Search

Achieving the concurrent manifestation of thermally activated delayed fluorescence (TADF) and aggregation‐induced emission (AIE) within a single molecular system is highly sought after for organic light‐emitting diodes (OLEDs), yet remains rare. In this study, we present a novel TADF‐AIE dye, named PQMO‐PXZ, which has been designed, synthesized, and systematically characterized. Our comprehensive investigation, which includes structural analysis, theoretical calculations, and optical studies, evaluates the potential of PQMO‐PXZ for integration into OLEDs. Unlike existing azaryl‐ketone‐based emitters, PQMO‐PXZ exhibits red‐shifted emission and enhanced luminescence efficiency, due to its rigid structure and strong intramolecular charge transfer characteristics. Significantly, PQMO‐PXZ demonstrates pronounced AIE properties and TADF with a short delayed lifetime. When utilized as the emissive core, OLED devices based on PQMO‐PXZ achieve a respectable external quantum efficiency of up to 11.8 % with minimal efficiency roll‐off, underscoring PQMO‐PXZ's promise as a highly efficient candidate for OLED applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An intramolecular-locked azaryl ketone acceptor IQLO is designed for TADF emitters. • The new compounds exhibit notable TADF properties, facilitating efficient triplet-to-singlet spin conversion. • IQLO-PXZ and IQLO-DMAC show long-wavelength emission with decent PLQYs of 42% and 47%, respectively. • High electroluminescence efficiency with EQE of up to11.7% is demonstrated. We have developed two novel thermally activated delayed fluorescence (TADF) emitters, IQLO-PXZ and IQLO-DMAC, featuring an intramolecularly locked indeno[1,2- b ]quinolin-11-one (IQLO) acceptor. Our comprehensive investigation, including structural analysis, theoretical calculations, and photophysical studies, aims to assess the viability of IQLO-PXZ and IQLO-DMAC as light emitters in electroluminescent devices. Unlike existing aryl ketone-based emitters, IQLO-PXZ and IQLO-DMAC exhibit red-shifted emission due to their structurally rigid and electron-deficient IQLO moiety. The stronger intramolecular charge transfer effect in IQLO-PXZ results in longer-wavelength emission compared to IQLO-DMAC. Both emitters demonstrate significant TADF properties, facilitating efficient triplet-to-singlet spin conversion. When utilized as the emissive core in electroluminescent devices, IQLO-PXZ and IQLO-DMAC achieved long-wavelength electroluminescence peaking at 612 nm and 578 nm, with commendable external quantum efficiencies of 10.3 % and 11.7 %, respectively. These findings underscore the potential of IQLO as an effective acceptor for constructing high-performance TADF electroluminescent materials. [ABSTRACT FROM AUTHOR]

Semiconductor junctions are among the most important material interfaces in modern technology. The solid polymer light‐emitting electrochemical cell (PLEC) possesses a semiconducting polymer homojunction that is reminiscent of a conventional p–n junction but also exhibits distinct features that are profoundly intriguing. The PLEC junction is formed under bias when the propagating p‐ and n‐doping fronts make contact. The PLEC junction can be immobilized by cooling after the initial junction formation. Further, the resulting frozen junction can be relaxed, or partially de‐doped into a p–i–n junction by controlled heating/cooling cycles. It is on such a frozen polymer p–i–n junction that the authors observed one of the most puzzling phenomena in organic electroluminescence (EL). The frozen p–i–n junction displays the brightest reverse bias (RB) EL ever imaged in a polymer junction and a large photovoltage. Moreover, the RB EL exhibits hypersensitivity to temperature, increasing in intensity by 22.6% K−1 when the de‐doped cell is cooled from 250 to 200 K. A model based on the tunnel injection of charge carriers with fast transit time across the intrinsic region explains the RB EL's hypersensitivity to temperature and super‐linear dependence on cell current. [ABSTRACT FROM AUTHOR]

Pure organic room‐temperature phosphorescence (RTP) materials are considered as potential candidates for replacing precious metal complexes to fabricate highly efficient organic light‐emitting devices (OLEDs). However, applications of the reported RTP materials in OLEDs are seriously impeded by their low photoluminescence quantum yields (PLQYs) in a thin film state. To overcome these obstacles, we established a new strategy to construct highly efficient OLEDs based on a pure organic RTP material sensitized fluorescence emitter by selecting benzimidazole‐triazine molecules (PIM‐TRZ), 2,6‐di(phenothiazinyl)naphthalene (β‐DPTZN), and 5,6,11,12‐tetraphenylnaphthacene (rubrene) as host, phosphor sensitizer, and fluorescent emitter, respectively. The perfect combination of host, phosphorescent sensitizer, and fluorescent emitter in the emitting layer ensure the outstanding performance of the devices with an external quantum efficiency (EQE) of 15.7 %. [ABSTRACT FROM AUTHOR]

Theoretical understanding of organic light-emitting diodes started from the quest to the nature of the primary excitation in organic molecular and polymeric materials. We found the electron correlation strength, bond-length alternation as well as the conjugation extent have strong influences on the orderings of the lowest lying excited states through the first application of density matrix renormalization group theory to quantum chemistry. The electro-injected free carriers (with spin 1/2) can form both singlet and triplet bound states. We found that the singlet exciton formation ratio can exceed the conventional 25% spin statistics limit. We proposed a vibration correlation function formalism to evaluate the excited-state decay rates, which is shown to not only give reasonable estimations for the quantum efficiency but also a quantitative account for the aggregation-induced emission (AIE). It is suggested to unravel the AIE mechanism through resonance Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygenmolecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence.

Plant factories for the steady production of high-quality vegetables year round, and which can be divided into solar and artificial-light types, have recently been expanding in Japan as trigged by a report by a collaboration study group in 2009 and the Great East Japan Earthquake in 2011. Common solar-type plant factories with mulch-span roofs are often difficult to construct in the northern areas of Japan, especially along the Japan Sea coast, because of limited sunshine duration and heavy winter snowfall, while artificial light-type factories are more promising in this region although high running costs due to electricity bills for irradiating plants and cooling the room often hinder the promotion of such facilities. The use of LEDs has recently increased in artificial light-type plant factories, but fluorescent lights are still predominant for economic reasons. Generally only small plants can be grown commercially in artificial light-type factories and the light intensity reaching the lower leaves decreases continuously as the stem of the plant elongates, deteriorating light use efficiency. Flexible organic electroluminescent devices able to cover the whole plant when irradiation is required and that can easily be applied/removed like a plastic film are expected to be introduced in both types of plant factories.

Several examples of a new class of materials which exhibit thermally-activated delayed fluorescence (TADF) were designed and synthesised. Structure-activity relationships were explored in order to colour-tune the fluorescence (from yellow to blue) and to improve the luminescence quantum yield. Device architectures were optimised for four materials in this class. Notably, the yellow device (CIE1931xy coordinates 0.407, 0.557) displays a maximum external quantum efficiency (EQE) of 14.3%. [ABSTRACT FROM AUTHOR]

Plant factories for the steady production of high-quality vegetables year round, and which can be divided into solar and artificial-light types, have recently been expanding in Japan as trigged by a report by a collaboration study group in 2009 and the Great East Japan Earthquake in 2011. Common solar-type plant factories with mulch-span roofs are often difficult to construct in the northern areas of Japan, especially along the Japan Sea coast, because of limited sunshine duration and heavy winter snowfall, while artificial light-type factories are more promising in this region although high running costs due to electricity bills for irradiating plants and cooling the room often hinder the promotion of such facilities. The use of LEDs has recently increased in artificial light-type plant factories, but fluorescent lights are still predominant for economic reasons. Generally only small plants can be grown commercially in artificial light-type factories and the light intensity reaching the lower leaves decreases continuously as the stem of the plant elongates, deteriorating light use efficiency. Flexible organic electroluminescent devices able to cover the whole plant when irradiation is required and that can easily be applied/removed like a plastic film are expected to be introduced in both types of plant factories. [ABSTRACT FROM AUTHOR]

Highly-efficient blue phosphorescent light-emitting diodes were fabricated based on a conjugated-polymer host by doping bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) into poly(9,9-dioctylfluorene) (PFO). Previously, conjugated polymers were not considered as potential hosts for blue phosphorescent dyes because of their low-lying triplet energy levels. Energy back transfer would occur and lead to poor luminescent efficiency in both photoluminescence (PL) and electroluminescence (EL) processes. However, by inserting a hole-transporting layer of poly( N-vinylcarbazole) (PVK), the energy back transfer was suppressed. At low FIrpic-doping concentrations, PFO emissions were completely quenched; with 8 wt% FIrpic, a maximum luminous efficiency of 11.5 cd/A was achieved. [ABSTRACT FROM AUTHOR]

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygenmolecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence. [ABSTRACT FROM AUTHOR]

Abstract: A novel soluble terpolymer (P8FO-Th-BT) containing 9,9-dioctylfluorene, thiophene, and 2,1,3-benzothiadiazole units were synthesized by Still coupling reaction. The single layer and multi-layer organic light emitting diodes (OLEDs) based on P8FO-Th-BT was fabricated. A deep red-emission device with the configuration of ITO/poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS)/P8FO-Th-BT:N,N′-di(3-methylphenyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4-diamine (TPD) (weight ratio being 1:1)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, 15nm)/tris(8-hydroxyquinoline) aluminum (Alq3, 15nm)/LiF(5Å)/Al(150nm) was obtained, and the maximum luminance was measured to be 226cd/m2 at the bias voltage of 10V. The electroluminescent peak located at 708nm, and the spectrum covered both the red and infrared regions. Moreover, the Commission International De L’Eclairage (CIE) chromaticity coordinates of the device were inalterable when the bias voltage varied, which was beneficial to the application on display. [Copyright &y& Elsevier]

We report a new class of host materials for phosphorescent iridium complexes. These materials were designed to have ambipolar character. The host materials share a 2,2′-diimidazole core and typically triarylamine or carbazole containing motifs which may give the materials electron-transporting and hole-transporting utility, respectively. We have since synthesised a new host material (MMH-001) and have applied this material in OLED devices with two different emitters; FIrpic, and our own proprietary blue Iridium emitter; MMPBD-001. The MMH-001/FIpic device has CIE1931 coordinates measured as (0.15, 0.34) and performance measured as 5.5 V, 27.2 cd/A, 15.6 lm/W, at 1 mA/cm2. The MMH-001/MMPBD-001 device shows a deeper blue colour (CIE1931 0.15, 0.24) and performance measured as 5.4 V, 21.0 cd/A, 12.0 lm/W, at 1 mA/cm2. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports series of highly efficient organic light-emitting diodes (OLEDs) with high-quality blue emission that employs an aromatic enyne derivative (E)-CPEY doped in the CBP (4, 4′-N, N′-dicarbazolylbiphenyl) host with the easily controlled doping concentrations as the emitters. The peak EL efficiencies (>8.5cdA−1, >5.5lmW−1 and ⩾6.0%) of these blue OLEDs with the stable CIE (0.15, 0.10±0.01) are the highest values ever reported for the saturated deep-blue OLEDs up to now. Moreover, although the doping concentration of them changes such large span as 10–20wt%, the deviation for both the EL efficiency and the brightness always keep within a very small range during almost the whole driving process, which should lead to the easy and reproducible fabrication process of high performance blue OLEDs. [Copyright &y& Elsevier]

Abstract: A perylene diimide (PDI) derivative was used as a dopant in the hole transport layer (HTL) of an organic light emitting device. The HTL examined was poly (N-vinylcarbazole) (PVK) and the PDI used was N,N′-di-dodecylperylene-3,4,9,10-bis-(dicarboximide), (N-DODEPER). The structure of the device was ITO/PEDOT:PSS (70nm)/PVK:N-DODEPER(0, 0.2, 0.4, 0.8wt.%) (65nm)/Alq3 (35nm)/LiF (1.3nm)/Al (100nm). 0.8wt.% N-DODEPER presence exhibited a luminous efficiency of 7.87cd/A and an external quantum efficiency of 0.78% at 21mA/cm2 and a power efficiency of 3lm/W at 12mA/cm2. The luminous and power efficiency values were significantly enhanced by a factor of 15 with respect to that of undoped device. [Copyright &y& Elsevier]

Abstract: Organic electronic devices are generally sensitive to atmospheric conditions, especially to water vapor when combined with oxygen. Organic light-emitting devices are such an example. Usually, atmospheric water vapor has detrimental consequences on the devices performance. However, as shown by our experimental results, in some (still uncontrolled) circumstances, oxidation processes accelerated by water vapor can be beneficial to performance. Thus, high humidity level is not only a detrimental issue to OLEDs. In addition, it appears that the occurrence of antagonist mechanisms and the devices sensitivity to initial structural conditions of organic materials and electrodes leads to an unpredictable, chaotic-like, behaviour of organic light-emitting quantum yield when they are exposed to atmospheric water vapor. [Copyright &y& Elsevier]

The emission spectra of the electroluminescent devices based on novel zinc complexes of sulphonylamino substituted quinolines, 2-phenylbenzazoles, and oxadiazoles are reported. The spectra exhibit wide intensive bands probably of exciplex nature. The exciplex formation can probably be due to the interaction of nitrogen atoms of amino substituents of a zinc complex and amino-containing molecules of a hole-transporting layer. [ABSTRACT FROM AUTHOR]

The current-voltage and electroluminescent features of a novel star-burst 1H-pyrazolo[3,4-b]quinoline chromophore show that it has potential applications as a material for light-emitting diodes. The electroluminescence covers the white light spectral range from 420 nm up to 610 nm and achieves maximal value about 18 Cd/m2 at biased voltage 23 V. The photovoltaic efficiency achieved was equal to about 0.08%. [ABSTRACT FROM AUTHOR]

Abstract: Highly efficient organic light-emitting diode have been developed by using a fluorinated quinacridone derivative: N,N′-di(n-butyl)-2,9-difluoroquinacridone doped in Alq3 as the emitting layer. The device shows much lower driving-voltage (the turn-on voltage is 2.5V, the practical brightness of 100 and 1000cdm−2 are realized at 3.2 and 4.2V, respectively) and higher power efficiency (the peak value of 15.2lmW−1 is obtained at 4V and 598cdm−2) than that of devices based on all the other QA derivatives. The pronounced EL performance enhancement might be attributed to the improved electron injection induced by introducing the strong electron-withdrawing fluorine atoms into the QA derivative. [Copyright &y& Elsevier]

Abstract: We report highly efficient, variable-color light-emitting diodes (LEDs) realized via mixing of molecular exciton and excimer phosphorescent emissions from a new organic phosphor platinum N^C2^N-[1,3-di(4-methoxy-pyrid-2-yl)-4,6-difluorobenzene] chloride (PtL 26Cl), a member of the Pt(N^C^N) complex series, where N^C^N represents a cyclometallating tridentate ligand based on 1,3-dipyridylbenzene, L. PtL 26Cl-doped TCTA blends [TCTA=4,4′,4′′-tris(N-carbazolyl-triphenylamine)] have been used as either the low-concentration bluish-green (molecular) phosphorescence emitter or high-concentration red (excimer) phosphorescence emitter. By adjusting the relative amount of blue and red emissive species, the color of the light emission was tuned from bluish-green through green and white up to red. The concentration-optimized devices can easily reach high brightness up to B =10,000cd/m2, achieving extremely high external quantum efficiency (EQE) up to 20% at low-current densities (<10−2 mA/cm2) and up to 17% at B =500cd/m2. High purity white light emission [CIE coordinates (x =0.34, y =0.35)] was realized at this B, QE=11.5%, power efficiency of 6.8lm/W and color rendering index (CRI)=74, though CRI=81 has been achieved with CIE coordinates (x =0.42, y =0.38). The reported performance data are among the best achievements reported for color and white emission organic LEDs. [Copyright &y& Elsevier]

Abstract: A review of recent studies of pyrazoloquinoline and quinoxaline derivative chromophore used as organic light emitting diodes and photovoltaic elements is done. We present both the principal ways of modifications of these materials as well as a possible chemical modifications to achieve more suitable technological parameters. [Copyright &y& Elsevier]

Abstract: An improved method for electrochemical deposition (ED) of a novel precursor (peripheral carbazole substituted 9,9′-spirobifluorene (TCPC)) for fabricating highly efficient luminescent films and devices has been developed. Electrochemical deposition often leaves residual charged ion species within the film. These species can negatively impact the performance of these films in OLED applications. The amount of residual charged species in the films can be reduced by controlling the oxidation and reduction potentials, by using electrolytes with different counter anions, and by washing with solvents. An optimized ED process showed a significant decrease in the doping level; up to 0.07% in ED film. The films prepared under a scan potential range from 0.85 to −0.8V, using TBAAsF6 as the supporting electrolyte, and washed with solvent mixtures of acetonitrile and CH2Cl2 (V/V =2/3) demonstrated excellent device performance. Light-emitting devices fabricated by electrochemical deposition achieved deep blue emission (x, y)=(0.16, 0.06) in CIE coordinates. High luminance efficiencies of 2.3cdA−1 were achieved for single-layer device; luminescence efficiencies of 4.4cdA−1 were achieved for a double-layer device. Finally, the problem that ED films usually exhibit low electroluminescent efficiency is solved. [Copyright &y& Elsevier]

In organic light emitting devices (LEDs) various types of emissive states are created: (i) molecular excited states (localized excitons), or bimolecular (B-M) species: excimers, electromers, exciplexes and electroplexes. The consequences of the formation of B-M excited species for optical and electrical characteristics of organic LEDs are discussed and illustrated by various examples. While molecular excitons can be viewed in some sense as correlated electron--hole (e-h) pairs with the inter-charge mean separation less than an intermolecular spacing, the size of B-M excited states amounts usually to one or two intermolecular spacings. The B-M species can be classified as electrically balanced states, formed under energy and charge exchange between neighbour molecules, and have either a singlet or a triplet character. The focus of the paper is on excimer and exciplex forming single phosphorescent dopant blends-based emitting layers but characteristic features of other B-M excited species (electromers and electroplexes) and their emissions are also mentioned. Of particular interest in modern optoelectronics are white and infrared organic LEDs. It is shown how excimer and exciplex emissions can be employed in manufacturing such devices. Examples include efficient white and near-infrared LEDs, based on single dopant emitters of an efficient N-C-N-coordinated platinum(II) complex phosphor, and their improved versions, obtained by modification of the emitter matrix materials and electron injecting electrodes. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of organic light-emitting device were prepared with the same structure of ITO/PVK:Ir(ppy)3(100:2)/BCP(10nm)/Alq3(20nm)/Al, but with different evaporation conditions for the hole-blocking layer BCP and the charge-transporting layer Alq3. The films of BCP and Alq3 in device 1 were prepared with the chamber in complete darkness, and in device 2 they were prepared with light irradiation from a 100W filament lamp during the thermal evaporation process. The current density and light power versus voltage in the two devices are reported. The results show that the current density and light power of device 2 were respectively 2.5 times and 4 times respectively as high as that of device 1 under the same driving voltage 20V. [Copyright &y& Elsevier]

The electroluminescent properties of some new materials based on novel zinc complexes of sulphonylamino substituted quinolines and 2-phenylbenzazoles are reported. The electroluminescent devices based on the new complexes exhibit a bright luminosity of green or nearly white color with good luminosity efficiency up to 25-30 cd/Å. [ABSTRACT FROM AUTHOR]

Abstract: We introduce a series of organic LEDs that exploit the monomer and excimer emissions from single phosphor dopant emitters. These organic LEDs were found to be effective in the simultaneous creation of blue and red emission bands essential for plant growth. By varying the concentration of novel phosphorescent dopants selected from a series of newly synthesized platinum complexes [PtL 22–25Cl], we have manufactured the blue-biased LEDs [with the Commission Internationale de L’Eclairage (CIE) coordinates (x, y) (0.27, 0.37)] and the red-biased LEDs [CIE coordinates (0.53, 0.38)], at a high luminance of ≈500cd/m2 and with external electroluminescence (EL) quantum efficiency of 15–18% photon/electron (→ power efficiency 8–12lm/W). The EL spectrum most suitable for the action spectrum of photosynthesis yield was that of a device incorporating 20wt.% content of [PtL 23Cl]. This LED yielded photosynthetic photon flux (PPF) approaching 10μmols−1 W−1 of the electrical power, a value which significantly exceeds that for the professional lamps used commonly for horticultural lighting. [Copyright &y& Elsevier]

Abstract: The four fluorene-based trimers with various aromatic and alkyl substituents (T1–T4) are synthesized and characterized. These oligomers show the similar electronic absorption and emission characteristics (e.g., absorption peak at 351nm, and highly efficient deep blue emission at 394nm in solution), indicating that the major electronic properties of the core chromophore are essentially independent of the substituents. However, the condensed state structures and thermal properties of four trimers are found to be different from each other, from crystalline (full alkyl (T1) or full aromatic (T2) substituted trimers) to amorphous (mixed aromatic and alkyl (T4) substituted trimers). The effect of different condensed state structures on electroluminescence device properties is presented: The blue light-emitting devices with accordant structure of ITO/PEDOT:PSS/TCTA (40nm)/trimers (40nm)/BCP (10nm)/Alq3 (20nm)/LiF/Al exhibit different EL efficiency (2.9% of T2, 1.8% of T3 and 2.7% of T4). Using amorphous T4, the white light-emitting device of ITO/TCTA (40nm)/rubrene (0.1nm)/T4 (8nm)/Alq3(52nm)/LiF/Al is fabricated with high efficiency (6.15cdA−1), high brightness (9500cdm−2) and good white light CIE coordinates (0.32, 0.37). [Copyright &y& Elsevier]

Abstract: We have developed highly efficient blue and white organic electroluminescent devices based on a blue fluorescent styrylamine dopant EBDP. The blue and white organic light emitting diodes (OLEDs) with the structures: Indium–tin oxide (ITO)/copper phthalocyanine(CuPc)/N,N′-bis-(1-naphenyl)-N,N′-biphenyl-1,1′-bipheny1-4-4′-diamine (NPB)/2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN):EBDP/tris(8-hydroxyquinoline)aluminum(Alq3)/LiF/Al and ITO/CuPc/NPB/TBADN:EBDP: 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/Alq3/LiF/Al were studied by using EBDP as blue dopant. For the blue device, the maximum luminance and maximum efficiency were 26961cd/m2 and 8.29cd/A, respectively, the luminance at a current density 20mA/cm2 was 1597cd/m2. For the white device, the maximum luminance of 32,291cd/m2, maximum efficiency 8.31cd/A and the luminance of 1413cd/m2 at a current density 20mA/cm2 were obtained. The slow decrease of efficiency with the increase of current density indicates weak exciton–exciton annihilation, which is resulted from the large steric hindrance due to the non-planar structure of the fluorescence dye EBDP. [Copyright &y& Elsevier]

Abstract: A novel red–orange emitting material with a branched molecular structure, 2,4,6-tris[2-(N-ethyl-3-carbazole)carboxethenyl]-1,3,5-s-triazine (TC3), has been synthesized and characterized using UV–visible, photoluminescence (PL) and electroluminescence (EL) spectroscopy. White EL devices were fabricated using TC3 as a red–orange emitter and 8-hydroxyquinolinolato lithium (Liq) as a blue–green emitter. N,N-bis(3-methylphenyl)-N,N-diphenylbenzidine (TPD) as the adjustor for charge carrier mobility was introduced between the two emitting layers to improve the stability of the white emission color on bias voltage. The EL devices of ITO/poly(N-vinylcarbazole) (PVK):TC3 (56nm)/TPD (5nm)/Liq (30nm)/Mg:Ag exhibited good quality white emission. The Commission Internationale De L’Eclairage chromaticity coordinates are (0.34,0.39) and are stable on the bias voltage. [Copyright &y& Elsevier]

Abstract: Efficient polymer white-light-emitting diodes (WPLEDs) have been fabricated with a single layer of fluorescent polymer blend. The device structure consists of ITO/PEDOT/PVK/emissive layer/Ba/Al. The emissive layer is a blend of poly(9,9-dioctylfluorene) (PFO), phenyl-substituted PPV derivative (P-PPV) and a copolymer of 9,9-dioctylfluorene and 4,7-di(4-hexylthien-2-yl)-2,1,3-benzothiadiazole (PFO-DHTBT), which, respectively, emits blue, green and red light. The emission of pure and efficient white light was implemented by tuning the blend weight ratio of PFO: P-PPV: PFO-DHTBT to 96:4:0.4. The maximum current efficiency and luminance are, respectively, 7.6cd/A at 6.7V and 11930cd/m2 at 11.2V. The CIE coordinates of white-light emission were stable with the drive voltages. [Copyright &y& Elsevier]

In this paper, the vapor-deposited and solution-processed organic light-emitting diode (OLED) technology development paradigms are described and then compared with respect to their prospects for enabling general lighting applications. Two key development needs are improved device efficiency and lower cost fabrication methods. Progress in these areas for solution-processed OLEDs is illustrated by describing recent methods for attaining high efficiency blue emission and introducing novel low cost process methods for device fabrication which enable high performance devices without the need for any vacuum processing steps [ABSTRACT FROM PUBLISHER]

Abstract: Rare-earth four-fold compounds of Eu3+ with HTTA, N-HPA and 1,10-phenanthroline have been synthesized. The characteristic of the compounds have been studied by UV, IR, DTA–TG, XRD and fluorescence spectroscopy. The complex of Eu(III) emits strong red fluorescence when excited by UV light. UV absorption spectrum shows the absorption energy of complexes mostly from ligands. IR spectra suggest that complexes have been successfully synthesized. It is proved by TG curve that the complex is stable, ranging from ambient temperature to 210°C in air. The organic–inorganic combined structural device (ITO/PVK: Eu/ZnS/Al) is fabricated based on layered optimization scheme. Europium (Eu) ions may also be excited by intramolecular energy transfer from ligands. There are two kinds of excitation mechanisms: impacted excitation and injected recombination for the combined structural device. The electroluminescence (EL) intensity of the combined structural device is strongly improved and reaches up to 381cd/m2 at 20V compared with the pure organic structural device. It may be an effective method to improve the EL intensity of the lanthanide complex by using electric characteristics of inorganic semiconductor materials. [Copyright &y& Elsevier]

We have synthesized some new chelate metal complexes based on 8-mercaptoquinoline and 8-aminoquinoline derivatives with different metals (Zn, Cd, Ga) and studied their spectral and electroluminescent properties. This is the first use of the compounds containing other heteroatoms instead of oxygen atoms in chelate cycles for OLED applications. The new compounds are characterized by blue and green luminescence. OLEDs prepared on the base of the new materials exhibit bright light emission with an efficiency of about 10 cd/A. [ABSTRACT FROM AUTHOR]

Abstract: A zinc complex with a schiff base, ZnL, was synthesized and characterized by elemental analyses, infrared spectra, differential thermal analysis and thermogravimetry, in which the ligand compound is N, N′-bis(2-hydroxy-1-naphthylidene)-3, 6-dioxa-1, 8-diaminooctane (H2L). The blue fluorescence of the complex in both solution and solid states was observed. The electroluminescence devices with the ZnL complex as the emitting layer were constructed, which exhibited blue emission with a peak at 455 nm and the maximum brightness of 650 cd m−2. [Copyright &y& Elsevier]

The molecular structures of the ground state and the first singlet excited state for diphenylboron analogs of Alq3 [Ph2Bq where q is 8-hydroxyquinoline (QH)] and its three derivatives were optimized with the Density Functional Theory and ab initio “configuration interaction with single excitations” method, respectively. The frontier molecular orbital characteristics of Ph2Bq were analyzed systematically in order to study the electronic transition mechanism. Electronic and spectroscopic properties of complexes have been investigated with Time-Dependent Density Functional Theory, which indicates that the emissions of Ph2Bq and its derivatives originate from the electronic π → π* transitions within the QH ligands. That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand. Similar calculations were carried out for isolated QH and its three derivatives for comparison. We found that the highest occupied molecular orbital and the lowest unoccupied molecular orbital of Ph2Bq are similar to those of QH and their spectroscopic properties change similarly when they are substituted by the same group, which suggests that one can search possibility of a red or blue emission from Ph2Bq derivatives by analyzing QH and its derivatives. [ABSTRACT FROM AUTHOR]

Abstract: A novel green emitting material of 2,4,6-Tristriphenylamine-1,3,5-s-triazine (TT3) was synthesized and the organic light-emitting diodes of indium tin oxide (ITO)/TT3/ biphasic calcium phosphate (BCP)/Mg:Ag based on TT3 as the hole transporting and emitting layer were fabricated. The electroluminescent properties were studied. The devices gave pure and bright green light emission peaked at 513 nm and the full width at half maximum of the emission was narrowed by 13.2% compared with the typical green EL device of ITO/TPD:PVK/tris(8-hydroxyquinolinato)aluminium/Mg:Ag, and the brightness was higher than that of the typical device at the same voltage. [Copyright &y& Elsevier]

Abstract: Two highly efficient blue light-emitting materials, 9-phenyl-9-pyrenylfluorene substituted pyrenes (P1, P2), were designed and synthesized. The two compounds demonstrated highly thermal stability and bright blue emission both in solution and in the solid state. Even after being annealed at 150°C under nitrogen for 24h, the solid emission spectra showed no obvious changes. The high energy levels of the HOMO (about −5.2eV) exhibit that they have improved hole-injection/transporting ability. A three layer blue OLED of ITO/TCTA (8nm)/P2 (30nm)/BCP (40nm)/Mg:Ag was obtained with high efficiency (3.08cd/A, 1.17lm/W), low turn-on voltage (3.5V) and high brightness (19885cd/m2) in ambient air, which is competitive with the best of the doped and nondoped blue OLEDs. These results revealed that these materials are promising as blue emitters for high efficiency OLEDs with a much simpler architecture. We thus exemplified that introducing 9-phenyl-9-pyrenylfluorene onto large aromatic rings is a new method to employ fluorescent dyes with large planar aromatic rings as the blue emitters in nondoped OLEDs without a hole-injection layer. [Copyright &y& Elsevier]

Abstract: A new complex of zinc with a Schiff base, zinc(N,N′-bis(salicylidene)-3, 6-dioxa-1, 8-diaminooctane monohydrate) (ZnBSO·H2O), was synthesized and characterized by means of elemental analyses, IR spectra and DTA-TG. Its structure was determined by X-ray single crystal analysis. It was demonstrated that the zinc atom is coordinated by the two oxygen atoms in phenolate and two nitrogen atoms in imine of the ligand in a slightly distorted tetrahedral geometry, while the two oxygen atoms from the oxa-alkyl chain are not coordinated to Zn(II) atom. The energy levels of the HOMO, LUMO and the electrochemical band gap were determined by cyclic voltammeter. The electroluminescent devices with the complex as the emitter showed bright blue emission with a peak at 450nm, which is same as the fluorescence of the complex in both solution and solid states. [Copyright &y& Elsevier]

We report the generation and detection of bipolar organic electroluminescence of porphyrin molecules from a nanoscale junction in an ultrahigh vacuum scanning tunneling microscope (STM). Clear molecular fluorescence from porphyrin molecules near metal substrates has been realized through highly localized electrical excitation of molecules in proximity to a sharp tip apex. The molecular origin of the luminescence, arising from the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) radiative transitions of neutral molecules, is clearly established by the observed well-defined vibrationally resolved fluorescence spectra that match perfectly with conventional photoluminescence data from molecular thin films. The molecules fluoresce at low onset voltages for both bias polarities, presenting an example of bipolar organic electroluminescence at the nanoscale. Such bipolar operation suggests a double-barrier model for electron transport, with hot electron injection into unoccupied states of molecules in both polarities. The optical behavior of molecules in the tunnel junction is also found sensitive to the electronic properties of molecules and energy level alignment at the interface. These results offer new information to the optoelectronic behavior of molecules in a nanoscopic environment and may open up new routes to the development of single-molecule science and molecular scale electronics. [ABSTRACT FROM AUTHOR]