The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C ∧ N) ligands and a single monoanionic, ...bidentate ancillary ligand (LX), i.e., C ∧ N 2Ir(LX). The C ∧ N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all β-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C ∧ N 2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1−0.6), and microsecond lifetimes (e.g., 1−14 μs). The strongly allowed phosphorescence in these complexes is the result of significant spin−orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C ∧ N 2Ir(acac) complexes is a mixture of 3MLCT and 3(π−π*) states. By choosing the appropriate C ∧ N ligand, C ∧ N 2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C ∧ N ligands, which lead to bathochromic shifts of the free ligands, lead to similar bathochromic shifts in the Ir complexes of the same ligands, consistent with “C ∧ N 2Ir”-centered emission. Three of the C ∧ N 2Ir(acac) complexes were used as dopants for organic light emitting diodes (OLEDs). The three Ir complexes, i.e., bis(2-phenylpyridinato-N,C2‘)iridium(acetylacetonate) ppy 2Ir(acac), bis(2-phenyl benzothiozolato-N,C2‘)iridium(acetylacetonate) bt 2Ir(acac), and bis(2-(2‘-benzothienyl)pyridinato-N,C3‘)iridium(acetylacetonate) btp 2Ir(acac), were doped into the emissive region of multilayer, vapor-deposited OLEDs. The ppy 2Ir(acac)-, bt 2Ir(acac)-, and btp 2Ir(acac)-based OLEDs give green, yellow, and red electroluminescence, respectively, with very similar current−voltage characteristics. The OLEDs give high external quantum efficiencies, ranging from 6 to 12.3%, with the ppy 2Ir(acac) giving the highest efficiency (12.3%, 38 lm/W, >50 Cd/A). The btp 2Ir(acac)-based device gives saturated red emission with a quantum efficiency of 6.5% and a luminance efficiency of 2.2 lm/W. These C ∧ N 2Ir(acac)-doped OLEDs show some of the highest efficiencies reported for organic light emitting diodes. The high efficiencies result from efficient trapping and radiative relaxation of the singlet and triplet excitons formed in the electroluminescent process.
Deep brain stimulation (DBS) to the superolateral branch of the medial forebrain bundle (MFB) has been reported to lead to rapid antidepressant effects. In this longitudinal study, we expand upon the ...initial results we reported at 26 weeks (Fenoy et al., 2016), showing sustained antidepressant effects of MFB DBS on six patients with treatment-resistant depression (TRD) over 1 year. The Montgomery-Åsberg Depression Rating Scale (MADRS) was used as the primary assessment tool. Deterministic fiber tracking was used to individually map the target area; analysis was performed to compare modulated fiber tracts between patients. Intraoperatively, upon stimulation at target, responders reported immediate increases in energy and motivation. An insertional effect was seen during the 4-week sham stimulation phase from baseline (28% mean MADRS reduction, p = 0.02). However, after 1 week of initiating stimulation, three of six patients had a > 50% decrease in MADRS scores relative to baseline (43% mean MADRS reduction, p = 0.005). One patient withdrew from study participation. At 52 weeks, four of remaining five patients have > 70% decrease in MADRS scores relative to baseline (73% mean MADRS reduction, p = 0.007). Evaluation of modulated fiber tracts reveals significant common orbitofrontal connectivity to the target region in all responders. Neuropsychological testing and
F-fluoro-deoxyglucose-positron emission tomography cerebral metabolism evaluations performed at baseline and at 52 weeks showed minimal changes and verified safety. This longitudinal evaluation of MFB DBS demonstrated rapid antidepressant effects, as initially reported by Schlaepfer et al. (2013), and supports the use of DBS for TRD.
We report the synthesis, crystal structure, and photophysical and electroluminescent properties of a new charge transporting host material for short wavelength phosphor-doped organic light emitting ...devices (OLEDs) based on 2,7-bis(diphenylphosphine oxide)-9,9-dimethylfluorene (PO6). The PO moiety is used as a point of saturation between the fluorene bridge and the outer phenyl groups so that the triplet exciton energy of PO6 is 2.72 eV, similar to that of a dibromo substituted fluorene, but it is more amenable to vacuum sublimation and has good film forming properties. Computational analysis (B3LYP/6-31G*) predicts the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of PO6 to be lower by 1.5 and 0.59 eV, respectively, compared to a similar diphenylamino substituted derivative. In a simple bilayer OLED device, PO6 exhibits structured UV electroluminescence at a peak wavelength of 335 nm and structured lower energy emission with peaks at 380 and 397 nm, similar to the solid film and crystalline solid photoluminescence spectra. The longer wavelength peaks are attributed to aggregate formation via strong intermolecular interactions (PO···HC and edge-to-face CH···π contacts) and longer range electrostatic interactions between PO moieties leading to ordered regions in the film. Devices incorporating PO6 as the host material doped with iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) exhibited sky blue emission with peak external quantum efficiency (ηext,max) of 8.1% and luminous power efficiency (ηp,max) of 25.1 lm/W. At a brightness of 800 cd/m2, generally considered to be sufficient for lighting applications, the ηext and ηp are 6.7% and 11.8 lm/W and the operating voltage is 5.6 V, which is significantly lower than has been demonstrated previously using this dopant.
Dibenzofuran (DBF) is converted to a vacuum-sublimable, electron-transporting host material via 2,8-substitution with diphenylphosphine oxide moieties. Close π−π stacking and the inductive influence ...of PO moieties impart favorable electron-transport properties without lowering the triplet energy. A maximum external quantum efficiency of 10.1% and luminance power efficiency of 25.9 lm/W are realized using this material as the host for the blue-green electrophosphorescent molecule, iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C 2‘)picolinate (FIrpic).
We relate the chemical structure of a series of methyl (Me) substituted group III metal tris(8-quinolinolato) chelates (nMeq3M: n = 0, 3, 4, 5; M = Al3+, Ga3+) to their photoluminescence (PL), ...electroluminescence, and thermal properties. Methylation of the 8-quinolinol ligand at the 3 or 4 position (pyridyl ring) results in a factor of 1.4 and 3.0 enhancement of PL quantum efficiency (φPL), respectively, whereas methylation at the 5 position (phenoxide ring) results in a factor of ∼3.0 decrease in φPL relative to the unsubstituted analogue. Electroluminescent quantum efficiencies of undoped organic light-emitting devices using the aluminum tris(8-quinolinolato) chelates are 1, 0.45, 1.4, and 0.80% for unsubstituted 5-, 4-, and 3-methyl-8-quinolinol ligands, respectively. Devices made with the latter two ligands have a higher operating voltage to generate the same current density. Similar trends were observed for methylation of gallium tris(8-quinolinolato) chelates. We relate these results to the thermal properties of the compounds measured by simultaneous differential scanning calorimetry and thermal gravimetric analysis. The C-4 methylated derivatives exhibit ∼60 °C lower crystalline melting points than all other derivatives, indicating the weakest cohesive forces between molecules. Unlike Alq3, both the C-4 and C-5 methylated derivatives show no recrystallization of the glassy state below 500 °C and exhibit ∼20−25 °C higher glass transition temperatures. We infer that methylation of the 8-quinolinol ligand reduces intermolecular interactions and consequently impedes charge transport through the film.
Three-Color, Tunable, Organic Light-Emitting Devices Shen, Zilan; Burrows, Paul E.; Bulović, Vladimir ...
Science (American Association for the Advancement of Science),
06/1997, Letnik:
276, Številka:
5321
Journal Article
Recenzirano
An independently controlled, three-color, organic light-emitting device was constructed with a vertically stacked pixel architecture that allows for independent tuning of color, gray scale, and ...intensity. The 12-layer device structure consists of sequentially stacked layers of metal oxide, amorphous organic, crystalline organic, and metal thin films deposited by a combination of thermal evaporation and radio-frequency sputtering. Each of the three addressable colors is sufficiently bright for flat panel video display applications. A novel inverted structure is used for the middle device in the stack to lower the maximum drive voltage of the compound pixel.
We show that the inductive electron-withdrawing effect of diphenylphosphoryl (Ph2PO) groups lowers both the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of a carbazole ...chromophore. This improves electron injection from a cathode without affecting the high triplet exciton energy (E T ≈ 3.0 eV) of the host material. Three new carbazole derivatives, 3,6-bis(diphenylphosphoryl)-9-ethylcarbazole (PO10), 3,6-bis(diphenylphosphoryl)-9-phenylcarbazole (PO9), and N-(4-diphenylphosphoryl phenyl) carbazole (MPO12), were investigated as host materials in blue phosphor-doped organic light-emitting devices (OLEDs). Photophysical characterization showed all three carbazole derivatives exhibit monomer UV fluorescence (367−385 nm) in solution and contributions from molecular aggregates or excimers in solid-state films (378−395 nm). The polar MPO12 derivative exhibited solvatochromism and had the highest propensity for aggregate formation in the solid state. Testing of OLEDs using PO9, PO10, and MPO12 as host materials for the sky blue organometallic phosphor iridium(III) bis(4,6-(difluorophenyl)-pyridinato-N,C 2′) picolinate (FIrpic) gave external quantum efficiencies (EQE) and operating voltages at a similar current density (J = 13 mA/cm2) of 6−8% at <7 V. The best device performance was exhibited using MPO12 as the host when an appropriate hole-blocking layer was implemented. The higher performance of MPO12 was attributed to the ambipolar charge-transporting character of the polar carbazole derivative. However, exciton relaxation on nonradiative aggregate states of all host materials studied may limit further improvements in device efficiencies.
A simple and general postdeposition electrode patterning technique for active organic electronic devices is demonstrated and is applied to patterning the metal cathodes of organic light-emitting ...devices. Selective lift-off of the metal cathode layer is achieved by pressing a prepatterned, metal-coated silicon stamp on the unpatterned device layers. Under pressure, the metal coating on the stamp cold-welds to the metal cathode coating the underlying organic films. Subsequent separation of the stamp from the substrate results in removal of the cathode metal in the regions contacted by the stamp, resulting in submicrometer feature definition. A 17 x 17 passive matrix display, with a pixel size of 440 micrometers by 320 micrometers, was fabricated with this process. Cold-welding followed by lift-off of the cathode metal allows simple, cost-effective, and high-throughput large-area fabrication of organic electronic devices.
Data that can be used to monitor biodiversity through time are essential for conservation and management. The reef-forming worm, Sabellaria alveolata (L. 1767) is currently classed as ‘Data ...Deficient’ due to an imbalance in the spread of data on its distribution. Little is known about the distribution of this species around Ireland. Using data archaeology, we collated past and present distribution records and discovered that S. alveolata has a discontinuous distribution with large gaps between populations. Many regions lack data and should be targeted for sampling. Biodiversity surveys revealed that S. alveolata supported diverse epibiotic algal communities. Retrograding (declining) reefs supported greater infaunal diversity than prograding (growing) reefs or sand, suggesting that S. alveolata is a dynamic ecosystem engineer that has a lasting legacy effect. Similar research should be carried out for other Data Deficient species, habitats and regions. Such data are invaluable resources for management and conservation.
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•Improving the knowledge base of data deficient species will enable greater protection.•We identified knowledge gaps for the distribution of a Data Deficient species in a poorly mapped region.•S. alveolata reefs supported diverse epibiotic algal assemblages.•Retrograding (declining) reefs supported greater infaunal diversity than prograding (growing) reefs.•Such research should be done for other Data Deficient species and habitats.
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