round flask equipped with a condenser and mechanical stirrer.
The reaction mixture was heated to 65 uC for 6.5 h. After
completion of the reaction, the chloroform was removed by
rotary evaporator. The residual product (30 g, 96.8%) was
sufficient for the following synthetic step.
electrolyte. Each potential was calibrated with ferrocene as a
reference. The HOMO levels of BCP and DTBT were obtained
from the measurement of the LUMO levels and the optical
bandgaps of the materials, respectively. The detailed proce-
dures and discussion are described in the ESI.{ The electron
mobilities of DTBT and BAlq were measured by the time-of-
flight (TOF) method. The devices for the measurement
consisted of a single organic layer sandwiched between two
electrodes on top of a glass substrate. The bottom electrode
was transparent patterned ITO with a thickness of 150 nm.
The top electrode was 100 nm thick Al. The thickness of the
organic layer was in the range 2–5 mm. After deposition, all
devices were sealed using glass encapsulation in N2 atmo-
sphere. For the TOF measurements, 600 ps pulses at 337 nm
from a nitrogen laser (USHO KEC-150) were used as optical
excitation. A resistor with a value between 10 V and 1 kV
was connected in series to the samples. The photocurrent
was measured with a digitizing oscilloscope (TEKTRONIX
TDS3052B). All measurements were carried out at 298 K.
The electron mobility of BCP was measured by the transient
Synthesis of 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine
4-Bromo-N-benzylideneaniline (25.9 g, 0.1 mol) and benzami-
dine (24 g, 0.2 mol) were dissolved in chloroform. The reaction
mixture was heated to 80 uC for 24 h. The product was
precipitated by cooling to room temperature and filtered to
obtain 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine (color-
less needles). The yield was 15%. 1H NMR (300 MHz,
CDCl3) d [ppm]: 8.74 (d, 4H, Ar-H), 8.63 (d, 2H, Ar-H), 7.64
(d, 3H, Ar-H), 7.62 (m, 5H, Ar-H). MS (ESI) (calcd for
C21H14N3Br, 387.0; found, 388) m/z: 388, 363, 338, 310, 270,
251, 236, 200, 145, 101.
Synthesis of 2,4-diphenyl-6-(49-triphenylsilanyl-biphenyl-4-yl)-
1,3,5-triazine (DTBT)
electroluminescence (EL) spectroscopy method. Using
a
voltage pulse as an excitation source, the delay time for
the EL was measured and interpreted as the electron transit
time. Electron mobility was extracted by considering the
luminance mechanism within the devices.16 Current density–
voltage–luminescence characteristics of OLEDs were measured
with a Keithley 2400 source meter and a SpectraColorimeter
PR650.
2-(4-Bromophenyl)-4,6-diphenyl-1,3,5-triazine(5.5g, 0.0145mol),
tetrakis(triphenylphosphine)palladium(0) (0.08 g, 0.072 mol),
2 M K2CO3 (48 ml) and toluene (150 ml) were added to a
250 ml three-necked flask under nitrogen. The prepared
4-phenylboronic acid triphenylsilane (4.6 g, 0.012 mol) was
added to the solution and heated to 110 uC for 5 h. After
cooling to room temperature, the reaction mixture was
diluted with diethyl ether and organic phase was washed
with water. After drying over MgSO4, the solvent was
removed. The resulting crude product was passed through a
flash column chromatograph to remove impurities and
recrystallized from ethanol to obtain a white solid product.
Acknowledgements
This work was supported by the Ministry of Commerce,
Industry and Energy through the OLED center and
Cavendish-KAIST Cooperation Program.
1
The yield of product was 63%. H NMR (300 MHz, CDCl3)
d [ppm]: 7.60 (d, 4H, Ar-H), 7.54 (m, 10H, Ar-H), 7.48 (d,
4H, Ar-H), 7.36 (m, 13H, Ar-H), 7.22 (t, 2H, Ar-H). MS
(ESI) (calcd for C45H33N3Si, 643.2; found, 644) m/z: 644,
510, 438, 373, 360, 331, 303, 271, 259, 209.
References
1 M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson and
S. R. Forrest, Appl. Phys. Lett., 1999, 75, 4.
2 V. I. Adamovich, S. R. Cordero, P. I. Djurovich, A. Tamayo,
M. E. Thompson, B. W. D’Andrade and S. R. Forrest, Org.
Electron., 2003, 4, 77.
Characterization and device fabrication
3 (a) J.-W. Kang, S.-H. Lee, H.-D. Park, W.-I. Jeong, K.-M. Yoo,
Y.-S. Park and J.-J. Kim, Appl. Phys. Lett., 2007, 90, 223508; (b)
T. Tsutsui, M.-J. Yang, M. Yahiro, K. Nakamra, T. Watanabe,
T. Tsuji, Y. Fukuda, T. Wakimoto and S. Miyaguchi, Jpn. J. Appl.
Phys., 1999, 38, L1502.
4 H. J. Peng, X. L. Zhu, J. X. Sun, X. M. Yu, M. Wong and
H. S. Kwok, Appl. Phys. Lett., 2006, 88, 033509.
5 M. Ikai, S. Tokito, Y. Sakamoto, T. Suzuki and Y. Taga, Appl.
Phys. Lett., 2001, 79, 156.
Absorption spectra of solutions were recorded with
a
VARIAN Cary1 5000 UV-Vis spectrophotometer from
250 to 700 nm. Photoluminance (PL) spectra were measured
in a system comprising a He : Cd CW laser (Melles-Griot
45MRS802-230) and a monochromator with a photomultiplier
tube (Acton Research P2/PD-471). Phosphorescence spectra at
12 K were measured by using an ICCD camera (Princeton
Instruments 7397-0005) with a Nd–YAG laser (Continuum
Surelite 11-10) as an excitation source. Excitation laser power
was a few tens of mJ, which is close to the detection limit of
phosphorescence emission. Cyclic voltammetry studies were
carried out with a potentiostat (Princeton Applied Research
model VSP). using a three electrode cell assembly comprising
Ag/Ag+ as the reference electrode and Pt as the counter
and working electrodes. Measurements were carried out in
N2-saturated N,N-dimethylformamide (for BCP and DTBT)
and dichloromethane (for BAlq) solution with tetrabutyl-
ammonium hexafluorophosphate (0.1 M) as a supporting
6 C. Adachi, R. Kwong, P. Djurovichi, V. Adamovichi, M. Baldo,
M. E. Thompson and S. R. Forrest, Appl. Phys. Lett., 2001, 79,
2082.
7 R. C. Kwong, M. R. Nugent, L. Michalski, T. Ngo, K. Rajan,
Y.-J. Tung, M. S. Weaver, T. X. Zhou, M. Hack, M. E. Thompson,
S. R. Forrest and J. J. Brown, Appl. Phys. Lett., 2002, 81, 162.
8 X. Jiang, Z. Zhang, W. Zhao, W. Zhu, B. Zhang and Z. Xu,
J. Phys. D: Appl. Phys., 2000, 33, 473; C. Wang, G. Jung, Y. Hua,
C. Pearson, M. R. Bryce, M. C. Petty, A. S. Batsanov, A. E. Goeta
and J. A. K. Howard, Chem. Mater., 2001, 13, 1167.
9 D. Kolosov, V. Adamovichi, P. Djurovichi, M. E. Thompson and
C. Adachi, J. Am. Chem. Soc., 2002, 124, 9945.
10 J. L. Kim, J. K. Kim, H. N. Cho, D. Y. Kim, C. Y. Kim and
S. I. Hong, Macromolecules, 2000, 33, 5880.
3718 | J. Mater. Chem., 2007, 17, 3714–3719
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