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Table 1 Physical data of GnFB and electroluminescent data of the green OLEDs
film c
e
EL
i
j
k
lseoml/l
Comp (nm)
Tg/T5d
(1C)
HOMO/
l
max
/
Von
/
Lmax (V)
Jmax
Zmax
em
d
h
FF
Eogpt/Eegle f (eV) LUMOg (eV) FWHM (nm) V100 (V) (cd mꢀ2, V) (mA cmꢀ2
)
(cd Aꢀ1
)
CIE (x, y)
G1FBa 540/539
G2FBa 534/529
G3FBa 530/523
G4FBa 528/514
0.18 142/332 2.54/2.42
0.13 256/360 2.58/2.33
0.09 305/372 2.60/2.32
0.05 364/378 2.61/2.30
ꢀ5.49/ꢀ2.95 540/72
ꢀ5.39/ꢀ2.81 525/71
ꢀ5.39/ꢀ2.79 521/70
ꢀ5.39/ꢀ2.78 509/70
4.2/8.0
4.1/6.1
4.0/6.0
4.0/6.9
2.2/3.4
472/11.2
4328/10.6
8521/14.4
2079/15.6
36 122/9.2
231
245
391
224
1631
0.21
2.19
9.12
10.01
4.32
0.37, 0.59
0.31, 0.62
0.27, 0.62
0.22, 0.56
0.28, 0.52
Alq3b
514/519
0.28
172/– 2.7
ꢀ5.8/ꢀ3.1
518/92
a
b
c
ITO/PEDOT:PSS/GnFB(spin-coating)/BCP/LiF:Al. ITO/PEDOT:PSS/NPB(evaporating)/Alq3/LiF:Al. Measured in CH2Cl2 and as thin films.
d
e
f
Measured in CH2Cl2 with quinine sulfate as a standard. Obtained from DSC/TGA measured at 10 1C minꢀ1 under N2. Calculated from
Eogpt = 1240/lonset; Egele = E
ꢀ E
.
Estimated from HOMO = ꢀ(4.44 + E
); LUMO = Eogpt ꢀ HOMO. Turn-on voltages at 1 and 100 cd mꢀ2
.
re
onset
ox
onset
g
ox
onset
h
i
j
k
Maximum luminance at the applied voltage. Current density at maximum luminance. Luminance efficiency.
and CBP:Ir(ppy)3-based phosphorescence devices (lEL = 512, supporting the SSFRN for the Joint PhD Program, PERCH-CIC
539sh; CIE = 0.32, 0.61).15 The EL spectra of all diodes match and the SAST.
with their spin-coated thin film PL spectra. No emission
shoulder at a longer wavelength due to excimer and exciplex
species formed at the interface of the EML and BCP layers,
which often occurs in devices fabricated from EMLs with planar
Notes and references
1 B. Geffroy, P. le Roy and C. Prat, Polym. Int., 2006, 55, 57.
2 S. C. Lo and P. L. Burn, Chem. Rev., 2007, 107, 1097.
molecular structure,16 is detected. In addition, stable green
emissions are obtained from all devices and the EL spectra did
not change over the entire driven voltages (ESI†). The G3–G4FB-
based green OLEDs are the two best performing devices among
all these analogues. These devices exhibit maximum brightness
(Lmax) up to 8521 cd mꢀ2 at 14.4 V, high maximum luminance
efficiencies (Zmax) of 9.12–10.01 cd Aꢀ1, and turn-on voltages
(Von) of 4.0 V. Whereas the G2FB-based device shows somewhat
lower EL properties with a Lmax and an Zmax of 4328 cd mꢀ2 and
2.19 cd Aꢀ1 at 50.13 mA cmꢀ2, respectively. The efficiencies of
G3–G4FB-based diodes are far superior to that of the reference
3 (a) S. Bernhardt, M. Kastler, V. Enkelmann, M. Baumgarten and
K. Mu¨llen, Chem.–Eur. J., 2006, 12, 6117; (b) C. C. Kwok and
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evaporated NPB:Alq3-based device (Zmax = 4.32 cd
A
ꢀ1).
Although the device configuration is yet to be optimized, the
performances of the devices based on our new dendrimers are
outstanding compared with those of current non-doped green
OLEDs17 and all our reported green OLEDs,14,18 and also 12 C. Tang, F. Liu, Y.-J. Xia, J. Lin, L.-H. Xie, G.-Y. Zhong, Q.-L. Fan and
W. Huang, Org. Electron., 2006, 7, 155.
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14 (a) A. M. Thangthong, N. Prachumrak, R. Tarsang, T. Keawin,
comparable with those of highly efficient vacuum-deposited
non-doped green OLEDs reported in recent years.7–9,19 The EL
efficiency of G3FB (Zmax = 10.01 cd Aꢀ1 at 3.93 mA cmꢀ2) is
much better than that of Alq3,10,14,18,20 a widely investigated
green emitter, clearly indicating the high potential of the
S. Jungsuttiwong, T. Sudyoadsuk and V. Promarak, J. Mater. Chem.,
2012, 22, 6869; (b) A. M. Thangthong, D. Meunmart, N. Prachumrak,
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Organic Light Emitting Diode, InTech., 2010.
16 D. Y. Kim, H. N. Cho and C. Y. Kim, Prog. Polym. Sci., 2000, 25, 1089.
17 (a) N. Li, S.-L. Lai, P. Wang, F. Teng, Z. Liu, C.-S. Lee and S.-T. Lee,
efficient EL devices for both display and lighting applications.
In summary, we have demonstrated the synthesis of bis(fluorenyl)-
benzothiadiazole-cored carbazole dendrimers (GnFB) as green emit-
ters for OLEDs. By using carbazole dendrons as the end-caps, we are
able to reduce the crystallization and retain the high green emissive
ability of a fluorescent core in the solid state, as well as improve the
amorphous stability and solubility of the material. A solution
processed double-layer OLED using GnFB as EML emits stable pure
Appl. Phys. Lett., 2009, 95, 133301; (b) Y. Li, A.-Y. Li, B.-X. Li,
J. Huang, L. Zhao, B.-Z. Wang, J.-W. Li, X.-H. Zhu, J. B. Peng,
Y. Cao, D.-G. Ma and J. Roncali, Org. Lett., 2009, 11, 5318.
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S. Jungsuttiwong, T. Keawin, T. Sudyoadsuk and V. Promarak, Eur.
J. Org. Chem., 2012, 5263; (b) V. Promarak, M. Ichikawa,
T. Sudyoadsuk, S. Saengsuwan, S. Jungsuttiwong and T. Keawin,
Synth. Met., 2007, 157, 17.
green color with high luminance efficiencies (up to 10.01 cd Aꢀ1) and 19 (a) Y. Li, B.-X. Li, W.-Y. Tan, Y. Liu, X.-H. Zhu, F.-Y. Xie, J. Chen,
D.-G. Ma, J. Peng, Y. Cao and J. Roncali, Org. Electron., 2012,
13, 1092; (b) Y. Yuan, G.-Q. Zhang, F. Lu, Q.-X. Tong, Q.-D. Yang,
H.-W. Mo, T.-W. Ng, M.-F. Lo, Z.-Q. Guo, C. Wu and C.-S. Lee,
CIE coordinates of (0.27, 0.62). This report offers a useful strategy to
decorate the highly efficient but planar fluorophore to be suitable for
applications in solution processed OLEDs and to prepare high Tg
amorphous materials for high temperature applications.
This work was financially supported by the TRF (RMU5080052).
We acknowledge the scholarship support from the OHEC for
Chem.–Asian J., 2013, 8, 1253–1258.
20 (a) Z. Chu, D. Wang, C. Zhang, F. Wang, H. Wu, Z. Lv, S. Hou, X. Fan
and D. Zou, Synth. Met., 2012, 162, 614; (b) J. Li, C. Ma, J. Tang,
C.-S. Lee and S. Lee, Chem. Mater., 2005, 17, 615; (c) Y. Zou, T. Ye,
D. Ma, J. Qin and C. Yang, J. Mater. Chem., 2012, 22, 23485.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun.