Alternative radical pairs for cryptochrome-based magnetoreception

There is growing evidence that the remarkable ability of animals, in particular birds, to sense the direction of the Earth''s magnetic field relies on magnetically sensitive photochemical reactions of the protein cryptochrome. It is generally assumed that the magnetic field acts on the radical pair [FAD^•− TrpH^•+] formed by the transfer of an electron from a group of three tryptophan residues to the photo-excited flavin adenine dinucleotide cofactor within the protein. Here, we examine the suitability of an [FAD^•− Z^•] radical pair as a compass magnetoreceptor, where Z^• is a radical in which the electron spin has no hyperfine interactions with magnetic nuclei, such as hydrogen and nitrogen. Quantum spin dynamics simulations of the reactivity of [FAD^•− Z^•] show that it is two orders of magnitude more sensitive to the direction of the geomagnetic field than is [FAD^•− TrpH^•+] under the same conditions (50 µT magnetic field, 1 µs radical lifetime). The favourable magnetic properties of [FAD^•− Z^•] arise from the asymmetric distribution of hyperfine interactions among the two radicals and the near-optimal magnetic properties of the flavin radical. We close by discussing the identity of Z^• and possible routes for its formation as part of a spin-correlated radical pair with an FAD radical in cryptochrome.     

Cryptochrome magnetoreception: four tryptophans could be better than three

The biophysical mechanism of the magnetic compass sensor in migratory songbirds is thought to involve photo-induced radical pairs formed in cryptochrome (Cry) flavoproteins located in photoreceptor cells in the eyes. In Cry4a—the most likely of the six known avian Crys to have a magnetic sensing function—four radical pair states are formed sequentially by the stepwise transfer of an electron along a chain of four tryptophan residues to the photo-excited flavin. In purified Cry4a from the migratory European robin, the third of these flavin–tryptophan radical pairs is more magnetically sensitive than the fourth, consistent with the smaller separation of the radicals in the former. Here, we explore the idea that these two radical pair states of Cry4a could exist in rapid dynamic equilibrium such that the key magnetic and kinetic properties are weighted averages. Spin dynamics simulations suggest that the third radical pair is largely responsible for magnetic sensing while the fourth may be better placed to initiate magnetic signalling particularly if the terminal tryptophan radical can be reduced by a nearby tyrosine. Such an arrangement could have allowed independent optimization of the essential sensing and signalling functions of the protein. It might also rationalize why avian Cry4a has four tryptophans while Crys from plants have only three.     

Compass magnetoreception in birds arising from photo-induced radical pairs in rotationally disordered cryptochromes

According to the radical pair model, the magnetic compass sense of migratory birds relies on photochemical transformations in the eye to detect the direction of the geomagnetic field. Magnetically sensitive radical pairs are thought to be generated in cryptochrome proteins contained in magnetoreceptor cells in the retina. A prerequisite of the current model is for some degree of rotational ordering of both the cryptochromes within the cells and of the cells within the retina so that the directional responses of individual molecules do not average to zero. Here, it is argued that anisotropic distributions of radical pairs can be generated by the photoselection effects that arise from the directionality of the light entering the eye. Light-induced rotational order among the transient radical pairs rather than intrinsic ordering of their molecular precursors is seen as the fundamental condition for a magnetoreceptor cell to exhibit an anisotropic response. A theoretical analysis shows that a viable compass magnetoreceptor could result from randomly oriented cryptochromes contained in randomly oriented cells distributed around the retina.     

Magnetoreception in birds: the effect of radio-frequency fields

The avian magnetic compass, probably based on radical pair processes, works only in a narrow functional window around the local field strength, with cryptochrome 1a as most likely receptor molecule. Radio-frequency fields in the MHz range have been shown to disrupt the birds'' orientation, yet the nature of this interference is still unclear. In an immuno-histological study, we tested whether the radio-frequency fields interfere with the photoreduction of cryptochrome, but this does not seem to be the case. In behavioural studies, birds were not able to adjust to radio-frequency fields like they are able to adjust to static fields outside the normal functional range: neither a 2-h pre-exposure in a 7.0 MHz field, 480 nT, nor a 7-h pre-exposure in a 1.315 MHz field, 15 nT, allowed the birds to regain their orientation ability. This inability to adjust to radio-frequency fields suggests that these fields interfere directly with the primary processes of magnetoreception and therefore disable the avian compass as long as they are present. They do not have lasting adverse after-effects, however, as birds immediately after exposure to a radio-frequency field were able to orient in the local geomagnetic field.     

The magnetic compass mechanisms of birds and rodents are based on different physical principles.

Recently, oscillating magnetic fields in the MHz-range were introduced as a useful diagnostic tool to identify the mechanism underlying magnetoreception. The effect of very weak high-frequency fields on the orientation of migratory birds indicates that the avian magnetic compass is based on a radical pair mechanism. To analyse the nature of the magnetic compass of mammals, we tested rodents, Ansell's mole-rats, using their tendency to build their nests in the southern part of the arena as a criterion whether or not they could orient. In contrast to birds, their orientation was not disrupted when a broad-band field of 0.1-10MHz of 85nT or a 1.315MHz field of 480nT was added to the static geomagnetic field of 46000nT. Even increasing the intensity of the 1.315MHz field (Zeeman frequency in the local geomagnetic field) to 4800nT, more than a tenth of the static field, the mole-rats remained unaffected and continued to build their nests in the south. These results indicate that in contrast to that of birds, their magnetic compass does not involve radical pair processes; it seems to be based on a fundamentally different principle, which probably involves magnetite.     

Preparation, characterization and luminescence of a new green-emitting phosphor: Gd2TeO6 doped with Tb

Novel green-emitting Gd_2 − xTb_xTeO₆ powder phosphor has been prepared by the oxidation of corresponding rare-earth oxytellurides. The photoluminescence (PL) properties were reported. Five dominant bands centered at 302 nm, 318 nm, 339 nm, 353 nm and 378 nm characterize the excitation spectrum. Under the excitation of 378 nm UV light, the emission spectrum exhibits an intense peak centered at 543-548 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. This phosphor can be excited by light with wavelengths of 350-400 nm and therefore can be used as a green phosphor for white lighting devices utilizing near-UV LED as a light source.     

Modeling the mechanics of light activated shape memory polymers

Shape memory polymers (SMP’s) are a relatively new kind of smart materials and have significant technological applications ranging from biomedical devices to aerospace technology. First generation SMP’s relied on changes in temperature to fix the temporary shape and have been studied quite extensively in the past. In the last few years a new generation of SMP’s have been synthesized in which the temporary shape is fixed by exposure to light at specific wavelengths (typically in the Ultraviolet, UV, range). Exposure to light at certain wavelengths causes photosensitive molecules, which are grafted on the polymer chains comprising the material, to form covalent bonds. These bonds act as crosslinks and are responsible for the temporary shape. On exposure to light at a different wavelength these bonds cleave and the material returns to its original shape. Our research focuses on modeling the mechanics associated with such light activated shape memory polymers (LASMP’s) undergoing complex deformations. The modeling is done using a framework based on the theory of multiple natural configurations taking into consideration the different aspects of modeling this material, which include developing a model for the original virgin network and for the other networks with different stress-free states, formed due to exposure to light. In addition to this, we also model the initiation and the formation of the light activated networks and the reverse transition resulting in the dissolution of these networks. Anisotropy in the mechanical response is also incorporated into the model. The model is then used to simulate results for specific boundary value problems, such as uni-axial extension and inflation of a cylinder.     

Structural study, photoluminescence, and photocatalytic activity of semiconducting BaZrO3:Bi nanocrystals

Wide band gap nanocrystalline bismuth doped barium zirconate is synthesized by a facile hydrothermal method at 100 °C. The obtained cubic perovskites are characterized by powder X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy, and photocatalytic activity. The estimated band gap in the 2.4-4.9 eV range, depending on Bi concentration, suggests nanocrystalline BaZrO₃:Bi as a useful visible-light activated photocatalyst under excitation wavelengths <800 nm. Displacement of main XRD pattern peaks suggest that bismuth ion mostly substitutes into Zr⁴⁺ sites within the BaZrO₃ host lattice. It is found that BaZrO₃:Bi decomposes methylene blue (MB) under both UV and visible light irradiation. The photocatalyst efficiency depends strongly on Bi content and induced defects.     

Synthesis,crystal structure and luminescence in Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript>

Bluish green emitting phosphor, Ca₃Al₂O₆:Ce³⁺, is prepared by low-temperature combustion method. X-ray diffraction, photoluminescence, scanning electron microscopy techniques are used to characterize the synthesized phosphor. The most efficient bluish green (483 nm) emission is observed under the excitation by near UV light. The emission characteristics are credited to 5d → 4f type transitions in Ce³⁺. The luminescence properties of Eu²⁺ are predicted for the first time from those of Ce³⁺. Also, photoluminescence of Eu³⁺ is studied in the same host. The emission spectrum of Ca₃Al₂O₆:Eu³⁺ shows the peak at 592 (orange) and 614 nm (red) wavelengths. Ca₃Al₂O₆:Ce³⁺phosphor can be a potential blue phosphor for field emission display, solid-state lighting and LED.     

Characterization of various Eu2+ sites in Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ by high-pressure spectroscopy

Photoluminescence of Ba₂SiO₄ and Ca₂SiO₄ activated with Eu²⁺ was investigated at various temperatures (from 10 K to 300 K) and pressures (from ambient to 200 kbar). At ambient pressure and room temperature, under UV excitation both phosphors yielded a green emission band with maxima at 505 nm and 510 nm for Ba₂SiO₄ and Ca₂SiO₄, respectively. The energies of these bands depended on pressure; the pressure shifts were ?12:55 cm^?1/kbar for Ba₂SiO₄:Eu²⁺; and ?5:59 cm^?1/kbar for Ca₂SiO₄:Eu²⁺. In the case of Ca₂SiO₄:Eu²⁺, we observed additional broadband emission at lower energies with a maximum at 610 nm (orange band). The orange and green emission in Ca₂SiO₄:Eu²⁺ had different excitation spectra: the green band could be excited at wavelengths shorter than 470 nm, whereas the orange band — at wavelengths shorter than 520 nm. The pressure caused a red shift of orange emission of 7.83 cm^?1/kbar. The emission peaked at 510 nm was attributed to the 4f⁶5d→4f⁷(⁸S₇₌₂) transition of Eu²⁺ in the β — Ca₂SiO₄:Eu²⁺ phase, whereas the emission peaked at 610 nm — to the γ — Ca₂SiO₄:Eu²⁺ phase. The emission of Ba₂SiO₄:Eu²⁺ peaked at 505 nm was attributed to the 4f⁶5d→ 4f⁷(⁸S_7/2) transition of Eu²⁺ in the β — Ba₂SiO₄ phase.     

New aspects of π–d interactions in magnetic molecular conductors

The 2 : 1 cation radical salts of bent donor molecules of ethylenedithio-tetrathiafulvalenoquinone-1,3-dithiolemethide (EDT-TTFVO), ethylenedithio-diselenadithiafulvalenoquinone-1,3-dithiolemethide (EDT-DSDTFVO), ethylenedithio-diselenadithiafulvalenothioquinone-1,3-diselenolemethide (EDT-DSDTFVSDS), ethylenedioxy-tetrathiafulvalenoquinone-1,3-dithiolemethide (EDO-TTFVO) and ethylenedioxy-tetrathiafulvalenoquinone-1,3-diselenolemethide (EDO-TTFVODS) with FeX₄⁻ (X = Cl, Br) ions are prepared by electrocrystallization. The crystal structures of these salts are composed of alternately stacked donor molecule and magnetic anion layers. The band structures of the donor molecule layers are calculated using the overlap integrals between neighboring donor molecules and are compared with the observed electronic transport properties. The magnetic ordering of the Fe(III) d spins of FeX₄⁻ ions is determined from magnetization and heat capacity measurements. The magnetic ordering temperatures are estimated by considering a combination of a direct d–d interaction between the d spins and an indirect π–d interaction between the conduction π electron and the d spins, whose magnitudes are separately calculated from the crystal structures with an extended Hückel molecular orbital method. The occurrence of a π–d interaction is proved by the negative magnetoresistance, and the magnitude of magnetoresistance reflects the strength of the π–d interaction. The effect of pressure on the magnetoresistance is studied, and the result indicates that the magnitude of magnetoresistance increases, namely, the π–d interaction is enhanced with increasing pressure. From these experimental results it is shown that (EDT-TTFVO)₂•FeBr₄ is a ferromagnetic semiconductor, (EDT-DSDTFVO)₂•FeX₄ (X = Cl, Br) and (EDT-DSDTFVSDS)₂•FeBr₄ are metals exhibiting antiferromagnetic ordering of the d spins, and (EDO-TTFVO)₂•FeCl₄ and (EDO-TTFVODS)₂•FeBr₄•(DCE)_0.5 (DCE =-dichloroethane) are genuine antiferromagnetic metals. Among them, the (EDT-TTFVO)₂•FeBr₄ salt is the first π–d molecular system where the d spins of FeBr₄⁻ ions are ferromagnetically ordered through antiferromagnetic interaction with the conduction π electrons. Corresponding to this ferromagnetic ordering, an anomalous dielectric slow-down phenomenon toward the ordering temperature is observed. The π–d interaction in (EDT-DSDTFVSDS)₂•FeBr₄ is very large and comparable to that in λ-(BETS)₂•FeCl₄, which has the highest reported value so far, while the d–d interaction is fairly small. Concerning the ratio between the magnitudes of π–d and d–d interactions (J_πd/J_dd), this salt is currently the best π–d molecular system.     

新型磁性离子交换吸附TiO_2@Fe_3O_4/聚吡咯树脂复合材料制备及其吸附性能

首先采用溶胶-凝胶法制备TiO_2@Fe_3O_4核壳结构的磁性纳米粒子,然后与聚吡咯(PPy)采用原位聚合法制备TiO_2@Fe_3O_4/PPy磁性离子交换吸附剂。通过TEM、SEM对样品的形貌及粒径进行表征,用XRD表征分析物相,FTIR表征样品的表面性质,用VSM测定磁性能,由紫外-可见分光光度计测定吸光度,并对孔雀石绿溶液进行吸附性能测试。结果表明,PPy与TiO_2@Fe_3O_4纳米粒子复合后形貌未变,团聚现象明显改善,磁强度为5.384emu·g~(-1),具有超顺磁性。在pH=7,温度为298K条件下,用0.05g TiO_2@Fe_3O_4/PPy吸附剂对25mL 20mg·L~(-1)孔雀石绿溶液(MG)进行吸附,饱和吸附容量为312.50mg·g~(-1),且30min内去除率可达到99.1%。与活性炭相比较,TiO_2@Fe_3O_4/PPy磁性离子交换吸附树脂可以进行大面积动态交换与吸附,吸附性能优于活性炭。     

Ramanspektroskopische Charakterisierung von ultra‐dünnen Kohlenstoff‐Schutzschichten für die Magnetspeichertechnologie

Raman‐spectroscopy is a standard tool for structural characterization of ultra‐thin (<10 nm) amorphous carbon films which are used as protective overcoats in the magnetic storage industry. It provides powerful information on the bonding structure of the films. The Raman‐spectra of amorphous carbons are dominated by the D‐ and G‐bands at around 1350 cm^‐1 – 1600 cm^‐1 whose position and intensity are used for interpreting the carbon bonding. Several carbon films have been investigated using green (λ = 514.5 nm) and ultraviolet (λ = 244 nm) laser‐light. The dispersion of the G‐peak is the most crucial of parameters to describe the internal structure of the films since it distinguishes between graphite‐ and diamond‐like carbon. A high G‐peak‐dispersion corresponds to a high sp³‐fraction. These information are not available by single wavelength investigations due to the so called hysteresis effect causing the Raman‐spectra of different samples accidentally to look similar albeit having a different internal structure. The dual‐method we are here introducing avoids the hysteresis effect and provides good estimations on the sp³‐content and the mass density of different carbon systems. Furthermore, UV‐Raman analysis leads to quantification of the nitrogen content of nitrogen‐doped carbon layers by using the relative intensity of the 2200 cm^‐1 band in the UV‐spectrum. The great advantage of ramanspectroscopic investigations is its celerity. Acquisition times are seldom higher than 1.5 min. Additionally, Raman‐spectroscopy is a non‐destructive tool which leaves the investigated samples undamaged for further processing and makes it an attractive method for insitu‐analysis in the magnetic storage industry.     

Synthesis and magnetic characterization of magnetite obtained by monowavelength visible light irradiation

Magnetite (Fe₃O₄) nanoparticles were controllably synthesized by aerial oxidation Fe^IIEDTA solution under different monowavelength light-emitting diode (LED) lamps irradiation at room temperature. The results of the X-ray diffraction (XRD) spectra show the formation of magnetite nanoparticle further confirmed by Fourier transform infrared spectroscope (FTIR) and the difference in crystallinity of as-prepared samples. Fe₃O₄ particles are nearly spherical in shape based on transmission electron microscopy (TEM). Average crystallite sizes of magnetite can be controlled by different irradiation light wavelengths from XRD and TEM: 50.1, 41.2, and 20.3 nm for red, green, and blue light irradiation, respectively. The magnetic properties of Fe₃O₄ samples were investigated. Saturation magnetization values of magnetic nanoparticles were 70.1 (sample M-625), 65.3 (sample M-525), and 58.2 (sample M-460) emu/g, respectively.     

Ultrahigh Responsivity in Graphene–ZnO Nanorod Hybrid UV Photodetector

Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid‐channel field‐effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time‐dependent behaviors of hybrid‐channel FETs reveal a high sensitivity and selectivity toward the near‐UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (R_I ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid‐channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V _Dirac) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10¹⁰ and 4 × 10¹⁰ per mW, respectively. The maximum values of R_I and G infer from the fitted curves of R_I and G versus UV intensity are 3 × 10⁵ A W^?1 and 10⁶, respectively. Therefore, the hybrid‐channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.     

Lobelia trigona Roxb ‐based nanomedicine with enhanced biological applications: in vitro and in vivo approach

This is the first study to report the green synthesis of Lobelia trigona Roxb‐ mediated silver nanoparticles (LTAgNPs). The optical and structural properties of the synthesised LTAgNPs were analysed using ultraviolet–visible spectroscopy, scanning electron microscopy, Fourier transform infrared, dynamic light scattering and energy dispersive X‐ray. LTAgNps were evaluated for their anti‐bacterial and anti‐fungal properties against 18 pathogens and exhibited significant inhibition against all the strains tested. LTAgNPs had potential scavenging effects on the DPPH, ^• OH, O₂ ^•− free radical scavenging assays and reducing power assay. LTAgNps possess strong anti‐cancer activity against five human cancer cell lines (A549, MCF‐7, MDA‐MB‐231, HeLa and KB) in a dose‐dependent manner. The antiproliferative, anti‐inflammatory and genotoxicity effects of LTAgNPs were further confirmed by the lactate dehydrogenase release assay, nitric oxide inhibitory assay and comet assay. Furthermore, the incision, excision and burn wound‐healing activity of formulated LTAgNPs ointment was assessed in rats. All the wounds had significant healing in groups treated with LTAgNPs ointment compared to the groups treated with the commonly prescribed ointment (Silverex^TM). This study shows and suggests that the previously unreported LTAgNPs could be used as a nanomedicine with significant biological applications.Inspec keywords: molecular biophysics, biomedical materials, scanning electron microscopy, biochemistry, cancer, microorganisms, silver, cellular biophysics, nanofabrication, wounds, nanomedicine, ultraviolet spectra, toxicology, antibacterial activity, light scattering, nanoparticles, enzymes, visible spectra, Fourier transform infrared spectraOther keywords: Lobelia trigona Roxb‐based nanomedicine, biological applications, Lobelia trigona Roxb‐mediated silver nanoparticles, optical properties, structural properties, ultraviolet‐visible spectroscopy, dynamic light scattering, antibacterial properties, antifungal properties, scavenging effects, free radical scavenging, power assay, anticancer activity, antiinflammatory effects, genotoxicity effects, lactate dehydrogenase release assay, nitric oxide inhibitory assay, excision, burn wound‐healing activity, formulated LTAgNPs ointment, in vivo approach, in vitro approach, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X‐ray analysis, pathogens, strains, A549 human cancer cell lines, MCF‐7 human cancer cell lines, MDA‐MB‐231 human cancer cell lines, HeLa human cancer cell lines, antiproliferative effects, comet assay, Ag     

Study of structural and optical properties of Ge doped ZnO films

The Ge doped ZnO films were deposited on quartz substrates by radio frequency magnetron sputtering. The effects of doping and substrate temperature on the structural and optical properties of the Ge doped ZnO films were investigated by means of X-ray diffraction (XRD), UV-visible transmission spectra, X-ray photoelectron spectroscopy and photoluminescence (PL) spectra. The XRD patterns showed that Zn₂GeO₄ phases were formed in the films. With the increase of substrate temperature the crystallization of Zn₂GeO₄ was improved, and that of ZnO phases turned worse, and no diffraction peak of ZnO was observed when the substrate temperature was 700 °C. Obvious ultraviolet (UV) light emission was found due to ZnO grains, and it was much stronger than that of un-doped ZnO films. The enhancement of UV light emission at about 380 nm may be caused by excitons which were formed at the interface between Zn₂GeO₄ and ZnO grains. In the visible region of the PL spectra, the green light emission peak of samples at about 512 nm was associated with defects in ZnO. A red shift of the green light emission peak was observed which can be explained by the fact that there is a luminescence center at about 548 nm taking the place of the defect emission of ZnO with the increase of substrate temperature. The red shift of the green light emission peak and the 548 nm green light emission peaks of the PL spectrum show that some Ge²⁺ should replace the Zn²⁺ positions during the Zn₂GeO₄ grains growth and form the Ge²⁺ luminescence centers in Zn₂GeO₄ grains.     

A novel green emitting phosphor Ca2GeO4:Tb3+

A novel green emitting phosphor, Tb³⁺-doped Ca₂GeO₄ was prepared for the first time by a solid-state reaction. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄ → ⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 and 550 nm under UV excitation. In addition, Al³⁺ or Li⁺ co-doping enhances the green emission from Ca₂GeO₄:Tb³⁺ by about 18 and 4 times, respectively, under UV excitation. The excellent luminescence properties make it a possible candidate for flat panel display application.     

Quinine Actinometry as a Method for Calibrating Ultraviolet Radiation Intensity in Light-Stability Testing of Pharmaceuticals

Abstract

A collaborative study was carried out by seven different laboratories to evaluate quinine actinometry as a universal, standardized method for calibrating UV radiation intensity from light sources used in light-stability testing of pharmaceutical products. Near UV fluorescent lamps, white fluorescent lamps, metal halide lamps and xenon arc lamps were employed as light sources. The increase in absorbance at 400 nm of aqueous quinine solutions was found to be proportional to the integrated UV energy emitted from the light sources. The linearity observed between absorbance and integrated UV energy indictates that quinine actinometry can be used to measure the intensity of UV radiation at wavelengths around 330 nm. The slopes of regression curves of absorbance vs integrated UV energy varied among the lamps used due to differing spectral distributions. Light degradation of nifedipine, a model photosensitive drug, was studied based on quinine actinometry.     

Ultrahigh‐Efficiency Green PHOLEDs with a Voltage under 3 V and a Power Efficiency of Nearly 110 lm W−1 at Luminance of 10 000 cd m−2

Maintaining high power efficiency (PE) under high brightness is still a pressing problem for the practical application of organic light‐emitting diodes (OLEDs). Here, ultrahigh‐efficiency green phosphorescent OLEDs (PHOLEDs) with a record‐low voltage at luminance above 5000 cd m^?2 are fabricated, by developing a novel anthracene/pyridine derivative as the electron‐transporting material (ETM) combined with a material displaying thermally activated delayed fluorescence as the host. The pyridine units of the ETM not only facilitate charge injection, but also enhance the electron‐transporting mobility, profiting from the closely packed molecules caused by the intermolecular H‐bonding. The optimized green PHOLEDs show record‐low driving voltages of 2.76 and 2.92 V, with EQEs/PEs of 28.0%/102 lm W^?1 and 27.9%/97 lm W^?1 at 5000 and 10 000 cd m^?2, respectively. Furthermore, device optimization exhibits an unprecedented high PE of 109 lm W^?1 at 10 000 cd m^?2 with voltage under 3 V. Those values are the state‐of‐the‐art among all reported green OLEDs so far, paving their way toward practical applications.