A new phosphorescent material of cyclometalated alkynylgold(III) complex, [Au(2,5-F(2)C(6)H(3)-C∧N∧C)(C≡C-C(6)H(4)N(C(6)H(5))(2)-p)] (1) (2,5-F(2)C(6)H(3)-HC∧N∧CH = 2,6-diphenyl-4-(2,5-difluorophenyl)pyridine), has been synthesized, characterized, and its device performance investigated. This luminescent gold(III) complex was found to exhibit rich PL and EL properties and has been utilized as phosphorescent dopants of OLEDs. At an optimized dopant concentration of 4%, a device with a maximum external quantum efficiency (EQE) of 11.5%, corresponding to a current efficiency of 37.4 cd/A and a power efficiency of 26.2 lm/W, has been obtained. Such a high EQE is comparable to that of Ir(ppy)(3)-based devices. The present work suggests that the alkynylgold(III) complex is a promising phosphorescent material in terms of both efficiency and thermal stability, with the additional advantages of its relatively inexpensive cost and low toxicity.
The
advancement of high-efficiency luminescent and thermally stable
organometallic complexes has offered opportunities for the commercialization
of metal phosphors for fabricating organic light-emitting devices
(OLEDs). Since the first report on the potential use of iridium(III)
and platinum(II) complexes for applications in OLEDs in the late 1990s,
extensive efforts have been made by researchers on the development
of various heavy metal-containing compounds with rich photophysical
and luminescence properties and the engineering of device architectures
to improve device efficiencies. Apart from the more well-studied iridium(III)
and platinum(II) complexes, complexes of gold(III) recently have demonstrated
their capabilities to serve as phosphorescent or thermally stimulated
delayed phosphorescent or thermally activated delayed fluorescent
emitters, and their promising performances in OLEDs have attracted
growing interest in the past decade. Nowadays, complexes of gold(III)
with emission energies ranging from sky-blue to near-infrared with
high electroluminescence performances have been obtained. In addition,
high-efficiency vacuum-deposited and solution-processed OLEDs with
benchmark efficiencies comparable to those of the iridium(III) and
platinum(II) complexes have been realized. This Focus Review summarizes
the development of various series of luminescent gold(III) complexes
to date and highlights important milestones in the development and
advancement of gold(III)-based OLEDs. Focus will be made on the molecular
design strategies for gold(III) emitters for application as dopants
in OLEDs, including those fabricated by vacuum-deposition and solution-processing
techniques.
Why is mammalian cervical count fixed across the historically long and ecologically broad mammalian radiation? Multiple lines of evidence, considered together, suggest a link between fixed cervical count and the muscularization of the diaphragm, a key innovation in mammalian history. We test this hypothesis by documenting the anteroposterior (AP) movement of the diaphragm, a lateral plate derivative, relative to that of the somitic thoracolumbar transition in unusually patterned mammals, by comparing the temporal occurrence of an osteological proxy for the diaphragm and fixed cervical counts in the fossil record, and by quantifying morphological differentiation within the mammalian cervical series. We then integrate these anatomical observations with details of diaphragm function and development to propose a sequence of innovations in mammalian evolution that could have led to fixed cervical count. We argue that the novel commitment of migratory muscle precursor cells (MMPs) of mid-cervical somites to a fate in the abaxial diaphragm defined these somites as a new and uniquely mammalian modular subunit. We further argue that the coordination of primaxial abaxial patterning constrained subsequent AP migration of the forelimb, thereby secondarily fixing cervical count.
To
address and overcome the difficulties associated with the increased
reactivity and susceptibility of blue emitters to deactivation pathways
arising from the high-lying triplet excited states, we have successfully
demonstrated an innovative strategy of harvesting triplet emission
via the “thermally stimulated delayed phosphorescence”
mechanism, where thermal up-conversion of excitons from the lower-energy
triplet excited states (T1) to higher-energy triplet excited
states (T1′) are observed to generate blue emission.
The lower-lying T1 excited state could serve as a mediator
to populate the emissive T1′ state by up-conversion
via reverse internal conversion, which could enhance the photoluminescence
quantum yield by over 20-folds. Organic light-emitting devices with
respectable external quantum efficiencies of up to 7.7% and sky-blue
emission with CIE coordinates of (0.17, 0.37) have been realized.
The operational stability for the device based on complex 1 has also been explored, and the device is found to show fairly respectable
lifetime. This work opens up a new avenue to the design and synthesis
of blue phosphorescent emitters.
High-performance deep-blue emitting phenanthroimidazole derivatives with a structure of donor−linker−acceptor were designed and synthesized. By using different linkers and different linking positions, four deep-blue emitters were obtained and used as emitters or bifunctional hole-transporting emitters in OLEDs. Such devices show low turn-on voltages (as low as 2.8 V), high efficiency (2.63 cd/A, 2.53 lm/W, 3.08%), little efficiency roll-off at high current densities, and stable deepblue emissions with CIE y < 0.10. Performances are among the best comparing to recently reported deep-blue emitting devices with similar structures. The results suggest that the combination of the phenanthroimidazole and the donor−linker− acceptor structure can be an important approach for developing high performance deep-blue emitters in particular for lighting applications.
Encouraging efforts on the design of high-performance organic materials and smart architecture during the past two decades have made organic light-emitting device (OLED) technology an important competitor for the existing liquid crystal displays. Particularly, the development of phosphorescent materials based on transition metals plays a crucial role for this success. Apart from the extensively studied iridium(III) complexes with d(6) electronic configuration and octahedral geometry, the coordination-unsaturated nature of d(8) transition metal complexes with square-planar structures has been found to provide intriguing spectroscopic and luminescence properties. This article briefly summarizes the development of d(8) platinum(II) and gold(III) complexes and their application studies in the fabrication of phosphorescent OLEDs. An in-depth understanding of the nature of the excited states has offered a great opportunity to fine-tune the emission colors covering the entire visible spectrum as well as to improve their photophysical properties. With good device engineering, high performance vacuum-deposited OLEDs with external quantum efficiencies (EQEs) of up to 30 % and solution-processable OLEDs with EQEs of up to 10 % have been realized by modifying the cyclometalated or pincer ligands of these metal complexes. These impressive demonstrations reveal that d(8) metal complexes are promising candidates as phosphorescent materials for OLED applications in displays as well as in solid-state lighting in the future.
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