Recent Advances in Solution-Processed White Organic Light-Emitting Materials and Devices

Solution-processed white organic light-emitting diodes (WOLEDs) have drawn great attention both in the academic and industrial research communities due to the potential application in low-cost, large-area, solid-state lightings. Issues related to the device efficiencies are largely hampering progress in this field. Alongside the development of new materials and novel device architectures, distinct progress has been made for such white devices. In particular, the all-phosphorescent light-emitting strategy has been intensively developed in recent years, mainly focusing on a host guest, doping-system-based, single-active-layer structure and a solution-processed, multilayer device structure. Novel approaches, including white single polymers and excimer-/exciplex-based white devices, have also appeared as a promising choice and received great attention. As a prerequisite, the issue of the morphology of the emissive layer is also important and has an influence on the optoelectronic behavior of the device. Herein, major advances in solution-processed WOLEDs based on polymers, dendrimers, or solution-processed small molecules are summarized. Special attention is focused on the main progress in high-efficiency, solution-processed WOLEDs with the key strategies mentioned above and the morphology issue in these systems. The remaining challenges in pursuing the development of reliable and energy-saving lighting devices are also discussed.     

Synthesis,Characterization, and Electroluminescent Properties of Iridium(III) 2-Phenylpyridine-type Complexes Containing Trifluoromethyl Substituents and Various Main-Group Moieties

New heteroleptic cyclometalated iridium(III) 2-phenylpyridine-type complexes with trifluoromethyl substituents and various main-group moieties were synthesized and their photophysical, electrochemical, and electroluminescent (EL) properties studied. The emission color can be tuned by a facile derivatization of the phenyl moiety of 2-phenylpyridine with various main-group moieties, and we have prepared new yellowish green to orange triplet emitters with enhanced charge injection/charge transporting features, which can furnish attractive EL performance in phosphorescent organic light-emitting devices (OLEDs). Attempts were also made to fabricate two-color white-light OLEDs based on a combination of fluorescent blue and phosphorescent orange emitters.     

带烷氧基的苯基蒎烯吡啶铱配合物在聚合物电致发光器件中的应用研究

采用旋涂法将一组带烷氧基的苯基蒎烯吡啶铱（Ⅲ）配合物（It（ROPPPY）3）磷光材料掺杂到PVK中,制作出了聚合物电致发光器件：ITO／PEDOT：PSS（40nm）／PVK0.7：PBD0．3：（x％．）Ir—complex（80nm）／CsV（1．5nm）／Mg：Ag（200nm）．实验结果表明,带有长烷氧基链配体的铱（Ⅲ）配合物能表现出更好的器件行为,当掺杂浓度为3．2％时,器件的最高发光效率达19．9cd／A（7．8lm／W,9．1V）,CIE为（0．20,0．56）;器件最大亮度为15700cd／m^2（8．4V）．通过对这组铱（Ⅲ）配合物的光物理行为及电化学性能的研究,考察了主体材料与配合物之间的能级配置以及能量转移的机理、     

Deep-Blue Phosphorescent Emitters with Phosphoryl Groups for Organic Light-Emitting Diodes by Solution Processes

The new deep-blue iridium complex, Ir(dppfm)₂pic, consisting of a phosphoryl group at the 3′-position of the phenyl ring and a methyl group at the 4-position of pyridine, was synthesized and characterized for applications in organic light-emitting diodes (OLEDs). Ir(dppfm)₂pic exhibited an emission peak of 455 nm and high photoluminescence quantum yields of 73 %. Phosphorescent OLEDs based on Ir(dppfm)₂pic exhibited a maximum external quantum efficiency of 7.8 % and Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.22).     

Recent Advances in Solid-State White Light-Emitting Electrochemical Cells

Compared to organic light-emitting diodes, solid-state light-emitting electrochemical cells (LECs) exhibit advantages of simple device structures, low operation voltages, and compatibility with air-stable metal electrodes. Since the first demonstration of white LECs in 1997, the cells have been studied extensively, due to their potential applications in solid-state lighting. This article reviews the development of white LECs based on conjugated polymers and cationic transition metal complexes. Important achievements of each work on white LECs are highlighted. Finally, the outlook for future development of white LECs is discussed.     

Recent Advances in Light Energy Conversion with Biomimetic Vesicle Membranes

Lipid bilayer membranes are ubiquitous in natural chemical conversions. They enable self-assembly and compartmentalization of reaction partners and it becomes increasingly evident that a thorough fundamental understanding of these concepts is highly desirable for chemical reactions and solar energy conversion with artificial systems. This minireview focusses on selected case studies from recent years, most of which were inspired by either membrane-facilitated light harvesting or respective charge transfer. The main focus is on highly biomimetic liposomes with artificial chromophores, and some cases for polymer-membranes will be made. Furthermore, we categorized these studies into energy transfer and electron transfer, with phospholipid vesicles, and polymer membranes for light-driven reactions.     

Recent Advances in the Design of Targeted Iridium(III) Photosensitizers for Photodynamic Therapy

Photodynamic therapy (PDT) is a noninvasive treatment for certain types of cancer, bacterial, fungal and viral infections, and skin diseases. In recent years, adaptation of this treatment so as to achieve more specific targeted cancer therapy in particular has attracted significant attention. We focus herein on the design of novel iridium‐based photosensitizers (PSs) with tunable photophysical and photobiological properties as efficient PDT agents. We highlight the ability of some Ir^III photosensitizers to target specific cellular components, including their activation by one‐ and two‐photon irradiation.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

铱配合物磷光探针的合成及细胞荧光成像

磷光铱配合物具有良好的光热稳定性、发光颜色可调性、较长的激发寿命和较高的发光效率等特点。以2-苯基并噻唑衍生物(含有醛基、乙氧基和叔丁基)为主配体、1,10-邻菲罗啉为辅助配体,合成3个磷光铱配合物。通过核磁共振谱和高分辨质谱对其结构进行表征,利用荧光光谱和紫外-可见吸收光谱对其发光性能进行研究,并测试了磷光铱配合物的细胞荧光成像作用。     

Hybrid Organic Light-Emitting Diodes with Low Color-Temperature and High Efficiency for Physiologically-Friendly Night Illumination

Low color-temperature (CT) light sources are preferred for physiologically-friendly illumination at night due to their low suppression of melatonin secretion. We fabricated low-CT hybrid organic light-emitting diodes (OLEDs) by constructing a double emissive-layer (EML) structure, with a blue-red fluorescent-phosphorescent hybrid EML and a green phosphorescent EML, separated by a bipolar interlayer. By doping a red phosphor in a blue fluorescent mixed-host with a decent concentration, blue and red emissions from the host and dopant, respectively, were obtained. The CT of the optimized device was tuned to less than 2500 K, with the brightness ranging from 100 to 10,000 cd m⁻². In addition, the low-CT OLED exhibited much higher efficacy than other low-CT light sources, such as incandescent bulbs and candles. The maximum power efficiency and external quantum efficiency of the hybrid OLED reached 54.6 lm W⁻¹ and 24.3 %, respectively, which only rolled off to 44.2 lm W⁻¹ and 23.6 % at 1000 cd m⁻², with a CT of 1910 K. Low-CT OLEDs with high efficacy provide a promising alternative for night lighting that will safeguard human health.     

Tunable colors and applications of Dy3+/Eu3+ co-doped CaO-B2O3-SiO2 glasses

A series of Dy³⁺/Eu³⁺ single- and co-doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt-quenching method. A compact glass structure is obtained by the addition of Dy³⁺/Eu³⁺ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy³⁺/Eu³⁺ fill in the interspaces of glass network and contribute to the conversion of [BO₃] to [BO₄]. Dy³⁺/Eu³⁺ co-doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white-emitting glasses have proved the existence of energy transfer. The average lifetime of Dy³⁺ decreases from 0.251 to 0.165 ms with the increasing Eu³⁺ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy³⁺/Eu³⁺ co-doped glass shifts from cyan to white with increasing excitation wavelength. A white-light emission is obtained when the concentration of Dy³⁺ and Eu³⁺ equals to 4% and 2%, respectively. Moreover, the Dy³⁺/Eu³⁺ co-doped calcium borosilicate glass shows high-thermal stability and it may be applicable for high-quality white LEDs based on high power near ultraviolet (n-UV) LED chip in the future.     

Recent Advances in Hybrid Optoelectronics

Polymer/organic optoelectronic devices have drawn the attention of both the academic and industrial research communities due to the potential for a low-cost, large-area, solution-processable technology alternative to conventional inorganic optoelectronics. Issues related to the stability and degradation of the organic/polymer-based optoelectronics are hampering the progress in the field. The use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS) as the anode and reactive metals as the cathode, as well as the degradation of organic semiconductors in ambient atmosphere, are some of the stability issues to be addressed. To resolve these issues, in the past decade, there has been a growing interest in research of hybrid optoelectronic devices which employ metal oxides as air-stable charge injecting/extracting layers that sandwich the photo-responsive organic active layer and protect it from the ambient oxygen and moisture and prevent photo-oxidation by absorbing UV light. Herein, we review the recent advances made in hybrid optoelectronics and discuss the tremendous potential of these devices.     

Tuning the luminescence properties of blue and far-red dual emitting Gd2MgTiO6: Bi3+, Cr3+ phosphor for LED plant lamp

Blue and far-red light play a key role in plant growth, so it is necessary to develop blue and far-red dual emitting phosphors. However, the match between phosphors and plant pigments is not satisfactory. In this work, we synthesized a series of blue and far-red dual emission Gd₂MgTiO₆: Bi³⁺, Cr³⁺ (GMTO: Bi³⁺, Cr³⁺) phosphors and discussed the luminescence performance. The blue emission at 430 nm is ascribed to ³P₁ → ¹S₀ transition of Bi³⁺ and the far-red emission is ascribed to ⁴T₂ → ⁴A₂ and ²E → ⁴A₂ transitions of Cr³⁺. Notably, because of the energy competition between Cr³⁺ ions and host materials, the luminescence tuning realized with the content of Cr³⁺ doping. In addition, an energy-transfer performance occurred from Bi³⁺ ions to Cr³⁺ ions and the photoluminescence intensity of Cr³⁺ can be enhanced by Bi³⁺. The pc-LEDs devices were synthesized by GMTO: Bi³⁺, Cr³⁺ phosphor, and ultraviolet (UV) chips. Finally, the emission of GMTO: Bi³⁺, Cr³⁺ phosphor matched well with the absorption spectra of plant pigments which indicated the potential applications in LED plant lamp.     

A Luminescent Cyclometalated Iridium(III) Complex Accumulates in Mitochondria and Induces Mitochondrial Shortening by Conjugation to Specific Protein Targets

We report the cellular properties of a luminescent cyclometalated iridium(III) complex, [Ir(pq)₂(phen‐ITC)](PF₆) (Ir‐ITC; Hpq=2‐phenylquinoline, phen‐ITC=5‐isothiocyanate‐1,10‐phenanthroline), that efficiently and specifically labels mitochondria in living mammalian cells. Ir‐ITC can be covalently conjugated to its protein targets, and its luminescence survived cell lysis, protein extraction, and gel electrophoresis under denaturing conditions. The conjugation of Ir‐ITC with live‐cell proteins is rapid and highly selective; the process requires active cellular metabolism, as the conjugation is abolished at nonphysiological temperature or in the presence of sodium azide. Based on measurements of the luminescence intensity, we have devised a biochemical fractionation procedure that allows the enrichment of the conjugated proteins, and their subsequent separation by two‐dimensional gel electrophoresis (2DGE). Luminescent protein spots were picked from the gel and analyzed by mass spectrometry; this resulted in the identification of 46 proteins. Many of the strongly luminescently labeled proteins are mitochondrial proteins. One of the targets is VDAC1 (voltage‐dependent anion channel 1). Consistent with known phenotypes of VDAC1 deregulation, prolonged exposure of cells to Ir‐ITC led to significant mitochondrial shortening and fragmentation. As far as we know, this is the first report on the molecular characterization of the interactions of a luminescent dye with its biological targets. As many biological dyes exhibit specific intracellular staining patterns, the identification of their molecular targets can help elucidate the mechanisms behind their staining specificities and cytotoxicity. We believe our biochemical approach can be applied to identify the targets of a wide range of fluorescent and luminescent probes.     

The Synthesis of Highly Active Iridium(I) Complexes and their Application in Catalytic Hydrogen Isotope Exchange

A series of robust iridium(I) complexes bearing a sterically encumbered N‐heterocyclic carbene ligand, alongside a phosphine ligand, has been synthesised and investigated in hydrogen isotope exchange processes. These complexes have allowed isotope incorporation over a range of substrates with the use of practically convenient deuterium and tritium gas. Moreover, these active catalysts are capable of isotope incorporation to particularly high levels, whilst employing low catalyst loadings and in short reaction times. In addition to this, these new catalyst species have shown flexible levels of chemoselectivity, which can be altered by simple manipulation of preparative approaches. Furthermore, a number of industrially‐relevant drug molecules has also been labelled, including the sulfonamide containing drug, Celecoxib. Alongside detailed NMR experiments, initial mechanistic investigations have also been performed, providing insight into both substrate binding energies, and, more importantly, relative energies of key steps in the mechanistic cycle as part of the overall exchange process.

     

Preparation and Bioactivity of Iridium(III) Phenanthroline Complexes with Halide Ions and Pyridine Leaving Groups

A series of half-sandwich structural iridium(III) phenanthroline (Phen) complexes with halide ions (Cl⁻, Br⁻, I⁻) and pyridine leaving groups ([(η⁵-Cp^X)Ir(Phen)Z](PF₆)_n, Cp^x: electron-rich cyclopentadienyl group, Z: leaving group) have been prepared. Target complexes, especially the Cp^xbiph (biphenyl-substituted cyclopentadienyl)-based one, showed favourable anticancer activity against human lung cancer (A549) cells; the best one ( Ir8 ) was almost five times that of cisplatin under the same conditions. Compared with complexes involving halide ion leaving groups, the pyridine-based one did not display hydrolysis but effectively caused lysosomal damage, leading to accumulation in the cytosol, inducing an increase in the level of intracellular reactive oxygen species and apoptosis; this indicated an anticancer mechanism of oxidation. Additionally, these complexes could bind to serum albumin through a static quenching mechanism. The data highlight the potential value of half-sandwich iridium(III) phenanthroline complexes as anticancer drugs.     

Emission spectra of Cs2KTbCl6 and Cs2KEuCl6, and Tb3 →Eu3 non-radiative energy transfer in Cs2KTb0.9Eu0.1Cl6

A spectral assignment of the first excited states of Tb³⁺ in Cs₂KTbC1₆ and Eu³⁺ in Cs₂KEuCl₆ obtained from excitation and emission spectra is presented. A non-radiative energy transfer process from Tb³⁺ to Eu³⁺ ions was found to occur in Cs₂KTb_0.99Eu_0.1Cl₆. This process is strongly temperature dependent, such that it becomes quenched at low temperature. The most probable mechanisms responsible for such energy transfer are suggested for the case in which the Tb³⁺⁵D₄ state is excited.     

Recent Advances in Organometallic Polymers as Highly Efficient Electrophosphorescent Emitters

Recent progress and development of organometallic electrophosphorescent polymers, which attracted increasing interest of researchers in the field of phosphorescent light-emitting devices, has been reviewed. The synthesis, structural characterization, photoluminescence, electroluminescence and possible application of electrophosphorescent polymers are surveyed and discussed. This paper is dedicated to the outstanding scientific accomplishments of Professor Ian Manners to the field of inorganic and organometallic polymers.     

Regioselective Reduction of Quinolines Catalyzed by Rhodium and Iridium Complexes with mono-, di-, and tri-dentated Phosphine Ligands

The systems prepared in situ by addition of the corresponding equivalents of the respective phosphine (mono-, di- and tri-dentated), called M₂Cl₂(COE)₄/n phosphine (M = Rh, Ir; and COE = cyclooctene), are efficient and regioselective precatalysts for the hydrogenation of quinoline, isoquinoline, 5,6- and 7,8-benzoquinoline and acridine. The Rh systems were more active than the corresponding Ir ones, being the systems with 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) more active than those with 1,2-bis(diphenylphosphino)ethane (dppe), except for the case of acridine, where the inversed tendencies were observed (Ir > Rh and dppe > triphos). The systems with triphenylphosphine showed the lowest activities.