts have been devoted to the development of continuous-wave (cw) lasing in organic materials. However, the operation of organic solid-state lasers under optical cw excitation or pulse excitation at a very high repetition rate (quasi-cw excitation) is extremely challenging. In this work, we have demonstrated quasi-continuous-wave (quasi-cw) surface-emitting lasing in a distributed feedback device which combines a second-order grating with an organic thin film of a host material 4,4’-bis(N-carbazolyl)-1,1’-biphenyl (CBP) blended with an organic laser dye 4,4’-bis[(N-carbazole)styryl]biphenyl (BSBCz). When pumping the device with optical picosecond pulse excitation, the quasi-cw laser operation maintained up to a repetition rate of 8 MHz. The lasing threshold was around 0.25 J cm−2 which was almost independent of the repetition rates. For our laser devices, the maximum repetition rate (8 MHz) is the highest ever reported, and the lasing threshold (0.25 J cm−2) is the lowest ever reported. These superior quasi-cw lasing characteristics in BSBCz are accomplished by the less generation of triplet excitons via intersystem crossing because a photoluminescence quantum yield of the blend film is nearly 100% and there is no significant spectral overlap between laser and triplet absorption.[1,2] Triplet quenchers, generally used for the fabrication of organic thin-film lasers, were not necessary in our devices because of negligible accumulation of triplet excitons and a small spectral overlap between emission and triplet absorption. Therefore, we believe that BSBCz is the most promising candidate for the first realization of electrically pumped organic laser diodes in terms of optical characteristics. However, electrical characteristics such as charge carrier mobility, charge carrier capture cross section, etc., are also extremely important and will need further investigation and enhancement for realization of electrically pumped organic lasers. 1. Aimono, T.; Kawamura, Y.; Goushi, K.; Yamamoto, H.; Sasabe, H.; Adachi, C. Appl. Phys. Lett. 2005, 86, 071110–071112. 2. Nakanotani, H.; Adachi, C.; Watanabe, S.; Katoh, R. Appl. Phys. Lett. 2007, 90, 231109.

High-efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.

We demonstrate two efficient blue-green thermally activated delayed fluorescence (TADF) compounds comprising a dimeric phenylcarbazole and four cyano substituents on the phenyl rings. A comparison ...

An afterglow organic light-emitting diode (OLED) that displays electroluminescence with long transient decay after it is turned off is demonstrated. This OLED exhibits blue and green dual emission originating from fluorescence and phosphorescence, respectively. A phosphorescence lifetime of 4.3 s is achieved.

We investigated the influence of the substrate's thermal conductivities (k) and the widths of the electrical pulses (τpulse) on the maximum current densities (Jmax) in organic thin-film devices. We also estimated the temperature rise (ΔT) inside devices under the pulse operation using numerical calculations to interpret the observed differences in Jmax. For a long τpulse of 5 μs, Jmax is higher for devices with high-k sapphire substrates (around 1.2 kA/cm2) than devices with low-k plastic substrates (around 0.4 kA/cm2). This is because high-k sapphire substrates can work as heat sinks to relax ΔT for such a long τpulse. Operation of devices with high-k sapphire substrates for a short τpulse of 70 ns resulted in further relaxation of ΔT, leading to an increase of Jmax to around 5 kA/cm2. Interestingly, for such a short τpulse, devices with high-k sapphire and low-k plastic substrates showed similar Jmax and ΔT values, the reason for which may be that it is difficult for the generated Joule heat to travel to the substrate across a low-k organic layer within this short time.We investigated the influence of the substrate's thermal conductivities (k) and the widths of the electrical pulses (τpulse) on the maximum current densities (Jmax) in organic thin-film devices. We also estimated the temperature rise (ΔT) inside devices under the pulse operation using numerical calculations to interpret the observed differences in Jmax. For a long τpulse of 5 μs, Jmax is higher for devices with high-k sapphire substrates (around 1.2 kA/cm2) than devices with low-k plastic substrates (around 0.4 kA/cm2). This is because high-k sapphire substrates can work as heat sinks to relax ΔT for such a long τpulse. Operation of devices with high-k sapphire substrates for a short τpulse of 70 ns resulted in further relaxation of ΔT, leading to an increase of Jmax to around 5 kA/cm2. Interestingly, for such a short τpulse, devices with high-k sapphire and low-k plastic substrates showed similar Jmax and ΔT values, the reason for which may be that it is difficult for the generated Joule heat to travel t...

Structural characteristics of liquid silicon (l-Si) have been examined by molecular-dynamics calculations using the Tersoff empirical potential. Generated l-Si possesses a broad distribution of the coordination number dominated by the sixfold coordination. The average bond length increases with the coordination number. The bond angle distribution function indicated that l-Si has a preference for the bond angles of 60\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{}. The 60\ifmmode^\circ\else\textdegree\fi{} peak mainly occurs from the atoms with longer bonds of the coordination number \ensuremath{\geqslant}5. We have also discussed a possible short-range order in l-Si that includes the atomic configurations with a close-packed layer, such as the simple hexagonal structure. \textcopyright{} 1996 The American Physical Society.

頸動脈に浸潤が疑われる頭頸部扁平上皮癌症例において, 我々は, 超音波のリアルタイム画像をモニターしつつ触診を行い, 頸動脈壁とリンパ節の間の可動性を観察している。今回平成2年から5年の間に, CTまたはMRI画像で頸動脈浸潤を疑われた症例を対象に, 超音波所見と術中所見, 頸動脈切除症例では組織学的検討を行った。超音波法で頸動脈と癒着を認めない症例では, 術中の頸動脈剥離も容易で頸動脈は温存された。一方, 癒着を認めた症例の頸動脈合併切除標本では, 外膜周囲に広範な浸潤を示すものが多く, 外膜内への浸潤は1例で確認された。

A 63-year-old woman with Behçet disease presented with epigastric pain due to refractory gastric ulcers. Examinations indicated that these ulcers were caused by gastrointestinal Behçet disease. Steroid therapy proved ineffective, so we gave 5mg/kg of infliximab. However, since the patient responded poorly to the treatment the infliximab was discontinued and a total gastrectomy was performed. After surgery, a marginal ulcer developed and infliximab was again administered. Although this brought about improvement in the conditions of the marginal ulcer, infusion-related hypersensitivities in the patient caused polyarthralgia. We therefore discontinued the infliximab treatment and began 40 mg of adalimumab every other week. After 3 months of the new treatment, the patient's marginal ulcer completely healed and her epigastric pain disappeared. This case suggests that adalimumab may be as useful as infliximab for treating refractory gastrointestinal Behçet disease.

A 57-year-old man presented with jaundice. Abdominal computed tomography showed a 10-cm left hepatic lobe heterogeneous solid mass with low attenuated areas in the mass, multiple liver metastases and lung metastasis. Serology for hepatitis B and C were negative. Serum alpha-fetoprotein, CEA and CA19-9 were normal. The patient died a few weeks later of progressive liver failure and an autopsy was performed. Histologically, the tumor consisted of sarcomatoid mononuclear cells and osteoclast-like giant cells. The liver tissue surrounding the tumor showed no cirrhotic pattern. The osteoclast-like giant cells were uniformly and strongly immunoreactive with CD68. The mononuclear cells demonstrated expression of vimentin but were negative for CAM5.2. The MIB-1 index was 20% for the mononuclear cells. In conclusion, the histopathological diagnosis revealed an osteoclast-like giant cell tumor of the liver.

We developed organic light-emitting diodes (OLEDs) with nanopatterned current flow regions using electron-beam lithography with the aim of suppressing singlet–polaron annihilation (SPA). Nanopatterns composed of lines and circles were used in the current flow regions of nano-line and nano-dot OLEDs, respectively. Excitons partially escape from the current flow regions where SPA takes place. As such, current densities where external quantum efficiencies were half of their initial values (J0) increased as line width and circle diameter were decreased to close to the exciton diffusion length. Circles were more efficient at enhancing exciton escape and increasing J0 than lines. The J0 increase in the nano-dot OLEDs containing nanopatterned circles with a diameter of 50 nm was approximately 41-fold that of a conventional OLED with a current flow region of 4 mm2. The dependence of J0 on the size and shape of the nanopatterns was well explained by an SPA model that considered exciton diffusion. Nanopatterning of...