Synthesis and Characterization of Dibenzo[a,d]cyclohepten-5-one Derivatives for Light-Emitting Diodes

Article abstract of DOI:10.1002/cjoc.201500322

Three novel dibenzo[a,d]cyclohepten-5-one derivatives containing hole-transporting groups were synthesized and characterized. These compounds exhibit good thermal stabilities. Single crystals of DBHO-TPA and DBHO-DPA were successfully grown from dichloromethane and their crystal structures were determined from X-ray diffraction data. Two molecules, DBHO-TPA and DBHO-DPA, have a nonplanar structure while seven-membered ring comprised in dibenzo[a,d]cyclohepten-5-one is not planar. Electrochemical properties of three compounds indicate that the different substituents on 3,7-positions of the dibenzo[a,d]cyclohepten-5-one derivatives have a small effect on the energy levels of the highest occupied molecular orbitals. The blue-green light-emitting diodes based on dibenzo[a,d]cyclohepten-5-one derivatives were fabricated. Three novel dibenzo[a,d]cyclohepten-5-one derivatives containing the hole-transporting groups were synthesized and characterized. Blue-green organic light-emitting diodes were fabricated based on these materials.

Full text of DOI:10.1002/cjoc.201500322

FULL PAPER
DOI: 10.1002/cjoc.201500322
Synthesis and Characterization of Dibenzo[a,d]cyclohepten-
-one Derivatives for Light-Emitting Diodes
5
,a
a,b
b
,b
Liping Wang,* Limin Wang, Jianyao Huang, and Gui Yu*
a
Department of Materials Physics and Chemistry, School of Materials Science and Engineering,
University of Science and Technology Beijing, Beijing 100083, China
Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China
b
Three novel dibenzo[a,d]cyclohepten-5-one derivatives containing hole-transporting groups were synthesized
and characterized. These compounds exhibit good thermal stabilities. Single crystals of DBHO-TPA and
DBHO-DPA were successfully grown from dichloromethane and their crystal structures were determined from
X-ray diffraction data. Two molecules, DBHO-TPA and DBHO-DPA, have a nonplanar structure while seven-
membered ring comprised in dibenzo[a,d]cyclohepten-5-one is not planar. Electrochemical properties of three
compounds indicate that the different substituents on 3,7-positions of the dibenzo[a,d]cyclohepten-5-one derivatives
have a small effect on the energy levels of the highest occupied molecular orbitals. The blue-green light-emitting
diodes based on dibenzo[a,d]cyclohepten-5-one derivatives were fabricated.
Keywords dibenzo[a,d]cyclohepten-5-one derivatives, photoluminescent properties, single crystals, blue-green
emission, light-emitting diodes
Introduction
one of the major challenges.
Aromatic amines are known as strong electron do-
Organic light-emitting diodes (OLEDs) have at-
tracted considerable interest due to their promising ap-
plications in full-color flat-panel displays and solid-state
nors or hole transporting materials for OLED de-
[1,21,22]
vices.
Functionalization of these molecules was
investigated for various applications. trans-4,4′-Bis(di-
[
1-4]
lighting sources.
Luminescent materials are the most
arylamino)stilbene derivatives are excellent fluorescent
crucial factors affecting electroluminescent (EL) prop-
erties of the OLED devices.
[23,24]
materials,
whereas their ready photoisomerization
[
5-10]
In most applications,
from trans- to cis-configuration significantly limits their
emissive materials with excellent all-round properties
are required for OLED devices. To achieve high-per-
formance OLED devices, the organic luminescent mate-
rials usually need to meet some requirements, such as
good thermal stabilities, excellent film-forming proper-
ties, good carrier injection/transport abilities, appropri-
ate energy levels, and outstanding photoluminescent (PL)
characteristics, etc. During the past decades, great ef-
forts were focused on the development of novel EL ma-
[25,26]
applications in OLED.
To prevent the configuration
transfer through photoisomerization, we design a series
of dibenzo[a,d]cyclohepten-5-one derivatives with a
seven-membered ring which confines the cis-stilbene
into a cyclic framework through a carbonyl group.
Three novel dibenzo[a,d]cyclohepten-5-one derivatives
with hole-transporting groups were synthesized. Crystal
structures of DBHO-TPA and DBHO-DPA indicate
that the seven-membered ring contained in dibenzo-
[11-15]
terials.
Organic molecules with conjugated π-elec-
[
a,d]cyclohepten-5-one is not planar. Thermal stability,
tron systems have been extensively studied and demon-
strated as ideal materials for applications in OLEDs in
electrochemical property, and photophysical character-
istics of these three compounds were studied. In addi-
tion, blue-green OLED devices based on DBHO-TPA,
DBHO-DPA, and DBHO-C were fabricated.
[16-20]
recent years.
Luminescent properties and charge
carrier transporting characteristics of a conjugated mole-
cule can be tuned by modification of its molecular
structure, which may provide valuable routes to con-
struct new materials with excellent all-round properties.
However, development of luminescent materials with
excellent charge carrier transporting abilities remains
Experimental
Chemicals and instruments
1,3-Dibromo-1,3,5-triazine-2,4,6-trione (DBI), 10,
*
E-mail: lpwang@mater.ustb.edu.cn; yugui@iccas.ac.cn
Received April 21, 2015; accepted June 9, 2015; published online August 12, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500322 or from the author.
948
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 948—954

Synthesis and Characterization of Dibenzo[a,d]cyclohepten-5-one Derivatives
1
1-dihydro-dibenzo[a,d]heptene-5-one, n-BuLi, and
for 4 h. After cooling to room temperature, the mixture
was poured in a solution containing CH Cl , MeOH,
and water under stir for 12 h followed by extraction.
The organic phase was dried over anhydrous MgSO . A
t-BuONa were of 97%－99% purity and purchased
from Alfa. 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane, 4-bromotriphenylamine, and Pd(dba) were
of 97%－99% purity and purchased from Aldrich. All
other regular reagents were of analytical grade and
commercially available from local chemical companies.
2
2
4
yellow solid, compound 2 (490 mg, 42.3%), was finally
obtained after filtration, evaporation, and recrystalliza-
1
tion with CH
2
Cl
2
. H NMR (300 MHz, CDCl
3
) δ: 8.35
1
13
H NMR and C NMR spectra were collected with a
(s, 2H), 7.74 (d, J＝8.22 Hz, 2H), 7.41 (d, J＝8.31 Hz,
＋
Bruker AV400 or Bruker DMX300 spectrometer with
tetramethylsilane (TMS) as an internal standard. HRMS
were obtained on a Waters TOF-MS spectrometer for
matrix assisted laser desorption ionization with time-of-
flight mode (MALDI-TOF-MS). Thermogravimetric
analysis (TGA) was performed on a Perkin-Elmer
thermogravimeter (Model TGA7) under a dry nitrogen
atmosphere at a heating rate of 10 ℃•min . Cyclic
voltammetry (CV) experiments were carried out on an
electrochemistry workstation (CHI660A, Chenhua
2H), 7.02 (s, 2H). EI-MS m/z (%): 364 (M , 100%).
3,7-Bis-4-(diphenylaminophenyl)-dibenzo[a,d]-
cyclohepten-5-one (DBHO-TPA) The compounds 2
(48.74 mg, 0.135 mmol) and 4-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)triphenylamine (100 mg, 0.27
−
1
mmol) were dissolved in THF, and then 2 mol•L of
CO was added. Pd(PPh (7.8 mg) was added into
the solution under a N atmosphere. The solution was
K
2
3
3 4
)
−1
2
refluxed at 70 ℃ for 48 h. After that, solvent was
evaporated under vacuum. The sediment was dissolved
Shanghai) using an anhydrous and N
2
saturated solution
in CH
inorganic residues. The organic phase was dried over
anhydrous MgSO . DBHO-TPA, a yellow solid (57 mg,
2 2
Cl and extracted with a NaCl solution to remove
−1
of 0.1 mol•L
tetrabutylammoniumhexafluorophos-
phate in dichloromethane as an electrolyte and an
Ag/AgCl electrode as a reference electrode. UV-visible
4
61.1%), was finally obtained after filtration, evaporation,
and chromatography on silica gel with a mixed solvent
(
UV-vis) absorption and PL spectra were performed on
1
a Hitachi U-3010 spectrometer and a Hitachi F-4500
luminescence spectrometer, respectively.
of petroleum ether and acetylacetate. H NMR (300
3
MHz, CDCl ) δ: 8.45 (d, J＝1.76 Hz, 2H), 7.81 (d, J＝
The DBHO-TPA and DBHO-DPA single crystals
1.92 Hz, 2H), 7.56 (d, J＝8.36 Hz, 6H), 7.22－7.27 (m,
1
3
were grown from dichloromethane (CH
2
Cl
2
). X-ray
8H), 7.11－7.14 (m, 12H), 7.00－7.05 (m, 6H);
C
crystallographic data were obtained on a Bruker Smart
CCD diffractometer with graphite-monochromated Mo
Kα radiation (λ＝0.71073 Å). The data were collected at
NMR (400 MHz, CDCl ) δ: 192.7, 147.8, 147.4, 140.8,
138.6, 133.6, 133.1, 131.6, 130.9, 129.7, 129.3, 127.9,
127.7, 124.6, 123.5, 123.1. HRMS (EI) calcd for
3
1
73 K for DBHO-TPA and DBHO-DPA. The structure
C
51
H
36
N
2
O: 692.28; found 692.2834.
3,7-Bis-(diphenylamino)-dibenzo[a,d]cyclohepten-
5-one (DBHO-DPA) The compounds 2 (245 mg,
.677 mmol) and diphenylamine (230 mg, 1.36 mmol)
was solved by direct method with SHELXL97 program
and refined with full-matrix least-squares methods.
0
Synthesis and characterization of intermediates and
target molecules
were dissolved in toluene. t-BuONa (146.4 mg, 1.52
mmol) was added into the solution and the mixture was
3
,7-Dibromo-10,11-dihydro-dibenzo[a,d]cyclohep-
stirred at room temperature for 0.5 h under a N
phere. Subsequently, Pd (dba) (19.55 mg, 0.03 mmol)
and P(t-Bu) (1 mL) were added and the solution was
refluxed at 100 ℃ for 16 h. After that, the solvent was
evaporated under vacuum. The sediment was dissolved
in acetylacetate and extracted with a NaCl solution to
remove inorganic residues. The organic phase was dried
over anhydrous MgSO . DBHO-DPA, a light yellow
solid (122 mg, 33.4%), was finally obtained after chro-
matography on silica gel with a mixed solvent of petro-
leum ether and acetylacetate. H NMR (300 MHz,
2
atmos-
ten-5-one (1) 10,11-Dihydro-dibenzo[a,d]cyclohep-
2
3
ten-5-one (5.86 g, 28.16 mmol) was dissolved in con-
centrated sulfuric acid, then was added dropwise to ob-
tained solution DBI (8.021 g, 28.16 mmol), and the so-
lution was stirred overnight. After reaction, the mixture
was poured in icy water to obtain a milky solution, to
which an appropriate amount of NaOH solution was
added for the neutralization of unreacted sulfuric acid.
The neutralized mixture was transferred to CH
extraction to remove inorganic residues. The organic
phase was separated, and dried over anhydrous MgSO
3
4
2
Cl
2
for
1
4
.
CDCl ) δ: 7.82 (s, 2H), 7.35 (t, J＝6.76 Hz, 2H), 7.24 (t,
3
Finally, the crude product was filtered, evaporated, and
J＝5.64 Hz, 10H), 7.09 (d, J＝8.00 Hz, 8H), 7.03 (t,
J＝7.12 Hz, 4H), 6.86 (d, J＝1.6 Hz, 2H); C NMR
1
3
chromatographed on silica gel to obtain the product 1
1
(
2.355 g, 23%), a light yellow solid. H NMR (400 MHz,
(400 MHz, CDCl ) δ: 191.4, 148.3, 147.2, 139.0, 132.4,
3
CDCl
3
) δ: 8.13 (d, J＝1.94 Hz, 2H), 7.54－7.55 (m, 2H),
129.9, 129.7, 129.3, 126.3, 125.2, 124.0, 122.8. HRMS
7
3
.11 (d, J＝8.12 Hz, 2H), 3.14 (s, 4H). EI-MS m/z (%):
(EI) calcd for C H N O: 540.22; found 540.2208.
3
9
28
2
＋
66 (M , 100%).
,7-Dibromo-dibenzo[a,d]cyclohepten-5-one (2)
Compound 1 (1.165 g, 3.2 mmol), PCl (1.47 g, 7.04
mmol), and POCl (2.88 mL) were added and mixed in
a three-necked flask. The mixture was stirred and heated
3,7-Di(carbazo-9-yl)-dibenzo[a,d]cyclohepten-5-
one (DBHO-C) The compound 2 (245 mg, 0.677
mmol) and carbazole (227 mg, 1.36 mmol) were dis-
solved in toluene. t-BuONa (146.4 mg, 1.52 mmol) was
added into the solution and the mixture was stirred at
3
5
3
Chin. J. Chem. 2015, 33, 948—954
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949

Wang et al.
FULL PAPER
room temperature for 0.5 h under a N
Subsequently, Pd(dba) (19.55 mg, 0.03 mmol) and
2
2
atmosphere.
4140B semiconductor parameter analyzer. All of the
measurements were performed under ambient atmos-
phere at room temperature.
P(t-Bu) (1 mL) were added and the solution was re-
fluxed at 100 ℃ for 16 h. After that, the solvent was
evaporated under vacuum. The sediment was dissolved
in acetylacetate and extracted with a NaCl solution to
remove inorganic residues. The organic phase was dried
Results and Discussion
Synthesis of dibenzo[a,d]cyclohepten-5-one deriva-
tives
over anhydrous MgSO
200 mg, 55.1%), was finally obtained after chromatog-
raphy on silica gel with a mixed solvent of petroleum
4
. DBHO-C, a light yellow solid
(
The synthetic routes of the novel dibenzo[a,d]cy-
clohepten-5-one derivatives are shown in Scheme 1.
The compound 1 was achieved by a bromination reac-
tion of 10,11-dihydro-dibenzo[a,d]cyclohepten-5-one
using DBI as a bromination reagent in concentrated
sulfuric acid. The obtained diboronic compound 1 was
1
ether and acetylacetate. H NMR (300 MHz, CDCl
.55 (s, 2H), 8.14 (t, J＝7.65 Hz, 4H), 7.89 (d, J＝13.23
Hz, 4H), 7.49 (t, J＝4.59 Hz, 4H), 7.42 (m, 4H), 7.32 (d,
3
) δ:
8
1
3
J＝6.12 Hz, 2H), 7.24 (d, J＝13.35 Hz, 4H); C NMR
400 MHz, CDCl ) δ: 190.8, 140.5, 139.7, 138.7, 133.9,
33.2, 131.4, 130.3, 128.3, 126.4, 124.0, 120.6, 109.8.
MS (EI) calcd for C39 O: 536.19; found 536.2.
(
3
5 3
treated with PCl and POCl to obtain the compound 2
1
with a yield of 42.3%. The Suzuki coupling reaction
between 2 and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)triphenylamine was employed to give the
compound DBHO-TPA in a yield of 61.1%. 4-(4,4,5,5-
Tetramethyl-1,3,2-dioxaborolan-2-yl)triphenylamine
24 2
H N
Fabrication of LED devices
To investigate the electroluminescent properties of
the compounds DBHO-TPA, DBHO-DPA, and
DBHO-C, light-emitting diodes were fabricated with a
structure of ITO/NPB (25 nm)/dibenzo[a,d]cyclohepten-
[21]
synthesis was based on literature procedure.
The
compound DBHO-DPA was synthesized by a Pd cata-
lyzed reaction of 2 with diphenylamine in the presence
of Pd (dba) and P(t-Bu) in a yield of 33.4%. The
5
3
-one derivatives (50 nm)/Alq (20 nm)/LiF (1 nm)/Al
2
3
3
(
100 nm), where indium tin oxide (ITO) and Al were
compound DBHO-C was obtained in a similar reaction
between 2 and carbazole in a yield of 55.1%. The prod-
ucts DBHO-TPA, DBHO-DPA, and DBHO-C were
purified by column chromatography on silica gel and/or
train vacuum sublimation. The products were character-
used as a cathode and an anode, respectively, LiF is a
modification layer of the anode; N,N′-diphenyl-N,N′-
bis(1-naphenyl)-1,1′-biphenyl-4,4′-diamine (NPB) and
3
Alq were used as a hole and electron transport material,
1
13
respectively. The emitting area of the EL devices was 4
ized by H NMR, C NMR, and high-resolution ma-
trix-assisted laser desorption ionization time-of-flight
mass spectrometry (see Figures S1－10).
2
mm . The organic layers were evaporated by means of a
conventional vacuum vapor deposition under a vacuum
−4
of 2×10 Pa. Finally, a thin layer of electron injec-
tion-facilitating LiF was introduced, followed by the
deposition of aluminum cathode. The thickness of the
thin films was monitored by a quartz crystal oscillator
placed near the substrate and was calibrated ex situ by
an Ambios Technology XP-2 surface profilometer. EL
spectra and brightness were recorded on a Photo Re-
search 650 spectra scan colorimeter. Current-voltage
characteristics were measured with a Hewlett-Packard
Crystal structures
The compounds DBHO-TPA, DBHO-DPA, and
DBHO-C can be readily dissolved in CH
acterize the crystal structure, single crystals were ob-
tained from CH Cl solution using solvent volatilization
2 2
Cl . To char-
2
2
method. The DBHO-TPA and DBHO-DPA single
crystals are yellow plate-like and light yellow needle-
like ones, respectively. However, single crystal of
Scheme 1 Synthetic routes of the compounds DBHO-TPA, DBHO-DPA, and DBHO-C
H
O
N
O
2 4
H SO
3 5
POCl /PCl
+
N
N
5 o
2
C
12 h
Br
Br
Br
Br
Br
Br
O
2
O
O
O
1
Ar =
N
DBHO-TPA
O
Pd(PPh
3
)
4
/K
2
CO
3
Ar
B
2
+
Ar
Ar
O
o
O
O
THF, 70 C, 48 h
N
N
Ar =
Ar =
DBHO-DPA
DBHO-C
t-BuONa
Ar
H
2
+
Pd (dba) /P(t-Bu)
3
2
3
Ar
Ar
o
toluene, 100 C, 16 h
950
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 948—954

Synthesis and Characterization of Dibenzo[a,d]cyclohepten-5-one Derivatives
compound DBHO-C was not available using the same
method. Crystal data of DBHO-TPA and DBHO-DPA
are summarized in Table 1, and the selected bond
lengths and torsion angles are listed in Table 2. The
crystal structures of compounds DBHO-TPA and
DBHO-DPA are shown in Figure 1. Both compounds,
DBHO-TPA and DBHO-DPA, are crystallized in a
monoclinic system with a space group P2(1)/c. These
molecules show a C2 rotational symmetry and the sev-
en-membered ring comprised in dibenzo[a,d]cyclo-
hepten-5-one is not planar. The structure of dibenzo-
＜DBHO-C (419.7 ℃).
Table 1
Summary of crystal data for DBHO-DPA and
DBHO-TPA, including data collection and refinement details
DBHO-DPA DBHO-TPA
Empirical formula
C
39
H
28
N
2
O
51 36 2
C H N O
M
r
540.63
692.82
Crystal system
Space group
a/Å
monoclinic
P2(1)/n
16.375(3)
7.4998(15)
23.543(5)
90
monoclinic,
P2(1)/c
7.8523(16)
46.778(9)
9.7495(19)
90
[
a,d]cyclohepten-5-one in the compounds DBHO-TPA
b/Å
and DBHO-DPA shows a similar torsional degree with
C10-C11-C12-C13 torsion angles of 13.85°－15.12°,
C11-C12-C13-C4 torsion angles of 177.51°－178.79°,
C1-C12-C13-C5 torsion angles of 172.39°－177.53°,
and C12-C13-C5-O torsion angles of 151.33°－151.83°.
Therefore, these two molecules DBHO-TPA and
DBHO-DPA exhibit a nonplanar molecular structure.
The longest and shortest C － C bond lengths of
dibenzo[a,d]cyclohepten-5-one were obtained in 2,4,6-
cyclo-heptatriene-1-one ring and the corresponding data
of bond lengths are 1.487－1.507 Å for C5－C14 and
C13－C5 (single) bonds and 13.41－1.356 Å for C10－
C11 (double) bond.
c/Å
α/(°)
β/(°)
106.75(3)
90
92.10(3)
90
γ/(°)
3
V/Å
2768.5(10)
4
3578.7(12)
4
Z
F(000)
1136
1456
−
3
D(calcd)/(Mg•m )
μ/mm−
1.297
1.286
1
0.078
0.076
Temp./K
λ/Å
293(2)
113(2)
0.71073
2.60－25.02
R1＝0.0532
0.71073
1.74－25.02
R1＝0.0514
2
θ range/(°)
Final R indices [I＞2σ(I)]
R indices (all data)
wR ＝0.1178 wR ＝0.1232
2
2
R1＝0.0797
R1＝0.0648
wR ＝0.1319 wR ＝0.1311
2
2
2
Goodness-of-fit on F
1.045
1.048
Table 2 Selected bond lengths and angles for the compounds
DBHO-DPA and DBHO-TPA
a
Structural parameter
C5－C14
DBHO-DPA
1.493(3)
1.412(3)
1.451(3)
1.356(3)
1.454(3)
1.411(3)
1.487(3
1.412(3)
1.385(3)
1.396(3)
1.390(3)
1.399(3)
1.229(2)
15.12
DBHO-TPA
1.507(2)
1.410(2)
1.450(2)
1.341(2)
1.445(2)
1.415(2)
1.502(2)
1.407(2)
1.360(3)
1.407(3)
1.401(2)
1.405(2)
1.223(2)
13.85
C14－C15
C15－C10
C10－C11
C11－C12
C12－C13
Figure 1 Crystal structures of the compounds DBHO-DPA and
DBHO-TPA.
C13－C5
C12－C1
C1－C2
Thermal stabilities and electrochemical properties
C2－C3
The thermal stabilities of the three compounds
DBHO-TPA, DBHO-DPA, and DBHO-C were inves-
tigated by thermogravimetric analysis (TGA). The TGA
scans for the three dibenzo[a,d]cyclohepten-5-one de-
rivatives are shown in Figure 2. All compounds reveal
excellent thermal stabilities with a decomposition tem-
C3－C4
C4－C13
C5－O
C10－C11－C12－C13
C11－C12－C13－C4
C1－C12－C13－C5
178.79
177.51
d
perature (T ) higher than 370 ℃. The substituents on
177.53
172.39
the 3,7-positions of dibenzo[a,d]cyclohepten-5-one de-
rivatives have a large effect on the decomposition tem-
C12－C13－C5－O
151.33
151.83
a
perature with a 5% weight loss. T
d
increases in the order
Torsion angles are reported in degrees, while bond lengths are in
angstroms.
of DBHO-DPA (338.9 ℃)＜DBHO-TPA (413.9 ℃)
Chin. J. Chem. 2015, 33, 948—954
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951

Wang et al.
FULL PAPER
ents with hole-transporting properties, (4-diphenyl-
aminophenyl, diphenylamino, and carbazo-9-yl groups),
on the 3,7-positions of dibenzo[a,d]cyclohepten-5-one
derivatives have insignificant effect on the HOMO en-
ergy levels.
1.0
0.8
0.6
0.4
0.2
Absorption and photoluminescent properties
Figure 4 shows absorption and PL spectra of the
compounds DBHO-TPA, DBHO-DPA, and DBHO-C
in CH Cl solution. Upon UV excitation, the three
DBHO-TPA
DBHO-DPA
DBHO-C
2
2
compounds show similar blue-green emission color with
emission maxima in the range of 490－506 nm. The
full-width at half-maximum (FWHM) for each individ-
ual emission is from 68 to 84 nm. The maximum ab-
sorption locates at 379, 392, and 342 nm for compounds
DBHO-TPA, DBHO-DPA, and DBHO-C, respectively.
In comparison with DBHO-TPA, the compound
DBHO-DPA displays an almost the same main emis-
sion peak, whereas it exhibits a more narrow emission
accompanied by a shoulder peak at 530 nm. However,
the absorption and emission maximum of DBHO-C
shows a 37 and 12 nm blue-shift, respectively, com-
pared with those of DBHO-TPA. Figure 5a shows PL
spectra of the DBHO-TPA, DBHO-DPA, and
DBHO-C thin films. Upon UV-light irradiation, the
DBHO-TPA, DBHO-DPA, and DBHO-C thin films
display a blue-green emission with an emission peak at
0
200
400
600
o
Temperature/ C
Figure 2 TGA curves of the compounds DBHO-TPA, DBHO-
DPA, and DBHO-C.
To investigate the feature of charge injection, the
electrochemical properties of the compounds are studied
by cyclic voltammetry (CV). The redox performance
was probed in a three-electrode cell setup in a 0.1
mol•L tetrabutylammoniumhexafluorophosphate
Bu NPF ) supporting electrolyte in anhydrous CH Cl
2
with Ag/AgCl reference electrodes. Figure 3 shows the
cyclic voltammograms of compounds DBHO-TPA,
DBHO-PA, and DBHO-C measured at room tempera-
ture. The three compounds display strong and reversible
oxidation processes in a voltage range of 0.6－1.4 V,
indicating that they might be operated as hole trans-
porting materials. The compounds DBHO-TPA and
DBHO-C show one reversible anodic redox couples at
−
1
(
4
6
2
5
02－507 nm. The three compounds have similar PL
spectra with almost the same main emission peaks in
solution and thin films, indicating that there are weak
intermolecular interactions in thin films.
1
.04 and 1.06 eV (E1/2), respectively. However, the
compound DBHO-DPA exhibits two reversible anodic
redox couples at 0.89 and 1.11 eV (E1/2). In addition,
almost the same onset potentials for oxidation were ob-
tained at 0.80－0.88 eV for the three compounds. Ac-
cording to the equation of EHOMO＝−e(Eonset ＋4.4) eV,
energy levels of the highest occupied molecular orbitals
DBHO-TPA
1
.0
.8
.6
0.4
.2
.0
1.0
0.8
0.6
0.4
0.2
0.0
DBHO-DPA
DBHO-C
0
ox
0
(HOMO) were calculated to be 5.28 eV for DBHO-
TPA, 5.20 eV for DBHO-DPA, and 5.23 eV for
DBHO-C. The above results indicate that the substitu-
0
0
DBHO-TPA
DBHO-DPA
DBHO-C
3
00 350 400 450 500 550 600 650
Wavelength/nm
Figure 4 UV-vis absorption and PL spectra of the compounds
2 2
DBHO-TPA, DBHO-DPA, and DBHO-C in CH Cl solution.
Molecular orbitals
To provide more insight into the molecular orbitals
and electronic structures of three dibenzo[a,d]cyclo-
hepten-5-one derivatives, the quantum chemical calcu-
lations for the three compounds were carried out by
density functional theory (DFT) calculations, using the
0.0
0.4
0.8
1.2
1.6
Potential/V
[27]
Gaussian 03 program at the B3LYP 6-31G* level.
Figure 3 Cyclic voltammogram curves of the compounds
DBHO-TPA, DBHO-DPA, and DBHO-C.
Figure 6 shows molecular orbital amplitude plots of the
LUMOs and HOMOs of the compounds DBHO-TPA,
952
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 948—954

Synthesis and Characterization of Dibenzo[a,d]cyclohepten-5-one Derivatives
1
.0
.8
.6
.4
.2
.0
1.0
0.8
0.6
0.4
0.2
0.0
DBHO-TPA
DBHO-DPA
DBHO-C
DBHO-TPA
DBHO-DPA
DBHO-C
0
0
0
0
0
450
500
550
600
650
450
500
550
600
650
700
Wavelength/nm
Wavelength/nm
Figure 5 PL spectra of the compounds DBHO-TPA, DBHO-DPA, and DBHO-C in thin films, and EL spectra of the OLED devices
based on the three compounds.
DBHO-DPA, and DBHO-C. For the DBHO-TPA
molecule, HOMOs mainly arise from the whole mole-
cules whereas LUMOs are mainly localized on a diben-
zo[a,d]cyclohepten-5-one. Similar results were observed
for the HOMOs and LUMOs of DBHO-DPA and
DBHO-C. The energy levels of HOMOs and LUMOs
for the three dibenzo[a,d]cyclohepten-5-one derivatives
are also depicted in Figure 5. The calculated HOMO and
LUMO energy levels of DBHO-TPA are −4.87 and
ITO/NPB/dibenzo[a,d]cyclohepten-5-one derivatives/
lq /LiF/Al, where NPB and Alq were used as hole- and
3
3
electron-transporting layers, respectively. The combina-
tion electrode of a thin LiF layer and Al layer was dem-
onstrated to be an efficient cathode. Figure 5b shows the
EL spectra of the devices. The OLED devices based on
DBHO-TPA and DBHO-C exhibit a blue-green emis-
sion and show EL spectra similar to the PL spectra of
the corresponding thin films. Meanwhile, no emission
−
1.75 eV, respectively. The different substituents on the
,7-positions of dibenzo[a,d]cyclohepten-5-one have a
from either NPB or Alq
cates that NPB and Alq
3
was observed. This result indi-
only play a carrier transporting
3
3
role in the OLED devices based on DBHO-TPA and
DBHO-C, and the EL emission originates from
DBHO-TPA or DBHO-C. However, EL spectrum of
DBHO-DPA displays an emission peak at 525 nm sim-
large effect on the HOMO and LUMO energy levels. To
compare with DBHO-TPA containing diphenylamino-
phenyl groups, DBHO-DPA with diphenylamino groups
shows higher HOMO and LUMO energy levels whereas
DBHO-C with carbazo-9-yl groups displays lower ones.
ilar to PL emission of Alq
3
, indicating that emission may
accompanied by
come from the main emission of Alq
3
the weak emission of DBHO-DPA. Figure 7 shows the
luminous efficiency curves of the OLED devices based
on the compounds DBHO-TPA, DBHO-DPA, and
DBHO-C. The EL devices based on DBHO-TPA ex-
−2
hibit a brightness of 1460 cd•m with a maximum cur-
−
1
rent efficiency of 0.91 cd•A . However, both the
1.0
.
0.5
DBHO-TPA
DBHO-DPA
DBHO-C
Figure 6 Molecular orbital amplitude plots of the LUMO and
HOMO of the compounds DBHO-TPA, DBHO-DPA, and
DBHO-C.
0.0
0
50
100
150
2
200
-
.
Current density/(mA cm )
Electroluminescent properties
To investigate EL properties, OLED devices were
fabricated using compounds DBHO-TPA, DBHO-DPA,
and DBHO-C as the emissive layer with a structure of
Figure 7 The luminous efficiency curves of the OLED devices
based on the compounds DBHO-TPA, DBHO-DPA, and
DBHO-C.
Chin. J. Chem. 2015, 33, 948—954
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
953

Wang et al.
FULL PAPER
OLEDs based DBHO-DPA and DBHO-C show device
performance lower than that of the devices based on
DBHO-TPA. The DBHO-DPA-based devices display a
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−2
maximum brightness of 436 cd•m and a maximum
−1
current efficiency of 0.29 cd•A , whereas the DBHO-
C-based ones show a maximum brightness of 688
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cd•m with a maximum current efficiency of 0.56
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cd•A . For the three compounds, difference of EL
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[
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ferent substituents with hole-transporting properties.
Single crystals of DBHO-TPA and DBHO-DPA were
obtained from CH
2
Cl
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and crystallized in a monoclinic
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and photoluminescence. Properties of the OLED devices
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(Cheng, F.)
954
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 948—954