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High-efficiency narrowband near-ultraviolet (NUV) organic light-emitting diodes with high color purity have currently encountered great challenges. Here, using butyl (Bu) and cyanogen (CN) substituted strategy in the simplest polycyclic aromatic hydrocarbons of indolocarbazole (ICz), two simple emitters of BuICz and BuICzCN were demonstrated. This simple strategy was observed to enable both emitters to realize NUV emission at 380–381 nm with a small full width at half maximum (FWHM) of 21–23 nm and high photoluminescent quantum efficiency of 50%–59% in toluene solution. Furthermore, the BuICzCN doped devices exhibited a slightly blueshifted narrowband NUV electroluminescence at 388 nm with a small FWHM of 32.3 nm but a higher external quantum efficiency of 3.92% in comparison with the BuICz doped devices. This work provides a path to realize high-performance narrow-band NUV emission. [ABSTRACT FROM AUTHOR]

Hybridized local and charge‐transfer (HLCT) excited‐state emitters can effectively utilize non‐radiative triplet excitons through high‐lying reverse intersystem crossing (hRISC), but they are mostly limited to the donor‐π‐acceptor type molecules. It is a great challenge to develop high‐performance near‐ultraviolet (NUV) emitters with narrow‐band emission by HLCT due to the large carrier injection barriers and high triplet energy. In this work, by incorporating planar multi‐resonance (MR) skeleton of oxygen‐bridged triphenylborane (BO) and weak electron‐donating unit of tetraphenyl‐silane (TPS), two NUV emitters of tBOSi and tBOSiCz are developed, where an extra weak charge transfer (CT) channel between BO skeleton and peripheral phenyl in TPS is observed to increase CT component and activate hot exciton channel of hRISC. As a result, tBOSi and tBOSiCz show an outstanding narrow‐band NUV emission at 414 nm with a FWHM of about 32 nm in solution‐processed organic light‐emitting diodes (OLEDs), even at a heavy doping ratio. The best NUV electroluminescent properties are further achieved in the optimal tBOSi‐doped OLEDs with a record efficiency of 9.15% and a low CIEy of 0.034. This work provides a profound guidance for developing high‐performance narrow‐band NUV emitters by an extra weak CT channel into MR skeleton to activate HLCT emission. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) thermally activated delayed fluorescence (MR-TADF) materials, categorized for the B/N and carbonyl/amine fragments, are now intensively and widely studied due to their color purity. However, the relationship between the MR molecular structure and full width at half maximum (FWHM) of the emission remains elusive. In order to probe the factor of determining the emission FWHM of the MR emitters, a series of relevant molecules were synthesized where the MR core acceptor moiety, phenylborane or acetophenone, is fixed, while the donor moiety is altered to adjust the charge transfer (CT) strength. These potential MR molecules provide sufficient photophysical data to shed light on the emission bandwidth influenced by CT strength. Meanwhile, OLEDs fabricated using all the studied compounds achieve maximum external quantum efficiencies (EQEmax) around 7.0–15.3% because of the TADF character induced by the host/guest interaction in the excited state. The results provide further understanding on the fundamentals of the MR emitters. [ABSTRACT FROM AUTHOR]

The development of near-infrared (NIR)-emitting phosphorescent emitters are still urgently needed for solution-processed organic light-emitting diodes (SP-OLEDs) with high efficiency, radiant emittance, and low cost. Herein, we designed and synthesized a new iridium complex, namely (tBuTPA–DBPz)2Ir(acac), with the rigid C^N coordinated core of dibenzo[a,c] phenazine (DBPz) and an amplifying peripheral shell of 4,4′-di(tert-butyl)-triphenylamine (tBuTPA) attached at its 3,6-positions. The influence of the rigid DBPz core and big tBuTPA shell on the photophysical, electrochemical and electroluminescent properties of (tBuTPA–DBPz)2Ir(acac) was primarily studied in comparison with the archetype (DBPz)2Ir(dpm). The NIR emission peaked at 714 nm with an outstanding external quantum efficiency of 12.25% and a recorded radiant emittance of 45 330 mW Sr−1 m−2 was observed in the (tBuTPA–DBPz)2Ir(acac)-doped devices at an optimized dopant ratio of 8 wt%. The EQE is 1.57 times that of (DBPz)2Ir(dpm)-doped devices. Moreover, this NIR light-emitting device contains an Ir(III) content as low as 0.68 wt% and exhibits a bright NIR emission at 714 nm with outstanding efficiency and radiant emittance. Our results indicate that the NIR-emitting OLEDs with high efficiency, radiant emittance and low cost should be realized by developing core–shell type Ir(III) complexes with a rigid C^N coordinate core and an amplifying shell. [ABSTRACT FROM AUTHOR]

External quantum efficiency (EQE), color rendering index (CRI), color correlated temperature (CCT), and spectral stability are key challenges for constructing high-performance white organic light-emitting diodes (WOLEDs) with a simple device structure. Herein, in order to resolve these issues, we primarily employed a thermally activated delayed fluorescence (TADF) emitter of CzAcSF as a host emitter and a dinuclear platinum (III) complex (Pt-1) as a guest emitter to construct solution-processed single-emitting layer WOLEDs at low guest concentrations of 0.75–1.50 wt. %. Thanks to their broad coverage of visible spectra, efficient energy transfer, and weak charge trap of Pt-1, the optimized WOLEDs showed an increasing EQE of 11.93% and a current efficiency of 30.76 cd/A with a high CRI of 75 and a CCT of 5210 K. Furthermore, the stable electroluminescent spectra with CIE (commission internationale de L'Eclairage) coordinate deviations of Δx = 0.022 and Δy = 0.015 were exhibited. This is an outstanding example for high-performance WOLEDs via employing a TADF host-sensitized low-concentration dinuclear platinum (III) complex simultaneously with high efficiency, CRI, CCT, and color stability. [ABSTRACT FROM AUTHOR]

Research into organic light emitters employing multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is presently attracting a great deal of attention due to the potential for efficient deep-blue emission. However, the origins and mechanisms of successful TADF are unclear, as many MR-TADF materials do not show TADF behaviour in solution, but only as particular pure solids. Here, an investigation into a well-known MR-TADF material, DABNA-1, together with other new MR materials (9H-quinolino[3,2,1-kl]phenothiazin-9-one (QPO) and 9H-quinolino-[3,2,1-kl]-phenothiazin-9-one 5,5-dioxide (QP3O)), yields new insights regarding the origin of TADF. Although a material system may support the concept of MR, inefficiency in both forward and reverse intersystem crossings forbids TADF unless a suitable host material allows an exciplex-like host–emitter interaction that boosts TADF. This boosted-TADF mechanism can be generalized to any fluorescence dye that lacks TADF in the photoluminescence measurement but has a thermally accessible S1–T1 energy gap, opening the way to high-performance organic light-emitting diodes. This study reveals the importance of host–guest interactions for effective multiple-resonance thermally activated delayed fluorescence in organic light emitters. [ABSTRACT FROM AUTHOR]

Flowslides that override a liquefied substrate can vastly enhance a disaster after failure initiation. These effects may result from the rapid velocity and long runout distance from slides mobilized into flows. It is thus crucial to provide an improved understanding of the transformation mechanisms of catastrophic flowslides for hazard evaluation. This study examines the Saleshan landslide in Gansu, China, which occurred in 1983 and killed more than 200 people. The Saleshan landslide travelled for approximately 1 km due to pore water pressure generation resulting from overrunning and liquefication of the alluvial sands in the river valley below. We used geomorphologic and topographic maps to determine its dynamic features and mobilization behaviors on the landslide body, and placemarks and seismic signals to identify its approximate velocity at different sites. Electrical resistivity tomography (ERT) surveys also revealed the hydrogeological conditions post‐landslide, showing a clear groundwater table along with the liquefied alluvial sand and gravel layers. Particle size distributions and triaxial shear behaviors confirmed more ready liquefaction of superficial loess and underlying alluvial sand in comparison with the red soil above and below them. Novel loading impact triaxial testing was also performed on the alluvial sand to elucidate its liquefaction potential in undrained and drained conditions. The alluvial sand was found to be markedly prone to liquefaction in undrained conditions due to impact‐induced increased pore water pressure. The results further demonstrated that the Saleshan landslide underwent a transformation from a slowing slide on a steep slope, where it originated, to flow on a nearly flat terrace with abundant groundwater that it overrode. The transformation mechanism involved the liquefied alluvium sand substrate, which greatly enhanced the landslide mobility. Along with recent, similar findings from landslides globally, substrate liquefaction may result in a widespread, significant increase in landslide mobility and thus hazard, and the present study identifies the requisite conditions for this phenomenon to occur. [ABSTRACT FROM AUTHOR]

The classical problem of supervised learning is to infer an accurate estimate of a target variable $Y$ from a measured variable $X$ using a set of labeled training samples. Motivated by the increasingly distributed nature of data and decision making, this paper considers a variation of this classical problem in which the inference is distributed between two nodes, e.g., a mobile device and a cloud, with a rate constraint on the communication between them. The mobile device observes $X$ and sends a description $M$ of $X$ to the cloud, which computes an estimate $\hat {Y}$ of $Y$. We follow the recent minimax learning approach to study this inference problem and show that it corresponds to a one-shot minimax noisy lossy source coding problem. We then establish information theoretic bounds on the risk-rate Lagrangian cost, leading to a general method for designing a near-optimal descriptor-estimator pair. A key ingredient in the proof of our result is a refined version of the strong functional representation lemma previously used to establish several one-shot source coding theorems. Our results show that a naive estimate-compress scheme for rate-constrained inference is not optimal in general. When the distribution of $(X,Y)$ is known and the error is measured by the logarithmic loss, our bounds on the risk-rate Lagrangian cost provide a new one-shot operational interpretation of the information bottleneck. We also demonstrate a way to bound the excess risk of the descriptor-estimator pair obtained by our method. [ABSTRACT FROM AUTHOR]

The correlation between molecular packing structure and its room-temperature phosphorescence (RTP), hence rational promotion of the intensity, remains unclear. We herein present racemism enhanced RTP chiral chromophores by 2,2-bis-(diphenylphosphino)-1,1-napthalene (rac-BINAP) in comparison to its chiral counterparts. The result shows that rac-BINAP in crystal with denser density, consistent with a long standing Wallach's rule, exhibits deeper red RTP at 680 nm than that of the chiral counterparts. The cross packing between alternative R- and S- forms in rac-BINAP crystal significantly retards the bimolecular quenching pathway, triplet-triplet annihilation (TTA), and hence suppresses the non-radiative pathway, boosting the RTP intensity. The result extends the Wallach's rule to the fundamental difference in chiral-photophysics. In electroluminescence, rac-BINAP exhibits more balanced fluorescence versus phosphorescence intensity by comparison with that of photoluminescence, rendering a white-light emission. The result paves an avenue en route for white-light organic light emitting diodes via full exploitation of intrinsic fluorescence and phosphorescence. Room temperature phosphorescence (RTP) is a topic which is currently widely studied, but a study on the correlation between types of molecular solid and RTP properties is lacking. Here the authors show that RTP is enhanced in the racemic form of axial chiral molecules due to its denser R- and S- cross packing arrangement. [ABSTRACT FROM AUTHOR]

Four isomeric dinuclear platinum complexes of (C^N)2Pt2(μ-OXT)2 are synthesized and characterized with different C^N cyclometalating ligands and the same ancillary ligand of 5-(4-octylphenyl)-1,3,4-oxadiazole-2-thiol (μ-OXT). These isomeric C^N ligands are 1-naphthyl-1-isoquinoline (niq), 2-naphthyl-1-isoquinoline (2niq), 1-naphthyl-2-quinoline (nq) and 2-naphthyl-2-quinoline (2nq). The isomeric effect on the photophysical, electrochemical and electroluminescence properties of (C^N)2Pt2(μ-OXT)2 was systematically studied. It is found that the emissions were easy to tune from deep red to near infrared for (C^N)2Pt2(μ-OXT)2 by changing the C^N isomers. Furthermore, the complexes with 2-naphthyl presented better electroluminescence (EL) properties than the complexes with 1-naphthyl in these solution-processable polymeric light-emitting devices. In contrast to the (2nq)2Pt2(μ-OXT)2-doped devices displaying a deep-red emission peaked at 686 nm with an external quantum efficiency (EQE) of 3.21%, the (2niq)2Pt2(μ-OXT)2-doped devices exhibited a near-infrared emission peaked at 704 nm with a significantly increased EQE of 8.86% and a radiant emittance of 986 μW cm−2. Our research provides an efficient strategy to tune emission from deep red to near infrared by a simple isomeric engineering of dinuclear platinum(II) complexes. [ABSTRACT FROM AUTHOR]

Consider a memoryless relay channel, where the relay is connected to the destination with an isolated bit pipe of capacity $C_{0}$. Let $C(C_{0})$ denote the capacity of this channel as a function of $C_{0}$. What is the critical value of $C_{0}$ , such that $C(C_{0})$ first equals $C(\infty)$ ? This is a long-standing open problem posed by Cover and named “The Capacity of the Relay Channel,” in Open Problems in Communication and Computation, Springer-Verlag, 1987. In this paper, we answer this question in the Gaussian case and show that $C(C_{0})$ cannot equal to $C(\infty)$ unless $C_{0}=\infty $ , regardless of the SNR of the Gaussian channels. This result follows as a corollary to a new upper bound we develop on the capacity of this channel. Instead of “single-letterizing” expressions involving information measures in a high-dimensional space as is typically done in converse results in information theory, our proof directly quantifies the tension between the pertinent $n$ -letter forms. This is done by translating the information tension problem to a problem in high-dimensional geometry. As an intermediate result, we develop an extension of the classical isoperimetric inequality on a high-dimensional sphere, which can be of interest in its own right. [ABSTRACT FROM AUTHOR]

Metal atoms with excellent magnetic, electrical and optical properties that are integrated into liquid crystal molecules – metallomesogens – have attracted much attention from chemists, physicists and engineers and many materials based on e.g. Ag, Pt, Pd, Ir, Ni, Cu and lanthanide ions have been reported. Though several reviews and books have been published on metallomesogens, few refer to their photophysical properties. Additionally, metallomesogens with good emission properties in solution or in neat film are still scarce. Owing to the 100% theoretical internal quantum efficiency, phosphorescent liquid-crystalline materials were developed recently. Here, a brief overview of recent research on such materials based on platinum and iridium complexes including their molecular design and structure–property relationships is reported. It is hoped that this review will stimulate further development of luminescent metallomesogens. [ABSTRACT FROM AUTHOR]

Two new zig-zag type di- and mono-nuclear platinum(ii) complexes of (BuPh-BDIQ)Pt2(dpm)2 and (BuPh-BDIQ)Ptdpm were synthesized and characterized by using a zig-zag type cyclometalating ligand 3,10-di(tert-butyl)-5,12-bis(4-(tert-butyl)phenyl)-benzodiisoquinoline (BuPh-BDIQ). Their single-crystal structures, and photophysical, electrochemical and electroluminescent properties were primarily investigated. Compared with (BuPh-BDIQ)Ptdpm, (BuPh-BDIQ)Pt2(dpm)2 exhibited a significantly increased photoluminescent efficiency of 3.64% and a red-shifted near-infrared (NIR) emission peak at 718 nm owing to its enhanced rigid planar structure in a nitrogen atmosphere. As a result, only (BuPh-BDIQ)Pt2(dpm)2 presented NIR electroluminescent emission in a doped polymeric light-emitting diode. The highest external quantum efficiency of 0.97% and a radiant intensity of 146 μW cm−2 were observed for the device at 2 wt% dopant concentration, which is higher than the values of previous NIR-emitting di-nuclear platinum complexes constructed with cyclometalated ligands. Furthermore, efficiency roll-off was efficiently inhibited. This indicates that high-efficiency NIR-emitting di-nuclear platinum complexes can be obtained by designing a zig-zag type C^N–C^N tetradentate cyclometalating ligand with a big rigid planar saw band. [ABSTRACT FROM AUTHOR]

Directly polarized organic light emitting diodes (OLEDs) have the potential to significantly improve the efficiency and reduce the cost of liquid-crystal displays (LCDs) among other applications. However, fluorescent liquid crystals are currently used to achieve this, while phosphorescent emitters would further improve efficiency. To this end, the metallomesogens based on ionic iridium complexes bearing different aliphatic chains substituent, named 7a and 7b, were designed and prepared in this contribution. Both iridium complexes showed smectic mesophase evidenced by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. Deep-red emission was observed for the iridium complexes in solution and solid state, and complex 7a clearly presented aggregation-induced emission (AIE) behavior in THF–water solvent mixture. Non-doped polarized OLEDs employing complex 7a or 7b as emitter were fabricated and direct linearly polarized electroluminescence with a polarization ratio of 4 was achieved, which is the highest ratio reported for metallomesogens-based phosphorescent OLEDs. Importantly, the choice of linker between the core complex and mesogenic pendent groups is key to achieve distinctive polarization of electroluminescence and AIE. These results are a first step towards the development phosphorescent OLEDs able to efficiently produce polarized electroluminescence. [ABSTRACT FROM AUTHOR]

The cut-set bound developed by Cover and El Gamal in 1979 has since remained the best known upper bound on the capacity of the Gaussian relay channel. We develop a new upper bound on the capacity of the Gaussian primitive relay channel, which is tighter than the cut-set bound. Our proof uses Gaussian measure concentration to establish geometric relations, satisfied with high probability, between the $n$ -letter random variables associated with a reliable code for communicating over this channel. We then translate these geometric relations into new information inequalities that cannot be obtained with classical methods. Combined with a tensorization argument proposed by Courtade and Ozgur in 2015, our result also implies that the current capacity approximations for Gaussian relay networks, which have linear gap to the cut-set bound in the number of nodes, are order-optimal and lead to a lower bound on the pre-constant. [ABSTRACT FROM AUTHOR]

We consider the discrete memoryless symmetric primitive relay channel, where, a source X wants to send information to a destination Y with the help of a relay Z and the relay can communicate to the destination via an error-free digital link of rate , while Y and Z are conditionally independent and identically distributed given X . We develop two new upper bounds on the capacity of this channel that are tighter than existing bounds, including the celebrated cut-set bound. Our approach significantly deviates from the standard information-theoretic approach for proving upper bounds on the capacity of multi-user channels. We build on the blowing-up lemma to analyze the probabilistic geometric relations between the typical sets of the n -letter random variables associated with a reliable code for communicating over this channel. These relations translate to new entropy inequalities between the needed for the Z – Y link in order for the capacity of the relay channel to be equal to that of the broadcast cut. We consider the special case when the X – Y and X . More interestingly, we show that when p\to 1/2 , R0^{*}\geq 0.1803 ; even though the broadcast channel becomes completely noisy as p\to 1/2 and its capacity, and therefore the capacity of the relay channel, goes to zero, a strictly positive rate R0 is required for the relay channel capacity to be equal to the broadcast bound. Existing upper bounds on the capacity of the relay channel, and the cut-set bound in particular, would rather imply R0^{*}\to 0 , while achievability schemes require R0^{*}\to 1 . We conjecture that R0^{*}\to 1 as $p\to 1/2$ . [ABSTRACT FROM PUBLISHER]

The data center network (DCN), wired or wireless, features large amounts of many-to-one (M2O) sessions. Each M2O session is currently established using point-to-point (P2P) communications and store-and-forward (SAF) relays, and is generally followed by a certain computation at the destination, typically a weighted summation of the received information digits. Fundamentally different from this separate P2P/SAF-based-transmission and computation framework, this paper proposes simultaneous transmission and air computation (STAC), a novel physical layer scheme that achieves STAC in wireless DCNs. In particular, STAC builds on a number of distinguishing characteristics of DCs to take advantage of the superposition nature of electromagnetic signals. With STAC, multiple sources transmit in the same time slot with appropriately chosen parameters, such that the superimposed signal can be directly transformed to the desired summation at the receiver. To enable STAC, we propose an enhanced software-defined network architecture, where a wired low-bandwidth backbone provides wireless transceivers with external reference signals. We also discuss some new challenges that STAC brings to scheduling and routing. Theoretical analysis and simulation results show that STAC can significantly improve both bandwidth and energy efficiency in DCNs. [ABSTRACT FROM PUBLISHER]

Decode-and-forward (D-F) and compress-and-forward (C-F) are two fundamentally different relay strategies proposed by Cover and El Gamal in 1979. Individually, either of them has been successfully generalized to multirelay channels. In this paper, to allow each relay node the freedom of choosing either of the two strategies, we propose a unified framework, where both the D-F and C-F strategies can be employed simultaneously in the network. It turns out that, to incorporate in full the advantages of both the best known D-F and C-F strategies into a unified framework, the major challenge arises as follows: For the D-F relay nodes to fully utilize the help of the C-F relay nodes, decoding at the D-F relay nodes should not be conducted until all the blocks have been finished; however, in the multilevel D-F strategy, the upstream nodes have to decode prior to the downstream nodes in order to help, which makes simultaneous decoding at all the D-F relay nodes after all the blocks have been finished inapplicable. To tackle this problem, nested blocks combined with backward decoding are used in our framework, so that the D-F relay nodes at different levels can perform backward decoding at different frequencies. As such, the upstream D-F relay nodes can decode before the downstream D-F relay nodes, and the use of backward decoding at each D-F relay node ensures the full exploitation of the help of both the other D-F relay nodes and the C-F relay nodes. The achievable rates under our unified relay framework are found to combine both the best known D-F and C-F achievable rates and include them as special cases. It is also demonstrated through a Gaussian network example that our achievable rates are generally better than the rates obtained with existing unified schemes and with D-F or C-F alone. [ABSTRACT FROM PUBLISHER]

A novel red-emitting binuclear platinum complex (dfppy)Pt(COXT) was synthesized and characterized, in which dfppy represents 2-(4′,6′-difluorophenyl)pyridinato unit and COXT is abbreviated for 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiol as a bridging ancillary ligand. Its photophysical, electrochemical and electroluminescent characteristics were primarily studied. The made single-emissive-layer (SEL) polymer light-emitting devices using (dfppy)Pt(COXT) as emitter exhibited a saturated red emission peaked at 620 nm. The best device performances were obtained in the device at 8 wt% dopant concentration, with a maximum external quantum efficiency of 8.4%, a current efficiency of 4.2 cd/A and brightness of 3228 cd/m. This work provides an effective approach to obtain high-efficiency red emission through construction of new binuclear platinum complex and its doped SEL devices. [ABSTRACT FROM AUTHOR]

In the classical compress-and-forward relay scheme developed by Cover and El Gamal, the decoding process operates in a successive way: the destination first decodes the compression of the relay's observation and then decodes the original message of the source. Recently, several modified compress-and-forward relay schemes were proposed, where the destination jointly decodes the compression and the message, instead of successively. Such a modification on the decoding process was motivated by realizing that it is generally easier to decode the compression jointly with the original message, and more importantly, the original message can be decoded even without completely decoding the compression. Thus, joint decoding provides more freedom in choosing the compression at the relay. However, the question remains in these modified compress-and-forward relay schemes—whether this freedom of selecting the compression necessarily improves the achievable rate of the original message. It has been shown by El Gamal and Kim in 2010 that the answer is negative in the single-relay case. In this paper, it is further demonstrated that in the case of multiple relays, there is no improvement on the achievable rate by joint decoding either. More interestingly, it is discovered that any compressions not supporting successive decoding will actually lead to strictly lower achievable rates for the original message. Therefore, to maximize the achievable rate for the original message, the compressions should always be chosen to support successive decoding. Furthermore, it is shown that any compressions not completely decodable even with joint decoding will not provide any contribution to the decoding of the original message. The above phenomenon is also shown to exist under the repetitive encoding framework recently proposed by Lim , which improved the achievable rate in the case of multiple relays. Here, another interesting discovery is that the improvement is not a result of repetitive encoding, but the benefit of delayed decoding after all the blocks have been finished. The same rate is shown to be achievable with the simpler classical encoding process of Cover and El Gamal with a block-by-block backward decoding process. [ABSTRACT FROM PUBLISHER]