A star-shaped 1,3,5-triazine/cyano hybrid molecule CN-T2T was designed and synthesized as a new electron acceptor for efficient exciplex-based OLED emitter by mixing with a suitable electron donor ...(Tris-PCz). The CN-T2T/Tris-PCz exciplex emission shows a high ΦPL of 0.53 and a small ΔE T‑S = −0.59 kcal/mol, affording intrinsically efficient fluorescence and highly efficient exciton up-conversion. The large energy level offsets between Tris-PCz and CN-T2T and the balanced hole and electron mobility of Tris-PCz and CN-T2T, respectively, ensuring sufficient carrier density accumulated in the interface for efficient generation of exciplex excitons. Employing a facile device structure composed as ITO/4% ReO3:Tris-PCz (60 nm)/Tris-PCz (15 nm)/Tris-PCz:CN-T2T(1:1) (25 nm)/CN-T2T (50 nm)/Liq (0.5 nm)/Al (100 nm), in which the electron–hole capture is efficient without additional carrier injection barrier from donor (or acceptor) molecule and carriers mobilities are balanced in the emitting layer, leads to a highly efficient green exciplex OLED with external quantum efficiency (EQE) of 11.9%. The obtained EQE is 18% higher than that of a comparison device using an exciplex exhibiting a comparable ΦPL (0.50), in which TCTA shows similar energy levels but higher hole mobility as compared with Tris-PCz. Our results clearly indicate the significance of mobility balance in governing the efficiency of exciplex-based OLED. Exploiting the Tris-PCz:CN-T2T exciplex as the host, we further demonstrated highly efficient yellow and red fluorescent OLEDs by doping 1 wt % Rubrene and DCJTB as emitter, achieving high EQE of 6.9 and 9.7%, respectively.
The lack of structural information impeded the access of efficient luminescence for the exciplex type thermally activated delayed fluorescence (TADF). We report here the pump-probe Step-Scan Fourier ...transform infrared spectra of exciplex composed of a carbazole-based electron donor (CN-Cz2) and 1,3,5-triazine-based electron acceptor (PO-T2T) codeposited as the solid film that gives intermolecular charge transfer (CT), TADF, and record-high exciplex type cyan organic light emitting diodes (external quantum efficiency: 16%). The transient infrared spectral assignment to the CT state is unambiguous due to its distinction from the local excited state of either the donor or the acceptor chromophore. Importantly, a broad absorption band centered at ~2060 cm
was observed and assigned to a polaron-pair absorption. Time-resolved kinetics lead us to conclude that CT excited states relax to a ground-state intermediate with a time constant of ~3 µs, followed by a structural relaxation to the original CN-Cz2:PO-T2T configuration within ~14 µs.
Liquid crystals have great potential for developing photonic devices that control the optical behaviors of liquid crystals in smart devices with external stimulation. In this study, we have ...demonstrated a series of bistable cholesteric liquid crystal devices using the dual-frequency nematic liquid crystal HEF951 assisted by a predesigned chiral ferroelectric liquid crystal. The synthesized chiral ferroelectric liquid crystal was used to induce the formation of the cholesteric liquid crystal phase and decrease the driving voltages and response times of the fabricated bistable liquid crystal devices. The fabricated ferroelectric liquid crystal-assisted bistable cholesteric liquid crystal devices showed a stable opaque focal conic state and stable transparent planar state without any energy consumption once they were turned "from focal-conic to planar" and "from planar to focal-conic". To enhance the reliability, the fabricated bistable cholesteric liquid crystal devices were further stabilized by polymer matrixes. Switching of the bistable liquid crystal cells from one state to another was achieved by a one-step voltage bias with various frequencies. Furthermore, the response time of the sample cell was calculated as 1.7 ms. These results suggest that fabricated ferroelectric liquid crystal-assisted bistable cholesteric liquid crystal devices can be applied to produce energy-saving green liquid crystal displays and other related smart devices.
Fabricated polymer-stabilized bistable cholesteric liquid crystal devices show a stable opaque focal conic state and a stable transparent planar state without any energy consumption once they are turned.
The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton ...delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region.
Alcohol oxidation reactions are widely used for the preparation of aldehydes and ketones. The electrolysis of alcohols to carbonyl compounds have been underutilized owing to low efficiency. Herein, ...we report an electrochemical oxidation of various alcohols in a continuous-flow reactor without external oxidants, base or mediators. The robust electrochemical oxidation is performed for a variety of alcohols with good functional group tolerance, high efficiency and atom economy, whereas mechanistic studies support the benzylic radical intermediate formation and hydrogen evolution. The electrochemical oxidation proves viable on diols with excellent levels of selectivity for the benzylic position.
Acupuncture is recommended by the World Health Organization (WHO) as an alternative and complementary strategy for stroke treatment and for improving stroke care. Clinical trial and meta-analysis ...findings have demonstrated the efficacy of acupuncture in improving balance function, reducing spasticity, and increasing muscle strength and general well-being post-stroke. The mechanisms underlying the beneficial effects of acupuncture in stroke rehabilitation remain unclear. The aim of this study was to conduct a literature review, summarize the current known mechanisms in ischemic stroke rehabilitation through acupuncture and electroacupuncture (EA) therapy, and to detail the frequently used acupoints implicated in these effects. The evidence in this review indicates that five major different mechanisms are involved in the beneficial effects of acupuncture/EA on ischemic stroke rehabilitation: (1) Promotion of neurogenesis and cell proliferation in the central nervous system (CNS); (2) Regulation of cerebral blood flow in the ischemic area; (3) Anti-apoptosis in the ischemic area; (4) Regulation of neurochemicals; and, (5) Improvement of impaired long-term potentiation (LTP) and memory after stroke. The most frequently used acupoints in basic studies include Baihui (GV20), Zusanli (ST36), Quchi (LI11), Shuigou (GV26), Dazhui (GV14), and Hegu (LI4). Our findings show that acupuncture exerts a beneficial effect on ischemic stroke through modulation of different mechanisms originating in the CNS.
Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid‐state lighting and full‐color displays. Here, the design and synthesis of three ...triarylamine‐pyridine‐carbonitrile‐based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔEST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light‐emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A–1, and a power efficiency of 136.3 ± 2.2 lm W–1. The highest device efficiency of 39.8% appears to be record‐breaking among TADF‐based OLEDs to date. In addition, the TPAmPPC‐based device shows superior operation lifetime and high‐temperature resistance. It is worth noting that the TPA‐PPC‐based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.
Three 2,6‐diphenylpyridine‐3,5‐dicarbonitrile‐based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (3LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light‐emitting diodes based on them exhibit a record‐high external quantum efficiency of 39.8% without any optical extraction technique.
Aryl‐ and heteroarylzinc pivalates can be aminated with O‐benzoylhydroxylamines at 25 °C within 2–4 h in the presence of 2.5–5.0 % CoCl2⋅2 LiCl to furnish the corresponding tertiary arylated or ...heteroarylated amines in good yields. This electrophilic amination also provides access to diarylamines and aryl(heteroaryl)amines. A new tuberculosis drug candidate (Q203) was prepared in six steps and 56 % overall yield by using this cobalt‐catalyzed amination as the key step.
Animating aminations: A range of aryl‐ and heteroarylzinc pivalates underwent cobalt‐catalyzed electrophilic aminations with O‐benzoylhydroxylamines in good yields under mild conditions. This reaction can be applied to prepare arylamines and diarylamines. A new tuberculosis drug candidate was prepared in six steps and 56 % overall yield by using the cobalt‐catalyzed amination as the key step.
By using the thiazolo5,4-dthiazole (TzTz) moiety as the core of a proton acceptor, compounds 2,2′-(thiazolo5,4-dthiazole-2,5-diyl)bis(4-tert-butylphenol) ( t -HTTH) and ...4-tert-butyl-2-(5-(5-tert-butyl-2-methoxyphenyl)thiazolo5,4-dthiazol-2-yl)phenol ( t -MTTH) have been strategically designed and synthesized. Upon photoexcitation, both t -HTTH and t -MTTH undergo a reversible type excited-state intramolecular proton transfer (ESIPT), the underlying mechanism of which has been verified by femtosecond early relaxation dynamics in various solvents. The pre-equilibrium in the excited state leads to both normal (∼440 nm) and proton-transfer tautomer (∼560 nm) emissions, for which the intensity ratio is dependent on both the molecular structure and the polarity of surrounding media. As a result, the emission can be widely tuned from blue to yellow via white-light luminescence. On the basis of t -MTTH, a white organic light emitting diode (WOLED) was successfully fabricated, which achieved external quantum efficiency (ηext) of 1.70% with Commission Internationale de L’Eclairage coordinates of (0.29, 0.33). More importantly, the electroluminescent spectra show superior color stability that is independent of luminance. The result demonstrates for the first time a credible WOLED based on a unimolecular ESIPT reaction, which may have far-reaching implications for practical application.
Through the incorporation of various halogen‐substituted chiral organic cations, the effects of chiral molecules on the chiroptical properties of hybrid organic–inorganic perovskites (HOIPs) are ...investigated. Among them, the HOIP having a Cl‐substituted chiral cation exhibits the highest circular dichroism (CD) and circular polarized luminescence (CPL) intensities, indicating the existence of the largest rotatory strength, whereas the F‐substituted HIOP shows the weakest intensities. The observed modulation can be correlated to the varied magnetic transition dipole of HOIPs, which is sensitive to the d‐spacing between inorganic layers and the halogen–halogen interaction between organic cations and the inorganic sheets. These counteracting effects meet the optimal CD and CPL intensity with chlorine substitution, rendering the rotatory strength of HOIPs arranged in the order of (ClMBA)2PbI4>(BrMBA)2PbI4>(IMBA)2PbI4>(MBA)2PbI4>(FMBA)2PbI4.
Through the incorporation of Cl‐substituted chiral organic cations, the chiroptical properties of 2D chiral perovskites can be significantly enhanced. The observed circular dichroism and circular polarized luminescence intensities are found to be associated with the d‐spacing of hybrid organic–inorganic perovskites and the strength of the halogen–halogen interaction within the system.
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