1
80
T. Yu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 109 (2013) 179–185
OLEDs doped phosphorescent metal complexes, both singlet
were measured by using an X-4 microscopic melting point appara-
tus made in Beijing Taike Instrument Limited Company, and the
thermometer was uncorrected.
and triplet excitons can be harvested for light owing to intersystem
crossing of the singlet excited states to the triplet states, can exhi-
bit high external quantum efficiency (EQE) of >20% [10–12], which
is much higher than the theoretical limit of 5% for fluorescent
OLEDs. In the phosphorescent metal complexes, cyclometalated
iridium complexes are the most valuable emitting materials due
to their high quantum efficiency, brightness, color diversity and
short excited-state lifetime.
Synthesis and characterization of (4-(9H-carbazol-9-
0
yl)phenyl)methyl-2-(2 -pyridyl)benz-imidazole (L)
The synthetic routes of ligand L are shown in Scheme 1.
4-(9H-carbazol-9-yl)benzaldehyde: 0.090 g (3.7 mol%) of
Although Cu(I) complexes have relatively low quantum yields as
compared with the rare and noble metal complexes, phosphorescent
Cu(I) complexes have attracted much attention as a new class of
optoelectronic materials in chemical sensors, probes of biological
systems and OLEDs because of their advantages of less toxic, low
cost, stable supply of copper metal and environmental friendliness
3 2
P(t-Bu) and 0.035 g (1.3 mol%) Pd(OAC) were added to 80 mL de-
gassed toluene, followed by 2.5 g (0.0135 mol) of 4-bromobenzal-
dehyde and 2.000 g (0.0120 mol) of 9H-carbazole and 4.150 g
(0.0300 mol) anhydrous K
to 115 °C for 24 h. The solvent was removed under vacuum, and
150 mL CH Cl was added. The material was washed with
2 ꢂ 50 mL 20% NaOH, washed with 1 ꢂ 50 mL brine, and dried with
anhydrous MgSO . The solvent was removed under vacuum, and
2 3
CO . The reaction mixture was heated
2
2
[
13–18]. Recently, some OLEDs doped phosphorescent Cu(I)
complexes realized efficiencies comparable to those doped Ir(III)
complexes [17,19]. Wada and co-workers [19] reported a high
efficiency OLEDs containing [Cu(QuTz)(DPEphos)]BF4 (QuTz = 2-
4
the residue was purified by column chromatography on silica gel
using ethyl acetate/petroleum ether (1:20, v/v) as the eluent to
(
5-tetrazolyl)quinoline, DPEphos = bis(2-(diphenylphosphino) phe-
give 4-(9H-carbazol-9-yl)benzaldehyde as white powder (2.65 g,
1
nyl)ether) which displayed efficient luminescence with EQE = 7.4%.
The OLEDs using a highly emissive dinuclear Cu(I) complex
3
81.7%). m.p.: 156–158 °C. H NMR (CDCl , d, ppm): 10.13 (s, 1H,
ACHO), 8.16 (dd, J = 8.5 Hz, 4H), 7.81 (d, J = 8.0 Hz, 2H), 7.52 (d,
J = 8.0 Hz, 2H), 7.45 (t, J = 7.6 Hz, 2H), 7.34 (t, J = 8.0 Hz, 2H).
(4-(9H-carbazol-9-yl)phenyl)methanol: 2.200 g (0.008 mol) of
4-(9H-carbazol-9-yl)benzaldehyde, 0.153 g (0.5 eq, 0.004 mol) of
t
t
ꢀ
[
(PNP- Bu)Cu]
2
(PNP- Bu = bis(2-diisobutylphosphino-4-tert-
butylphenyl)amido) exhibited a maximum external quantum effi-
ciency of 16.1% [17]. Hashimoto et al. [16] reported on the photo-
physical properties of a series of highly emissive three-coordinate
Cu(I) complexes containing
(
vices with (dtpb)CuBr as dopant exhibited bright green lumines-
cence with a current efficiency of 65.3 cd/A and a maximum
external quantum efficiency of 21.3%. These examples were indi-
cated that the inexpensive and non-toxic Cu(I) complexes could be
used as promising candidates for OLEDs applications.
NaBH
THF and 37 mL MeOH. The solution was stirred for 16 h at room
temperature. The reaction mixture was poured into 100 mL H O,
and then neutralized with 3 M HCl. The solution was extracted
with CH Cl
(3 ꢂ 50 mL) and then dried over anhydrous MgSO
After filtering, the solvent was removed under vacuum, and the
residue was taken up in 10 mL hot CH Cl . Hexanes were added
4
, and 1.2 mL 20% NaOH were added to a mixture of 37 mL
a chelating bisphosphine ligand
dtpb = 1,2-bis(o-ditolylphosphino)benzene), and the best OLED de-
2
2
2
4
.
2
2
dropwise until (4-(9H-carbazol-9-yl)phenyl)methanol precipitated
Herein two new mononuclear Cu(I) complexes containing hole-
out. 1.83 g of fine needles of the alcohol product was obtained. The
transporting carbazoly moiety, [Cu(L)(DPEphos)](BF
PPh ](BF
4
) and [Cu(L)
(L = (4-(9H-carbazol-9-yl)phenyl)methyl-2-(2 -pyri-
total yield of (4-(9H-carbazol-9-yl)phenyl)methanol was 1.83 g
0
1
(
)
3 2
4
)
3
(82.57%). m.p.: 120–122 °C. H NMR (CDCl , d, ppm): 8.15 (d,
dyl)benzimidazole), were synthesized and characterized by elemen-
tal analysis, H NMR and single crystal X-ray crystallography. The
photophysical properties of the complexes were examined by using
UV–vis, photoluminescence spectroscopies analysis.
J = 7.4 Hz, 2H), 7.63 (d, J = 8.8 Hz, 2H), 7.58 (d, J = 8.4 Hz, 2H),
7.42 (t, J = 7.4 Hz, 2H), 7.32 (d, J = 8.2 Hz, 2H), 7.29 (t, J = 7.4 Hz,
2H), 4.85 (d, J = 5.6 Hz, 2H), 1.81 (t, J = 5.6 Hz, 1H).
9-(4-(bromomethyl)phenyl)-9H-carbazole: 2.400 g (0.0088 mol)
of (4-(9H-carbazol-9-yl)phenyl)methanol was added to 60 mL of dry
1
THF under N
was added dropwise and then stirred for 16 h at room temperature.
The mixture was neutralized with NaHCO , and then extracted with
CH Cl
(3 ꢂ 50 mL). The organic phase was washed with 2 ꢂ 50 mL
brine and dried over anhydrous MgSO . The solvent was removed un-
2 3
and cooled to 0 °C. 0.42 mL (0.5 eq, 0.0044 mol) PBr
Experimental
3
Materials and methods
2
2
4
Cu(BF
phos) and carbazole were purchased from Aldrich. 2-(2-Pyri-
dyl)benzimidazole and triphenylphosphine (PPh ) were obtained
4
)
2
ꢁ6H
2
O, bis[2-(diphenylphosphino)phenyl]ether (DPE-
der vacuum, leaving an orange-brown solid. The crude was not purified
and directly used for subsequent preparation of the ligand L.
0
3
(4-(9H-carbazol-9-yl)phenyl)methyl-2-(2 -pyridyl)
from Acros Organics. p-Bromobenzaldehyde was bought from
Aladdin Chemistry Co., Ltd. Tri-tert-butylphosphine was purchased
from Puyang Huicheng Electronic Materials Co., Ltd. Sodium
borohydride was obtained from Shanghai Zhongqin chemical
reagent Co. Ltd. Copper power was from Shenyang Keda Chemical
Reagent Factory (China). All other chemicals were analytical grade
reagent.
2
benzimidazole (L): Under N , solid NaH (60% dispersed in mineral
oil, 0.120 g) and 2-(2-pyridyl)benzimidazole (0.680 g, 0.0035 mol)
in 20 mL of anhydrous DMF was stirred at 80 °C for 2 h. The result-
ing solution was cooled to room temperature and 9-(4-(bromo-
methyl)penyl)-9H-carbazole (1.400 g, 0.0042 mol) was added.
The mixed solution was stirred at 80 °C for 36 h. After completing,
the reaction mixture was poured into 100 mL of cool water, and
was extracted with dichloromethane (3 ꢂ 50 mL). The organic
[
Cu(NCCH
3
)
4
](BF
4
) was obtained by reaction of Cu(BF
4
)
2
ꢁ6H
2
O
and copper power in acetonitrile according to the method reported
by Kubas [20].
4
phase was washed with water and dried over anhydrous MgSO .
After removal of solvent, the residue was purified by column chro-
matography using ethyl acetate/petroleum ether (1: 4, v/v) as the
eluent to give a white powder. Yield: 81%. m.p.:186–188 °C. IR
IR spectra (400–4000 cm 1) were measured on a Shimadzu
ꢀ
1
IRPrestige-21 FT-IR spectrophotometer. H NMR spectra were
ꢀ
1
obtained on Unity Varian-500 MHz. C, H, and N analyses were
obtained using an Elemental Vario-EL automatic elemental analy-
sis instrument. UV–vis absorption and photoluminescent spectra
were recorded on a Shimadzu UV-2550 spectrometer and on a
Perkin–Elmer LS-55 spectrometer, respectively. Melting points
(KBr pellet cm ): 3041 (Aryl-CH), 2931 (ACH
2
A), 1614, 1456,
1
1328, 1150, 750. H NMR(CDCl
3
, d, ppm): 8.70 (d, 1H, J = 7.4 Hz,
Aryl-H), 8.50 (d, 1H, J = 8.0 Hz, Aryl-H), 8.11 (d, 2H, J = 7.6 Hz,
Aryl-H), 7.92–7.86 (m, 2H, Aryl-H), 7.48–7.41 (m, 5H, Aryl-H),
7.38–7.33 (m, 7H, Aryl-H), 7.25 (t, 2H, J = 8.8 Hz, Aryl-H), 6.32 (s,