Yellow electrophosphorescent devices with hosts containing N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine and tetraphenylsilane units

Article abstract of DOI:10.1039/c5ra02475g

Two novel host materials, N¹-(naphthalen-1-yl)-N¹,N⁴-diphenyl-N⁴-(4-(triphenylsilyl)phenyl) naphthalene-1,4-diamine (SiP) and N¹-(naphthalen-1-yl)-N¹,N⁴-diphenyl-N⁴-(3-(triphenylsilyl) phenyl)naphthalene-1,4-diamine (SiM), were synthesised by incorporating a hole-transporting moiety, N¹-(naphthalen-1-yl)-N¹,N⁴-diphenylnaphthalene-1,4-diamine (NPNA2) and typical electron-transporting tetraphenylsilane moiety. SiP and SiM materials exhibit high thermal and morphological stability with a glass transition temperature higher than 110°C and decomposition temperature above 350°C. Using Ir(bt)₂(acac) (bis(2-phenylbenzothiozolato-N,C²′)iridium(acetylacetonate)) as an emitter, yellow phosphorescent organic light-emitting diodes of ITO/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/host: Ir(bt)₂(acac) (15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) show maximum current and power efficiency of 40.81 cd A^-1 and 33.60 lm W^-1 with low efficiency roll-off. The current efficiency of 40.10 cd A^-1 is still observed at the practically useful brightness value of 1000 cd m^-2.

Full text of DOI:10.1039/c5ra02475g

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: S. Zhang, Q. Xu,
Y. Jing, X. Liu, G. Lu, Y. Zheng and X. Liang, RSC Adv., 2015, DOI: 10.1039/C5RA02475G.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Page 1 of 8
RSC Advances
View Article Online
DOI: 10.1039/C5RA02475G
Graphical abstract
SiP
SiM
40
30
20
10
0
Si
Si
N
N
N
N
0
200
400
600
800
1000
Luminance (cd/m2)
Two novel host materials SiP and SiM with high glass transition temperature were
synthesized and yellow phosphorescent OLEDs show maximum current and power
efficiency of 40.81 cd A-1 and 33.60 lm W-1 with low efficiency roll-off.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
RSC Advances
Page 2 of 8
View Article Online
DOI: 10.1039/C5RA02475G
RSC Advances
RSCPublishing
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.
www.rsc.org/
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
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1ꢀ3 | 1

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Page 3 of 8
ARTICLE
RSC Advances
View Article Online
Journal Name
DOI: 10.1039/C5RA02475G
N,C2′)iridium(acetylacetonate)),8 and efficient energy transfer from
o
transition temperature in the range of 26ꢀ53 C.9 The high Tg values
the host materials to the Ir(bt)2(acac) is expected.
of these host materials may be mainly attributed to the configuration
of the dimer of the Nꢀphenylnaphthalenꢀ1ꢀamine, which can suppress
intermolecular aggregation and improve the film morphology. The
high Td and Tg values of SiP and SiM are expected to decrease the
phase separation rate of the guestꢀhost system upon heating and have
the potential use in high performance devices fabricated by vacuum
thermal evaporation technology.10
Results and discussion
Synthesis and thermal property
Photophysical and electrochemical property
PL-emission
UV-absorption
Ir(bt)2(acac) (298 K)
SiP
SiP (298 K)
SiM (298 K)
SiP (77 K)
SiM (77 K)
SiM
Ir(bt)2(acac)
Scheme 1. Synthetic routes of SiP and SiM.
Scheme 1 shows the synthetic routes and structures of SiP and SiM.
1,4ꢀDibromobenzene and 1,3ꢀdibromobenzene were sequentially
treated with nꢀbutylꢀlithium and chlorotriphenylsilane to obtain (4ꢀ
bromophenyl) triphenylsilane and (3ꢀbromophenyl) triphenylsilane,
respectively. BuchwaldꢀHartwig crossingꢀcoupling of both organic
halides with N1ꢀ(naphthalenꢀ1ꢀyl)ꢀN1,N4ꢀdiphenylnaphthaleneꢀ1,4ꢀ
diamine (NPNA2) gave SiP and SiM with yields higher than 65%.
300
400
500
600
700
Wavelength (nm)
Fig. 2 UVꢀvis spectra of SiP, SiM and Ir(bt)2(acac) in dichloromethane
solution at room temperature; photoluminescence spectra in dichloromethane
solution at 298 K of SiP, SiM and Ir(bt)2(acac); phosphorescence spectra in
dichloromethane solution glass matrix of SiP and SiM at 77 K.
100
SiP
SiM
The absorption spectra of SiP, SiM and Ir(bt)2(acac) were tested in
dichloromethane solution (Fig. 2). The absorption at 268 nm is
attributed to the NPNA2ꢀcentered nꢀπ* transition. The longer
wavelength absorption observed at 378 nm for SiP and 381 nm for
SiM are attributed to the the πꢀπ* transitions from the electronꢀ
donating NPNA2 moiety to the electronꢀaccepting tetraphenylsilane
moiety. The absorption bands of (bt)2Ir(acac) at 441 and 481 nm are
belong to the absorption transition from ground state to singlet
80
DSC
60
116oC
134oC
40
20
0
60
80
100
120
140
160
180
200
3
1MLCT and triplet MLCT excited state.11 The photoluminescence
Temperature( )
oC
spectra of SiP, SiM host materials and Ir(bt)2(acac) at room
temperature or 77 K are also shown in Fig 2. The maximum
emission peak of Ir(bt)2(acac) located at 560 nm with a slight
shoulder at 597 nm. The emission peaks of SiP and SiM at room
temperature are 452 and 451 nm, respectively, suggesting the
position of triphenylsilane on phenyl linker has negligible effect on
the emission. There is a good overlap between the fluorescence
bands of two novel hosts and the MLCT absorption of Ir(bt)2(acac),
suggesting a possible energy transfer from SiP and SiM to
Ir(bt)2(acac). The triplet energies of the SiP and SiM were
determined as 2.64 and 2.67 e V, respectively, from the highest
energy vibronic subꢀband of their phosphorescence spectra at 77 K
(Table 1). From their triplet alignments, it also can be speculated that
there should be an efficient energy transfer from host triplet states to
the Ir(bt)2(acac) triplet states and an excellent triplet energy
confinement on the Ir(bt)2(acac) molecules within the emissive
layers.
0
100
200
300
400
500
600
700
Temperature (oC)
Fig. 1 TG curves of SiP (black line) and SiM (red line). Inset: DSC curves of
SiP (black line) and SiM (red line).
The thermal property of host material is very important for stable
OLEDs. The thermal gravimetric analysis (TGA) and differential
scanning calorimetry (DSC) curves of SiP and SiM under a nitrogen
atmosphere were listed in Fig. 1. Both compounds exhibit good
thermal stabilities and the decomposition temperatures (Td), which
correspond to a 5% weight loss upon heating during TGA, were
o
measured as 397 and 351 C for SiP and SiM, respectively. And
their corresponding glass transition temperatures (Tg) are 134 and
116 oC, respectively. The Tg values of the new compounds are much
higher than those of the most reported bipolar hosts, such as the
analogous silaneꢀmodified UGHs which had undesired low glass
2 | J. Name., 2012, 00, 1ꢀ3
This journal is © The Royal Society of Chemistry 2012