Synthesis and luminescence of silicon-bridged bithiophene- And triarylamine-containing molecules

Article abstract of DOI:10.1021/om049626e

A new family of dithienosiloles that contain two peripheral triarylamine moieties have been synthesized for use in organic light-emitting devices (OLEDs). The compounds are strongly fluorescent. We studied EL (electroluminescent) properties of these compound in multilayer EL devices having the following structure: ITO/TPD/compound 2b-5b/BCP/Alq₃/Al:Li (ITO = indium tin oxide; TPD = 1,4-bis(phenyl-m-tolylamino)biphenyl; BCP = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; Alq₃ = tris(8-hydroxyqumolinolato)aluminum (III)). Among the devices, green light-emitting device ITO/TPD/2b/BCP/Alq₃/Al:Li exhibits the highest EL performance.

Full text of DOI:10.1021/om049626e

5280
Organometallics 2004, 23, 5280-5285
Syn th esis a n d Lu m in escen ce of Silicon -Br id ged
Bith iop h en e- a n d Tr ia r yla m in e-Con ta in in g Molecu les
Taegweon Lee,† Il J ung,† Kyu Ho Song,† Hyungsup Lee,‡ J iyoung Choi,‡
Kyuwang Lee,‡ Byung J o Lee,§ J aeYoun Pak,§ Chongmok Lee,§
Sang Ook Kang,*,† and J aejung Ko*,†
Department of Chemistry, Korea University, J ochiwon, Chungnam 339-700, Korea,
Department of Chemistry, Myunggi University, Youngin, Kyunggido 449-728, Korea, and
Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea
Received May 26, 2004
A new family of dithienosiloles that contain two peripheral triarylamine moieties have
been synthesized for use in organic light-emitting devices (OLEDs). The compounds are
strongly fluorescent. We studied EL (electroluminescent) properties of these compound in
multilayer EL devices having the following structure: ITO/TPD/compound 2b-5b/BCP/Alq3/
Al:Li (ITO ) indium tin oxide; TPD ) 1,4-bis(phenyl-m-tolylamino)biphenyl; BCP ) 2,9-
dimethyl-4,7-diphenyl-1,10-phenanthroline; Alq3 ) tris(8-hydroxyquinolinolato)aluminum
(III)). Among the devices, green light-emitting device ITO/TPD/2b/BCP/Alq3/Al:Li exhibits
the highest EL performance.
In tr od u ction
properties. Hole-transporting and electron-transporting
properties are opposing functions associated with dif-
ferent structural features. Recently, synthetic research
has been carried out incorporating the above functions
in the same molecule in an effort to attain a better
performance.9 Adachi et al.10 synthesized interesting
bipolar materials that were composed of oxadiazole and
triphenylamine groups as an EM (emitting material).
Later many bipolar materials featuring combinations
such as triarylamineoxadiazole,11 triarylaminopyri-
dine,12 dialkylaminopyran,13 and triarylaminoboryl14
were synthesized and applied in OLED. These com-
pounds were shown to improve electron and hole injec-
tion into the emitting layer due to a high HOMO
(highest occupied molecular orbital) and low LUMO
Amorphous triaryldiamines of benzidine with high
glass transition temperatures (Tg) are widely used as
thermally stable hole-transporting layers for organic
light-emitting devices.1 Another synthetic method of
forming amorphous glasses can be achieved by replacing
the benzidine group by heteroarenes with a low sym-
metry, such as thiophene,2 2,2′-bithiophene,3 isothianaph-
thalenes,4 and 2,2′:5′,2′′-terthiophene.5 Such thiophene
bis(triarylamines) and diarylaminophenyl compounds
show interesting hole-transporting properties and color-
tunable emitting materials.6 π-Conjugated systems,
silole, on the other hand, have been intensively studied
as a novel core component for efficient electron-
transporting materials due to the small band gap and
high electron affinity.7 Ohshita et al.8 have reported the
synthesis of silicon-bridged bithiophenes and demon-
strated that they exhibit high electron-transporting
(8) (a) Ohshita, J .; Nodono, M.; Kai, H.; Watanabe, T.; Kunai, A.;
Komaguchi, K.; Shiotani, M.; Adachi, A.; Okita, K.; Harima, Y.;
Yamashida, K.; Ishikawa, M. Organometallics 1999, 18, 1453. (b)
Ohshita, J .; Kai, H.; Takata, A.; Iida, T.; Kunai, A.; Ohta, N.;
Komaguchi, K.; Shiotani, M.; Adachi, A.; Sakamaki, K.; Okita, K.
Organometallics 2001, 20, 4800.
(9) (a) Lee, Y.-Z.; Chen, X.; Chen, S.-A.; Wei, P. K.; Fann, W.-S. J .
Am. Chem. Soc. 2001, 123, 2296. (b) Song, S.-Y.; J ang, M. S.; Shim,
H.-K.; Hwang, D.-H.; Zyung, T. Macromolecules 1999, 32, 1482. (c) Ng,
S. C.; Lu, H. F.; Chan, H. S. O.; Fujii, A.; Laga, T.; Yoshino, K. Adv.
Mater. 2000, 12. 1122.
(10) (a) Hamada, Y.; Adachi, C.; Tsutsui, T.; Saito, S. J pn. J . Appl.
Phys. 1992, 31, 1812. (b) Hamada, Y.; Adachi, C.; Tsutsui, T.; Saito,
S. Optoelectronics 1992, 7, 83.
(11) (a) Tamoto, N.; Adachi, C.; Nagai, K. Chem. Mater. 1997, 9,
1077. (b) Mochizuki, H.; Hasui, T.; Kawamoto, M.; Shiono, T.; Ikeda,
T.; Adachi, C.; Taniguchi, Y.; Shirota, Y. Chem. Commun. 2000, 1923.
(c) Peng, Z.; Bao, Z.; Galvin, M. E. Chem. Mater. 1998, 10, 2086. (d)
Patra, A.; Pan, M.; Friend, C. S.; Liu, T.-C.; Cartwright, A. N.; Prasad,
P. N.; Burzynski, R. Chem. Mater. 2002, 14, 4044.
* To whom correspondence should be addressed. Fax: 82 41 867
5396. Tel: 82 41 860 1337. E-mail: jko@korea.ac.kr.
† Korea University.
‡ Myunggi University.
§ Ewha Womans University.
(1) (a) Koene, B. E.; Loy, D. E.; Thompson, M. E. Chem. Mater. 1998,
10, 2235. (b) Chen, C. H.; Shi, J .; Tang, C. W. Macromol. Symp. 1997,
125, 1. (c) Shirota, Y. J . Mater. Chem. 2000, 10, 1. (d) O’Brien, D. F.;
Burrows, P. E.; Forrest, S. R.; Koene, B. E.; Loy, D. E.; Thompson, M.
E. Adv. Mater. 1998, 10, 1108.
(2) Watanabe, M.; Yamamoto, T.; Nishiyama, M. Chem. Commun.
2000, 133.
(3) (a) Wong, K.-T.; Hung, T. H.; Kao, S. C.; Chou, C. H.; Su, Y. O.
Chem. Commun. 2001, 1628. (b) Gerstner, P.; Rohde, D.; Hartmann,
H. Synthesis 2002, 17, 2487.
(4) Kisselev, R.; Thelakkat, M. Chem. Commun. 2002, 1530.
(5) Noda, T.; Imae, I.; Noma, N.; Shirota, Y. Adv. Mater. 1997, 9,
239.
(6) (a) Noda, T.; Ogawa, H.; Noma, N.; Shirota, Y. Adv. Mater. 1997,
9, 720. (b) Noda, T.; Ogawa, H.; Noma, N.; Shirota, Y. J . Mater. Chem.
1999, 9, 2177.
(7) (a) Tamao, K.; Yamaguchi, S.; Shiozaki, M.; Nakagawa, Y.; Ito,
Y. J . Am. Chem. Soc. 1992, 114, 5867. (b) Tamao, K.; Yamaguchi, S.;
Shiro, M. J . Am. Chem. Soc. 1994, 116, 11715. (c) Yamaguchi, S.; Goto,
T.; Tamao, K. Angew. Chem., Int. Ed. 2000, 39, 1695.
(12) (a) Wang, Y. Z.; Epstein, A. J . Acc. Chem. Res. 1999, 32, 217,
and references therein. (b) J enekhe, S. A.; Lu, L.; Alam, M. M.
Macromolecules 2001, 34, 7315.
(13) Li, J .; Liu, D.; Hong, Z.; Tong, S.; Wang, P.; Ma, C.; Lengyel,
O.; Lee, C.-S.; Kwong, H.-L.; Lee, S. Chem. Mater. 2003, 15, 1486.
(14) (a) Doi, H.; Kinoshita, M.; Okumoto, K.; Shirota, Y. Chem.
Mater. 2003, 15, 1080. (b) Shirota, Y.; Kinoshita, M.; Noda, T.;
Okumoto, K.; Ohara, T. J . Am. Chem. Soc. 2000, 122, 11021. (c)
Kuwabara, Y.; Ogawa, H.; Inada, H.; Noma, N.; Shirota, Y. Adv. Mater.
1994, 6, 677.
10.1021/om049626e CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/17/2004

Luminescence of Dithienosiloles
Organometallics, Vol. 23, No. 22, 2004 5281
Sch em e 1. Syn th esis of 4,4-Dip h en yl-2,6-bis(4-d ia r yla m in o-p-a r yl)d ith ien osiloles
(lowest unoccupied molecular orbital). Accordingly, when
we incorporated the diarylamino unit as a hole-
transporting compound and silicon-bridged bithiophene
as an electron-transporting unit into the molecular
structure of emitters, we could expect improved bipolar
character and EL characteristics.
We now describe (i) the successful incorporation of a
silicon-bridged bithiophene into diarylaminophenyl units;
(ii) the optical properties of novel bis(diarylaminophe-
nyl)silole; and (iii) the electroluminescent properties of
multiple-layer EL devices.
dibromodithienosilole (1)8 with the corresponding boro-
lane15 (2a and 3a ) by Suzuki coupling reaction in the
presence of Pd(PPh3)4 and K2CO3. 4,4-Diphenyl-2,6-bis-
[4-(dipyridylamino)phenyl]dithienosilole (4b) and 4,4-
diphenyl-2,6-bis[4-(7-azaindol-1-yl)phenyl]dithieno-
silole (5b) were synthesized by further stannylation of
2,2′-(dipyridylamino)phenyl and 4-(7-azaindol-1-yl)phen-
yl16 and subsequent Stille cross-coupling reaction with
dibromodithienosilole. All of the new compounds were
fully characterized with spectroscopic techniques, in-
1
cluding H and 13C NMR spectroscopy and high-resolu-
tion mass spectroscopy. The 13C NMR spectrum of 4b
reveals the expected 17 lines in the aromatic region. The
29Si NMR spectrum of 4b reveals a single resonance at
Resu lts a n d Discu ssion
Syn th esis a n d Th er m a l P r op er ties. The scheme
of synthesis and the structures of arylamine derivatives
and dibromodithienosilole are given in Scheme 1. The
4,4-diphenyl-2,6-bis(4-diarylamino-4-biphenylyl)dithieno-
siloles (2b and 3b) were obtained by the reaction of
(15) (a) Sohn, B.-H.; Kim, K.; Choi, D. S.; Kim, Y. K.; J eoung, S. C.;
J in, J .-I. Macromolecules 2002, 35, 2876. (b) Morin, J .-F.; Leclerc, M.;
Macromolecules 2002, 35, 8413. (c) Pu, Y.-J .; Soma, M.; Kido, J .;
Nishide, H. Chem. Mater. 2001, 13, 3817.
(16) Kang, Y.; Wang, S. Tetrahedron Lett. 2002, 43, 3711.

5282 Organometallics, Vol. 23, No. 22, 2004
Lee et al.
F igu r e 1. Molecular structure of 4b showing the atom-numbering scheme. Selected distances (Å) and angles (deg): C(22)-
Si(1) 1.880(2), C(1)-C(21) 1.454(3), C(24)-C(25) 1.475(3), C(2)-Si(1)-C(22) 91.62(11), C(41)-Si(1)-C(47) 109.27(11).
Ta ble 1. P h otop h ysica l a n d Electr och em ica l Da ta for th e Com p ou n d s 2b-5b
b
c
Tg,
°C
UVa λmax
,
PLa λmax
,
PL in film λmax
,
Φfl
,
E
ox({Eonset
V vs SCE
}
ox),
Eg
,
HOMO/LUMO,
eV
compd
nm
nm
nm
(%)
eV
2b
3b
4b
5b
92
112
387, 308
385
417, 324, 291
405, 324, 276
495
492
500
490
531
528
525
518
22
12
83
62
0.99 (0.91)
1.00 (0.92)
0.88 (0.83)
0.96 (0.89)
2.69
2.64
2.61
2.55
-5.31/-2.62
-5.32/-2.68
-5.23/-2.62
-5.29/-2.74
a
b
Measured in CHCl3. Determined by the dilution method. c Calculated by optical edge.
-20.4 ppm, in accord with the values for silicon-bridged
bithiophenes that appear at -20 ppm. The structure of
4b has been determined by X-ray crystallography.17 The
structure of 4b is shown in Figure 1. Crystallographic
data and processing parameters are given in ref 17. The
X-ray study of 4b indicates complete planarity in the
tricyclic system, possessing a C2 axis. The thiophene
rings are almost planar, with maximum deviations from
the mean plane of the thiophene ring of 0.03 Å for C24.
The bond angles and distances for 4b are comparable
to those found in silicon-bridged bithiophene.18 All of
the compounds are soluble in common organic solvents
such as dichloromethane, THF, and toluene.
The thermal properties of the new compounds were
determined by DSC and TGA measurements (Table 1).
F igu r e 2. Absorption and emission spectra of 2b-5b in
All the compounds are thermally stable up to 280 °C in
air. The compounds 2b-3b readily form glass on cooling
the melt sample. The glass transition temperatures (Tg
) 92-112 °C) are higher than those of commonly used
hole-transporting materials, 1,4-bis(1-naphthylphenyl-
amino)biphenyl (R-NPD, Tg ) 100 °C) and 1,4-bis-
(phenyl-m-tolylamino)biphenyl (TPD, Tg ) 60 °C).1a The
incorporation of the asymmetric nature of 2b-3b at the
peripheral amines is intended to facilitate formation of
amorphous glasses.
P h otoph ysical P r oper ties. The UV absorption spec-
tra were taken in CHCl3 and are shown in Figure 2,
with the λmax values collected in Table 1. The absorption
spectra of 2b-5b exhibit an intense absorption band
CHCl3.
between 385 and 417 nm, indicating that electronic
transitions are mostly πfπ*, originating from the
π-conjugation chain extending from the conjugated
substituents on the dithienosilole, and absorption bands
at <325 nm are assigned as nfπ* transitions. The
absorption maximum is significantly red-shifted (35-
70 nm) compared to that previously reported for
dithienosilole,8a but the absorption is comparable to that
of diaryldithienosiloles and 2,5-dithienylsilole deriv-
atives,8b indicating that the introduction of both aryl
groups on the central dithienosilole leads to a smaller
band gap energy. The red shifts of 4b and 5b from 2b
and 3b can be explained by the fact that the rigid
dipyridylamino and azaindole groups have stronger
electron-donating ability than the triarylamine groups.
Compounds 2b-5b exhibit intense fluorescence emis-
sion in the green wavelength region (492-500 nm). In
addition, the same emission spectra are obtained ir-
respective of the applied excited wavelengths, indicating
that downhill relaxation to the lowest excited state is
(17) Crystal data. Compound 4b:
C56H44N6O2S2Si, M ) 925.18,
triclinic, space group P1h, a ) 9.9720(10) Å, b ) 14.7777(16) Å, c )
16.6067(18) Å, R ) 74.422(2)°, â ) 84.049(2)°, γ ) 80.928(2)°, U )
2323.0(4) Å3, Z ) 2, µ(Mo KR) ) 0.192 mm-1, 14 374 reflections
measured, 10 384 unique (Rint ) 0.01621). The final Rw (F2) was 0.1664
(all data).
(18) Ohshita, J .; Nodono, M.; Watanabe, T.; Ueno, Y.; Kunai, A.;
Harima, Y.; Yamasita, K.; Ishikawa, M. J . Organomet. Chem. 1998,
553, 487.

Luminescence of Dithienosiloles
Organometallics, Vol. 23, No. 22, 2004 5283
F igu r e 4. Luminance vs applied electric field character-
istics of the devices A-D.
Electr olu m in escen t Devices. Since the compounds
2b-5b possess both silole and amino groups, they might
be used in OLED as hole-transporting, electron-trans-
porting, or emitting layer. We have investigated all
three possibilities in our device. Among the compounds,
2b was selected for the device fabrication because of its
better volatility and higher quantum efficiency. To check
whether 2b can permit the injection of both holes and
electrons from the electrodes and transport them in a
solid device, two devices were fabricated, with compound
2b having the following structures: ITO/TPD (50 nm)/
2b (50 nm)/Al:Li and ITO/2b (50 nm)/Alq3 (50 nm)/Al:
Li. The device ITO/TPD/2b/Al:Li (power efficiency, 0.092
lm/W; luminance, 64 cd/m2, external quantum efficiency,
0.04 at 100 mA of current density) failed to produce
reasonable light output. However, the device ITO/2b/
Alq3/Al:Li produced a green light and reached the
maximum value of 1530 cd/m2 at 13 V. The observation
clearly suggests that the compound 2b transports holes
better than it carries electrons. To evaluate emitting
properties of the compounds 2b-5b, we fabricated
multilayer EL devices: ITO/TPD (50 nm)/compounds
2b-5b (20 nm)/BCP (10 nm)/Alq3 (20 nm)/Al:Li with
device A, B, C, and D corresponding to 2b, 3b, 4b, and
5b, respectively. They consist of the emitting layer of
compounds 2b-5b with the hole-transporting layer of
TPD, the hole-blocking layer of BCP, and electron-
transporting layer of Alq3. The BCP, as an effective hole-
blocking layer, was deposited to prevent carrier recom-
bination in the Alq3. The I-V-L characteristics are shown
in Figure 4 and Figure 5. The turn-on voltage of the
devices A-D is about 4 V. Obviously device A has the
highest luminescence among all the devices. The EL
spectra (Figure 6) of the four devices fabricated from
2b-5b were superimposable to the PL spectra (Figure
2) of 2b-5b, which implies that charge combination
occurs in the 2b-5b layer. Table 2 summarizes the
maximum luminances, luminous efficiencies, and quan-
tum efficiencies of EL for the multiple-layer devices. The
device A is green emitting with the following perfor-
mance characteristics: maximum luminance (15 000 cd/
m2), luminous efficiency (1.4 lm/W at 300 cd/m2). The
high external quantum efficiency may be due to higher
fluorescence efficiency in the solid film than in the
solution. This result indicates that the layer of 2b as
an emitting source shows comparable luminous char-
F igu r e 3. Cyclic voltammograms of 1 mM 2b (A) and 4b
(B) at a platinum disk electrode (dia. ) 100 µm for A and
1.6 mm for B); in THF containing 0.1 M TBAP; v ) 0.5 V/s
for A and 0.1 V/s for B, respectively.
efficient.19 The somewhat large Stokes shift (∼110 nm)
of λem in 2b and 3b most likely stems from the excited
state induced coplanarity of the amino substituents.
Electr och em istr y. The cyclic voltammograms (CVs)
of 2b-5b were measured in THF containing 0.1 M
tetrabutylammonium perchlorate (TBAP). Table 1 sum-
marizes the oxidation potentials of 2b-5b, 0.88-1.00
V vs SCE, obtained from CV experiments. No reduction
waves of 2b -4b were observed in the potential scan
range from -1.76 to 1.09 V except 5b. A typical CV of
2b (Figure 3A) shows no redox waves arising from the
reduction of 2b but a redox wave arising from oxidation
of 2b at 0.99 V, where a platinum disk (dia. ) 100 µm)
electrode with a scan rate of 0.5 V/s was used. The shape
of the CV wave implies adsorption/precipitation of the
oxidation product of 2b presumably because of the
change of the solubility upon oxidation.20 A similar trend
was observed in the CV of 3b (not shown). However,
the reversibility of the redox wave arising from the
oxidation is much improved in 4b and 5b (Figure 3B).
The CV of 5b reveals two irreversible reduction waves
at -1.37 and -1.66 V, which is probably ascribed to the
7-azaindole moiety (not shown). Overall, the electro-
chemical properties of 2b -4b are similar to those of
diaryldithiensiloles reported by Oshita et al.8 Thus, their
assignments can be applied to these compounds.
The HOMO energy levels of 2b-5b are calculated
from the onset of oxidation potential according to the
equation IP (ionization potential) ) {(Eonset)
ox + 4.4} V,21
and the LUMO energy level is obtained by the subtrac-
tion of the optical band gap from the IP (Table 1).
(19) Suppan, P. Chemistry and Light; The Royal Society of Chem-
istry: London, 1994.
(20) Lee, C.; Kim, C.; Park, J . W. J . Electroanal. Chem. 1994, 374,
115.
(21) Agrawal, A. K.; J enekhe, S. A. Chem. Mater. 1996, 8, 579.

5284 Organometallics, Vol. 23, No. 22, 2004
Lee et al.
Exp er im en ta l Section
All experiments were performed under a nitrogen atmo-
sphere in a Vacuum Atmospheres drybox or by standard
Schlenk techniques. THF, toluene, and ether were distilled
from sodium benzophenone. n-Hexane, CH2Cl2, and pentane
were dried and distilled from CaH2. 1H, 13C, and 29Si NMR
spectra were recorded on a Varian Mercury 300 spectrometer.
The absorption and photoluminescence spectra were recorded
on a Perkin-Elmer Lambda 2S UV-visible spectrophotometer
and a Perkin-Elmer LS fluorescence spectrometer, respec-
tively. The fluorescence quantum yields in chloroform using
9,10-diphenylanthracene as the standard were determined by
the dilution method.22 The fluorescence decay curves were
recorded on a PTI fluorescence Master 2M1 luminescence
spectrophotometer using a PTIG2-3300 nitrogen laser for
excitation. DSC measurements were carried out on a Perkin-
Elmer DSC7 calorimeter at a heating rate of 10 °C/min under
a nitrogen atmosphere. All the electrochemical measurements
were carried out in THF solutions containing 1 mM complex
and 0.1 M tetrabutylammonium perchlorate (TBAP) at room
temperature using a BAS 100B electrochemical analyzer.
Freshly distilled, degassed THF was used as the solvent. A
platinum microdisk (dia. 100 µm) or disk (dia. 1.6 mm)
electrode and platinum wire were used as a working and
counter electrode, respectively. The reference electrode used
was Ag|AgNO3 (BAS). Then, all the potential values shown
were calibrated vs SCE, unless otherwise specified, by cor-
recting Fc|Fc+ redox potential measured in 0.2 M LiClO4/CH3-
CN as 0.31 V vs SCE.23 4,4-Diphenyl-2,6-dibromodithienosilole,8b
4-bromo-4′-(1-naphthylphenylamino)biphenyl, 4-bromo-4′-(phen-
yl-m-tolylamino)biphenyl,16 dipyridin-2-yl-(4-bromophenyl)-
amine, and 1-(4-bromophenyl)pyrrolo[2,3-b]pyridine17 were
prepared according to the literature.
F igu r e 5. Luminance vs current density characteristics
of the devices A-D.
2-{4-[4′-(P h en yl-m -t olyla m in o)-4-b ip h en ylyl]}-4,4,5,5-
tetr a m eth yl-1,3,2-d ioxa bor ola n e (2a ). To a stirred THF
solution (25 mL) of 4-bromo-4′-(phenyl-m-tolylamino)biphenyl
(0.50 g, 1.20 mmol) was added a solution of n-BuLi (1.5 mL,
1.6 M in hexane) at -78 °C, and the reaction mixture was
stirred for 30 min. To this was added 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (0.25 mL). The reaction mix-
ture was warmed to ambient temperature and stirred for 24
h. The solvent was removed under reduced pressure and
extracted with CH2Cl2. The pure product 2a was isolated by
chromatographic workup (eluent: CH2Cl2/hexane (1:1), Rf )
0.2) in 75% yield. Mp: 91-93 °C. 1H NMR (CDCl3): δ 7.85 (d,
2H, J ) 8.1 Hz), 7.58 (d, 2H, J ) 8.1 Hz), 7.49 (d, 2H, J ) 8.1
Hz), 7.29-6.85 (m, 11H), 2.28 (s, 3H, Ph-CH3), 1.36 (s, 12H,
C-CH3). 13C{1H} NMR (CDCl3): δ 147.7, 143.4, 142.5, 139.6,
138.4 135.3, 134.6, 130.9, 129.8, 128.5, 128.0, 127.7, 126.1,
125.8, 125.1, 124.2, 124.0, 123.2, 83.9, 25.0, 21.1. MS: m/z 461
[M+]. Anal. Calcd for C31H32BNO2: C, 80.70; H, 6.99. Found:
C, 80.22; H, 6.76.
2-{4-[4′-(1-Naph th ylph en ylam in o)-4-biph en ylyl]}-4,4,5,5-
tetr a m eth yl-1,3,2-d ioxa bor ola n e (3a ). Compound 3a was
prepared using the same procedure as described for 2a in 72%
yield. Mp: 95-97 °C. 1H NMR (CDCl3): δ 7.96 (d, 1H, J ) 8.2
Hz), 7.90 (d, 1H, J ) 8.0 Hz), 7.84 (d, 2H, J ) 8.2 Hz), 7.64 (d,
1H, J ) 8.0 Hz), 7.57-6.90 (m, 15H), 1.35 (s, 12H, C-CH3).
13C{1H} NMR (CDCl3): δ 148.24, 143.49, 143.44, 135.44,
135.36, 133.88, 131.40, 130.32, 129.09, 128.58, 127.96, 127.76,
127.33, 126.77, 126.43, 125.94, 125.36, 124.38, 122.67, 122.17,
121.87, 121.40, 83.88, 25.02. MS: m/z 497 [M+]. Anal. Calcd
for C34H32BNO2: C, 82.09; H, 6.48. Found: C, 81.72; H, 6.26.
Dip yr id in -2-yl-(4-tr im eth ylsta n n ylp h en yl)a m in e (4a ).
To a stirred THF solution (30 mL) of dipyridin-2-yl-(4-
bromophenyl)amine (0.73 g, 2.24 mmol) was added a solution
of n-BuLi (1.69 mL, 1.6 M)/hexane at -78 °C, and the mixture
F igu r e 6. EL spectra of devices A-D.
Ta ble 2. Electr olu m in escen ce Ch a r a cter istics of
Devices
maximum
luminance
(cd/m2)
luminous
efficiency at
quantum
efficiency
(%)
devicea
300 cd/m2 (lm/W)
A
B
C
D
15 000 (at 11 V)
10 000 (at 11 V)
5200 (at 12.5 V)
6400 (at 11.5 V)
1.4
1.2
0.88
0.69
0.92
0.87
0.63
0.85
a
Devices are fabricated as follows: ITO/TPD (50 nm)/com-
pounds 2b-5b (20 nm)/BCP (10 nm)/Alq3 (20 nm)/Al:Li with device
A, B, C, and D corresponding to 2b, 3b, 4b, and 5b, respectively.
acteristics relative to the layer of Alq3, which is known
as a typical green-emitting substance and that the EL
originates from the electronically excited singlet state
of compound 2b.
In summary, we were able to incorporate a dithieno-
silole group into bis(diarylamino)aryl using the Suzuki
coupling reaction or Stille cross-coupling reaction. Com-
pounds 2b-5b exhibit intense fluorescence emission in
the green wavelength region. EL devices based on
compounds 2b-5b were fabricated. Device A with 2b
as the emitter offers bright green emission with good
luminous efficiency and very high luminance, which is
comparable to those of Alq3.
(22) Parker, C. A.; Rees, W. T. Analyst 1960, 85, 587.
(23) Bard, A. J .; Faulkner, L. R. Electrochemical Methods: Funda-
mentals and Applicatoions, 2nd ed.; Wiley: New York, 2001; p 811.

Luminescence of Dithienosiloles
Organometallics, Vol. 23, No. 22, 2004 5285
was stirred for 1 h at that temperature. The solution was
warmed to ambient temperature and stirred for 1 h. The
solution was cooled to -78 °C, and Me3SnCl (2.7 mL, 1 M in
THF) was added. The solution was warmed to room temper-
ature and stirred for 12 h. The pure product 4a was isolated
by chromatographic workup (eluent: EA/hexane (1:1), Rf )
0.3) in 63% yield. 1H NMR (CDCl3): δ 8.32 (d, 2H, J ) 6.2
Hz), 7.53 (dd, 2H, J ) 6.8 Hz, 6.2 Hz), 7.48 (d, 2H, J ) 8.7
Hz), 7.15 (d, 2H, J ) 8.7 Hz), 6.99 (d, 2H, J ) 8.1 Hz), 6.91
(dd, 2H, J ) 8.1 Hz, J ) 6.8 Hz), 0.28 (s, 9H, Sn-CH3). 13C-
{1H} NMR (CDCl3): δ 158.2, 148.7, 148.4, 145.1, 139.1, 137.5,
126.7, 118.2, 117.1, -9.5. MS: m/z 411 [M+]. Anal. Calcd for
[M+]. Anal. Calcd for C76H52N2S2Si: C, 84.09; H, 4.83. Found:
C, 83.78; H, 4.72.
4,4-Dip h e n yl-2,6-b is[4-(d ip yr id yla m in o)p h e n yl]d i-
th ien osilole (4b). To a stirred toluene solution (20 mL) of 4a
and silole 1 (0.19 g, 0.48 mmol) was added LiCl (0.08 g, 1.92
mmol) and Pd(PPh3)2Cl2 (0.01 g). The solution was refluxed
for 3 days. The solvent was removed in vacuo and extracted
with CH2Cl2. The solution was chromatographed using ethyl
1
acetate as eluent to afford 4b. H NMR (CDCl3): δ 8.34-7.16
(m, 36H). 13C{1H} NMR (CDCl3): δ 158.1 157.9, 149.4, 148.8,
148.4, 145.6, 144.2, 144.1, 140.9, 137.6, 135.4, 131.5, 127.3,
126.9, 118.5, 117.4, 116.9. 29Si NMR (CDCl3): δ -20.4. MS:
m/z 836 [M+]. Anal. Calcd for C52H36N6S2Si: C, 74.61; H, 4.33.
Found: C, 74.39; H, 4.15.
C
19H21N3Sn: C, 55.65; H, 5.16. Found: C, 55.45; H, 5.05.
1-(4-Tr im et h ylst a n n ylp h en yl)p yr r olo[2,3-b]p yr id in e
(5a ). Compound 5a was prepared using the same procedure
as described for 4a in 54% yield. 1H NMR (CDCl3): δ 8.37 (dd,
1H, J ) 4.8 Hz, J ) 1.5 Hz), 7.97 (dd, 1H, J ) 7.8 Hz, J ) 1.5
Hz). 7.73 (d, 2H, J ) 7.8 Hz), 7.65 (d, 2H, J ) 7.8 Hz), 7.51 (d,
1H, J ) 4.8 Hz), 7.12 (dd, 1H, J ) 7.8 Hz, J ) 4.5 Hz), 6.62 (d,
1H, J ) 4.5 Hz), 0.33(s, 9H, Sn-CH3). 13C{1H} NMR (CDCl3):
δ 143.9, 143.4, 140.3, 138.6, 136.8, 129.1, 127.7, 123.7, 121.6,
117.3, 116.1, -9.9. MS: m/z 358 [M+]. Anal. Calcd for C16H18N2-
Sn: C, 53.82; H, 5.08. Found: C, 53.61; H, 4.97.
4,4-Dip h en yl-2,6-bis{4-[4′-(p h en yl-m -tolyla m in o)-4-bi-
p h en ylyl]}d ith ien osilole (2b). To a mixture of borolane 2a
(0.46 g, 1.00 mmol), silole 1 (0.21 g, 0.42 mmol), and Pd(PPh3)4
(0.05 g) were added degassed 2 M K2CO3 (2.1 mL, 4.2 mmol)
and toluene (30 mL). The yellow solution was refluxed for 3
days. The solvent was removed in vacuo and extracted with
CH2Cl2. The solution was chromatographed using CH2Cl2/
hexane (1:1) as eluent to afford 2b in 72% yield. Mp: 130C.
1H NMR (CDCl3): δ 7.66-6.86 (m, 46H), 2.28 (s, 6H, Ph-CH3).
13C{1H} NMR (CDCl3): δ 147.8, 147.6, 144.4, 141.1, 140.1,
140.0, 139.3, 136.3, 135.7, 135.6, 134,9. 134.0, 132.3, 132.2,
131.9, 130.5, 129.8, 128.4, 127.7, 127.3, 127.1, 126.9, 126.2,
125.1, 124.3, 123.3, 122.7, 121.2, 21.8. 29Si NMR (CDCl3): δ
-19.4. MS: m/z 1012 [M+]. Anal. Calcd for C70H52N2S2Si: C,
82.96; H, 5.17. Found: C, 83.22; H, 5.30.
4,4-Diph en yl-2,6-bis[4-(7-azain dol-1-yl)ph en yl]dith ien o-
silole (5b). Compound 5b was prepared using the same
procedure as described for 4b. H NMR (CDCl3): δ 8.40 (dd,
1
2H, J ) 4.2 Hz, J ) 1.5 Hz), 7.98 (dd, 2H, J ) 4.8 Hz, J ) 1.5
Hz), 7.83-7.77 (m, 12H), 7.55 (d, 2H, J ) 3.6 Hz), 7.49 (s, 2H),
7.47-7.39 (m. 6H), 7.15 (dd, 2H, J ) 8.1 Hz, J ) 4.8 Hz), 6.65
(d, 2H, J ) 3.6 Hz). 13C{1H} NMR (CDCl3): δ 149.7, 145.5,
143.0, 141.2, 137.6, 136.2, 134.9, 132.4, 131.5, 129.5, 128.9,
128.4, 128.0, 127.3, 126.3, 126.0, 124.8, 121.8. 29Si NMR
(CDCl3): δ -21.6. MS: m/z 730 [M+]. Anal. Calcd for
C
46H30N4S2Si: C, 75.58; H, 4.14. Found: C, 75.31; H, 3.98.
F a br ica tion of OLED Devices. The ITO electrode was
cleaned by sonication in a detergent solution for 4 min and
washed with distilled water. Further sonication in 1,1,1-
trichloroethane for 3 min was done before blowing dry under
nitrogen. Organic EL devices were fabricated by sequential
vacuum deposition of organic materials onto an ITO, followed
by vacuum deposition of Li and Al onto the organic layer. The
organic layers were deposited at a rate of 0.2 nm/s at 10-5 Torr.
The current-voltage and luminance were measured with a
Keithley 2400 Source and a Newport Optical meter.
Ack n ow led gm en t. This work was supported by a
Korea University Grant (2002) and the R&D center of
the Korea Energy Management Corporation (KEMCO)
through the Energy Technology R&D program of the
Korea Ministry of Commerce, Industry.
4,4-Dip h en yl-2,6-bis{4-[4′-(1-n a p h th ylp h en yla m in o)-4-
bip h en ylyl]}d ith ien osilole (3b). Compound 3b was pre-
pared using the same procedure as described for 2b. 1H NMR
(CDCl3): δ 7.96 (d, 2H, J ) 8.1 Hz), 7.90 (d, 2H, J ) 8.1 Hz),
7.80 (d, 2H, J ) 8.3 Hz), 7.66-6.98 (m, 46H). 13C{1H} NMR
(CDCl3): δ 148.2, 148.1, 145.4, 144.3, 144.1, 143.4, 140.1, 140.0,
136.4, 135.7, 135.6, 135.4, 134.9, 133.2, 132.2, 132.1, 131.4,
129.1, 128.5, 128.3, 127.9, 127.5, 126.8, 126.4, 124.4, 122.7,
122.2, 121.9, 120.4. 29Si NMR (CDCl3): δ -19.8. MS: m/z 1085
Su p p or tin g In for m a tion Ava ila ble: This material is
available free of charge via the Internet at http://pubs.acs.org.
OM049626E