Synthesis and optoelectronic properties of a novel dinuclear cyclometalated platinum(II) complex containing triphenylamine-substituted indolo[3,2-b] carbazole derivative in the single-emissive-layer WPLEDs

Article abstract of DOI:10.1016/j.tet.2013.12.069

A novel bi-picolinic acid derivative of H₂dipic-BTICz containing binary triphenylamine-substituted indolo[3,2-b]carbazole (BTICz) unit and its dinuclear platinum(II) complex of (dfppy)₂Pt₂(dipic-BTICz) were synthesized as a single-component emitter used in the white polymer light-emitting diodes (WPLEDs), where dfppy is 2-(2,4-difluorophenyl)pyridine and dipic-BTICz is an anion of H₂dipic-BTICz. The photophysical and electrochemical properties of (dfppy)₂Pt₂(dipic-BTICz) were investigated. Compared with the reported mononuclear platinum complex of (dfppy)Pt(pic), (dfppy)₂Pt₂(dipic-BTICz) exhibited a red-shifted photoluminescent peak at 434 nm in dilute dichloromethane (10 ^-5 M), but a weakened and red-shifted aggregation emission peak at 640 nm besides its intrinsic emission at 445 nm in its neat films. Stable pure white emissions with CIE coordinates of (0.325±0.005, 0.345±0.015) and a maximum brightness of 208 cd/m² were observed in the (dfppy)₂Pt₂(dipic-BTICz)-doped single-emissive-layer (SEL) PLEDs using a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole as a host matrix at 1 wt % dopant concentrations under applied voltages from 9 to 14 V. It indicates that the intrinsic and aggregation emissions of this dinuclear platinum complex were effectively tuned by inserting a new BTICz fluorophore in the dual picolinic acid derivative. Therefore, it is a promising single-component emitter to get white emission in SEL PLEDs.

Full text of DOI:10.1016/j.tet.2013.12.069

Tetrahedron 70 (2014) 1246e1251
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and optoelectronic properties of a novel dinuclear
cyclometalated platinum(II) complex containing
triphenylamine-substituted indolo[3,2-b]carbazole derivative
in the single-emissive-layer WPLEDs
*
Junting Yu, Jian Luo, Qing Chen, Keqi He, Fanyuan Meng, Xianping Deng, Yafei Wang ,
*
Hua Tan, Haigang Jiang, Weiguo Zhu
College of Chemistry, Key Lab of Environment-Friendly Chemistry and Application in Ministry of Education, Xiangtan University, Xiangtan 411105, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel bi-picolinic acid derivative of H2dipic-BTICz containing binary triphenylamine-substituted indolo
[3,2-b]carbazole (BTICz) unit and its dinuclear platinum(II) complex of (dfppy)2Pt2(dipic-BTICz) were
synthesized as a single-component emitter used in the white polymer light-emitting diodes (WPLEDs),
where dfppy is 2-(2,4-difluorophenyl)pyridine and dipic-BTICz is an anion of H2dipic-BTICz. The pho-
tophysical and electrochemical properties of (dfppy)2Pt2(dipic-BTICz) were investigated. Compared with
the reported mononuclear platinum complex of (dfppy)Pt(pic), (dfppy)2Pt2(dipic-BTICz) exhibited a red-
shifted photoluminescent peak at 434 nm in dilute dichloromethane (10ꢀ5 M), but a weakened and red-
shifted aggregation emission peak at 640 nm besides its intrinsic emission at 445 nm in its neat films.
Stable pure white emissions with CIE coordinates of (0.325ꢁ0.005, 0.345ꢁ0.015) and a maximum
brightness of 208 cd/m2 were observed in the (dfppy)2Pt2(dipic-BTICz)-doped single-emissive-layer
(SEL) PLEDs using a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-
oxadiazole as a host matrix at 1 wt % dopant concentrations under applied voltages from 9 to 14 V. It
indicates that the intrinsic and aggregation emissions of this dinuclear platinum complex were effec-
tively tuned by inserting a new BTICz fluorophore in the dual picolinic acid derivative. Therefore, it is
a promising single-component emitter to get white emission in SEL PLEDs.
Received 12 September 2013
Received in revised form 12 December 2013
Accepted 24 December 2013
Available online 31 December 2013
Keywords:
Dinuclear platinum complex
White polymer light-emitting devices
Indolo[3,2-b]carbazole
Electrophosphorescence
Aggregation emission
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
white-emittingSELdevices.Ononehand,multi-emitterswithvarious
emissive colors are used in the same host matrix as the activity
Since Kido and his co-workers reported the first white organic
light-emitting diode in 1994,1 white organic and polymer light-
emitting diodes (WOLEDs/WPLEDs) have attracted significant atten-
tion in both academic and industrial communities for their intrinsic
characteristics, such as low driving voltages, non-glare light, ho-
mogenous illumination and for their potential applications in energy
saving solid-state lighting sources.2e4 Up to date, various WOLEDs/
WPLEDs have been reported with single-emissive-layer (SEL),1,5,6
multiple-emissive-layer (MEL),3,7,8 tandem,9e11 and microcavity
structures.12,13 Among these white-emitting devices, the SEL-based
ones possess a simple process technique and were considered as
a class of promising commercial lighting sources. To the best of our
knowledge, two approaches are mainly presented to construct the
layer.1,14e18 However, this type of devices displays an inherent prob-
lem incolor stabilityasthe blueemitterhas a shorterlifetime than the
green and red emitters. On the other hand, a single-component
emitter with a wide spectral band emission is employed in the host
matrix as the emitting layer.19,20 In this case, stable white emission
was obtained due to simultaneously mixing the intrinsic emission in
short-wave region and the aggregate (excimers or electromers)
emission in long-wave region.21e23 Usually, the single-component
emitters in the second devise type are blue-emitting fluores-
cent24,25 and phosphorescent materials22,23,26e28 with a planar mo-
lecular structure. Compared to fluorescent materials, phosphorescent
materials exhibited higher luminescent efficiency and have more
potential in developing high-efficiency white-emitting devices as
they can harvest single and triplet excitons leading to 100% internal
quantum efficiency intheory. To date, mostof thereportedphosphors
used as single-component emitters in the SEL WOLEDs were biden-
tate platinum(II) complex of (dfppy)Pt(acac)22 and NeCeN
* Corresponding authors. Tel.: þ86 731 58298280; fax: þ86 731 58292251; e-mail
addresses: wangyf_miracle@hotmail.com (Y. Wang), zhuwg18@126.com (W. Zhu).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.12.069

J. Yu et al. / Tetrahedron 70 (2014) 1246e1251
1247
coordinated tridentate platinum(II) complex of PtL2Cl.23,27,28 For ex-
ample, Jabbour et al. made a (dfppy)Pt(acac)-doped device using 2,6-
bis(N-carbazolyl) pyridine (26mCPy) as a host matrix, which exhibi-
ted near-white emission with a power efficiency of 29.1 lm/W and
a Commission Internationale de l’ Eclairage (CIE) 1931 chromaticity
coordinate of(0.46, 0.47).22 Cocchiet al. usedPtL2Cland its derivatives
as dopant to fabricate the WOLEDs with an external quantum effi-
ciency (EQE) of 18.3%, a power efficiency of 11.8 lm/W and a CIE co-
ordinate of (0.33, 0.38).23 Recently, we developed some mono-, di-
and tri-nuclear platinum(II) complexes as single-component emitters
in the SEL WPLEDs, and stable white emission was achieved in these
platinum-doped devices.29e34 However, the EQE and brightness, as
well as color stability have not reached satisfactory levels.
the di-picolinic acid derivative.39 1H NMR, 13C NMR spectra, MALDI-
TOF mass spectrometry, and elemental analysis confirmed that
(dfppy)2Pt2(dipic-BTICz) were successfully obtained.
3. Photophysical properties
The UVevis absorption spectra of (dfppy)2Pt2(dipic-BTICz) in
dichloromethane (CH2Cl2) and its neat film are shown in Fig. 1. For
comparison, the optophysical data of (dfppy)2Pt2(dipic-BTICz) and
the mononuclear platinum complex of (dfppy)Pt(pic)31e33 are listed
in Table 1. Three distinct absorption bands were observed for the
absorption spectrum of (dfppy)2Pt2(dipic-BTICz) in CH2Cl2 solution.
Intense absorption in high-lying region about 287e309 nm is
In order to further study the relationship between the molec-
ular structure of the dinuclear platinum(II) complex and high-
efficiency white-emitting SEL WPLEDs, we here designed and
synthesized another novel dual picolinic acid derivative of H2dipic-
BTICz with a donoreacceptor (DeA) structure and its hetero-
dinuclear cyclometalated platinum(II) complex of (dfppy)2Pt2(-
dipic-BTICz), in which a triphenylamine-substituted indolo[3,2-b]
carbazole (BTICz) group as the D unit and two pending picolinic
acid as the A units were non-conjugatedly connected by hexyloxy.
We expected that the BTICz group should be able to enhance the
blue emission component and carrier-transporting ability. The
non-conjugated linkage between the D and A units is available to
control intra- and inter-molecular energy transfer, as well as im-
prove the film-formation and dispersibility. Furthermore, the ag-
gregation (excimer/exciplex) emission of the resulting dinuclear
platinum complex can be efficiently tuned in a host matrix.
Therefore, this dinuclear cyclometalated platinum(II) complex is
expected to become a promising single-component white-emitting
phosphor used in WPLEDs. In this context, the photophysical,
assigned to the ligand-centered (LC) spin-allowed
transition of the BTICz unit. The absorption band about
321e338 nm is attributed to the singlet intraligand (IL)
pep electron
*
pep
*
electron transition and/or the ligand to ligand charge transfer
(LLCT) transition.40 The weak absorption in the low-lying region at
393e420 nm is originated from the spin-allowed and spin-for-
bidden singlet metal-to-ligand charge transfer (1MLCT and 3MLCT)
transitions, to a certain extent, together with the contribution of
the triplet 3IL
pep
*
transition and 3LLCT transition. Compared to
the mononuclear counterpart of (dfppy)Pt(pic), (dfppy)2Pt2(dipic-
BTICz) exhibited an additional intense absorption band from the
BTICz unit, which should be available to improve the energy-
transfer efficiency from the host matrix to the dinuclear platinum
complex in PLEDs. In addition, we noted that (dfppy)2Pt2(dipic-
BTICz) displayed 10 nm red-shift and enhanced absorption spec-
trum in its neat film instead of its solution. This implies the in-
creasing intermolecular interaction existed in the solid state.
The photoluminescence (PL) spectra of (dfppy)2Pt2(dipic-BTICz)
in CH2Cl2 and its neat film at RT are also shown in Fig. 1. Similar PL
profiles were observed for both mono- and di-nuclear platinum(II)
complexes in dilute CH2Cl2 (10ꢀ5 M). The typical emission peak
located at 435 nm, which is assigned to the electronic transition
from MLCT to ground state.41 Compared to the PL of (dfppy)Pt(pic),
the PL spectrum of (dfppy)2Pt2(dipic-BTICz) displayed a bath-
ochromic shift by 16 nm due to more intramolecular interaction
resulting from the DeA system.42 Interestingly, the PL spectra in
Fig. S1 exhibited varieties with increasing (dfppy)2Pt2(dipic-BTICz)
electrochemical,
and
electroluminescent
properties
of
(dfppy)2Pt2(dipic-BTICz) were studied. As expected, this AeDeA-
type dinuclear platinum complex presented controllable aggrega-
tion (excimer/exciplex) emission in a blend of poly(N-vinyl-
carbazole) (PVK) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-
oxadiazole (PBD) under electric field. Stable white emissions with
CIE coordinates of (0.315ꢁ0.015, 0.375ꢁ0.045) were observed in
the SEL PLEDs using (dfppy)2Pt2(dipic-BTICz) as
a single-
component emitter and PVKePBD as a host matrix from 1 to
2 wt % dopant concentrations. Compared to the previous (dfppy-
mhb-dfppy)Pt2(acac)2 and (dfppy)2Pt2(dipic)2,31,32 this novel
dinuclear cyclometalated platinum(II) complex exhibited more
stable white emission with a maximum brightness of 208 cd/m2 in
the device at the doped concentration of 1 wt % due to the addi-
tional effect of the inserting BTICz fluorophore. To our best
knowledge, this is a new example on stable white emission from
the dinuclear cyclometalated platinum(II) complexes-doped SEL
PLEDs at the dopant concentrations from 1 to 2 wt %. Therefore,
this dinuclear cyclometalated platinum(II) complex with a blue-
emitting fluorophore inserted into the dual piconilic acid de-
rivative should become a novel promising single-component
emitter used in the SEL WPLEDs with stable white emission.
concentrations from 10ꢀ6
M M in CH2Cl2 (see
to 10ꢀ2
Supplementary data). In this situation, the above typical emission
peak was gradually red-shifted with increasing concentrations. This
phenomenon is attributed to the different aggregation states at
various concentrations in CH2Cl2. However, (dfppy)2Pt2(dipic-
BTICz) displayed two resolved emission peaks at around 445 nm
and 640 nm in the neat film. The emission intensity from the high-
lying is much stronger than that from the low-lying one. It is ob-
vious that (dfppy)2Pt2(dipic-BTICz) exhibited weaker aggregation
emission than (dfppy)Pt(pic), which indicates that the non-
conjugated linkage among the BTICz unit and two terminal
(dfppy)Pt(pic) chromophores is available to make the dinuclear
platinum(II) complex exhibit tunable aggregation emission.
2. Synthesis and characterization
4. Thermal property
As shown in Scheme 1, compounds of 2 and 3 were prepared
following the literature procedures.35e37 Compound 4 was syn-
thesized according to the general alkylation procedure.37,38 Methyl
picolinate derivative (5) was synthesized via an etherification re-
action using cesium carbonate as base and acetone as solvent. In-
termediate 6 was obtained by hydrolyzation of compound 5 in the
present of sodium hydroxide aqueous solution and THF.
(dfppy)2Pt2(dipic-BTICz) was achieved according to our previous
procedures by a chloride cleavage of the (dfppy)2Pt2Cl2 dimer with
The thermal stability of (dfppy)2Pt2(dipic-BTICz) was charac-
terized by Thermogravimetric Analysis (TGA) under nitrogen at-
mosphere. The recorded TGA curve is shown in Fig. S2 (see
Supplementary data). The decomposition temperature (Td) value
with a 5% weight loss is 284 ꢂC, which is comparable to that of
(dfppy)Pt(pic). It implies that (dfppy)2Pt2(dipic-BTICz) has a good
thermal stability. The non-conjugatedly inserted BTICz unit be-
tween the dual picolinic acid has only a minor effect on the thermal
stability of its dinuclear cyclometalated platinum(II) complex.

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J. Yu et al. / Tetrahedron 70 (2014) 1246e1251
Scheme 1. Synthesis of dinuclear platinum(II) complex of (dfppy)2Pt2(dipic-BTICz).
5. Electrochemical property
ꢀ5.54 eV and ꢀ2.68 eV according to the empirical formula:
ELUMO¼ꢀ(Eredþ4.34) and EHOMO¼ꢀ(Eoxþ4.34), respectively.43 Ob-
viously, (dfppy)2Pt2(dipic- BTICz) exhibited increasing EHOMO and
ELUMO values compared to the (dfppy)Pt(pic). The BTICz unit is favor
to improve the hole injection and transportation for its resultant
dinuclear platinum(II) complex.
The electrochemical property of the (dfppy)2Pt2(dipic-BTICz)-
based neat film was examined by cyclic voltammetry, and its cor-
responding data are listed in Table 1. A reversible oxidation po-
tential (Eox) was observed at 1.1 eV. The Ered value was estimated by
the energy band gap (Eg) and Eox according to the following for-
mula: Ered¼EoxꢀEg, in which Eg was generally evaluated from the
onset of the low-lying absorption. As a result, the highest occupied
molecular orbit (HOMO) and the lowest unoccupied molecular
orbit (LUMO) energy levels (EHOMO and ELUMO) were calculated to be
6. Electroluminescent property
To
illustrate
electrophosphorescent
performance
of
(dfppy)2Pt2(dipic-BTICz), the SEL devices with a configuration of

J. Yu et al. / Tetrahedron 70 (2014) 1246e1251
1249
concentration from 1 to 8 wt %. White emissions were achieved
from these devices at 1 and 2 wt % dopant concentrations under
different applied voltages from 9 to 14 V. Fig. 3a and b shows the
EL spectra and CIE chromaticity diagrams of the devices at 1 and
2 wt % dopant concentrations under different applied voltages
from 9 to 14 V. In this situation, the CIE coordinates were very
stable at (0.325ꢁ0.005, 0.345ꢁ0.015) at 1 wt % dopant concen-
tration, and had a minor change from (0.31, 0.35) to (0.33, 0.42) at
2 wt % dopant concentration. When the dopant concentrations
increased to 4 and 8 wt %, the (dfppy)2Pt2(dipic-BTICz)-doped
devices presented near-white emission and orange-yellow emis-
sion with stable CIE coordinates, respectively (see Supplementary
data, Figs. S3 and S4).
Fig. 1. UVevis absorption spectra and PL spectra of (dfppy)2Pt2(dipic-BTICz) in dilute
CH2Cl2 solution (10ꢀ5 M) and its neat film at 298 K.
Table 1
UVevis absorption, PL, and electrochemistry properties of (dfppy)2Pt2(dipic-BTICz)
and (dfppy)Pt(pic)
Compound
UVevisa
lab/nm)
287,309,321, 434
Emissionb Emissionc EHOMO ELUMO Eg
(
(
lem/nm) lem/nm) (eV) (eV) (eV)
(
(dfppy)2Pt2
(dipic-BTICz) 338,393,420
445, 478, ꢀ5.42 ꢀ2.68 2.74
520, 640
(dfppy)Pt(pic)
264, 325, 348 418
427, 601
ꢀ6.63 ꢀ3.46 3.17
Measured in CH2Cl2 at RT at a concentration of 10ꢀ5 mol/L.
Measured in CH2Cl2 at RT (lex¼400 nm).
Evaluated in the neat film.
a
b
c
ITO/PEDOT:PSS (50 nm)/Pt(II) complex (x wt %)þPVK:PBD (70 nm)/
LiF (0.5 nm)/Al (150 nm) were fabricated by a spin-coating process.
The electroluminescent (EL) spectra and their corresponding CIE
chromaticity diagrams of the (dfppy)2Pt2(dipic-BTICz)-doped de-
vices at dopant concentrations from 1 to 8 wt % at 13 V are shown in
Fig. 2.
Fig. 3. The EL spectra and CIE chromaticity diagram of the (dfppy)2Pt2(dipic-BTICz)-
doped devices at dopant concentrations of 1 wt % (a) and 2 wt % (b) under different
applied voltages.
Fig. 4a and b exhibits the luminanceevoltage (LeV) and the
current densityevoltage (JeV) curves of the (dfppy)2Pt2(dipic-
BTICz)-doped devices at dopant concentrations from 1 to 8 wt %,
respectively. The EL performances of these devices are summa-
rized in Table S1 (see Supplementary data). The pure white
emission was observed in the device with the maximum
brightness of 208 cd/cm2 and a maximum current efficiency of
0.16 cd/A at 1 wt % dopant concentration at different applied
voltages from 9 to 14 V. Although these EL performances could
not reach an ideal level, the (dfppy)2Pt2(dipic-BTICz)-doped de-
vices exhibited stable white emission from 1 to 2 wt % dopant
concentrations at various applied voltages. Therefore, this dinu-
clear platinum(II) complex could be a promising phosphorescent
Fig. 2. The EL spectra and CIE chromaticity diagram of the (dfppy)2Pt2(dipic-BTICz)-
doped devices at dopant concentrations from 1 to 8 wt % under an applied voltage of
13 V.
Three distinct peaks at about 437, 500, and 548 nm were ob-
served in the EL spectra, respectively. Their CIE coordinates varied
from (0.32, 0.33) to (0.39, 0.46) with increasing dopant

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J. Yu et al. / Tetrahedron 70 (2014) 1246e1251
8. Experimental
8.1. Methods
All 1H NMR spectra were acquired using a Bruker Dex-400 NMR
instrument using CDCl3 as a solvent. Mass spectra (MS) were
recorded on a Bruker Autoflex TOF/TOF (MALDI-TOF) instrument
using dithranol as a matrix. The UVevis absorption and photo-
luminescence spectra were measured on a Varian Cray 50 and
PerkineElmer LS50B luminescence spectrometer, respectively. Cy-
clic voltammetry was carried out on a CHI660A electrochemical
workstation in
a
0.1 mol/L tetrabutylammonium hexa-
fluorophosphate (Bu4NPF6) acetonitrile solution at a 100 mV/s scan
rate under nitrogen protection. A micro-platinum spar (ø¼0.8 mm),
a platinum wire and KCl saturated Hg/HgO were used as the work
electrode, counter electrode and reference electrode, respectively.
The thermogravimetric analysis (TGA) was carried out with
a NETZSCH STA449 from 25 to 600 ꢂC at a 20 ꢂC/min heating rate
under a nitrogen atmosphere.
8.2. Device fabrication and characterization
Electroluminescence spectra were recorded with an InstaSpec
IV CCD system (Oriel). Luminance was measured with a Si photo-
diode and calibrated by a PR-705 spectra scan spectrophotometer
(Photo Research). The SEL devices were fabricated by a spin-coating
process with a configuration of ITO/PEDOT:PSS (50 nm)/(dfppy)2-
Pt2(dipicBTICz)þPVKePBD (70 nm)/LiF (0.5 nm)/Al (150 nm),
where indium tin oxide (ITO) acted as the anode, poly(-
ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS)
acted as the hole-injection layer, LiF and Al were employed as
electron injection layer and cathode layer, respectively. The emit-
ting layer consisted of the (dfppy)2Pt2(dipic-BTICz) dopant and
a blend of PVK and PBD (PVKePBD) used as the host matrix. The
weight ratio of PBD was 30 wt % in PVKePBD blend. Dopant con-
centrations varied from 1, 2, 4 to 8 wt %.
Fig. 4. The LeV (a) and JeV (b) curves of the (dfppy)2Pt2(dipic-BTICz)-doped devices at
dopant concentrations from 1 to 8 wt %.
material in application of SEL WPLEDs. To our best knowledge,
this is a new example on the stable white emission from the
dinuclear platinum(II) complex-doped SEL PLEDs. Compared to
the (dfppy)Pt(pic), the (dfppy)2Pt2(dipic-BTICz) with a BTICz
fluorescent unit exhibited more controllable aggregation (exci-
mer/exciplex) emission and is available to get stable white
emission in the SEL PLEDs as a single-component dopant. It
implies that the dinuclear rather than mononuclear cyclo-
metalated platinum(II) complex has a more potential application
in the SEL WPLEDs.
8.3. General information
All solvents were carefully dried and distilled prior to use.
Commercially available reagents were used without further puri-
fication unless otherwise stated. All reactions were performed
under a nitrogen atmosphere and were monitored by thin-layer
chromatography (TLC). Flash column chromatography and pre-
parative TLC were carried out using silica gel from Merck (200e300
mesh). 6,12-Bis(4-diphenylaminophenyl)-5,11-dihydroindolo[3,2-
b]carbazoles (3)36,37 and (dfppy)Pt(pic) were synthesized according
to the described procedures before.
7. Conclusions
In summary, a novel dinuclear cyclometalated platinum(II)
complex of (dfppy)2Pt2(dipic-BTICz) containing a dual picolinic
acid and an blue-emitting BTICz fluorophore was synthesized.
Inserting the blue-emitting BTICz fluorophore into the dual
picolinic acid by non-conjugated linkage was proved to effectively
tune the aggregation emission for its dinuclear cyclometalated
platinum(II) complex. Stable pure white emissions with the CIE
coordinates of (0.325ꢁ0.005, 0.345ꢁ0.015) and a maximum
brightness of 208 cd/m2 were achieved in the (dfppy)2Pt2(dipic-
BTICz)-doped SEL PLEDs at 1 wt % dopant concentration under
different applied voltages. This work provides another way to
obtain stable white emission in the SEL PLEDs employing a novel
dinuclear cyclometalated Pt(II) complex of (dfppy)2Pt2(dipic-
BTICz) as a single-component phosphorescent emitter. In order to
further improve the device performance, device optimization is
being studied in our laboratory.
8.4. 6,12-Bis(4-diphenylaminophenyl)-5,11-di(6-bromohexyl)
indolo[3,2-b]carbazole (4)
A mixture of compound 3 (3.2 g, 4.3 mmol), 1,6-dibromohexane
(14.7 g, 60.3 mmol), aqueous sodium hydroxide (33%; 20 mL), and
tetrabutylammonium bromide (TBAB, 0.1 g) in DMF was stirred
vigorously at 80 ꢂC under the nitrogen for 24 h. The mixture was
cooled to RT and extracted with DCM (3ꢃ50 mL). The combined
extracts were dried over magnesium sulfate and evaporated under
reduced pressure. The excess 1,6-dibromohexane was recovered
from the mixture by Kugelrohr distillation. The crude product was
purified by dry flash chromatography using hexane/DCM (1:1, v/v)
as eluent to give as a yellow solid. 1H NMR (400 MHz, CDCl3, TMS),
d
(ppm): 7.55 (d, J¼8.15 Hz, 4H), 7.40e7.33 (m, 16H), 7.29 (d,
J¼7.2 Hz, 4H), 7.20 (d, J¼7.6 Hz, 2H), 7.10 (t, J¼7.05 Hz, 4H),
6.99e6.96 (m, 4H), 6.82 (d, J¼7.88 Hz, 2H), 4.04 (t, J¼5.72 Hz, 4H),

J. Yu et al. / Tetrahedron 70 (2014) 1246e1251
1251
3.38 (t, J¼6.72 Hz, 4H), 1.85e1.78 (m, 4H), 1.62e1.60 (m, 4H),
1.44e1.38 (m, 4H), 1.30e1.12 (m, 4H).
11JJ3061), the Scientific Research Fund of Xiangtan University
(11QDZ18, 2011XZX08), and the Postgraduate Science Foundation
for Innovation in Hunan Province (CX2012B249).
8.5. Compound 5
Supplementary data
A mixture of compound 4 (1.61 g, 1.50 mmol), methyl 3-
hydroxypicolinate (0.46 g, 3.00 mmol), potassium iodide (100 mg,
0.60 mmol), cesium carbonate (4.89 g, 15 mmol), and 18-crown-6
(80 mg, 0.30 mmol) in 80 mL acetone was heated to reflux under
stirring for 48 h. After cooled to RT, the mixture was filtered. The
collected solid was washed by DCM three times. The combined
organic solution was distilled successively under ordinary and re-
duced pressure. The residue was purified by silica gel column
chromatography using EA/PE (3:2, v/v) as eluent to provide a yel-
low solid in a yield of 44.08%. 1H NMR (400 MHz, CDCl3, TMS),
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.12.069.
References and notes
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Acknowledgements
Financial support from the National Natural Science Foundation
of China (51273168, 21202139, 50973093), the Innovation Group in
Hunan Natural Science Foundation (12JJ7002), the Scientific Re-
search Fund of Hunan Provincial Education Department (10A119,
11CY023, 10B112), Natural Science Foundation of Hunan (12JJ4019,