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RSC Advances
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DOI: 10.1039/C5RA02475G
RSC Advances
ARTICLE
Yellow electrophosphorescent devices with hosts containing
N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine
Cite this: DOI:
10.1039/x0xx00000x
and tetraphenylsilane units
Song Zhang, QiuꢀLei Xu, YiꢀMing Jing, Xuan Liu, GuangꢀZhao Lu, Xiao Liang,
YouꢀXuan Zheng*, JingꢀLin Zuo
Received 00th January 2012,
Accepted 00th January 2012
Two
naphthaleneꢀ1,4ꢀdiamine
novel host materials, N1ꢀ(naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀdiphenylꢀN4ꢀ(4ꢀ(triphenylsilyl)phenyl)
(SiP) and
N1ꢀ(naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀdiphenylꢀN4ꢀ(3ꢀ(triphenylsilyl)
DOI: 10.1039/x0xx00000x
phenyl)naphthaleneꢀ1,4ꢀdiamine (SiM), were synthesised by incorporating a holeꢀtransporting moiety,
N1ꢀ(naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀdiphenylnaphthaleneꢀ1,4ꢀdiamine (NPNA2) and typical electronꢀ
transporting tetraphenylsilane moiety. SiP and SiM materials exhibit high thermal and morphological
stability with high glass transition temperature higher than 110 °C and decomposition temperature above
350 °C. Using Ir(bt)2(acac) (bis(2ꢀphenylbenzothiozolatoꢀN,C2′)iridium(acetylacetonate)) as emitter,
yellow phosphorescent organic lightꢀemitting diodes of ITO/ TAPC (1,1ꢀbis[4ꢀ(diꢀpꢀ
tolylamino)phenyl]cyclohexane, 40 nm)/ host : Ir(bt)2(acac) (15 wt%, 20 nm)/ TmPyPB (1,3,5ꢀtri(mꢀ
pyridꢀ3ꢀylꢀphenyl)benzene, 40 nm)/ LiF (1 nm)/ Al (100 nm) show maximum current and power
efficiency of 40.81 cd Aꢀ1 and 33.60 lm Wꢀ1 with low efficiency rollꢀoff. The current efficiency of 40.10
cd Aꢀ1 is still observed at the practically useful brightness value of 1000 cd mꢀ2.
Therefore, the development of the bipolar host possessing high
triplet energy is still interesting for practical application. One of
Introduction
Organic lightꢀemitting diodes (OLEDs) have been available on the strategies adopted to suppress the donorꢀacceptor interactions for
market for over a decade and it is now a multiꢀbillion dollar confining the triplet energy on the emitting phosphors is to introduce
industryꢀmostly from touchꢀenabled activeꢀmatrix OLED a πꢀconjugated bridge with a twisted conformation, which can
(AMOLED) displays for mobile phones. In 1998, phosphorescent partially reduce the electronic coupling of the donor and acceptor in
OLEDs (PHOLEDs) were first reported by Ma and Forrest et al.1 In the ground state. More efficiently, the incorporation of saturated
contrast to typical fluorescent OLEDs, PHOLEDs have attracted centers such as sp3ꢀC or Si as the molecular bridge can usually block
considerable attention because they can reach to 100% of theoretical the electronic interactions between the holeꢀtransporting and
internal quantum efficiency by harvesting both singlet and triplet electronꢀtransporting substructures.4 Silicon atoms are used in host
excitons.1,2 In PHOLEDs, to reduce the quenching associated with materials due to many advantages, such as conjugation blocking for
the relatively long exciton lifetimes, long diffusion lengths of triplet a wide band gap and a tetrahedral geometry for morphology.6
emitters and tripletꢀtriplet annihilation, phosphorescent emitters of
The dimer of the Nꢀphenylꢀ1ꢀnaphthylamine, N1ꢀ(naphthalenꢀ1ꢀ
heavyꢀmetal complexes are usually doped into a suitable host yl)ꢀN1,N4ꢀdiphenylnaphthaleneꢀ1,4ꢀdiamine (NPNA2, ET = 2.67 eV,
material.3 It is desirable that the host materials ought to have a large low temperature photoluminescence spectra shown in Fig. S1), has
enough triplet energy gap for efficient energy transfer to the guest, ever been characterized to have high triplet energy, excellent holeꢀ
good carrier transport properties for a balanced recombination of transporting ability and high thermal stability. Our previous research
holes and electrons in the emitting layer, energyꢀlevel matching with also demonstrated the successful utilization of the dimer of Nꢀ
neighboring layers for effective charge injection4 and high thermal phenylꢀ1ꢀnaphthylamine as an effective electronꢀdonating moieties
and morphological stability. Among many design concepts for host in holeꢀtransporting layer.7 In the case of that, we adopted the holeꢀ
materials, bipolar host materials have been the subject of interest transporting moiety to two new siliconꢀbased host materials, N1ꢀ
because these materials have wellꢀbalanced charge transport (naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀdiphenylꢀN4ꢀ(4ꢀ(triphenylsilyl)phenyl)
properties that could extend the recombination zone, improve the naphthaleneꢀ1,4ꢀdiamine (SiP) and N1ꢀ(naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀ
device efficiency and simplify the device structure.5 The diphenylꢀN4ꢀ(3ꢀ(triphenylsilyl)phenyl)naphthaleneꢀ1,4ꢀdiamine
incorporation of holeꢀtransporting (donor) and electronꢀtransporting (SiM) by introducing triphenylsilane to the paraꢀ and metaꢀpositions
(acceptor) moieties into the multifunctional host materials has been of a phenyl linker (Scheme 1). The triplet energy of the two host
proved to be an efficient method to obtain bipolar small molecules. materials was almost the same because it is determined by the novel
However, the conjugation caused by intramolecular donorꢀacceptor holeꢀtransporting moiety NPNA2, which is higher than a widely
interactions may lower the triplet energies of bipolar molecules. used yellow phosphor of Ir(bt)2(acac) (bis(2ꢀphenylbenzothiozolatoꢀ
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