Oligo(2,7-fluorene ethynylene)s with pyrene moieties: Synthesis, characterization, photoluminescence, and electroluminescence

Article abstract of DOI:10.1021/jo7013388

(Chemical Equation Presented) A series of highly fluorescent, pyrene-modified oligo(2,7-fluorene ethynylene)s were synthesized and fully characterized. Different emissions were observed between pyrene-end-capped and pyrene-centered oligo(2,7-fluorene ethynylene)s. Moreover, these oligomers were applied to fabricate organic light-emitting diodes (OLEDs), and bright blue or green electroluminescence (EL) with good device performances was achieved in multilayer OLEDs. These pyrene-modified oligo(2,7-fluorene ethynylene)s could be used as optoelectronics materials or models to investigate fluorescent structure-property relationship of fluorene derivatives.

Full text of DOI:10.1021/jo7013388

Oligo(2,7-fluorene ethynylene)s with Pyrene Moieties: Synthesis,
Characterization, Photoluminescence, and Electroluminescence
Zujin Zhao,† Xinjun Xu,‡ Zhitao Jiang,† Ping Lu,*,† Gui Yu,‡ and Yunqi Liu*,‡
Department of Chemistry, Zhejiang UniVersity, Hangzhou 310027, PR China, and Laboratory of Organic
Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China
pinglu@zju.edu.cn
ReceiVed June 29, 2007
A series of highly fluorescent, pyrene-modified oligo(2,7-fluorene ethynylene)s were synthesized and
fully characterized. Different emissions were observed between pyrene-end-capped and pyrene-centered
oligo(2,7-fluorene ethynylene)s. Moreover, these oligomers were applied to fabricate organic light-emitting
diodes (OLEDs), and bright blue or green electroluminescence (EL) with good device performances was
achieved in multilayer OLEDs. These pyrene-modified oligo(2,7-fluorene ethynylene)s could be used as
optoelectronics materials or models to investigate fluorescent structure-property relationship of fluorene
derivatives.
1. Introduction
conjugated polymers are typically characterized by chemical
composition and distribution in chain length. The polydispersity
in chain lengths leads to complex structural characteristics of
the thin films and makes it very difficult for researchers to
establish a proper structure-property relationship.10 In contrast,
monodisperse conjugated oligomers are structurally uniform
Organic materials with extended π-conjugated systems, such
as conjugated polymers1 and monodisperse conjugated oligo-
mers,2 have been intensively studied in recent years because of
their potential applications in photonics and optoelectronics, such
as field-effect transistors (FETs),3-5 OLEDs,6,7 solar cells,8 and
solid-state lasers,9 and the academic interest on the structure-
property relationship of molecules. Purified by precipitation,
(4) Meijer, E. J.; de Leeuw, D. M.; Setayesh, S.; van Veenendaal, E.;
Huisman, B.-H.; Blom, P. W. M.; Hummelen, J. C.; Scherf, U.; Klapwijk,
T. M. Nat. Mater. 2003, 2, 678.
* To whom correspondence should be addressed. Phone: + 86-571-879-
52543.
(5) Horowitz, G. J. Mater. Res. 2004, 19, 1946.
† Zhejiang University.
(6) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burnss, P. L.; Holmes, A. B. Nature 1990, 347,
539.
‡ Chinese Academy of Sciences.
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10.1021/jo7013388 CCC: $37.00 © 2007 American Chemical Society
Published on Web 10/04/2007
J. Org. Chem. 2007, 72, 8345-8353
8345

Zhao et al.
SCHEME 1
with superior chemical purity accomplished by recrystallization
or column chromatography. Thus, oligomers generally possess
more predictable and reproducible properties, facilitating sys-
tematic investigation of structure-property relationship and
optimization. So there exists intensive interest in preparing
conjugated oligomers as model systems for conjugated polymer
investigations or as a distinct class of materials themselves.11
Recent studies have shown that fluorene-based materials hold
great potential applications,12 such as highly thermal stable and
efficient emissive materials for OLEDs and carrier transport
materials for FETs.13 Chemically, fluorene derivatives are
interesting since they contain a rigid biphenyl plane and the
facile substitution at the C9 site, which provides the possibility
of improving the solubility and processability and of controlling
interchain interactions to prevent excimer formation in the
excited state.14,15 Monodisperse oligofluorenes, which constitute
an important class of π-conjugated organic materials because
of their excellent chemical, thermal, and photochemical stabili-
ties as well as the ease of structure tuning to adjust the electronic
and morphological properties, have been extensively investigated
and explored for various functional properties including EL and
liquid crystalline and two-photon absorption properties for
optoelectronic applications in the past few years. They are
capable of self-organization into uniaxially aligned, defect-free
films for the realization of strongly polarized and highly efficient
organic EL at a performance level consistently better than that
of polymer analogues.16 On the other hand, pyrene-containing
molecular rods have been reported by Leroy-Lhez et al.17 These
π-conjugated oligomers exhibit intensive visible electronic
absorption and fluorescence emission properties. Here we
synthesized and characterized a series of well-defined, pyrene-
modified oligo(2,7-fluorene ethynylene)s based on the previous
works of other group and ourselves18 in order to study the
influence of pyrene on the PL and EL properties of the
oligomers. These oligomers exhibited good solubility, stable
thermal properties, and strong PL emission. Moreover, multi-
layer OLEDs using these oligomers as emissive layers were
fabricated and investigated.
2. Results and Discussion
2.1. Synthesis of Oligomers. The well-defined, pyrene-
containing oligo(2,7-fluorene ethynylene)s (Scheme 1) were
synthesized in moderate yields by the Pd/Cu-catalyzed Sono-
gashira coupling reaction. The synthetic routes are illustrated
in Scheme 2. Compounds 1, 2, 7, and 12 were prepared
according to references’ methods.18 1,6-Diethynylpyrene and
1,8-diethynylpyrene19 (13 and 14), synthesized by reference’s
method, served as cores of pyrene-centered oligomers. Initial
Sonogashira coupling of alkyne 1 with an excess amount of
diiodide 2 yielded intermediate 3. The excess diiodide 2 was
used to suppress the formation of troublesome byproduct 1,4-
di(pyren-1-yl)buta-1,3-diyne from self-coupling of 1. Then
treatment of 3 with 3-methyl-1-butyn-3-ol was followed by
(10) Jo, J.; Chi, C.; Ho¨ger, S.; Wegner, G.; Yoon, D. Y. Chem.sEur. J.
2004, 10, 2681.
(11) Wu, C.-C.; Liu, T.-I.; Lin, Y.-T.; Hung, W.-Y.; Ke, T.-H. Appl.
Phys. Lett. 2004, 85, 1172.
(12) (a) Wong, K.-T.; Chien, Y.-Y.; Chen, R.-T.; Wang, C.-F.; Lin, Y.-
T.; Chiang, H.-H.; Hsieh, P.-Y.; Wu, C.-C.; Chou, C. H.; Su, Y. O.; Lee,
G.-H.; Peng, S.-M. J. Am. Chem. Soc. 2002, 124, 11576. (b) Katsis, D.;
Geng, Y. H.; Ou, J. J.; Culligan, S. W.; Trajkovska, A.; Chen, S. H.;
Rothberg, L. J. Chem. Mater. 2002, 14, 1332. (c) Geng, Y.; Culligan, S.
W.; Trajkovska, A.; Wallace, J. U.; Chen, S. H. Chem. Mater. 2003, 15,
542. (d) Culligan, S. W.; Geng, Y.; Chen, S. H.; Klubek, K.; Vaeth, K. M.;
Tang, C. W. AdV. Mater. 2003, 15, 1176. (e) Wu, C.-C.; Lin, Y.-T.; Wong,
K.-T.; Chen, R.-T.; Chien, Y.-Y. AdV. Mater. 2004, 16, 61.
(13) (a) Li, Z. H.; Wong, M. S.; Fukutani, H.; Tao, Y. Chem. Mater.
2005, 17, 5032. (b) Yasuda, T.; Fujita, K.; Tsutsui, T. Chem. Mater. 2005,
17, 264. (c) Lai, W.-Y.; Zhu, R.; Fan, Q.-L.; Hou, L.-T.; Cao, Y.; Huang,
W. Macromolecules 2006, 39, 3707.
(16) (a) Geng, Y.; Chen, A. C. A.; Ou, J. J.; Chen, S. H.; Klubek, K.;
Vaeth, K. M.; Tang, C. W. Chem. Mater. 2003, 15, 4352. (b) Chen, A. C.
A.; Culligan, S. W.; Geng, Y.; Chen, S. H.; Klubek, K. P.; Vaeth, K. M.;
Tang, C. W. AdV. Mater. 2004, 16, 783.
(17) (a) Leroy-Lhez, S.; Parker, A.; Lapouyade, P.; Belin, C.; Ducasse,
L.; Oberle´, J.; Fages, F. Photochem. Photobiol. Sci. 2004, 3, 949. (b) Leroy-
Lhez, S.; Allain, M.; Oberle´, J.; Fages, F. New J. Chem. 2007, 31, 1013.
(18) (a) Lee, S. H.; Nakamura, T.; Tsutsui, T. Org. Lett. 2001, 3, 2005.
(b) Zhao, Z.; Xu, X.; Wang, F.; Yu, G.; Lu, P.; Liu, Y.; Zhu, D. Synth.
Met. 2006, 156, 209.
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(15) (a) Lemmer, U.; Hein, S.; Mahrt, R. F.; Scherf, U.; Hopmeir, M.;
Wiegner, U.; Go¨bel, R. O.; Mu¨llen, K.; Bassler, H. Chem. Phys. Lett. 1995,
240, 371. (b) Jenekhe, S. A.; Osaheni, J. A. Science 1994, 265, 765.
(19) Leroy-Lhez, S.; Fages, F. Eur. J. Org. Chem. 2005, 2684.
8346 J. Org. Chem., Vol. 72, No. 22, 2007

Oligo(2,7-fluorene ethynylene)s with Pyrene Moieties
SCHEME 2a
a Reagents and conditions: (a) CuI, Pd(PPh3)2Cl2, Ph3P, NEt3, N2, reflux; (b) 3-methyl-1-butyn-3-ol, CuI, Pd(PPh3)2Cl2, Ph3P, NEt3, N2, reflux; (c) KOH,
2-propanol, reflux.
FIGURE 1. Absorption spectra of oligomers in CH2Cl2 solutions (a) and in thin neat films (b).
deprotection and coupling cycles to afford intermediate 6.
Similar procedures were performed to get intermediates 8 and
11. Intermediates 4 and 9 were separated by column chroma-
tography (silica gel, hexane/dichloromethane/ethyl acetate as
eluent) and used in the next reaction without characterization.
Final coupling in the presence of Pd/Cu catalyst led to our
desired oligomers successfully. Compound Py2F,18b which had
been reported elsewhere, was used for comparative investigation.
All of these oligomers were highly soluble in common organic
solvents, such as CH2Cl2, CHCl3, tetrahydrofuran (THF), and
toluene, due to the n-heptyl substituents, and their molecular
melting points of these oligomers were detected by differential
scanning calorimetry (DSC), and the glass transition tempera-
tures were not clearly observed. The decomposition temperatures
(Td) measured by thermogravimetric analysis (TGA) (10 °C/
min, N2) were in the range of 382-414 °C with 5% loss of
initial weight.
2.2. Optical Properties. The normalized absorption spectra
of oligomers in dilute CH2Cl2 solutions and in thin neat films
are shown in Figure 1. For pyrene-end-capped oligomers Py2F,
Py2F3, and Py2F5, their optical absorption spectra in solution
were similar to those of oligo(2,7-fluorene ethynylene)s18a but
with a certain red shift. Their maximum absorption peaks of
Py2F, Py2F3, and Py2F5 were located at 426, 421, and 418
1
structures were verified by H and 13C NMR spectroscopy,
MALDI-TOF MS measurement, and element analysis. No
J. Org. Chem, Vol. 72, No. 22, 2007 8347

Zhao et al.
TABLE 1. Photophysical Properties of Oligomers
λAbs.a (nm)
CH2Cl2 (ꢀ × 105)
426 (1.23), 411 (1.30)
421 (2.53), 398 (2.21)
λ
Em. (nm)
b
c
Eg
E°x
(V)
HOMO/LUMOd
(eV)
Td
(°C)
1/2
compound
film
CH2Cl2
film
Φ
(eV)
Py2F
Py2F3
Py2F5
1,6-PyF6
1,8-PyF6
1,6-Py3F4
436
429
420
456
459
457
436, 464
430, 456
429, 455
464, 494
465, 495
465, 495
492
489
476
472, 504
472, 504
475, 504
0.78
0.93
0.98
0.81
0.82
0.84
2.78
2.83
2.85
2.63
2.64
2.63
0.42
0.47
0.45
0.45
0.42
0.49
-4.82/-2.04
-4.87/-2.04
-4.85/-2.00
-4.85/-2.22
-4.82/-2.18
-4.89/-2.26
382
404
410
392
401
414
418 (4.20), 398 (3.79)
450 (0.70), 430 (0.89), 378 (1.06)
452 (0.61), 430 (0.87), 382 (1.24)
451 (2.05), 421 (3.63), 398 (2.87)
a Mole absorption coefficient (ꢀ): M-1 cm-1 b Determined from UV-vis absorption spectra. c E°x ) half-wave oxidation potential; potentials vs Ag/
.
1/2
AgCl, working electrode Pt, 0.1 M Bu4NPF6-CH2Cl2, scan rate 100 mV/s. d HOMO ) E°x + 4.4 eV; LUMO ) HOMO - Eg (eV).
1/2
nm, respectively, which could be ascribed to the π-π* transition
of the molecular backbone.20 The interesting thing was that the
maximum absorption peak blue-shifted as the molecular chain
length increased, which was opposite to the findings for oligo-
(2,7-fluorene ethynylene)s.18a We inferred that the lowest-lying
energy chromophore of this series of compounds should localize
on the pyrene-containing segments with a certain extension
through ethynylene and fluorene units. However, with the
increment of the molecular length, the conjugated backbone
containing ethynylene unit(s) might have complicated intramo-
lecular conformations, which might not be necessary to have a
planar one all the time except for the case of Py2F. Two pyrene
units in Py2F could conjugate into the whole molecule backbone
efficiently, resulting in longest absorption wavelength. On the
other hand, with the elongation of chain length due to the
accumulation of the fluorene units, two pyrene units might not
conjugate to the whole molecular backbone efficiently at one
time, thus the influence of pyrene became weaker and the
absorption spectra showed the characteristic of oligo(2,7-
fluorene ethynylene).
1,6-PyF6 and 1,6-Py3F4, containing pyrene in the middle
of the molecular backbone, exhibited almost the same maximum
absorption peaks at ∼451 nm, which were red-shifted by ∼33
nm compare to that of pyrene-end-capped oligomer Py2F5.
Broad absorption band (from 360 to 420 nm) with continuously
large molar absorption coefficient (ꢀ) (Table 1) was observed
for 1,6-Py3F4, which indicated that this molecule could be
excited at a relative wide range with an efficient energy transfer.
The red-shifted absorption peak, which might be arising from
the pyrene core, could also be observed from other π-conjugated
systems, such as poly(fluorene-co-perylene),21 poly(fluorene-
co-anthracene),22 and poly(p-phenylene ethynylene-co-an-
thracene).23 1,8-PyF6 exhibited a similar maximum absorption
peak in comparison to that of 1,6-PyF6, but the relative
absorption intensity changed, which might be due to the
interruption of delocalization of the π-electrons along the
oligomer backbone by the 1,8-pyrene linkage. Consequently,
different location of pyrene units had different influence on the
oligomers’ absorption spectra. The strongly red-shifted absorp-
tion spectra were observed from these pyrene-centered oligomers
with respect to those of pyrene-end-capped ones. This should
be ascribed to the better π-conjugation of the disubstituted
pyrene core, and the vibronic features of pyrene were a good
indication.
Solid-state absorption spectra of all oligomers were almost
identical, but had a slightly bathochromic shift (2-10 nm)
compared to those in solutions, which indicated that these
oligomers exhibited very similar conformations in both states.24
By inspecting the edge of the absorption spectra, the energy
band gaps (Eg) of oligomers were obtained (Table 1). It was
observed that the Eg values slightly decreased with the increment
of the molecular length. Moreover, the obvious difference
between Eg of Py2F5 (2.85 eV) and that of 1,6-PyF6 (2.63 eV)
indicated that different position of pyrene in oligomers would
inevitably result in different energy states of the whole
molecules.
The normalized PL emission spectra of oligomers, excited
at 380 nm, in dilute CH2Cl2 solutions and in thin neat films are
shown in Figure 2. The emission peaks were independent of
excitation wavelength, and the excitation spectra, given in
Supporting Information, were similar to their absorption spectra.
In CH2Cl2 solutions, Py2F, Py2F3, and Py2F5 showed a main
emission peak at 436, 430, and 429 nm, respectively, with a
shoulder peak at 464, 456, and 455 nm, respectively. In
comparison with the emission spectrum of 1,1′-(9,9-dimethyl-
9H-fluorene-2,7-diyl)dipyrene (DPF),25 Py2F emitted light at
longer wavelength in CH2Cl2 solution. Emission difference
between Py2F and DPF should be ascribed to the ethynylene
linkages that elongated the conjugation length of the molecule
and made the molecule more planar. The blue-shifted emission
of Py2F3 and Py2F5 with respect to that of Py2F was ascribed
to the same reason for blue-shifted absorption spectra of them.
On the other hand, although the shapes of absorption spectra
of 1,6-PyF6, 1,8-PyF6, and 1,6-Py3F4 were different, these
compounds exhibited quit similar emission spectra. We inferred
that these compounds had similar transition energy gaps
resulting from the existence of disubstituted pyrene moieties in
both oligomers. By exciting these compounds at 380 nm, they
exhibited quite similar main emission peaks at about 465 nm
with shoulder peaks at about 495 nm, actually emanating from
disubstituted pyrene, which exhibited distinct red-shifted emis-
sions (∼35 nm) in comparison with those of oligomers end-
capped with pyrene moieties, such as Py2F5.
In thin neat films, the main emission peaks of Py2F, Py2F3,
and Py2F5 were located at 492, 489, and 476 nm, respectively,
with the disappearance of the fine structures of spectra.
Emissions were strongly red-shifted compared to those in
solutions (g47 nm). In terms of DPF,25 it exhibited an emission
peak at 460 nm in film as reported, which was blue-shifted (32
nm) with respect to that of Py2F. In some ways, the extended
structure between pyrene and fluorene resulting from the triple
(20) Zhou, X.-H.; Zhang, Y.; Xie, Y.-Q.; Cao, Y.; Pei, J. Macromolecules
2006, 39, 3830.
(21) Kla¨rner, G.; Lee, J.-I.; Davey, M. H.; Miller, R. D. AdV. Mater.
1999, 11, 115.
(22) Kla¨rner, G.; Davey, M. H.; Chen, W.-D.; Scott, J. C.; Miller, R. D.
AdV. Mater. 1998, 10, 993.
(23) Swager, T. M.; Gil, C. J.; Wrighton, M. S.; J. Phys. Chem. 1995,
99, 4886.
(24) Chen, S.; Xu, X.; Liu, Y.; Yu, G.; Sun, X.; Qiu, W.; Ma, Y.; Zhu,
D. AdV. Funct. Mater. 2005, 15, 1541.
(25) Tao, S.; Peng, Z.; Zhang, X.; Wang, P.; Lee, C.-S.; Lee, S.-T. AdV.
Funct. Mater. 2005, 15, 1716.
8348 J. Org. Chem., Vol. 72, No. 22, 2007

Oligo(2,7-fluorene ethynylene)s with Pyrene Moieties
FIGURE 2. PL emission spectra of oligomers in CH2Cl2 solutions (a) and in thin neat films (b).
FIGURE 3. Cyclic voltammogram of oligomers (0.5 mM) in 0.1 M Bu4NPF6-THF; scan rate 100 mV/s.
bonds reduced the steric hindrance of the bulky rigid pyrene
and made the molecule more planar.21,22,26 The strongly red-
shifted emission of Py2F in thin neat film should be due to the
facile formation of excimers between pyrene units,27 which
caused the low-energy emission.
2.3. Cyclic Voltammetric Studies. The electrochemical
properties of these oligomers were investigated by cyclic
voltammetry at room temperature, and the results are listed in
Table 1. Figure 3 shows cyclic voltammograms (CVs). All these
compounds displayed two oxidation peaks, the first was
reversible, and the second was irreversible. The half-wave
oxidation potential (Eox1/2) was in the range of 0.42-0.49 V.
HOMO and LUMO levels of these oligomers were determined
All the synthesized oligomers were highly fluorescent. The
PL quantum yields were measured in degassed cyclohexane
solutions using 9,10-diphenylanthracene (DPA, Φ ) 0.95)28 as
a standard. The PL quantum yields of these oligomers were in
the range of 0.78-0.98, which became higher with the increment
of the molecular length. Moreover, Py2F5 (Φ ) 0.98) exhibited
higher quantum yields than those of oligomers with similar chain
length, 1,6-PyF6 (Φ ) 0.81), 1,8-PyF6 (Φ ) 0.82), and 1,6-
Py3F4 (Φ ) 0.84). The difference of quantum yields might be
that excitons were confined to the whole backbone of Py2F5,
thereby giving higher quantum yields, whereas in the case of
pyrene-centered oligomers, some energy loss might happen
during the excitons migration.29
by the Eox1/2 and Eg (Table 1). HOMO levels (HOMO ) Eox
1/2
+ 4.4 eV) were in the range of -4.82 to -4.89 eV, which were
higher than that of the most widely used hole-transport material
4,4′-bis(1-naphthylphenylamino)biphenyl (NBP) (HOMO )
-5.5 eV, LUMO ) -2.4 eV) and thus might be beneficial for
the hole injection and transport.30 LUMO levels (LUMO )
HOMO - Eg) were in a range of -2.00 to -2.26 eV. Results
obtained here further supported that LUMO, HOMO, as well
as the energy gap of these oligo(2,7-fluorene ethynylene)s could
be easily modified or tuned by introduction of the pyrene into
(26) Lee, J.-I.; Zyung, T.; Miller, R. D.; Kim, Y. H.; Jeoung, S. C.; Kim,
D. J. Mater. Chem. 2000, 10, 1547.
(27) Nandy, R.; Subramoni, M.; Varghese, B.; Sankararaman, S. J. Org.
Chem. 2007, 72, 938.
(29) Li, Y.; Ding, J.; Day, M.; Tao, Y.; Lu, J.; D’iorio, M. Chem. Mater.
2004, 16, 2165.
(30) Yu, G.; Yin, S.; Liu, Y.; Shuai, Z.; Zhu, D. J. Am. Chem. Soc.
2003, 125, 14816.
(28) Melhuish, W. H. J. Phys. Chem. 1961, 65, 229.
J. Org. Chem, Vol. 72, No. 22, 2007 8349

Zhao et al.
FIGURE 4. Normalized electroluminescence (EL) spectra of oligomers.
FIGURE 5. Brightness-voltage diagrams for devices based on oligomers.
the different position of conjugated oligo(2,7-fluorene ethy-
nylene) backbone.
molecules to align under the electric field. Thus, the pyrene
groups on one Py2F molecule could be close to the pyrene
groups on the neighboring molecule, and when the distance
between the two fluorophores was appropriate, excimers were
formed under the electric excitation. It is well-known that
excimers could result in a red-shifted EL emission, so Py2F
exhibits more significantly red-shifted EL spectrum than Py2F3
and Py2F5.
On the other hand, for the EL spectra of 1,6-PyF6, 1,8-PyF6,
and 1,6-Py3F4, similar green emissions dominated with very
narrow bands from 472 to 504 nm, which were similar to their
PL emission spectra in films except for slight red shifts. The
similarity between PL and EL spectra of these pyrene-centered
oligomers indicated that both PL and EL originated from the
same radiative decay process of singlet excitons.32
The brightness-voltage characteristics for the EL devices
based on these oligomers are shown in Figure 5, and the device
performances are summarized in Table 2. The turn-on voltages
of these devices were in the range of 4.3-5.4 V. The device
based on Py2F exhibited maximum brightness at 2869 cd m-2
at 10.5 V and a highest external quantum efficiency of 0.64%.
While with the increase of the fluorene moiety, the device based
on Py2F3 and Py2F5 exhibited a substantial decrease of
maximum brightness from 918 cd m-2 at 9.0 V to 207 cd m-2
at 8.0 V as well as the external quantum efficiency of Py2F3
(0.41%) and Py2F5 (0.15%). The devices based on the other
2.4. Electroluminescent Properties. To investigate the EL
properties of these oligomers, devices with the same configura-
tions of ITO/poly(3,4-ethylenedioxythiophene):poly(4-styrene-
sulfonate) (PEDOT:PSS) (30 nm)/oligomer (50 nm)/1,3,5-tris(N-
phenylbenzimidazol-2-yl)benzene (TPBI) (20 nm)/Al (100 nm),
for the purpose of comparison, were fabricated. The EL spectra
and current density-voltage-brightness characteristics were
measured under ambient conditions. For oligomers Py2F,
Py2F3, and Py2F5, the EL emissions were observed from green
(532 nm) to blue (468 nm) with the increment of the fluorene
moieties (Figure 4). The EL emission of Py2F was significantly
red-shifted (40 nm) in comparison with that of PL emission in
film, while the EL emission of Py2F5 was slightly blue-shifted
(8 nm). Although similar emission color in solutions and in thin
neat films were obtained for these compounds, EL emissions
present different color. Since Py2F had the shortest chain length
among Py2F, Py2F3, and Py2F5, we thought that Py2F had
the highest chain mobility. Materials with repeating fluorene
units had been reported to undergo a process of alignment in
an electric field, and molecules with the high chain mobility
more easily formed excimers than molecules with low chain
mobility.31 Due to the higher chain mobility of Py2F compared
to that of Py2F3 and Py2F5, it was more possible for Py2F
(31) (a) Weinfurtner, K.-H.; Fujikawa, H.; Tokito, S.; Taga, Y. Appl.
Phys. Lett. 2000, 76, 2502. (b) Bradley, D. D. C.; Grell, M.; Long, X.;
Mellor, H.; Grice, A. Proc. SPIE 1998, 3145, 254.
(32) Shih, P.-I.; Tseng, Y.-H.; Wu, F.-I.; Dixit, A. K.; Shu, C.-F. AdV.
Funct. Mater. 2006, 16, 1582.
8350 J. Org. Chem., Vol. 72, No. 22, 2007

Oligo(2,7-fluorene ethynylene)s with Pyrene Moieties
FIGURE 6. Current density-voltage diagrams for devices based on oligomers.
TABLE 2. Summary of Device Performances
turn-on
EL
(nm)
fwhm
(nm)
voltage
(V)
ηext
ηmax, ext
(%)
ηmax, L
Lmax
device
Py2F
Py2F3
Py2F5
1,6-PyF6
1,8-PyF6
1,6-Py3F4
(%, 100 cd m-2
)
(cd A-1
)
(cd m-2, V)
532
496, 524
468
476, 500
476, 504
480, 504
113
94
76
60
63
54
4.5
4.3
5.4
4.9
5.4
4.4
0.57
0.32
0.08
0.21
0.19
0.13
0.64
0.41
0.15
0.22
0.22
0.14
2.03
1.06
0.21
0.44
0.44
0.28
2869, 10.5
918, 9.0
207, 8.0
493, 8.5
520, 8.5
340, 6.5
three 1,6-PyF6, 1,8-PyF6, and 1,6-Py3F4 exhibited comparable
brightness, 493 cd m-2 at 8.5 V, 520 cd m-2 at 8.5 V, and 340
cd m-2 at 6.5 V, respectively, as well as an external quantum
efficiency, 0.22, 0.22, and 0.14%, respectively. The interesting
thing was the decrease of the devices’ performances as chain
length elongated, for which the exact reason was not very clear
yet. One possible explanation for this phenomenon was that the
oligomers with more fluorene units were more easily crystallized
than the oligomers with fewer fluorene units. Geng et al.
reported that the chain length of oligofluorenes played an
important role in solid morphology, and with increasing the
chain length, the oligofluorenes tended to be crystallized.33 Due
to the fact that our oligomers also had fluorene units, we thought
that increasing the chain length (that was increasing the fluorene
units) would also cause the oligomers to be crystallized. It was
well-known that crystallization was disadvantageous to the
electroluminescent properties of organic materials. As a result,
the maximum luminance of these oligomers decreased with the
chain length.
The current-voltage characteristics for EL devices are
illustrated in Figure 6. From Figure 6a, it was obviously
observed that the current density became greater with the
increase of oligomeric length. This result was in accordance
with the previously reported dependence of carrier mobility on
oligomer length, that is, the mobilities of both carriers increased
with the backbone length.34 By comparison, relatively greater
current density could also be observed in oligomers with more
pyrene moieties.
synthesized and fully characterized. The results, obtained
through inspecting the emission spectra of these pure oligomers,
demonstrated a certain structure-property relationship of these
oligomers. Furthermore, bright blue or green EL emission with
good device performances was achieved in multilayer OLEDs
based on these oligomers, which indicated that they were
promising light-emitting materials for OLEDs.
4. Experimental Section
1-(2-(2-Ethynyl-9,9-diheptyl-9H-fluoren-7-yl)ethynyl)-
pyrene (3): 1-Ethynylpyrene (1) (0.2 g, 1 mmol), 9,9-diheptyl-
2,7-diiodo-9H-fluorene (2) (3 g, 5 mmol), cuprous iodide (10 mg,
0.05 mmol), Pd(PPh3)2Cl2 (3.5 mg, 0.005 mmol), triphenylphos-
phine (PPh3, 5 mg, 0.02 mmol), and 150 mL of dry triethylamine
were placed in a 250 mL round bottle flask equipped with a Teflon-
covered magnetic stir bar. After the solution was purged with
nitrogen for 30 min, it was refluxed under nitrogen for 4 h. The
reaction mixture was filtered, and the filtrate was evaporated under
reduced pressure. The residue was purified through column
chromatography (silica gel, hexane/dichloromethane as eluent). In
this way, 0.59 g (83% yield) of 3 was obtained: 1H NMR (CDCl3)
δ 0.65 (m, 4H), 0.81 (t, 6H, J ) 7.5 Hz), 1.08 (br, 12H), 1.17-
1.20 (m, 4H), 1.94-2.05 (m, 4H), 7.46 (d, 1H, J ) 8 Hz), 7.65-
7.71 (m, 5H), 8.02-8.14 (m, 4H), 8.19-8.24 (m, 4H), 8.72 (d,
1H, J ) 8.5 Hz) ppm; 13C NMR (CDCl3) δ 14.3, 22.8, 24.0, 29.2,
30.2, 40.5, 55.8, 89.4, 93.4, 96.4, 118.2, 120.2, 122.0, 122.7, 124.6,
124.8, 125.9, 126.2, 126.5, 127.5, 128.4, 128.6, 129.9, 131.2, 131.4,
131.5, 131.6, 132.1, 136.3, 140.4, 140.8, 150.6, 153.7 ppm. MS
(MALDI) (m/z): 712.2 (M+).
1-(7-Ethynyl-9,9-diheptyl-9H-fluoren-2-ylethynyl)pyrene
(5): 3 (712 mg, 1 mmol), 3-methyl-1-butyn-3-ol (126 mg, 1.5
mmol), cuprous iodide (10 mg, 0.05 mmol), Pd(PPh3)2Cl2 (3.5 mg,
0.005 mmol), triphenylphosphine (5 mg, 0.02 mmol), and 100 mL
of dry triethylamine were placed in a 150 mL round bottle flask
equipped with a Teflon-covered magnetic stir bar. After the solution
was purged with nitrogen for 30 min, it was refluxed under nitrogen
for 8 h. The reaction mixture was filtered, and the filtrate was
evaporated under reduced pressure. The residue was purified
3. Conclusions
In summary, a series of well-defined, pyrene-modified oligo-
(2,7-fluorene ethynylene)s with high quantum yields have been
(33) Geng, Y.; Trajkovska, A.; Katsis, D.; Ou, J. J.; Culligan, S. W.;
Chen, S. H. J. Am. Chem. Soc. 2002, 124, 8337.
(34) (a) Gundlach, D. J.; Nichols, J. A.; Zhou, L.; Jackson, T. N. Appl.
Phys. Lett. 2002, 80, 2925. (b) Gundlach, D. J.; Lin, Y.-Y.; Jackson, T. N.;
Schlom, D. G. Appl. Phys. Lett. 1997, 71, 3853.
J. Org. Chem, Vol. 72, No. 22, 2007 8351

Zhao et al.
through column chromatography (silica gel, hexane/dichloromethane/
ethyl acetate as eluent) to get 4. Then 4, 500 mg of KOH, and 100
mL of 2-propanol were placed in a 150 mL round bottle flask
equipped with a Teflon-covered magnetic stir bar. After the solution
was purged with nitrogen for 30 min, it was refluxed under nitrogen
for 4 h. The solvent was then removed, and the crude product was
purified by column chromatography (silica gel, hexane/dichlo-
romethane as eluent) to afford 5 (476 mg, 78% total yield): 1H
NMR (CDCl3) δ 0.63-0.65 (m, 4H), 0.80 (t, 6H, J ) 7.5 Hz),
1.07 (br, 12H), 1.16-1.19 (m, 4H), 1.99-2.04 (m, 4H), 3.17 (s,
1H), 7.50-7.52 (m, 2H), 7.67-7.68 (m, 2H), 7.71-7.75 (m, 2H),
8.02-8.16 (m, 4H), 8.20-8.25 (m, 4H), 8.73 (d, 1H, J ) 1.0 Hz)
ppm; 13C NMR (CDCl3) δ 14.3, 22.8, 24.0, 29.2, 30.2, 32.1, 40.6,
55.6, 77.6, 84.9, 89.4, 96.4, 118.2, 120.2, 120.4, 121.0, 122.6, 124.7,
124.8, 124.9, 125.9, 125.9, 125.9, 126.2, 126.5, 126.8, 127.6, 128.4,
128.6, 129.9, 131.2, 131.4, 131.6, 132.2, 140.9, 141.5, 151.3, 151.6
ppm. MS (MALDI) (m/z): 610.5 (M+).
122.4, 122.4, 123.1, 126.1, 126.2, 127.1, 127.8, 130.8, 131.0, 132.3,
136.2, 140.3, 140.6, 140.7, 140.8, 141.0, 141.7, 150.5, 151.0, 151.2,
151.3, 151.3, 153.6 ppm. MS (MALDI) (m/z): 1256.9 (M+).
1-(2-(9,9-Diheptyl-2-(2-(9,9-diheptyl-2-(2-(9,9-diheptyl-2-(2-
(pyren-1-yl)ethynyl)-9H-fluoren-7-yl)ethynyl)-9H-fluoren-7-yl)-
ethynyl)-9H-fluoren-7-yl)ethynyl)pyrene (Py2F3): The procedure
was analogous to that described for 6 (62% yield): 1H NMR
(CDCl3) δ 0.68 (br, 12H), 0.79-0.83 (m, 18H), 1.09 (br, 36H),
1.18-1.20 (m, 12H), 2.01-2.07 (m, 12H), 7.58-7.61 (m, 8H),
7.69-7.77 (m, 10H), 8.03-8.17 (m, 8H), 8.21-8.26 (m, 8H), 8.75
(d, 2H, J ) 9.0 Hz) ppm; 13C NMR (CDCl3) δ 14.3, 22.9, 24.1,
29.3, 30.3, 32.1, 55.6, 55.6, 89.4, 91.1, 96.5, 118.2, 120.3, 120.3,
120.4, 120.3, 122.3, 122.5, 124.7, 124.9, 125.9, 125.9, 126.2, 126.2,
126.5, 127.6, 128.4, 128.6, 129.9, 131.0, 131.2, 131.4, 131.5, 131.6,
132.2, 141.0, 141.2, 151.4, 151.5, 151.5 ppm. MS (MALDI)
(m/z): 1580.0 (M+). Anal. Calcd for C121H126: C, 91.96; H, 8.04.
Found: C, 91.99; H, 8.01.
1-[7-(9,9-Diheptyl-7-iodo-9H-fluoren-2-ylethynyl)-9,9-dihep-
tyl-9H-fluoren-2-ylethynyl]pyrene (6): 5 (610 mg, 1 mmol), 2
(1842 mg, 3 mmol), cuprous iodide (10 mg, 0.05 mmol), Pd(PPh3)2-
Cl2 (3.5 mg, 0.005 mmol), triphenylphosphine (5 mg, 0.02 mmol),
and 100 mL of dry triethylamine were placed in a 150 mL round
bottle flask equipped with a Teflon-covered magnetic stir bar. After
the solution was purged with nitrogen for 30 min, it was refluxed
under nitrogen for 4 h. The reaction mixture was filtered, and the
filtrate was evaporated under reduced pressure. The residue was
purified through column chromatography (silica gel, hexane/
dichloromethane as eluent). In this way, 790 mg (72% yield) of 6
was obtained: 1H NMR (CDCl3) δ 0.61-0.67 (m, 8H), 0.79-0.83
(m, 12H), 1.05-1.08 (m, 24H), 1.16-1.20 (m, 8H), 1.94-2.00 (m,
4H), 2.05-2.06 (m, 4H), 7.33-7.34 (m, 2H), 7.54-7.60 (m, 4H),
7.66-7.77 (m, 6H), 8.03-8.17 (m, 4H), 8.21-8.26 (m, 4H) 8.75
(d, 1H, J ) 9.0 Hz) ppm; 13C NMR (CDCl3) δ 14.3, 22.9, 23.1,
24.0, 29.2, 29.3, 30.3, 32.1, 32.1, 40.7, 40.8, 55.4, 55.6, 89.3, 90.6,
93.4, 96.5, 118.2, 119.9, 120.1, 120.2, 120.3, 121.9, 122.4, 123.1,
124.6, 124.8, 124.7, 125.7, 125.9, 126.1, 126.2, 126.5, 127.1, 127.5,
127.8, 128.4, 128.6, 129.9, 130.8, 131.0, 131.2, 131.4, 131.5, 131.5,
132.1, 132.3, 136.2, 140.3, 140.9, 141.2, 141.7, 150.5, 151.2, 151.4,
151.5, 153.6 ppm. MS (MALDI) (m/z): 1096.9 (M+).
2-((9,9-Diheptyl-9H-fluoren-2-yl)ethynyl)-9,9-diheptyl-7-iodo-
9H-fluorene (8): The procedure was analogous to that described
for 3 (86% yield): 1H NMR (CDCl3) δ 0.60 (br, 8H), 0.78-0.82
(m, 12H), 1.05-1.06 (m, 24H), 1.15-1.19 (m, 8H), 1.92-1.99 (m,
8H), 7.31-7.35 (m, 3H), 7.43 (d, 1H, J ) 8.5 Hz), 7.52-7.56 (m,
4H), 7.64-7.70 (m, 5H) ppm; 13C NMR (CDCl3) δ 14.3, 22.8,
23.9, 24.0, 29.2, 30.2, 30.3, 32.0, 40.5, 40.7, 55.4, 55.7, 90.5, 91.2,
93.3, 119.9, 120.1, 120.2, 121.7, 121.9, 122.6, 123.1, 126.1, 126.2,
127.1, 127.8, 130.8, 131.0, 132.4, 136.2, 140.4, 140.5, 140.7, 141.7,
150.5, 151.1, 151.3, 153.7 ppm. MS (MALDI) (m/z): 872.7 (M+).
2-((9,9-Diheptyl-9H-fluoren-2-yl)ethynyl)-7-ethynyl-9,9-dihep-
tyl-9H-fluorene (10): The procedure was analogous to that
described for 5 (73% yield): 1H NMR (CDCl3) δ 0.60 (br, 8H),
0.78-0.82 (m, 12H), 1.05 (br, 24H), 1.16-1.19 (m, 8H), 1.95-
1.99 (m, 8H), 3.15 (s, 1H), 7.31-7.35 (m, 3H), 7.47-7.50 (m,
2H), 7.54-7.57 (m, 4H), 7.63-7.70 (m, 4H) ppm; 13C NMR
(CDCl3) δ 14.3, 22.8, 24.0, 29.2, 30.2, 32.0, 40.6, 40.7, 55.4, 55.5,
77.5, 84.9, 90.5, 91.2, 119.9, 120.1, 120.2, 120.3, 120.9, 121.7,
122.6, 123.1, 126.2, 126.8, 127.1, 127.8, 130.8, 131.0, 131.5, 140.7,
141.5, 141.7, 151.1, 151.3, 151.4 ppm. MS (MALDI) (m/z): 771.2
(M+).
1-(2-(9,9-Diheptyl-2-(2-(9,9-diheptyl-2-(2-(9,9-diheptyl-2-(2-
(9,9-diheptyl-2-(2-(9,9-diheptyl-2-(2-(pyren-1-yl)ethynyl)-9H-
fluoren-7-yl)ethynyl)-9H-fluoren-7-yl)ethynyl)-9H-fluoren-7-yl)-
ethynyl)-9H-fluoren-7-yl)ethynyl)-9H-fluoren-7-yl)ethynyl)-
pyrene (Py2F5): The procedure was analogous to that described
for 4 (48% yield): 1H NMR (CDCl3) δ 0.64-0.68 (m, 20H), 0.79-
0.83 (m, 30H), 1.07-1.09 (m, 60H), 1.17-1.22 (m, 20H), 2.02-
2.07 (m, 20H), 7.57-7.61 (m, 16H), 7.70-7.77 (m, 14H), 8.03-
8.17 (m, 8H), 8.21-8.27 (m, 8H), 8.75 (d, 2H, J ) 9.0 Hz) ppm;
13C NMR (CDCl3) δ 14.3, 22.9, 24.0, 24.0, 29.3, 29.4, 30.03, 30.3,
32.1, 40.8, 55.0, 55.6, 89.4, 91.1, 96.5, 118.2, 120.3, 120.3, 120.4,
122.2, 122.3, 122.5, 124.6, 124.8, 124.9, 125.9, 126.2, 126.5, 127.6,
128.4, 128.6, 129.9, 131.0, 131.2, 131.4, 131.5, 131.6, 132.1, 141.0,
141.1, 151.4, 151.4, 151.5 ppm. MS (MALDI) (m/z): 2347.6 (M+).
Anal. Calcd for C179H198: C, 91.51; H, 8.49. Found: C, 91.50; H,
8.57.
1,6-Bis((7-((7-((9,9-diheptyl-9H-fluoren-2-yl)ethynyl)-9,9-di-
heptyl-9H-fluoren-2-yl)ethynyl)-9,9-diheptyl-9H-fluoren-2-yl)-
ethynyl)pyrene (1,6-PyF6): The procedure was analogous to that
described for 4 (48% yield): 1H NMR (CDCl3) δ 0.63-0.69 (m,
24H), 0.79-0.83 (m, 36H), 1.06-1.10 (m, 72H), 1.16-1.20 (m,
24H), 1.97-2.07 (m, 24H), 7.32-7.36 (m, 6H), 7.55-7.62 (m,
16H), 7.70-7.79 (m, 16H), 8.23 (d, 4H, J ) 8.0 Hz), 8.29 (d, 2H,
J ) 8.0 Hz), 8.78 (d, 2H, J ) 9.5 Hz) ppm; 13C NMR (CDCl3) δ
14.3, 22.9, 24.0, 29.2, 29.3, 30.3, 32.1, 32.1, 40.7, 40.8, 55.4, 55.5,
55.6, 89.3, 90.6, 91.1, 91.2, 91.2, 97.0, 118.9, 119.9, 120.3, 120.4,
121.7, 122.2, 122.4, 123.1, 124.6, 125.5, 126.2, 126.6, 127.1, 127.8,
128.4, 130.3, 130.8, 131.0, 131.0, 131.3, 131.3, 132.3, 140.7, 140.9,
140.9, 141.0, 141.3, 141.7, 151.1, 151.3, 151.4, 151.4, 151.5, 151.6
ppm. MS (MALDI) (m/z): 2507.8 (M+). Anal. Calcd for
C190H226: C, 90.92; H, 9.08. Found: C, 90.89; H, 9.12.
1,8-Bis((7-((7-((9,9-diheptyl-9H-fluoren-2-yl)ethynyl)-9,9-di-
heptyl-9H-fluoren-2-yl)ethynyl)-9,9-diheptyl-9H-fluoren-2-yl)-
ethynyl)pyrene (1,8-PyF6): The procedure was analogous to that
described for 4 (52% yield): 1H NMR (CDCl3) δ 0.63-0.69 (m,
24H), 0.79-0.83 (m, 36H), 1.06-1.10 (m, 72H), 1.17-1.19 (m,
24H), 1.97-2.09 (m, 24H), 7.34-7.35 (m, 6H), 7.56-7.62 (m,
16H), 7.71 (m, 10H), 7.74-7.79 (m, 6H), 8.11 (s, 2H), 8.20 (d,
2H, J ) 8.5 Hz), 8.29 (d, 2H, J ) 7.5 Hz), 8.92 (s, 2H) ppm; 13
C
NMR (CDCl3) δ 14.3, 14.3, 22.8, 22.9, 24.0, 29.2, 29.3, 30.3, 32.1,
40.7, 40.8, 55.4, 55.5, 55.6, 89.2, 90.6, 91.0, 91.1, 91.2, 97.0, 118.9,
119.9, 120.2, 120.3, 120.4, 120.4, 121.6, 122.2, 122.3, 123.1, 124.6,
125.5, 126.2, 126.8, 127.1, 127.8, 128.3, 130.3, 130.8, 131.0, 131.3,
131.6, 132.1, 140.7, 140.9, 141.0, 141.3, 141.7, 151.0, 151.2, 151.3,
151.4, 151.5 ppm. MS (MALDI) (m/z): 2507.3 (M+). Anal. Calcd
for C190H226: C, 90.92; H, 9.08. Found: C, 90.93; H, 9.09.
1,6-Bis((7-((9,9-diheptyl-7-(pyren-1-ylethynyl)-9H-fluoren-2-
yl)ethynyl)-9,9-diheptyl-9H-fluoren-2-yl)ethynyl)pyrene (1,6-
Py3F4): The procedure was analogous to that described for 4 (40%
yield): 1H NMR (CDCl3) δ 0.69 (br, 16H), 0.81-0.84 (m, 24H),
1.11 (br, 48H), 1.19-1.22 (m, 16H), 2.07-2.09 (m, 16H), 7.61-
7.64 (m, 8H), 7.71-7.72 (m, 4H), 7.75-7.79 (m, 12H), 8.04-
2-((9,9-Diheptyl-7-iodo-9H-fluoren-2-yl)ethynyl)-7-((9,9-di-
heptyl-9H-fluoren-2-yl)ethynyl)-9,9-diheptyl-9H-fluorene (11):
The procedure was analogous to that described for 6 (77% yield):
1H NMR (CDCl3) δ 0.61 (br, 12H), 0.78-0.83 (m, 18H), 1.06 (br,
36H), 1.17-1.18 (m, 12H), 1.94-2.02 (m, 12H), 7.33-7.34 (m,
3H), 7.44 (d, 1H, J ) 8.0 Hz), 7.52-7.58 (m, 8H), 7.66-7.71 (m,
7H) ppm; 13C NMR (CDCl3) δ 14.3, 14.3, 22.8, 23.9, 24.0, 29.2,
29.2, 29.3, 30.2, 30.3, 32.0, 32.1, 40.5, 40.7, 40.8, 55.4, 55.5, 55.7,
90.6, 90.9, 91.1, 91.2, 93.4, 119.9, 120.1, 120.2, 121.6, 121.9, 122.1,
8352 J. Org. Chem., Vol. 72, No. 22, 2007

Oligo(2,7-fluorene ethynylene)s with Pyrene Moieties
8.13 (m, 6H), 8.17 (d, 2H, J ) 8.0 Hz), 8.22-8.31 (m, 14H), 8.75-
8.80 (m, 4H) ppm; 13C NMR (CDCl3) δ 14.3, 22.9, 24.1, 29.2,
29.3, 30.3, 32.1, 40.8, 55.6, 89.3, 89.4, 91.1, 91.2, 96.5, 97.0, 118.2,
118.9, 120.4, 122.3, 122.4, 122.5, 124.6, 124.6, 124.8, 124.8, 125.5,
125.9, 126.2, 126.2, 126.5, 126.6, 127.5, 128.4, 128.6, 129.9, 130.3,
131.1, 131.2, 131.4, 131.4, 131.5, 132.1, 132.3, 140.9, 141.0, 141.1,
141.2, 151.4, 151.5 ppm. MS (MALDI) (m/z): 2187.7 (M+). Anal.
Calcd for C168H170: C, 92.17; H, 7.83. Found: C, 92.11; H, 7.90.
Fabrication and Characterization of OLEDs. All of the
devices were fabricated on bare ITO substrates that were subse-
quently cleaned by detergent, deionized water, acetone, and ethanol.
PEDOT:PSS was spin-coated on ITO glass and was baked at 100
°C for 2 h. Compounds Py2F, Py2F3, Py2F5, 1,6-PyF6, 1,8-PyF6,
and 1,6-Py3F4 were spin-coated onto the PEDOT:PSS layer from
their toluene solutions. Films of TPBI and Al cathode were formed
by vacuum deposition under a pressure of 3 × 10-4 Pa. The
deposition rate for TPBI and Al cathode layers was 1 and 5 Å/s,
respectively. The thickness of the thin films was monitored by a
quartz crystal oscillator placed near the substrates and was calibrated
ex situ by an Ambios Technology XP-2 surface profilometer. EL
spectra were recorded with a Photo Research PR-650 spectropho-
tometer. Current-voltage characteristics were measured with a
Hewlett-Packard 4140B semiconductor parameter analyzer. A
Newport 2835-C multifunction optical meter was used to measure
the luminescence output.
Acknowledgment. P.L. thanks the National Natural Science
Foundation of China (20674070) and the Natural Science
Foundation of Zhejiang Province (R404109). This work was
partially supported by the Major State Basic Research Develop-
ment Program and the Chinese Academy of Sciences.
Supporting Information Available: General information,
excitation spectra, and NMR and mass spectra of intermediates and
oligomers. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO7013388
J. Org. Chem, Vol. 72, No. 22, 2007 8353