With 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA) as the acceptor, thermally activated delayed fluorescence (TADF) emitters adopting an asymmetric configuration can achieve highly efficient blue-emitting OLEDs.
Three Ir(C∧N)2(acac)-type and one Ir(C1
∧N)(C2
∧N)(acac)-type coumarin-based cyclometalated
Ir(III) complex isomers (IrC5, IrC7, IrC7-A, and IrC8) have been obtained using three
coumarin-based isomers of 2-phenylpyridine (ppy)-type cyclometalating
ligands (L-C5, L-C7, and L-C8). Two coordination isomers emerging as principal products (IrC7 and IrC7-A) are obtained in the synthesis
of corresponding coumarin-based cyclometalated Ir(III) complexes because
of two different coordination sites in ligand L-C7 to
form a C–Ir bond. To the best of our knowledge, there are no
such isomers reported to date. Interestingly, a broad range of phosphorescent
color tuning from green (IrC8, λ = 516 nm) to red
(IrC5, λ = 608 nm) has been realized through variation
of the pyridyl substitution positions on the fused phenyl ring of
the coumarin skeleton. In addition, based on natural transition orbital
(NTO) analyses, features of the lowest triplet excited states (T1) from these coumarin-based cyclometalated Ir(III) complex
isomers can be tuned easily by these ligand isomers as well. IrC5, IrC7, and IrC7-A show prevailing 3MLCT character associated with their T1 states
which emit the phosphorescent signals, while the T1 state
of IrC8 exhibits the dominant ligand-centered π–π*
transition feature. Importantly, owing to the strong rigidity of the
coumarin skeleton, all the coumarin-based cyclometalated Ir(III) complex
isomers can show high phosphorescent quantum yields Φp (ca. 0.4–1). Together with the improved electron-injection/electron-transport
(EI/ET) ability, all the phosphorescent emitters display impressive
electroluminescence (EL) performance. The device based on IrC8 gives the highest EL efficiencies of external quantum efficiency
(ηext) 22.7%, current efficiency (ηL) 79.7 cd A–1, and power efficiency (ηP) 58.2 lm W–1, representing the most state-of-the-art
EL ability ever achieved by coumarin-based phosphorescent emitters.
All these encouraging data definitely suggest the great potential
of the coumarin skeleton in both easy tuning of the photophysical
properties of ppy-type Ir(III) phosphorescent complexes and developing
high-performance phosphorescent emitters.
Waterborne coating has recently been paid much attention. However, it cannot be used widely due to its performance limitations. Under the specified conditions of the selected resin, selecting the function pigment is key to improving the anticorrosive properties of the coating. Zinc phosphate is an environmentally protective and efficient anticorrosion pigment. In this work, zinc phosphate was used in modifying waterborne acrylic coatings. Moreover, the disbonding resistance of the coating was studied. Results showed that adding zinc phosphate can effectively inhibit the anode process of metal corrosion and enhance the wet adhesion of the coating, and consequently prevent the horizontal diffusion of the corrosive medium into the coating/metal interface and slow down the disbonding of the coating.
With
the 9-phenyl-9-phosphafluorene oxide (PhFlOP) moiety as the
acceptor (A) and various donors (D), a series of new organic emitters
have been synthesized with a D–A–D configuration. Their
photophysical and electrochemical behaviors and electroluminescent
(EL) performances have been characterized in detail. The photophysical
results have indicated that the PhFlOP-based emitters with acridyl,
phenoxazyl, and phenothiazyl as donors show efficient, thermally activated
delayed fluorescence (TADF) behavior, especially for the TADF emitter
with the phenoxazyl donor possessing an exceptionally high rate constant
of reverse intersystem crossing (k
RISC) of 6.2 × 105 s–1. It has also
been found that their TADF behavior can be greatly affected by the
substitution position of the donors. Different from the reported aryl
phosphine oxide (APO) acceptors in TADF emitters, the PhFlOP moiety
adopts a highly rigid configuration to guarantee a photoluminescent
quantum yield as high as 0.80 in the 4,4′-N,N′-dicarbazolebiphenyl film, representing
the top-ranking emission ability for the TADF emitters with APO-type
acceptors. Benefitting from their advanced TADF performances, the
doped organic light-emitting diodes/devices based on these PhFlOP-based
TADF emitters can achieve exceptional EL performances with the maximum
external quantum efficiency (ηext) of 23.3%, current
efficiency (ηL) of 83.7 cd A–1,
and power efficiency (ηP) of 59.1 lm W–1. These encouraging EL data show the great potential of the PhFlOP
moiety in developing highly efficient TADF emitters.
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