1224
350
300
250
200
150
100
50
5
4
3
2
1
0
14
12
10
8
C-2, CIE (x, y),(0.307, 0.652)
C-4, CIE (x, y),(0.314, 0.647)
under vacuum, its potential as a solution processed ETM is
under investigation. We have demonstrated that it is possible
to produce phenanthroline derivatives (example, C-4: 2,9-bis-
[2-(thiophen-2-yl)vinyl][1,10]phenanthroline) which can act as
good electron transporters and hole blockers with reasonably
long lifetimes even in their virgin form.
Alq
,CIE (x, y),(0.325, 0.623)
3
6
4
2
0
450
500
550
600
650
λ/nm
References and Notes
1
2
D. Tanaka, T. Takeda, T. Chiba, S. Watanabe, J. Kido, Chem. Lett.
C-4
3
4
H. Sasabe, T. Chiba, S.-J. Su, Y.-J. Pu, K. Nakayama, J. Kido, Chem.
M. Ichikawa, N. Hiramatsu, N. Yokoyama, T. Miki, S. Narita, T.
P. Kathirgamanathan, WO 00/32717, 2000.
C-2
Alq
3
0
0
2
4
6
8
10
12
14
16
18
20
Voltage/V
5
6
T. Sano, M. Fujita, T. Fujii, Y. Nishio, Y. Hamada, U.S. Patent
5456988, 1995.
Figure 5. Current density-voltage-luminance characteristics of ITO/
ZnTPTP (50 nm)/¡-NPB (50 nm)/Alq3:DPQA (50 nm:0.1 nm)/ETL
(20 nm)/LiF (0.5 nm)/Al.
7
8
9
A. P. Kulkarni, C. J. Tonzola, A. Babel, S. A. Jenekhe, Chem. Mater.
S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B. Lussem,
Y.-J. Li, H. Sasabe, S.-J. Su, D. Tanaka, T. Takeda, Y.-J. Pu, J. Kido,
lower operating voltage than Alq3-based devices in the low
voltage region, though the trend is reversed at higher voltages
(V > 13 V). For example, at 1000 cd m¹2, the devices with C-4
have 23% lower operating voltage compared to the devices with
Alq3. The power efficiency (lm W¹1) for devices with C-4 is
43% higher than that with Alq3, but the current efficiency is
comparable (Table 2). Devices with C-2 have lower power
efficiency and current efficiency than devices with Alq3. The
above observation can be explained on the basis of higher
mobility of C-4 (lower operating voltage and turn-on voltage)
compared Alq3 and the barrier height for the electron injection is
lowest for C-4 (0.4 eV), then Alq3 (0.5 eV) and highest for C-2
(0.6 eV). However, the turn-on voltage does not follow the
barrier height. The turn-on voltage follows the order: C-4 <
C-2 < Alq3. This can be explained on the basis of mobility
differences inferred from the color coordinates of the electro-
luminescent spectra (Figure 5, inset and Table 2).
10 S. R. Forrest, V. Bulovic, P. Peumans, U.S. Patent 6,451,415, B1,
2002.
11 H.-W. Lee, J.-G. An, H.-K. Yoon, H. Jang, N. G. Kim, Y. Do, Bull.
12 P. Kathirgamanathan, S. Surendrakumar, PCT Patent WO 078115 A1,
2008.
13 P. Kathirgamanathan, V. Arkley, S. Surendrakumar, Y. F. Chan, S.
Ravichandran, S. Ganeshamurugan, M. Kumaraverl, J. Antipan-Lara,
G. Paramaswara, V. R. Reddy, SID Symp. Dig. 2010, 41, 465.
17 K. Okumoto, H. Kanno, U.S. Patent 0051563A1, 2006.
18 J. P. Chen, X. C. C. Li, U.S. Patent 6,713,781,B1, 2009.
20 A mixture of neocuproine hydrate (24mmol) and aryl aldehyde
(50 mmol) was refluxed in acetic anhydride (20 mL) for 6 h and then
allowed to cool for 18 h. To the reaction mixture which contained the
product as solid, methanol and small amounts of water were added
(50:2). The product was filtered off under suction then washed
thoroughly with methanol, water, diethyl ether and dried under vacuum
at 80 °C for several hours. The product was purified by sublimation
The CIE color coordinates (x, y) for devices with C-2 are
more saturated green than devices with either C-4 or Alq3. The
more saturated the green color, the closer the emission is to the
hole transporter, ¡-NPB (interface) and in turn, higher mobility
of the compound in question. Further, the observed color
coordinates are consistent with the relative HOMO levels (i.e.,
hole blocking nature) of the ETM’s concerned. The HOMO
levels of C-4, C-2, and Alq3 are ¹6.0, ¹5.9, and ¹5.7 eV
respectively and the hole blocking ability is expected to be in the
same order. Lifetime of the devices was measured under constant
current driving. Devices with Alq3 as ETM (D-A) have half-life
of 3384 h (Initial luminance = 1120 cd m¹2) and 7552 h (Initial
¹7
(at 10¹6-10 Torr) to give an analytically pure material.
2,9-Bisstyryl[1,10]phenanthroline (C-1): No melting peak was
obtained on DSC, Tg 117 °C. Anal. Found: C, 87.35; H, 5.18; N,
7.43%. Calcd for C28H20N2: C, 87.47; H, 5.24; N, 7.28%.
2,9-Bis(4,4¤-trifluoromethylphenyl)vinyl[1,10]phenanthroline (C-2):
Obtained as a light yellow solid, mp 279 °C (DSC, onset); Anal.
Found: C, 69.54; H, 3.39; N, 5.40%. Calcd for C30H18N2F6: C, 69.23;
H, 3.49; N, 5.38%. 1H NMR (DMF-d6): ¤ 7.88 (d, J = 8 Hz, H-2, 2H),
7.93 (d, J = 16 Hz, H-4), 8.02 (s, H-8), 8.03 (s, H-7), 8.11 (d, J = 8 Hz,
H-1, 2H), 8.20 (d, J = 8.3 Hz, H-5), 8.26 (d, J = 16 Hz, H-3), 8.58 (d,
J = 8.3 Hz, H-6).
luminance = 678 cd m¹2) whereas the ones with C-4 (Device D-
C-4) have a lifetime of 3432 h (Initial luminance = 630 cd m
¹2
)
and C-2 (D-C-2) have a lifetime of only 384 h at initial
luminance of 704 cd m¹2. Though the lifetime of the devices
with C-4 is lower than that with Alq3, it is still 1000-fold higher
than corresponding devices with pristine BPhen as ETM whose
lifetime is only a few hours (the devices degrade within hours of
manufacture). Further work is on going in understanding the
mechanism of conduction of the devices based on C-2 and C-4
and their performance in blue devices where the ETM’s (C-2 and
C-4) are both employed as virgin and doped. This will be
published elsewhere. Although compound C-3 is not evaporable
2,9-Bis(4,4¤-cyanophenyl)vinyl[1,10]phenanthroline (C-3): Mp
289 °C (DSC, onset). Anal. Found: C, 82.67; H, 4.07; N, 12.82%.
Calcd for C30H18N4: C, 82.93; H, 4.18; N, 12.89%.
2,9-Bis[2-(thiophen-2-yl)vinyl][1,10]phenanthroline (C-4): Ob-
tained as a golden yellow solid, mp 298 °C (DSC, onset); Tg 111 °C.
Anal. Found: C, 72.85; H, 4.12; N, 7.10; S, 16.17%. Calcd for
1
C24H16N2S2: C, 72.70; H, 4.07; N, 7.06; S, 16.17%. H NMR (DMF-
d6): ¤ 7.21 (dd, H-3), 7.45 (d, J = 16 Hz, H-7), 7.52 (d, J = 3.5 Hz,
H-4), 7.67 (d, J = 5 Hz, H-2), 7.95 (s, H-10, 11), 8.15 (d, J = 8.3 Hz,
H-8), 8.32 (d, J = 16 Hz, H-6), 8.49 (d, J = 8.3 Hz, H-9).
Those Supporting Information is available electronically on the CSJ-
Chem. Lett. 2010, 39, 1222-1224
© 2010 The Chemical Society of Japan