Chemistry Letters Vol.34, No.6 (2005)
755
K. Nagai, and N. Tamoto, Appl. Phys. Lett., 66, 2679 (1995). e) S.
Tokito, K. Noda, and Y. Taga, J. Phys. D: Appl. Phys., 29, 2750
(1996).
A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed., 41, 4176 (2002); S.
Kotha, K. Lahiri, and D. Kashinath, Tetrahedron, 58, 9633 (2002);
A. Suzuki, J. Organomet. Chem., 576, 147 (1999); N. Miyaura and
A. Suzuki, Chem. Rev., 95, 2457 (1995).
For previous examples of the Suzuki cross-coupling for 1-aryl- and
1,3-diarylazulenes, see the followings: M. Porsh, G. Sigl-Seifert,
and J. Daub, Adv. Mater., 9, 635 (1997); K. L. Kane, Jr., K. M. Shea,
A. L. Crombie, and R. L. Danheiser, Org. Lett., 3, 1081 (2001);
K. Kurotobi, H. Tabata, M. Miyauchi, T. Murafuji, and Y. Sugihara,
Synthesis, 2002, 1013; A. L. Crombie, J. L. Kane, Jr., K. M. Shea,
and R. L. Danheiser, J. Org. Chem., 69, 8652 (2004).
J. P. Wolfe, S. Wagaw, J.-F. Marcoux, and S. L. Buchwald, Acc.
Chem. Res., 31, 805 (1998); J. P. Hartwig, Acc. Chem. Res., 31,
852 (1998); J. P. Hartwig, Pure Appl. Chem., 71, 1417 (1999);
J. P. Hartwig, Angew. Chem., Int. Ed., 37, 2046 (1998).
Selected properties of 1a: green microcrystals; mp 152–154 ꢂC.
1H NMR (CDCl3) ꢂ 3.00 (s, 12H), 6.91 (dm, J ¼ 8:6 Hz, 4H), 7.03
(t, J ¼ 9:8 Hz, 2H), 7.50 (dm, J ¼ 8:6 Hz, 4H), 7.53 (t, J ¼ 9:8 Hz,
1H), 8.02 (s, 1H), 8.44 (d, J ¼ 9:8 Hz, 2H). UV–vis (CH2Cl2) ꢃ
max 236 (log " ¼ 4:42), 279 (4.54), 312 (4.78), 384 (4.23), 657
(2.51). 1b: green needles; mp 279–281 ꢂC. 1H NMR (CDCl3) ꢂ
7.04 (t, J ¼ 8:0 Hz, 4H), 7.07 (t, J ¼ 10:0 Hz, 2H), 7.19 (d, J ¼
8:0 Hz, 8H), 7.21 (d, J ¼ 8:8 Hz, 4H), 7.29 (t, J ¼ 8:0 Hz, 8H),
7.51 (d, J ¼ 8:8 Hz, 4H), 7.54 (t, J ¼ 10:0 Hz, 4H), 8.09 (s, 1H),
8.53 (d, J ¼ 10:0 Hz, 2H). UV–vis (CH2Cl2) ꢃ max 230
(log " ¼ 4:53), 244sh (4.51), 303 (4.71), 330 (4.71), 347sh (4.63),
395sh (4.63), 577sh (2.32), 636 (2.45), 698sh (2.33). 1c: green
needles; mp 261–263 ꢂC. 1H NMR (CDCl3) ꢂ 7.25 (t, J ¼ 9:8 Hz,
2H), 7.33 (tm, J ¼ 7:7 Hz, 4H), 7.47 (tm, J ¼ 7:7 Hz, 4H), 7.58 (d,
J ¼ 7:7 Hz, 4H), 7.70 (t, J ¼ 9:8 Hz, 1H), 7.75 (d, J ¼ 8:1 Hz,
4H), 7.92 (d, J ¼ 8:1 Hz, 4H), 8.19 (d, J ¼ 7:7 Hz, 4H), 8.32 (s,
1H), 8.73 (d, J ¼ 9:8 Hz, 2H). UV–vis (CH2Cl2) ꢃ max 242
(log " ¼ 4:92), 288sh (4.68), 294 (4.78), 316 (4.74), 337sh (4.49),
377 (4.05), 390sh (4.01), 407 (3.25), 462 (2.79), 584sh (2.15), 617
(2.27), 653sh (2.10).
taining 0.1 M tetrabutylammonium perchlorate. The HOMO en-
ergy levels of 1a–1c were estimated from the first oxidation po-
tentials (Eox1), which are comparable to that of CuPc (Table 1).
It should be noted that the HOMO energy levels of 1a and 1b in-
termediate between those of HTL materials, such as TPD (5.4–
5.5 eV),10 ꢁ-NPD (5.4 eV)11 and TPTE (5.3 eV),12,13 and the
work function of the ITO electrode (4.6–5.0 eV),2d and that of
1c is the same as that of TPTE, suggesting that 1a–1c can be
used as HIL materials in organic EL devices.14
Transmittance of visible light through the thin films (10 nm)
of 1a–1c on quartz was compared with that of CuPc. While re-
duction of less than 15% of the initial light intensity in the
550–750 nm range through the film of 1a–1c was observed,
20–30% of the light in the same range was diminished through
the film of CuPc.15 Indeed, color fade was not observed with
the film of 1a–1c, as expected from their visible absorption spec-
tra. A preliminary application for EL devices was examined with
the multilayered structure depicted in Figure 1. The initial char-
acteristics and half-life time are shown in Table 2. Although the
initial luminance with 1a–1c was slightly lower than that with
CuPc, the half-life time with 1a–1c was much longer than that
of CuPc. While operation with a low initial voltage retards deg-
radation of a device in general,1d the device with 1a unusually
shows higher initial voltage and longer half-life time. Probably
the relatively greater hole drift mobility of 1a compared with
those of 1b and 1c16 may overcome its defect.
3
4
5
6
Al cathode
LiF
Alq3 (60 nm)
TPTE (50 nm)
HIL materials
(10 nm)
ITO elctrode
7
J. A. Soderquist, I. Rosado, and Y. Marrero, Tetrahedron Lett., 39,
3115 (1998); C. R. Johnson and M. P. Braun, J. Am. Chem. Soc.,
115, 11014 (1993); J. P. Wolfe, S. Wagaw, and S. L. Buchwald,
J. Am. Chem. Soc., 118, 7215 (1996).
M. R. Netherton and G. C. Fu, Org. Lett., 3, 4295 (2001).
The amination with dimethylamine was only conducted in a
sealed tube and those with the other amines were done under argon
atmosphere.
glass
Figure 1. The organic EL architecture investigated.
8
9
Table 2. The characteristics of the EL devices with CuPc and
1a–1c as HIL materials at 11 mA cmꢄ2
10 TPD is 4,40-bis[N-(m-tolyl)-N-phenylamino]biphenyl: a) J. D.
Anderson, E. M. Mcdonald, P. A. Lee, M. L. Anderson, E. L. Ritchie,
H. K. Hall, T. Hopkins, E. A. Mash, J. Wang, A. Padias, S.
Thayumanavan, S. Barlow, S. R. Marder, G. E. Jabbour, S. Shaheen,
B. Kippelen, N. Peyghambarian, R. M. Wightman, and N. R.
Armstrong, J. Am. Chem. Soc., 120, 9646 (1998). b) See also
Ref. 2b and 2d.
Initial
voltage
/V
HIL
materials
Initial luminance
/cd cmꢄ2
Half-life
time/h
1a
1b
1c
CuPc
578
567
543
602
8.42
5.52
5.09
7.35
630
400
600
150
11 ꢁ-NPD is 4,40-bis[N-(ꢁ-naphtyl)-N-phenylamino]biphenyl; the
HOMO energy level was obtained from photoelectron measure-
ments.
12 TPTE is 4,40-bis{N-[N,N-di(m-tolyl)-40-aminobiphenyl]-N-phenyl-
amino}biphenyl; the HOMO energy level was obtained from photo-
electron measurements.
13 H. Tanaka, S. Tokito, Y. Taga, and A. Okada, Chem. Commun.,
1996, 2175.
14 Since two methods for determining HOMO levels of the HIL and
HTL materials are different from each other, comparison of the
two HOMO levels is tentative so far.
In summary we have prepared novel derivatives of 1,3-
bis(aminophenyl)azulenes from 1,3-dihaloazulenes in two steps
involving the Suzuki cross-coupling and Pd(OAc)2-catalyzed
amination and demonstrated that these compounds can be used
as hole-injecting materials in EL devices with longer half-life
time than the widely used CuPc and without color fade.
15 Reduction of the transmittance with the 100 nm thick film of CuPc
was much clear. Similarly, transmittance of visible light through
the thin film (100 nm) of 1a–1c on quartz was compared with CuPc.
While only 20–30% of the light in the 500–800 nm range passed
through the film of CuPc, more than 80% of the light in all of the visi-
ble range passed through the film of 1a–1c.
References and Notes
1
2
C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 51, 913 (1987).
a) S. A. VanSlyke, C. H. Chen, and C. W. Tang, Appl. Phys. Lett., 69,
2160 (1996). b) Y. Shirota, Y. Kuwabara, H. Inada, T. Wakimoto, H.
Nakada, Y. Yonemoto, S. Kawami, and K. Imai, Appl. Phys. Lett.,
65, 807 (1994). c) T. Okamoto, E. Terada, M. Kozaki, M. Uchida,
S. Kikukawa, and K. Okada, Org. Lett., 5, 373 (2003). d) C. Adachi,
16 Hole drift mobilities of 1a–1c are 1:0 ꢃ 10ꢄ5, 1:0 ꢃ 10ꢄ6, and
1:0 ꢃ 10ꢄ6 cm2 Vꢄ1 sꢄ1, respectively.
Published on the web (Advance View) June 5, 2005; DOI 10.1246/cl.2005.754