Thermally cross-linkable thermally activated delayed fluorescent materials for efficient blue solution-processed organic light-emitting diodes

Article abstract of DOI:10.1039/c6tc02634f

Solution-processed organic light-emitting diodes (OLEDs) have attracted great attention due to their simple fabrication process and easy scalability of the solution process. In this work, a thermally cross-linkable thermally activated delayed fluorescent (TADF) molecule DV-MOC-DPS was designed and synthesized. Moreover, a thermally cross-linkable host material DV-CDBP with high triplet energy was also synthesized. With the incorporation of two cross-linkable vinylbenzyl ether groups, both these materials with excellent thermal stabilities can be fully cross-linked after heating at 180 °C. In addition, the cross-linked films with the different mass ratios of DV-CDBP and DV-MOC-DPS (1:0.06, 1:0.09 and 1:0.12) were investigated. The cross-linked films are quite smooth with the root-mean-square (RMS) roughness in the range from 0.622 nm to 0.725 nm. Simultaneously, the cross-linked film with a mass ratio of 1:0.09 exhibits the highest photoluminescence quantum yield of 0.71. By employing the cross-linked films as emitting layers, an efficient blue solution-processed OLED with a maximum external quantum efficiency of 2.0% was achieved. The molecular design reported here provides a novel route toward highly efficient solution-processed OLEDs.

Full text of DOI:10.1039/c6tc02634f

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Thermally cross-linkable thermally activated delayed fluorescence
materials for efficient blue solution-processed organic light-
emitting diodes
Received 00th January 20xx,
Accepted 00th January 20xx
Kaiyong Sun, Xiangfei Xie, Yao Liu, Wei Jiang,* Xinxin Ban, Bin Huang, and Yueming Sun*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Solution-processed organic light-emitting diodes (OLEDs) have attracted great attention due to the simple
fabrication process and easy scalability of the solution process. In this work, a thermally cross-linkable
thermally activated delayed fluorescence (TADF) molecule DV-MOC-DPS was designed and synthesized.
Moreover, a thermally cross-linkable host material DV-CDBP with high triplet energy was also synthesized.
With the incorporation of two cross-linkable vinylbenzyl ether groups, both of them with excellent thermal
stabilities can be fully cross-linked after heating at 180 °C. In addition, the cross-linked films with the
different mass ratios of DV-CDBP and DV-MOC-DPS (1:0.06, 1:0.09 and 1:0.12) were investigated. The
cross-linked films are quite smooth with the root-mean-square (RMS) roughness in the range from 0.622 nm
to 0.725 nm. Simultaneously, the cross-linked film with a mass ratio of 1:0.09 exhibits the highest
photoluminescence quantum yield of 0.71. Employing the cross-linked films as emitting layers, an efficient
blue solution-processed OLED with a maximum external quantum efficiency of 2.0% was achieved. The
molecular design reported here provides a novel route toward highly efficient solution-processed OLEDs.
these phosphorescent emitters contain rare metal elements which
make them expensive, hampering the commercial application of
1. Introduction
Organic light-emitting diodes (OLEDs) have attracted much
attention owing to their superior potential applications in both new
generation full-color flat-panel displays and new-generation solid-
state lighting.1-4 In the past decade, considerable efforts have been
devoted to exploring organic luminescent materials for fabricating
high-performance OLEDs.5-11 The traditional fluorescence-type
materials are limited by the internal quantum efficiency (IQE) of
25%. Accordingly, the heavy metal complex phosphorescent emitters
with IQE of 100% can be obtained by a strong spin-orbit coupling,
which have been attracted much attention.12-16 However, most of
OLEDs. As an alternative, pure organic materials with the feature of
TADF can harvest both singlet and triplet excited states to achieve a
theoretical internal quantum efficiency of 100%, which have many
desirable features.
Up until now, the focus of TADF research has been with great
progress in improving the efficiency of OLEDs by using small
molecule evaporated TADF materials.17-22 For example, Adachi et al
3,9,23
have reported the excellent blue, green and red TADF
molecules. Used them as emitting layers, the external quantum
efficiencies (EQEs) of the devices have reached 19.5%, 28.6% and
12.5%, respectively. Despite efficiency improvement, the evaporated
deposition process needs high cost, complicated structures, and
precise control, which limits the mass production of large-size
OLEDs. Comparatively, a solution process make fabrication process
simpler, more cost efficient, and easily scalable. To date, only a few
of TADF materials has been reported as solution processable
School of Chemistry and Chemical Engineering, Southeast University, Nanjing,
210096, Jiangsu, P. R. China
*E-mail: 101011462@seu.edu.cn (W. Jiang);
*E-mail: sun@seu.edu.cn (Y. Sun).
Electronic Supplementary Information (ESI) available: Electrochemical and
photophysical data for DV-CDBP and DV-MOC-DPS and films. See DOI:
10.1039/x0xx00000x
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emitters.24-26 Therefore, the development of solution-processed etherification with 4-vinylbenzyl chloride coVmiepwlAerttiecdle Ontlhinee
organic TADF materials is of significant importance. Yamamoto et al synthesis of DV-CDBP. Moreover, MOCD-DOIP: S10.w10a3s9/sCy6nTtCh0e2s6iz3e4dF
26
first reported the solution-processable, non-doped, carbazole by reacting 3-Methoxy-9H-carbazole with sodium hydride and
dendrimers TADF materials with
a triphenyl-s-triazine core. bis(4-fluorophenyl)sulfone. Hydroxylation of the methoxy
However, the synthetic methods is complicated. Polymers have been group with BBr3, followed by etherification with 4-vinylbenzyl
proven to be ideal emissive materials that suit to solution processes chloride completed the synthesis of DV-CDBP. The mixed
such as spin-coating, die-casting, or ink-jet printing.27-31 However, molecules of DV-CDBP and DV-MOC-DPS with the mass
the traditional emissive polymers can only harvest singlet excitons to ratios of 1:0.06, 1:0.09 and 1:0.12 (named as M6, M9 and M12),
realize a theoretical internal quantum efficiency of 25%, hampering respectively. The cross-linked films were prepared by the
32
the efficiency of OLEDs. Recently, Andrey et al
obtained a thermal cross-linking of DV-CDBP and DV-MOC-DPS with
solution processable polymer with the features of TADF. The devices the mass ratios of 1:0.06, 1:0.09 and 1:0.12 (named as P6, P9
were fabricated by low-cost wet processes with the EQE of the and P12), respectively. DV-MOC-DPS and DV-CDBP were
33
devices have reached 10%. In addition, Adachi et al designed and purified by column chromatography to give the pure products.
synthesized two TADF polymers. By using them as the emitters, the 1H and 13C NMR spectroscopy, mass spectrometry, and
maximum EQE of green and yellow devices have reached 8.1% and elemental analysis were used to characterize the molecular
34
9.3%, respectively. Meanwhile, Yang et al
utilized a single structures.
polymer with TADF characteristics as a bluish-green emitter to
obtain the solution-processed OLED with maximum EQE value of
4.3%. To the best of our knowledge, the TADF materials are usually
employed as dopants in a host material to prevent the concentration
quenching. Thus, the ratios of the host and TADF emitters need
precise control. However, these above-mentioned TADF polymers
are difficult to satisfy precise control and hard to purification.
Herein, the method that use the thermally cross-linkable host
and TADF materials as the emitting layers is a effective
approach to realize the efficient solution-processed OLEDs.
In this work, we designed and synthesized two thermally
cross-linkable materials, DV-CDBP and DV-MOC-DPS, which
act as host material and TADF emitter for solution-processed
OLED, respectively. DV-CDBP incorporates two vinylbenzyl
ether groups as cross-linking groups and 4,4’-bis(9-carbazolyl)-
2,2’-dimethylbiphenyl (CDBP) as the host. Simultaneously,
DV-MOC-DPS contains two vinylbenzyl ether groups as cross-
linking groups and bis[4-(3-methoxycarbazole)phenyl]sulfone
(MOC-DPS) as a TADF emitter. We choose DV-CDBP as the
host because of its high triplet energy of 2.95 eV.35
Simultaneously, DV-MOC-DPS exhibits obvious TADF
features and feasible molecular modification.36,37
Scheme 1. Synthetic routes of DV-CDBP and DV-MOC-DPS
In order to understand the electronic and geometrical structure of
DV-MOC-DPS,
a calculation was performed using density
functional theory (DFT) at the B3LYP/6-31G (d) level. As Fig. 1
shows, the optimized geometry of DMOC-DPS shows a large
dihedral angle of 50o between the phenyl ring and the carbazole
plane. This structure is close to that of DTC-DPS.36 The calculated
highest occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) of DV-MOC-DPS are mainly distributed
2. Results and discussion
The synthesis routes to DV-CDBP and DV-MOC-DPS are
shown in Scheme 1. A Vilsmeier–Haack formylation of a
CDBP with an excess of phosphorous oxachloride (POCl3) and
N,N-dimethylformamide (DMF) provided 1. Reduction of the
formyl group with sodium borohydride, followed by
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on the substituted carbazole units and the diphenyl sulfone units,
respectively. Simultaneously, the large spatial separation between the
HOMO and LUMO implies a small singlet–triplet splitting energy
for the transition that involves them. To predict the energy difference
(∆EST) between the lowest S1 and the lowest T1 levels, time
dependent density functional theory (TD-DFT) calculations were
performed, based on the ground state geometries when optimized by
the DFT (B3LYP/6-31G(d)). The ∆EST value of DV-MOC-DPS was
0.49 eV, indicating the potential as TADF emitter.
View Article Online
DOI: 10.1039/C6TC02634F
(a)
DV-CDBP
DV-MOC-DPS
1.0
0.8
0.6
0.4
0.2
0.0
DV-MOC-DPS
DV-CDBP
first scan
second scan
first scan
second scan
0
50
100
150
200
250
(o
Temperature C)
100
200
300
400
500
600
700
Temperature (oC)
Fig. 1 Optimized geometries and HOMO and LUMO distribution of DV-MOC-
DPS.
The thermal properties of DV-MOC-DPS and DV-CDBP are
measured by thermal gravimetric analyses (TGA) and differential
scanning calorimetry (DSC). Their decomposition temperatures (Td)
with 5% weight loss are 443 °C and 350 °C, respectively, which
indicate the excellent thermal stabilities. Their DSC curves in Fig. 2a
show both of them have endothermic peak followed by a narrow
exothermic peak in the first scan. The exothermic peaks of DV-
MOC-DPS and DV-CDBP around 175 °C and 181 °C, respectively,
which are assigned to the thermal polymerization of the styrene
group. On the basis of the DSC studies, we employed an isothermal
heating at 200 °C for 30 min under nitrogen atmosphere to ensure
complete cross-linking for all the films. In addition, the Td of P9 is
357 °C (Fig. S1) between the Td of DV-CDBP and DV-MOC-DPS,
which indicate that both of DV-CDBP and DV-MOC-DPS proceed
directly with the process of thermal polymerization. To evaluate the
morphological stabilities of P6-P12, we utilized atomic force
microscopy (AFM) to explore the surface images of the cross-linked
films. As shown in Fig 2b-2d, the cross-linked films are quite
smooth with the root-mean-square (RMS) roughness in the range
from 0.622 nm to 0.725 nm. Meanwhile, no pinholes or cracks could
be observed. These results suggest that P6-P12 exhibit high thermal
and morphological stabilities, which benefit the fabrication of the
solution-processed devices.
Fig. 2 TGA and DSC (a) traces of DV-CDBP and DV-MOC-DPS at a heating rate
of 10 °C min-1. AFM topographic images of P6 (b), P9 (c) and P12 (d).
Fig. 3 shows the absorption and fluorescence spectra of DV-
CDBP, DV-MOC-DPS and P6-P12 both in toluene and in the film
state. The absorption peaks of DV-CDBP at 351 nm and 300 nm
which can both be assigned to the absorption of the carbazole units.
The lowest-energy absorption peak of DV-MOC-DPS appears at
around 356 nm in toluene and 367 nm in film, respectively. DV-
CDBP shows two distinctive emission peaks at about 351 nm in
toluene and 367 nm in film. DV-MOC-DPS exhibits a broad and
structureless emission peak at 430 nm. Moreover, with the increasing
content of DV-CDBP, the peak intensity at 430 nm increases
gradually, indicating more efficient energy transfer from the host to
the TADF emitter. In the film state, the PL peaks of P6-P12 are
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formed by the overlap of the emission of both the DV-CDBP and the fluorescence. However, in oxygen-free toluene, the signals display a
View Article Online
DOI: 10.1039/C6TC02634F
DV-MOC-DPS. Simultaneously, with the increasing content of DV- fast decay followed by a slower one, which can be assigned to
MOC-DPS, the peaks are gradually red-shifted, which indicates that normal fluorescence and TADF, respectively. The TADF component
the TADF emitter makes more contribution to the emission profile of can be fitted to a single-exponential decay with a lifetime of 50 µs.
the P6-P12. The phosphorescence spectrum of DV-CDBP and cross- In oxygen-free toluene, the photoluminescence quantum yield
linked DV-CDBP at 77 K and the phosphorescence spectrum of DV- (PLQY) of DV-MOC-DPS was found to be 0.61, which is close to
MOC-DPS at 77 K with 10 ms delay were also measured (Fig. S2). the molecule of DTC-DPS (0.69) and DMOC-DPS (0.56).36,37 We
According to previous studies, the S1/T1 level of DV-CDBP and DV- also recorded the transient PL decay spectra of the P6-P12 in films.
MOC-DPS at 3.63 eV/2.95 eV and 3.24 eV/2.93 eV, respectively, As shown in Fig. 4b, they mainly display the prompt (7.2–8.4 ns)
can be determined from the onset of the fluorescence spectrum and and delayed (0.7–0.8 µs) component. This feature obviously
the highest energy peak of the phosphorescence spectrum, originates from the triplet states of the P6-P12. To further seek the
respectively. The T1 level of cross-linked film DV-CDBP at 2.98 eV origin of delayed fluorescence, the temperature dependence of
can be determined from the highest energy peak of the transient PL in films was measured. As shown in Fig. 4c, with the
phosphorescence spectrum, which indicate that the DV-CDBP is suit increasing of temperature, the DF lifetimes of P9 increased, which
to act as the host for the blue OLEDs. Moreover, the HOMO of DV- further confirms that the DF component comes from TADF. The
CDBP and DV-MOC-DPS were estimated to be -5.38 eV and -5.29 PLQY of P6-P12 in films are 0.63, 0.71, 0.64, respectively. The
eV, respectively (Fig. S3). The LUMO energy levels DV-CDBP and results indicate that P6-P12 have great potential as emitters in
DV-MOC-DPS were estimated from the HOMO energy level and Eg efficient blue solution-processed OLEDs.
were -1.88 eV and -2.03 eV.
(a)
1.0
1.0
0.8
0.6
0.4
0.2
0.0
DV-CDBP
DV-MOC-DPS
M6
M9
M12
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
Wavelength (nm)
DV-CDBP
DV-MOC-DPS
300
400
500
600
700
Wavelength (nm)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
DV-CDBP
DV-MOC-DPS
P6
P9
P12
350
400
450
Wavelength (nm)
500
550
DV-CDBP
DV-MOC-DPS
300
400
500
Wavelength (nm)
600
700
Fig. 3 Absorption and fluorescence (inset) spectra of DV-CDBP, DV-MOC-DPS
and P6-P12 both in toluene (a) and in the film state (b).
To certify the TADF character of DV-MOC-DPS, the transient
photoluminescence (PL) decay curves of DV-MOC-DPS in toluene
were obtained. As Fig 4a shows, the signals display a fast decay with
a lifetime of 11 ns in toluene, which can be assigned to normal
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devices based on P6–P12 exhibit electroluminescence (EL) spectra
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4
103
102
101
DOI: 10.1039/C6TC02634F
(a)
10
similar to the corresponding PL spectra of their neat films.
DV-MOC-DPS
Furthermore, the emission peaks in the EL spectra based on P6-P12
show slight red-shifts, which is consistent with the PL spectra. This
suggests that the emission from the TADF unit becomes more
dominant with the increasing concentration of the TADF units.
Among these devices, the device with P9 as the EML exhibited the
best performance. It turned on at 5.3 V and achieved a maximum
brightness of 899 cd m-2 at 12 V. Its EQE–current density
characteristics are shown in Fig. 5c. The maximum EQE of this
device is 2.0%. Simultaneously, the maximum current efficiency of
this device is 1.6 cd/A and the maximum power efficiency is 0.9
lm/W (Fig. S5). The detailed performance is summarized in Table
S1. It is worth noting that the efficiency of P9-based device remains
at 1.3% at a brightness of 100 cd/m2, which can be attributed to a
reduced rate of triplet–singlet and triplet–triplet annihilation
resulting from the small triplet exciton decay lifetime.
103
102
101
50
100
Time (ns)
150
0
100
200
300
Time (s)
4
(b)10
P6
P9
P12
103
102
0
1
2
3
Time (s)
104
(c)
300 K
200 K
150 K
103
102
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (s)
Fig. 4 (a) Transient PL decay of DV-MOC-DPS in oxygen-free toluene and in
toluene (inset) at 300 K. (b) Transient PL decay of the cross-linked films. (c)
Transient PL decay of P9 at different temperatures.
To investigate the characters of OLEDs, we fabricated the devices
with the structures of indium tin oxide (ITO)/PEDOT:PSS (30 nm)/
P6–P12 (50 nm)/TPBi (40 nm)/CsCO3 (2 nm)/Al (100 nm), where
poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonic
acid)
(PEDOT:PSS) and TPBi serves as the hole-injection layer and the
electron-transporting layer, respectively. The films P6–P12 are
employed as the emissive layers (EML). A schematic energy level
diagram of these OLEDs is illustrated in Figure 5a. The energy level
of P9 is measured by the absorption spectra and CV (Fig. S4). P9
with the HOMO at 5.5 eV, it mean that there are negligible hole-
injection barriers at the PEDOT:PSS/EML junction. Fig. 5b shows
current density–voltage–luminance (J–V–L) curves of the devices.
The turn on voltage of all devices are 5.3 V. As shown in Fig. 5c, the
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4. Experimental
View Article Online
DOI: 10.1039/C6TC02634F
General information
All solvents and materials were used as received from commercial
1
sources without further purification. H NMR and 13C HMR spectra
were recorded on a BRUKER AMX 300 MHz and 500 MHz
instrument relative to Si(CH3)4 as internal standard. Molecular
masses were determined by matrix-assisted laser desorption-
ionization time-of-flight mass spectrometry (MALDI-TOF-MS)
(b) 103
500
400
300
200
100
0
using
a
BRUKER DALTONICS instrument, with α-cyano-
matrix. Absorption and
P6
P9
P12
hydroxycinnamic acid as
a
102
photoluminescence emission spectra of the target compounds were
measured using a SHIMADZU UV-2450 spectrophotometer and a
HORIBA FLUOROMAX-4 spectrophotometer, respectively. The
solid PL quantum efficiency was measured with an integrating
sphere under an excitation wavelength of 380 nm. Cyclic
voltammetry were performed on a CHI750C voltammetric analyzer
in CH2Cl2 solutions (10-3 M) (oxidation process) at a scan rate of
100 mV s−1 with a platinum plate as the working electrode, a silver
wire as the pseudo-reference electrode, and a platinum wire as the
101
100
4
6
8
10
12
14
16
Voltage (V)
101
(c)
100
10-1
10-2
10-3
counter
electrode.
The
supporting
electrolyte
was
1.0
0.8
0.6
0.4
0.2
0.0
tetrabutylammonium hexafluorophosphate (0.1 M) and ferrocene
was selected as the internal standard. Thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC) curves were
recorded with a Netzsch simultaneous thermal analyzer (STA)
system (STA 409PC) and DSC 2910 modulated calorimeter under a
dry nitrogen gas flow at a heating rate of 10 °C min−1. The cross-
linked films preparation as follows: In a general procedure, the
quartz plate substrates were precleaned carefully and treated by UV
ozone for 4 min. The solutions with the concentration of 10 mg mL−1
were spin coated onto the quartz plate substrate and baked at 200 °C
for 30 minutes.
P6
P9
P12
P6
P9
P12
300
400
500
600
700
Wavelength (nm)
101
102
Brightness (cd/m2)
103
Fig. 5 (a) The energy level diagrams for the devices based on P6–P12. (b) Current
density–voltage–luminance curves of the devices. (c) External quantum efficiency
versus luminance for the devices.
3. Conclusions
In conclusion, the thermally cross-linkable host and TADF materials,
named as DV-CDBP and DV-MOC-DPS, respectively, have been
designed and synthesized. Both of them show good thermal and
morphological stabilities. DV-CDBP is chosen to act as the host for
blue OLEDs due to its high triplet energy of 2.95 eV.
Simultaneously, DV-MOC-DPS shows the characteristic of TADF,
which enabled efficient exciton-harvesting via spin up-conversion
from T1 states to S1 states. By employing the P6-P12 as the emitters
in OLEDs, a blue device gained a maximum EQE of 2.0% with a
peak EL wavelength of 444 nm. Although the device performance
should be improvable by careful optimization, but more importantly,
these materials provide a promising strategy to develop highly
efficient solution-processed OLEDs.
Devices measurements and characterization
The ITO substrates were degreased in acetone and ethanol
consecutively in an ultrasonic bath before UV-ozone treatment for
10 minutes. A layer of 30 nm thick PEDOT:PSS was spin-coated
onto the ITO substrate and then baked at 120 °C for 30 minutes. The
mixed solution of DV-CDBP and DV-MOC-DPS was spin-coated
onto the PEDOT:PSS layer from a chlorobenzene solution. Another
baking at 200 °C for 30 minutes was conducted before spin-coating
the light emitting polymers. To enhance the electron injection into
the emitting layer, a layer of TPBi was thermally deposited onto the
films. Then, a layer of CsCO3/Al was thermally deposited onto the
films. The current-voltage-luminance characteristics and the EL
spectra were measured simultaneously by a customized software
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controlling a PR655 spectrascan spectrometer and a Keithley 2400 mixture was stirred for 3 h and then cooled to 0 °C. V4ie-wViAnrtyicllbe eOnnzlinyel
DOI: 10.1039/C6TC02634F
source measurement unit. The power efficiency and the external chloride (0.76 mL, 5.4 mmoL) was added drop-wise. The reaction
quantum efficiency were calculated by assuming a Lambertion mixture was stirred for 24 h at 60 °C and then quenched with water.
emission profile.
The aqueous layer was extracted with CH2Cl2. The combined
organic layers were washed with brine, dried with MgSO4 and
Materials
The 9,9'-(2,2'-dimethyl-[1,1'-biphenyl]-4,4'-diyl)bis(9H-carbazole) concentrated in vacuo. The crude material was purified using column
1
(CDBP) was synthesized according to the literature methods.38
Preparation of 4,4’-Bis(9-carbazole-3-carbaldchyde)-2,2’-
dimethylbiphenyl (1)
chromatography to produce a white solid (0.44 g, 32%). H NMR
(300 MHz, CDCl3, δ): 2.29 (s, 6H), 4.61 (s, 4H), 4.77 (s, 4H), 5,23-
5.29 (t, 2H), 5,74 (d, J= 10.5 Hz, 2H), 6.70-6.76 (m, 2H), 7.30-7.33
To a stirred solution of CDBP (5 g, 9.8 mmol) in chlorobenzene (t, 2H), 7.36 (d, J= 4.8 Hz, 4H), 7.41-7.54 (m, 18H), 8.16 (d, J= 4.2
(150 mL) and DMF (40 mL) was added phosphoryl chloride (25 mL, Hz, 4H); 13C NMR (300 MHz, CDCl3, δ): 71.54, 72.68, 76.74,
0.28 mol) drop-wise at r.t. under a nitrogen atmosphere. The reaction 77.00, 77.25, 109.90, 113.72, 120.01, 123.36, 124.27, 126.00,
mixture was stirred at 60 °C for 9 h and then poured into cracked ice. 126.28, 136.68, 136.95, 137.96, 140.08, 140.68, 141.30; MS
After neutralizing with K2CO3, the aqueous layer was extracted with (MALDI-TOF) [m/z]: C58H48N2O2: 805.03, found: 804.91. Anal.
CHCl3. The combined organic layers were washed with brine, dried calcd (%) for C58H48N2O2: C, 88.54; H, 6.01; N, 3.48. Found: C,
with MgSO4 and concentrated in vacuo. The crude material was 88.54; H, 6.01; N, 3.47.
purified was purified using column chromatography to produce a
white solid (1.78 g, 32%).1H NMR (500 MHz, CDCl3, δ): 2.32 (s,
Preparation of 3-bromo-9H-carbazole (3)
To a stirred solution of carbazole (10 g, 60 mmol) in DMF at room
6H), 7.41-7.43 (m, 2H), 7.50-7.58 (m, 12H), 8.00 (d, J= 8.5 Hz, 2H), temperature was slowly added NBS (10.7 g, 60 mL). After the
8.24 (d, J=8.0 Hz, 2H), 8.71 (s, 2H), 10.16 (s, 2H); 13C NMR (300 addition was completed the mixture was stirred for 24 h. Then, the
MHz, CDCl3, δ):76.57, 77.00, 77.42, 110.27, 120.74, 121.28, solution was poured into 250 mL water and extracted with CH2Cl2 (3
124.49, 127.02, 128.52, 130.98, 192.69; MS (MALDI-TOF) [m/z]: × 200 mL). The organic layer was dried by anhydrous Na2SO4 and
C40H28N2O2: 568.68, found: 569.80. Anal. calcd (%) for evaporated in vacuo. The product was isolated by silica gel column
C40H28N2O2: C, 84.48; H, 4.96; N, 4.93. Found: C, 84.67; H, 4.98; chromatography using petroleum ether/ethyl acetate as eluent to
N, 4.93.
afford a colorless solid (13.55 g, 92%).1H NMR (300 MHz, DMSO-
d6, δ): 7.09-7.21 (m, 1H), 7.35-7.54 (m, 5H), 8.09-8.19 (m, 1H), 8.37
(s, 1H); 13C NMR (300 MHz, DMSO-d6, δ): 111.35, 111.63, 111.82,
Preparation
of
4,4’-Bis(9-carbazole-3-methanol)-2,2’-
dimethylbiphenyl (2)
To a stirred solution of 3 (1.3 g, 2.3 mmol) in THF (50 mL) and 119.37, 121.12, 123.17, 126.77, 128.29, 138.84, 140.59; MS
ethanol (50 mL) was added NaBH4 (0.43 g, 11.2 mmol). The (MALDI-TOF) [m/z]: calcd for C12H8BrN: 246.11, found: 246.08.
reaction mixture was stirred for 24 h and then slowly added water. Anal. calcd (%) for C12H8BrN: C, 58.56; H, 3.28; N, 5.69. Found: C,
The solvent was removed in vacuo. 0.1 M NaOH aq. and CHCl3 58.56; H, 3.27; N, 5.69.
were added. The mixture was stirred and vacuum filtered, leaving 6
as a white solid (1.26 g, 97%).1H NMR (500 MHz, CDCl3, δ): 2.29
Preparation of 3-Methoxy-9H-carbazole (4)
3-Bromo-9H-carbazole (5 g, 20.32 mmol) was dissolved in DMF
(s, 6H), 4.90 (s, 4H), 5.30 (s, 2H), 7.31-7.34 (t, 2H), 7.45-7.53 (m, (100 mL) under N2, and then NaOMe/MeOH (40 wt%, 50 mL) and
14H), 8.16 (d, J= 10.5 Hz, 4H); 13C NMR (300 MHz, CDCl3, δ): CuI (3.82 g, 20 mmol) was added. The mixture was heated to 120 °C
76.57, 77.00, 77.42, 110.06, 119.35, 120.06, 120.38, 124.27, for 24 h. After cooling to room temperature, the solution was poured
128.30,130.83; MS (MALDI-TOF) [m/z]: C40H32N2O2: 572.71, into 150 mL water and extracted with CH2Cl2 (3 × 150 mL), dried
found: 571.65. Anal. calcd (%) for C40H32N2O2: C, 83.89; H, 5.63; over MgSO4, and evaporated in vacuo. The crude product was
N, 4.89. Found: C, 83.71; H, 5.61; N, 4.88.
Preparation of 4,4’-Bis[3-(((4-vinylbenzyl)oxy)methyl)-9-
carbazole]-2,2’-dimethylbiphenyl (DV-CDBP)
further purified using column chromatography to give 2 as a white
solid (3.4 g, 85%).1H NMR (300 MHz, DMSO-d6, δ): 3.89 (s, 3H),
7.06-7.18 (m, 2H), 7.37-7.54 (m, 3H), 7.72 (s, 1H), 8.12 (d, J= 9 Hz,
To a stirred solution of bis[4-(carbazole-3-ol)phenyl]sulfone (1.00 1H); 13C NMR (300 MHz, DMSO-d6, δ ): 56.05, 103.48, 111.41,
g, 1.80 mmol) in DMF (30 mL) was added NaH (0.13 g, 5.4 mmol) 112.03, 116.18, 118.40, 125.78,135.00, 140.84, 153.44; MS
at room temperature under a nitrogen atmosphere. The reaction (MALDI-TOF) [m/z]: calcd for C13H11NO: 197.24, found: 197.02.
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J. Name., 2013, 00, 1-3 | 7
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Journal of Materials Chemistry C
Page 8 of 10
ARTICLE
Journal Name
Anal. calcd (%) for C13H11NO: C, 79.17; H, 5.62; N, 7.10. Found: C, stirred for 3 h and then cooled to 0 °C. 4-VinylbenzylVciehwloArritidcele O(0n.l7in6e
79.17; H, 5.62; N, 7.07.
mL, 5.4 mmoL) was added drop-wise. ThDeOrIe:a1c0t.1io0n39/mCi6xTtCur0e26w34aFs
stirred for 24 h at 60 °C and then quenched with water. The aqueous
layer was extracted with CH2Cl2. The combined organic layers were
Preparation
of
bis[4-(3-methoxycarbazole)phenyl]sulfone
(MOC-DPS)
To a stirred solution of 3-Methoxy-9H-carbazole (1.5 g, 7.6 washed with brine, dried with MgSO4 and concentrated in vacuo.
mmol) in dehydrated dimethylformamide (DMF) at room The crude material was purified using column chromatography to
temperature was added sodium hydride (0.4 g, 16 mmoL). After the produce a white solid (0.44 g, 32%). 1H NMR (300 MHz, CDCl3, δ):
solution was stirred at room temperature for 30 min, bis(p- 5.18 (s, 4H), 5.24-5.29 (t, 2H), 7.74 (d, J= 10.8 Hz, 2H), 6.70-6.76
fluorophenyl)sulfone (0.75 g, 3.0 mmol) in dehydrated DMF (15 (m, 2H), 7.10 (d, J= 6.6 Hz, 2H), 7.28-7.31 (t, 2H), 7.39-7.47 (m,
mL) was added, following which the mixture was stirred at 100 °C 4H), 7.67 (s, 2H), 7.79 (d, J= 5.1 Hz, 4H), 8.05 (d, J= 4.5 Hz, 2H),
for an additional 1 h. After cooling, the mixture was poured into 300 8.23 (d, J= 5.1 Hz, 4H); 13C NMR (300 MHz, CDCl3, δ): 70.89,
mL of water, and the yellow precipitate was filtered and dried. The 76.73, 76.98, 77.23, 105.16, 109.72, 110.43, 114.05, 115.95, 120.53,
crude product was isolated by silica gel column chromatography 120.72, 123.95, 124.71, 126.43, 126.84, 134.99, 136.46, 136.74,
using petroleum ether/ethyl acetate as eluent to produce pale green 137.37, 140.41, 142.94, 154.09; MS (MALDI-TOF) [m/z]:
solid (1.56 g, 86%).1H NMR (300 MHz, DMSO-d6, δ ): 3.88 (s, 6H), C54H40N2O4S: 812.98, found: 812.82. Anal. calcd (%) for
7.01 (d, J= 10.5 Hz, 2H), 7.26-7.31 (t, 2H), 7.37-7.45 (m, 4H), 7.49 C54H40N2O4S: C, 79.78; H, 4.96; N, 3.45. Found: C, 79.76; H, 4.96;
(d, J= 8.4 Hz, 2H), 7.82 (s, 2H), 7.92 (d, J= 9 Hz, 4H), 8.26 (d, J= N, 3.44.
7.8 Hz, 2H), 8.34 (d, J= 8.1 Hz, 4H); 13C NMR (300 MHz, DMSO-
Acknowledgements
d6, δ): 56.15, 104.07, 110.36, 111.20, 115.61, 121.24, 123.85,
126.94, 130.14, 134.41, 138.93, 140.11, 142.49, 155.07; MS
(MALDI-TOF) [m/z]: C38H28N2O4S: 608.71, found: 608.01. Anal.
calcd (%) for C38H28N2O4S: C, 74.98; H, 4.64; N, 4.60. Found: C,
74.95; H, 4.64; N, 4.60.
We are grateful for the grants from the National Natural Science
Foundation of China (51103023 and 21173042), National Basic
Research Program China (2013CB932902). We are also thankful for
the support of the Scientific Research Foundation of Graduate
School of Southeast University (NO. YBJJ1631).
Preparation of bis[4-(carbazole-3-ol)phenyl]sulfone (5)
Notes and references
To a stirred solution of bis[4-(3-methoxycarbazole)phenyl]sulfone
(1 g, 1.6 mmol) in dehydrated dichloromethane at 0 °C was added
BBr3 (0.9 g, 3.6 mmoL). After the addition was completed the
mixture was stirred for 24 h. The reaction was quenched by methyl
alcohol. The solution was evaporated in vacuo. The crude product
was further purified using column chromatography to produce pale
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DOI: 10.1039/C6TC02634F
These thermally cross-linkable materials reported here provide a novel route toward highly
efficient solution-processed OLEDs.