Synthesis and characterization of monodisperse oligofluorenes

Article abstract of DOI:10.1002/chem.200305659

An efficient synthesis of 9,9-bis(2-ethylhexyl)fluorene oligomers up to the heptamer is reported, with repetitive Suzuki and Yamamoto coupling reactions employed in the synthesis. The key steps for preparation of the essential intermediates include Pd-catalyzed transformation of aryl bromides to aryl boronic esters (Miyaura reaction) and the application of the much higher reactivity of aryl boronic esters over aryl bromides in the Pd-catalyzed cross-coupling reaction with aryl diazonium salts. Variation of the UV/Vis absorption and photoluminescence characteristics with chain length is reported. Moreover, glass transition and liquid-crystal characteristics of the oligomers are described and compared with those of the polymer.

Full text of DOI:10.1002/chem.200305659

FULL PAPER
Synthesis and Characterization of Monodisperse Oligofluorenes
Jungho Jo,+[b] Chunyan Chi,+[a] Sigurd Hˆger,[c] Gerhard Wegner,*[a] and Do Y. Yoon*[b]
Abstract: An efficient synthesis of 9,9-
bis(2-ethylhexyl)fluorene oligomers up
to the heptamer is reported, with repet-
itive Suzuki and Yamamoto coupling
reactions employed in the synthesis.
The key steps for preparation of the es-
sential intermediates include Pd-cata-
lyzed transformation of aryl bromides
to aryl boronic esters (Miyaura reac-
tion) and the application of the much
higher reactivity of aryl boronic esters
over aryl bromides in the Pd-catalyzed
cross-coupling reaction with aryl diazo-
nium salts. Variation of the UV/Vis ab-
sorption and photoluminescence char-
acteristics with chain length is report-
ed. Moreover, glass transition and
liquid-crystal characteristics of the
oligomers are described and compared
with those of the polymer.
Keywords: fluorene ¥ glasses ¥ liq-
uid crystals ¥ oligomerization ¥ pho-
toluminescence
Introduction
Polyfluorenes are readily prepared by Ni0-mediated cou-
pling of the corresponding dibromo monomers. Polymers
obtained by this method have weight-averaged molecular
weights (Mw) of the order of several hundred thousand with
polydispersities of around three (according to GPC analysis
against polystyrene standards). The long chain lengths and
the polydispersity in chain lengths lead to complex structur-
al characteristics of the thin films and make it very difficult
to establish a proper structure property relationship. More-
over, the normal synthetic procedure leads to incorporation
of a small amount of chemical defects, which may be re-
sponsible for undesirable green-band emission characteris-
tics.[8]
Therefore, for better understanding of the structure prop-
erty relationships of polyfluorenes, it would be very helpful
to study the properties of a series of pure oligomers with
well-defined length and no chemical defects. The absorption
spectra of a series of oligomers will allow the estimation of
the effective conjugation length of the polymer.[9] In addi-
tion, a detailed study of the photoluminescence spectra of
pure oligomers may help to solve questions concerning the
origin of the green-emission band observed in the photolu-
minescence and electroluminescence spectra of polyfluorene
films.[10] Moreover, well-defined, defect-free oligofluorenes
may also be welcome as active materials in organic light-
emitting diodes and organic thin-film transistors.
9,9-Disubstituted polyfluorenes find extensive scientific and
technological application as efficient organic blue-light-emit-
ting diode materials.[1,2] Polyfluorenes showextremely high
photoluminescence quantum yields, high thermal and oxida-
tive stability, and good solubility in common organic sol-
vents for easy processing by spin- or dip-coating methods.[3]
They also exhibit interesting thermotropic liquid-crystal
characteristics,[4] and consequently, upon annealing in the
nematic melts, the polymer chains were shown to be easily
aligned on a rubbed polyimide surface.[5] Such an alignment
of the polymer results in the polarization of the emitted
light and improves the charge carrier mobility, a prerequisite
for the fabrication of an organic thin-film transistor.[6] Thus,
the ability of the polyfluorenes to align excellently paves the
way to make thin films with highly anisotropic electrooptical
and electrical properties.[7]
[a] C. Chi,+ Prof. Dr. G. Wegner
Max Planck Institute for Polymer Research
Ackermannweg 10, 55128 Mainz (Germany)
Fax : (+49)6131-379-100
E-mail: wegner@mpip-mainz.mpg.de
[b] J. Jo,+ Prof. Dr. D. Y. Yoon
School of Chemistry, Seoul National University
San 56 1, Sillim-dong, Seoul, 151 747 (Korea)
Fax : (+82)2-877-6814
Monodispersed dialkyl fluorene oligomers were first re-
ported by Klaerner and Miller.[11] They showed that the Ni0-
mediated oligomerization of 2,7-dibromo-9,9-bis(n-hexyl)-
fluorene in the presence of 2-bromofluorene as an end-cap-
ping agent gives a mixture of oligomers and low-molecular-
weight polymers that could be fractionated by HPLC. From
the spectroscopic properties of the samples, the effective
E-mail: dyyoon@snu.ac.kr
[c] Prof. Dr. S. Hˆger
Polymer-Institut, Universit‰t Karlsruhe
Hertzstrasse 16, 76187 Karlsruhe (Germany)
[+] These authors contributed equally to this work as part of their Ph.D.
theses.
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G. Wegner, D. Y. Yoon et al.
FULL PAPER
conjugation length was estimated to be approximately
12 fluorene units. Lee and Tsutsui prepared a series of oli-
gofluorenes up to the tetramer by a repetitive 2n divergent
approach from 2,7-dibromo-9,9-bis(n-hexyl)fluorene, with
coupling with bis(n-hexyl)fluorene-2-borate and subsequent
bromination of the coupling product.[12] Anemian et al. syn-
thesized monodisperse dihexylfluorene oligomers up to the
hexamer by a combination of Suzuki and Yamamoto cou-
pling reactions.[13] Oligomers with n repeating units contain-
ing only one bromine atom at positions 2 or 7 on the end
fluorenes were prepared by coupling the corresponding
monoboronate (nꢀ1) with 2-bromo-7-iodo-9,9-bis(n-hexyl)-
fluorene at the iodo site, which is significantly more reactive
than the bromo site. The resulting monobromo oligomers
were then coupled by a Yamamoto reaction. Most recently,
a detailed description of the synthesis, optical properties,
and solid-state properties of defined oligofluorenes, up to
the hexadecamer, containing chiral substituents at position 9
was presented by Geng et al.[14] Here again, the iodo/bromo
selectivity in the Suzuki coupling reaction and the use of tri-
methylsilyl groups as dormant iodides were used as key fac-
tors in the oligomer synthesis.
The enormous success of the Suzuki reaction[15] in the
preparation of these oligomers arises from the high yield of
the coupling reaction together with the easy availability of
the boronic acids and the boronates.[16] They are prepared in
good to excellent yields by halogen metal exchange and
subsequent trapping of the aryl lithium compound with trial-
kylborates. Recently, the scope of this reaction has been dra-
matically expanded by the discovery that aryl boronates are
also available directly from the aryl halides by a Pd0-cata-
lyzed reaction with the pinacol ester of diboron (the
Miyaura reaction).[17] This transformation avoids the use of
strongly basic organometallic reagents and thus allows the
preparation of a wide variety of functionalized aryl boronic
esters.
Here, we present the synthesis of oligofluorenes from the
dimer up to the heptamer by Suzuki and Yamamoto reac-
tions,[18] with the Miyaura reaction employed for the first
time for the preparation of the aryl boronates. Also, we
have taken advantage of a large difference in the reactivity
between aryl diazonium salts and aryl bromides in the
Suzuki coupling reaction[19] in the preparation of the key in-
termediates. The oligomers have been characterized with re-
gards to their optical (absorption and photoluminescence)
properties and their phase behavior, including glass transi-
tion and liquid-crystal characteristics. Finally, the properties
of the oligomers are compared with those of the polymer in
order to gain newinsights into the polymer properties.
Scheme 1. Synthesis of the oligofluorenes: a) 2-Ethylhexyl bromide, 50%
aqueous NaOH/DMSO, room temperature; b) bis(pinacolato)diboron,
AcOK/DMF, [Pd(dppf)Cl2], 608C; c) [Pd(PPh3)4], toluene/aqueous
Na2CO3, reflux; d) BF3¥OEt2, butylnitrite/dichloromethane, ꢀ108C;
e) Pd(OAc)2/EtOH, reflux; f) Br2, dichloromethane, reflux; g) [Ni(cod)2],
COD, Bipy, toluene/DMF, 808C. DMSO=dimethylsulfoxide, DMF=
N,N-dimethylformamide, dppf=1,1’-bis(diphenylphosphanyl)ferrocene,
COD=cycloocta-1,5-diene, Bipy=2,2’-bipyridine.
Results and Discussion
14]
the literature.[11
However, in our synthesis, we trans-
Synthesis of oligofluorenes: The synthetic route towards the
oligofluorenes is shown in Scheme 1. First, 2,7-dibromofluor-
ene and 2-bromofluorene were alkylated with 2-ethylhexyl
bromide to give the di- and monobromides of fluorene, 1
and 3, respectively. Both of these compounds, as well as the
corresponding boronic acids, have already been reported in
formed the aryl bromides into the corresponding aryl boron-
ic esters with the Miyaura reaction. In these reactions the
corresponding boronic esters, 2 and 4, are formed in high
yields (>90%) and can easily be purified by column chro-
matography. Compounds 4 and 2 were then coupled with 3
to give the fluorenyl dimer 5 and trimer 6, respectively.
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Chem. Eur. J. 2004, 10, 2681 2688

Synthesis and Characterization of Monodisperse Oligofluorenes
2681 2688
To synthesize the longer fluorene oligomers, the unsym-
metrical monobrominated intermediates, such as 9 and 11,
are essential. However, these intermediates cannot be ob-
tained directly by bromination of 5 or 6 with bromine, since
statistical product mixtures are obtained which are very dif-
ficult to separate on a large scale. One possibility to obtain
the monobrominated intermediates is to use compounds
with one potential reaction site in a protected form (for ex-
ample, trimethylsilyl groups instead of bromo or iodo func-
tionalities[20]) as described by Geng et al.[14] Another way is
to use fluorene derivatives with two reaction sites of signifi-
cantly different reactivity. In the latter case, the use of bro-
moiodofluorene derivatives is quite obvious since the reac-
tivity of aryl iodides towards the Suzuki coupling is substan-
tially higher than the reactivity of aryl bromides; this con-
cept has already been used by Anemian et al.[13]
also be prepared by the bromination of 6, a detailed mass
spectral analysis of the crude reaction products showed that
varying amounts of tribromide contaminate the dibromide.
Since even small amounts of an impurity affect the liquid-
crystalline behavior of the oligomers, we avoided the bromi-
nation of the fluorenyl trimer and higher oligomers in our
oligomer synthesis. The fluorenyl heptamer 17 was obtained
in 38% yield by cross-coupling reaction of 10 and 16.
Optical properties of oligofluorenes: Electronic absorption
spectra of monodisperse oligo(9,9-bis(2-ethylhexyl)fluorene-
2,7-diyl) compounds 5, 6, 13, 14, 15, and 17 in diluted
chloroform solution with the same fluorene unit concentra-
tion (1.0î10ꢀ5 m) are shown in Figure 1 and the data are col-
lected in Table 1.
A good alternative approach is to use the large reactivity
difference between aryl diazonium salts and aryl bromides
in the cross-coupling reaction with aryl boronates. Since the
reaction with aryl diazonium salts does not need a base such
as Na2CO3, which is essential in the Suzuki coupling reac-
tion with aryl bromides, the coupling reaction takes place
only at the site of the diazonium salt. Hence, we employed
this reaction in our synthetic procedure as follows.
2-Amino-7-bromofluorene was alkylated with 2-ethylhex-
yl bromide to give 7 in 82% yield; 7 was subsequently trans-
formed into the corresponding diazonium salt 8 (81%).
Cross-coupling reaction of 4 and 8 with Pd(OAc)2 gave 9 in
70% yield within an hour. This result shows that the reactiv-
ity difference between aryl diazonium salts and aryl halides
is larger than that between aryl iodides and aryl bromides. 9
was transformed into the corresponding boronic ester 10 in
56% yield with the Miyaura reaction. Subsequently, the
cross-coupling reaction of 10 and 8 gave 11 in 48% yield.
Another method we have used to obtain the monobro-
mides is to treat the monoboronate with an excess of the di-
bromofluorene. Indeed, the coupling of 4 with an excess of
1 was successfully performed by using only 1.5 equivalents
of 1 to give the monobrominated dimer 9 in 50% yield (not
shown in Scheme 1). Similarly, the monobrominated trimer
11 was obtained in 45% yield by the reaction of 4 with 1.5-
fold excess of the dibrominated product 12, which was pre-
pared from 5 in 90% yield.[21] Both methods led to identical
compounds, thereby demonstrating the validity of our syn-
thetic methodology.
Figure 1. UV/Vis absorption of oligofluorenes (dimer to heptamer) in
chloroform solution at room temperature at a fixed concentration of flu-
orene repeat units of 1.0î10ꢀ5 moleLꢀ1
.
The oligofluorenes exhibit unstructured absorption bands,
as is also seen for polyfluorenes.[3] The absorption maximum
is red-shifted with increasing number (n) of fluorene units.
The molar extinction coefficients (e) of the oligofluorenes
showa good approximation of a linear increase with n from
dimer to heptamer, as seen in Table 1. The increment is
30.3î103 Lmolꢀ1 cmꢀ1 for each repeat unit. The plot of the
wave number of the maximum absorption versus 1/n follows
Yamamoto homocoupling re-
actions of 9 and 11 gave the flu-
Table 1. Summary of UV/Vis absorption (nmax(abs)) and photoluminescence (nmax(PL)) spectra for the fluorene
oligomers and polymer, from chloroform solutions and solid films.[a]
orenyl tetramer 13 and hexam-
er 15, respectively, both in
ꢁ50% yield. The fluorenyl
pentamer 14 was obtained with
a cross-coupling reaction of 9
and 2 in 47% yield. The high
reactivity of the diazonium salts
was also used to prepare the di-
Sample
Solution
Film
nmax(abs)
[cmꢀ1
emax
[L molꢀ1 cmꢀ1
nmax(PL)
[cmꢀ1
nmax(abs)
[cmꢀ1
nmax(PL)
[cmꢀ1
]
]
]
]
]
dimer 5
trimer 6
30580
28740
27930
27400
27170
26880
26110
49170
81330
111500
141700
173000
200300
27400
25380
24750
24450
24330
24270
24100
25970
30400
28650
27550
27030
26880
26810
25910
27100
25130
24390
23980
23810
23700
23590
25770
24100
23470
23150
23040
23040
22940
23870
23200
22940
22780
22730
22570
tetramer 13
pentamer 14
hexamer 15
heptamer 17
polymer
bromofluorenyl
trimer
16,
which was obtained in 54%
yield by coupling of 2 and 8.
Although 16 can, in principle,
[a] Since the resolution of the low-energy peak was too low at the temperature at which the data were record-
ed, only the nmax values of the two high-energy components are given.
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G. Wegner, D. Y. Yoon et al.
FULL PAPER
a linear fit, as shown in Figure 2. The polymer has a maxi-
mum absorption at 26110 cmꢀ1 (383 nm);[3] hence, we can
estimate an effective conjugation length of 14 repeat units
Figure 2. Plot of n˜max versus reciprocal degree of polymerization n.
from the plot in Figure 2, a figure that can be compared
with the reported value of 12 for poly(9,9-bis(n-hexyl)fluor-
ene-2,7-diyl).[11] The UV/Vis absorption spectra of thin films
of the oligofluorenes on quartz substrates are practically
identical to the solution data except for slight red-shifts in
the absorption maxima, as listed in Table 1.
Figure 3a shows the photoluminescence (PL) spectra of
the oligomers from dimer 5 to heptamer 17 in chloroform
with the same concentration of fluorene units (1.0î10ꢀ6 m),
excited at the corresponding energy of maximum absorp-
tion. Similar to polyfluorenes, three well-resolved fluores-
cence bands are observed. They may be assigned to the 0 0,
0 1, and 0 2 intrachain singlet transitions.[22] The spectral
position and the intensity of the PL maximum changes with
the number of fluorene units, n. This is explained by the in-
crease of effective conjugation from dimer 5 up to heptamer
17. Notably, the relative intensity of the three emission
bands also changes with n. The relative intensity of the 0 0
transition increases with n, while that of the 0 2 transition
decreases. This may be related to an increase of the intra-
chain coupling interaction with the molecule×s length.
Normalized solid-state PL spectra of oligofluorenes 5, 6,
13, 14, 15, and 17 from thin films on a quartz plate excited
at the absorption maxima are shown in Figure 3b and the
key data are listed in Table 1. Relative to the PL spectra
measured in solution, red shifts in the emission maxima are
observed and the relative intensities of the 0 2 intrachain
singlet transition increase in all cases. Most importantly, the
green-band emission usually seen for the polymer[3] is
absent for all of the oligomers (Figure 3b). Even upon high-
temperature annealing (1808C) in air, this green emission is
still negligible for the oligomers. This result casts doubt on
the widely discussed hypothesis that the green emission seen
with varable intensity in polymer samples (Figure 3b) origi-
nates from excimer formation by interchain interaction. It is
Figure 3. a) Fluorescence spectra of oligofluorenes (dimer to heptamer)
in chloroform solution at room temperature at a fixed concentration of
fluorene repeat units of 1î10ꢀ6 moleLꢀ1. b) Photoluminescence spectra
of thin films of the oligofluorenes (dimer to heptamer). The spectrum for
the polymer, also shown in this figure, was obtained for a sample an-
nealed at 1808C for 1 h in air.
difficult to see why such interchain interactions should be
suppressed in the case of oligomers if this explanation was
true.
Phase transition characteristics of oligofluorenes: The DSC
traces shown in Figure 4 clearly exhibit the glass transition
temperatures for all of the oligomers in the low-temperature
range, followed by an endothermic transition for the tetram-
er 13, pentamer 14, hexamer 15, and heptamer 17 as the
temperature is increased. The latter transition is identified
as the liquid-crystalline to isotropic transition from the po-
larized optical microscopy study. The Schlieren texture and
the very small enthalpy value of the transition, as shown in
Table 2, indicate that the liquid-crystal structure is probably
of nematic character, but a further study on this topic is in
progress.
The isotropization temperature Tiso of this liquid-crystal-
line to isotropic transition extrapolates to a hypothetical
Tiso(Polymer) for n!¥ of 4758C if plotted in the coordi-
nates Tiso =Tiso(n!¥)(1ꢀKXE) where XE is the mole frac-
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Synthesis and Characterization of Monodisperse Oligofluorenes
2681 2688
Conclusion
Oligofluorenes up to the heptamer can be synthesized on
the hundred-milligram scale by a stepwise route involving
Suzuki and Yamamoto coupling reactions. The synthesis of
the boronates for the Suzuki coupling is based on the Pd-
catalyzed transformation of aryl bromides into boronates, a
process that avoids strongly basic aryl lithium intermediates.
Therefore, this methodology has potential for the synthesis
of oligofluorenes containing a variety of functional groups.
The synthesis of mono- or dibrominated fluorenyl oligomers,
which are essential for expanding of the chain length, is
based on the much higher reactivity of aryl boronates over
aryl bromides in the Pd-catalyzed cross-coupling reaction
with aryl diazonium salts.
The pure oligomers as solid films do not showthe unde-
sired green-band emission characteristics of the polymer.
Moreover, they are found to align more readily to form
monodomains on various surfaces, as will be published else-
where. The oligomers from tetramer to heptamer show a
liquid-crystal phase with clearly defined isotropization tem-
peratures; this allows extrapolation to the expected isotropi-
zation temperature of the polymer at around 4758C, well
above the thermal decomposition temperature. Most impor-
tantly, the oligofluorenes do not showthe same high-order
phase that the polymer exhibits belowthe melting tempera-
ture of approximately 1608C. However, unlike the polymer,
the oligomers do showa glass transition temperature which
exhibits nꢀ1 dependence and allows extrapolation to a hypo-
thetical glass transition of the polymer at around 648C. As
this glass transition refers to a freezing of a liquid-crystal
phase not seen for the polymer, it is not too surprising that
this phenomenon cannot be detected for the polymer.
Figure 4. DSC traces for the oligofluorenes (dimer to heptamer; second
heating at 108Cminꢀ1). The DSC trace for the polymer is also shown for
comparison.
tion of end groups and K is an empirical constant. This tem-
perature is well above the decomposition range of the high
polymer. In this regard, it is important to note that the poly-
mer exhibits a well-known ™melting∫ transition around
1608C. Above 1608C the polymer exists in a nematic liquid-
crystal phase; belowthat temperature another solid phase is
formed, the true nature of which is not yet understood. It
may be of higher order smectic type but of such a rigidity of
the packing that a transition to a glassy state is suppressed.
Whether this substantial difference in the phase structure
and nature of transitions has consequences for the electro-
optical properties of these materials needs to be studied fur-
ther.
The glass transition temperatures, listed in Table 2, tend
to level off as the chain length increases and exhibit nꢀ1 de-
pendence of the type: Tg =64.0ꢀ174.7nꢀ1.
Experimental Section
General remarks: Reactions requiring an inert gas atmosphere were con-
ducted under argon and the glassware was oven-dried (1408C). Tetrahy-
drofuran (THF) was distilled from potassium prior to use. Commercially
available chemicals were used as received. 1H NMR and 13C NMR spec-
tra were recorded on Bruker DPX 250 or AC 300 spectrometers (250 and
300 MHz for 1H, 62.5 and 75.48 MHz for 13C). Chemical shifts are given
in ppm, referenced to residual proton resonances of the solvents. Thin-
layer chromatography was performed on aluminium plates precoated
with Merck 5735 silica gel 60 F254. Column chromatography was per-
formed with Merck silica gel 60 (230ꢂ400 mesh). Field desorption spec-
tra were recorded on a VG ZAB 2-SE FPD machine. Differential scan-
ning calorimetry was measured on a Mettler DSC 30 with a heating or
cooling rate of 10 Kminꢀ1. Polarization microscopy was performed on a
Zeiss Axiophot apparatus with a nitrogen-flushed Linkam THM 600 hot
stage. UV/Vis spectra were recorded at room temperature with a Perkin
Elmer Lambda 9 UV/Vis/NIR spectrophotometer. Photoluminescence
spectra were obtained on a Spex Fluorolog II (212) apparatus. Optical
properties of solid thin films were normally obtained for samples spin-
coated on a quartz substrate from dilute chloroform solutions and dried
under vacuum. Elemental analysis were performed by the University of
Mainz. Melting points were measured with a Reichert hot-stage appara-
tus and are uncorrected.
Table 2. Summary of glass transition temperature (Tg), isotropization
temperature (Tiso), and the enthalpy of isoptropization value (DHiso) for
the oligofluorenes.
Sample
Tg [K]
Tiso [K]
DHiso [J gꢀ1
]
dimer 5
trimer 6
tetramer 13
pentamer 14
hexamer 15
heptamer 17
252
274
295
301
307
315
337
399
463
519
0.50
0.47
0.71
0.74
Therefore, the extrapolated Tg for the polymer is estimat-
ed to be approximately 648C. The occurrence of this glass
transition is difficult, if not impossible, to see in the DSC
thermogram for the polymer (see Figure 4). This may be
due to the above-mentioned differences of the liquid-crystal
phases in the polymer and in the oligomers.
2,7-Dibromo-9,9-bis(2-ethylhexyl)fluorene
(1):
2-Ethylhexylbromide
(38.73 g, 185.18 mmol, 35.74 mL) was added to a mixture of 2,7-dibromo-
fluorene (25.0 g, 77.16 mmol) and triethylbenzylammonium chloride
(0.878 g, 3.86 mmol, 5 mol%) in DMSO (125 mL) and 50% aqueous
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G. Wegner, D. Y. Yoon et al.
FULL PAPER
NaOH (31 mL). The reaction mixture was stirred at room temperature
for 5 h. An excess of diethyl ether was added, the organic layer was
washed with water, diluted HCl, and brine, then dried over MgSO4. The
solvent was removed under vacuum and the residue was purified by
column chromatography over silica gel with n-hexane as the eluent (Rf =
0.78) and solidified from EtOH at ꢀ308C to give 1 as a white solid
(36.21 g, 85.6%): M.p. 45 548C; 1H NMR (250 MHz, CD2Cl2): d=7.57
7.43 (m, 6H), 1.94 (d, J=5.35 Hz, 4H), 0.89 0.68 (m, 22H), 0.55 0.41 (m,
8H) ppm; 13C NMR (62.5 MHz, CDCl3): d=152.3, 139.1, 130.1, 127.4,
121.0, 55.3, 44.3, 34.6, 33.6, 28.0, 27.1, 22.7, 14.0, 10.3 ppm; MS (FD):
m/z: 548.2 [M+].
for 27 h. After cooling to room temperature, the mixture was diluted
with ethyl acetate and the organic layer was washed with diluted HCl
and brine, then dried over MgSO4. The solvent was removed under
vacuum and the residue was purified by column chromatography over
silica gel with petroleum ether as the eluent (Rf =0.22) to give 6 as a col-
orless viscous gum (2.32 g, 63.8%): 1H NMR (250 MHz, CD2Cl2): d=
7.83 7.73 (m, 6H), 7.61 7.66 (m, 8H), 7.44 7.25 (m, 6H), 2.13 2.05 (m,
12H), 0.90 0.49 (m, 90H) ppm; 13C NMR (62.5 MHz, CDCl3): d=151.2,
150.9, 150.6, 141.1, 140.4, 140.1, 126.8, 126.3, 126.0, 124.1, 122.9, 119.7,
119.6, 54.9, 44.6, 34.6, 33.8, 28.2, 27.1, 22.8, 14.0, 10.3 ppm; MS (FD): m/
z: 1168.2 [M+]; elemental analysis: calcd for C87H122 (1167.9): C 89.47, H
10.53; found: C 89.26, H 10.42.
2-Bromo-9,9-bis(2-ethylhexyl)fluorene (3): Compound 3 was prepared ac-
cording to the method used for 1 by using 2-ethylhexylbromide (43.3 g,
224.5 mmol, 39.9 mL), 2-bromofluorene (25.0 g, 102.0 mmol), triethylben-
zylammonium chloride (1.16 g, 5.10 mmol, 5 mol%), DMSO (165 mL),
and 50% aqueous NaOH (41 mL). Purification by column chromatogra-
phy over silica gel with n-hexane as the eluent (Rf =0.72) gave 3 as a col-
2-Amino-7-bromo-9,9-bis(2-ethylhexyl)fluorene (7): Compound
7 was
prepared according to the method used for 1 by using 2-ethylhexylbro-
mide (7.78 g, 40.3 mmol, 7.2 mL), 2-amino-7-bromofluorene (5.0 g,
19.2 mmol), triethylbenzylammonium chloride (220 mg, 1 mmol,
5
mol%), DMSO (50 mL), and 50% aqueous NaOH (3.8 mL). The reac-
tion mixture was stirred for 2 h. Purification by column chromatography
over silica gel with n-hexane/dichloromethane (6.5:3.5) as the eluent
(Rf =0.47, 0.44, and 0.38; the title product separated into three spots, due
to the diaseteroisomers) gave 7 as a slightly yellowoily product (7.65 g,
1
orless liquid (43.14 g, 90.1%): H NMR (250 MHz, CD2Cl2): d=7.70 7.26
(m, 7H), 1.97 (m, 4H), 0.90 0.43 (m, 30H) ppm; 13C NMR (62.5 MHz,
CDCl3): d=152.8, 150.0, 140.3, 129.8, 127.3, 126.9, 124.0, 120.9, 120.4,
119.6, 55.1, 44.4, 34.6, 33.6, 28.0, 27.0, 22.7, 14.0, 10.4 ppm; MS (FD):
m/z: 470.2 [M+].
1
82%): H NMR (300 MHz, CD2Cl2): d=7.46 7.37 (m, 4H), 6.70 6.63 (m,
2H), 3.81 (brs, 2H), 1.84 1.90 (m, 4H), 0.92 0.73 (m, 22H), 0.57 0.52
(m, 8H) ppm; 13C NMR (75 MHz, CDCl3): d=152.5 152.4 (three peaks,
2îC), 146.9 146.8 (three peaks), 141.4, 131.5 131.4 (three peaks), 129.8,
127.4 127.3 (three peaks), 120.9, 119.9, 118.7 118.5 (three peaks), 114.2,
110.9 110.8 (three peaks), 55.2, 44.9 44.8 (four peaks), 35.0, 33.9 33.7
(four peaks), 28.5 28.3 (four peaks), 23.2, 14.3, 10.6 10.4 (four
peaks) ppm; MS (FD): m/z: 484.0 [M+].
2,7-Bis(4,4,5,5-tetramethyl[1.3.2]dioxaborolan-2-yl)-9,9-bis(2-ethylhexyl)-
fluorene (2): Under an argon atmosphere, 1 (2.43 g, 4.43 mmol), bis(pina-
colato)diboron (4.05 g, 15.94 mmol), KOAc (2.60 g, 26.57 mmol), and
Pd(dppf)Cl2 (0.226 g, 0.266 mmol) were dissolved in DMF (40 mL) and
heated to 608C overnight. After the reaction mixture was cooled to room
temperature, water and diethyl ether were added. The aqueous phase
was extracted with diethyl ether and the combined organic layers were
dried over MgSO4. The solvent was removed under vacuum and the resi-
due was purified by column chromatography over silica gel with petrole-
um ether/dichloromethane (3:1) as the eluent (Rf =0.34) and solidified
from EtOH at ꢀ308C to give 2 as a white solid (2.60 g, 91.5%): M.p.
85.5 87.68C; 1H NMR (250 MHz, CD2Cl2): d=7.84 7.69 (m, 6H), 2.00
(d, J=5.3 Hz, 4H), 1.36 (s, 24H), 0.86 0.50 (m, 22H), 0.48 0.45 (m,
8H) ppm; 13C NMR (62.5 MHz, CDCl3): d=150.1, 143.9, 133.5, 130.4,
119.2, 83.5, 54.7, 44.0, 34.6, 33.5, 27.8, 27.2, 24.8, 22.7, 14.1, 10.3 ppm; MS
(FD): m/z: 643.0 [M+].
2-Bromo-9,9-bis(2-ethylhexyl)fluorenyl-7-diazonium
tetrafluoroborate
(8): A solution of 7 (3.48 g, 7.18 mmol) in CH2Cl2 (10 mL) was slowly
added to BF3¥OEt2 (11.46 mmol, 1.42 mL) with stirring under an argon
athmosphere at ꢀ108C. After 10 min, a solution of butyl nitrite (1.18 mL,
10.01 mmol) in CH2Cl2 (4 mL) was slowly added and the mixture stirred
for additional 30 min at 08C. n-Pentane (200 mL) was added and the mix-
ture was stored at ꢀ208C overnight. The precipitate was filtered off,
washed with cold diethyl ether and dried in air to give 8 as a pale yellow
solid (3.39 g, 81%): 1H NMR (300 MHz, [D6]acetone): d=9.08 (m, 1H),
8.87 (m, 1H), 8.53 (m, 1H), 8.16 (m, 1H), 8.06 (s, 1H), 7.77 (m, 1H),
2.30 2.20 (m, 4H), 0.88 0.45 (m, 1H) ppm; 13C NMR (75 MHz, acetone-
d6): d=156.6, 154.2 153.9 (three peaks), 153.8, 137.9 137.8 (three peaks),
134.6, 132.6 132.5 (three peaks), 129.5 129.4 (three peaks), 129.0 128.8
(three peaks), 126.7, 125.8, 123.7 123.6 (three peaks), 111.9 111.6 (three
peaks), 57.6 57.5 (three peaks), 44.5 44.3 (four peaks), 35.9 35.8 (two
peaks), 34.7 33.9 (three peaks), 28.9 28.5 (three peaks), 28.0, 23.4 23.3
(two peaks), 14.3 14.2 (two peaks), 10.7 10.3 (three peaks) ppm; decom-
position temperature: 988C.
2-(4,4,5,5-Tetramethyl[1.3.2]dioxaborolan-2-yl)-9,9-bis(2-ethylhexyl)fluor-
ene (4): Compound 4 was prepared according to the method used for 2
by using
3
(14.07 g, 30.0 mmol), bis(pinacolato)diboron (12.19 g,
48.0 mmol), KOAc (8.82 g, 90.0 mmol), and [Pd(dppf)Cl2] (1.23 g,
1.5 mmol) in DMF (300 mL). Column chromatography over silica gel
with petroleum ether/dichloromethane (4:1) as the eluent (Rf =0.59) af-
forded
4
as an oily product (14.78 g, 95.5%): 1H NMR (250 MHz,
CD2Cl2): d=7.82 7.64 (m, 4H), 7.36 7.21 (m, 3H), 2.0 1.86 (m, 4H),
1.34 (s, 24H), 0.86 0.65 (m, 22H), 0.50 0.43 (m, 8H) ppm; 13C NMR
(62.5 MHz, CDCl3): d=151.0, 149.5, 144.2, 141.1, 133.6, 130.3, 126.6,
124.1, 120.0, 118.8, 83.5, 54.8, 44.5, 44.1, 34.6, 33.5, 28.2, 27.8, 27.3, 26.8,
24.8, 22.7, 14.1, 10.5, 10.1 ppm; MS (FD): m/z: 516.7 [M+].
7-Bromo-9,9,9’,9’-tetrakis(2-ethylhexyl)-2,2’-bifluorene (9): A mixture of
4
(0.90 g, 1.74 mmol), 8 (1.12 g, 1.92 mmol), and Pd(OAc)2 (40 mg,
0.178 mmol) in ethanol (30 mL) was heated to 608C for 1 h (no addition-
al base was added). After cooling to room temperature, the mixture was
diluted with diethyl ether and the organic layer was washed with brine
and dried over MgSO4. The solvent was removed under vacuum and the
residue was purified by column chromatography over silica gel with pe-
troleum ether as the eluent (Rf =0.49) to give 9 as an oily product
(1.04 g, 70%): 1H NMR (250 MHz, CD2Cl2): d=7.80 7.26 (m, 13H),
2.14 2.04 (m, 8H), 0.88 0.52 (m, 60H) ppm; 13C NMR (62.5 MHz,
CDCl3): d=153.0, 151.0, 150.6, 141.0, 140.5, 140.1, 139.2, 129.9, 127.4,
126.8, 126.4, 126.0, 124.1, 122.9, 120.9, 120.3, 119.6, 54.9, 44.5, 34.6, 33.8,
28.2, 27.1, 22.7, 14.0, 10.3 ppm; MS (FD): m/z: 857.6 [M+].
9,9,9’,9’-Tetrakis(2-ethylhexyl)-2,2’-bifluorene (5): A mixture of 4 (5.17 g,
10.0 mmol) and 3 (4.69 g, 10.0 mmol) in toluene (50 mL) and 2m aqueous
Na2CO3 solution (25 mL, 50 mmol) was degassed by pump and freeze
cycles (3î) and [Pd(PPh3)4] (0.577 g, 0.5 mmol) was added under argon.
The solution was heated to reflux with vigorous stirring for 20 h. After
the reaction mixture was cooled to room temperature, diethyl ether and
water were added. The organic layer was separated and washed with di-
luted HCl and brine, then dried over MgSO4. The solvent was removed
under vacuum and the residue was purified by column chromatograpy
over silica gel with petroleum ether as the eluent (Rf =0.47) to give 5
(7.08 g, 90.8%): 1H NMR (250 MHz, CD2Cl2): d=7.73 7.80 (m, 4H),
7.57 7.64 (m, 4H), 7.25 7.44 (m, 6H), 2.04 2.14 (m, 8H), 0.49 0.88 (m,
60H) ppm; 13C NMR (62.5 MHz, CDCl3):d=150.9, 150.6, 141.1, 140.4,
126.8, 126.3, 126.0, 124.1, 122.9, 119.6, 54.9, 44.5, 34.6, 33.8, 28.2, 26.9,
22.7, 14.0, 10.3 ppm; MS (FD): m/z: 779.4 [M+]; elemental analysis:
calcd for C58H82 (779.2): C 89.39, H 10.61; found: C 89.29, H 10.79.
2-[9,9,9’,9’-Tetrakis(2-ethylhexyl)-7,2’-bifluoren-2-yl]-4,4,5,5-tetrame-
thyl[1.3.2]dioxaborolan (10): Compound 10 was prepared according to
the method used for 2 by using 9 (970 mg, 1.1 mmol), bis(pinacolato)di-
boron (450 mg, 1.8 mmol), KOAc (326 mg, 3.3 mmol), and [Pd(dppf)Cl2]
(45 mg, 0.055 mmol) in DMF (10 mL). Column chromatography over
silica gel with n-hexane/CH2Cl2 (9:1) as the eluent (Rf =0.12) gave 10 as
an oily product (570 mg, 55.7%): 1H NMR (300 MHz, CD2Cl2): d=7.86
7.73 (m, 6H), 7.65 7.60 (m, 4H), 7.41 (m, 1H), 7.36 7.27 (m, 2H), 2.09
2.04 (m, 8H), 1.35 (s, 12H), 0.88 0.49 (m, 90H) ppm; 13C NMR (75 MHz,
CD2Cl2): d=152.8, 151.6, 151.3, 150.5 150.3, 144.6, 141.7, 141.1 140.6,
134.1, 131.1 130.9, 127.4, 127.0, 126.6 126.5, 124.8, 123.6 123.4, 120.8,
9,9,9’,9’,9’’,9’’-Hexakis(2-ethylhexyl)-2,2’-7’,2’’-terfluorene (6): Compound
6 was prepared according to the method used for 5 by using 2 (2.0 g,
3.12 mmol), 3 (4.40 g, 9.36 mmol), and [Pd(PPh3)4] (0.36 g, 0.31 mmol) in
toluene (30 mL) and 2m Na2CO3 aqueous solution (15.6 mL, 31.2 mmol)
2686
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 2681 2688

Synthesis and Characterization of Monodisperse Oligofluorenes
2681 2688
120.3 120.2, 119.4, 84.2, 55.6 55.5, 45.1 44.5, 35.4 35.3, 34.4 34.3, 28.8
28.5, 27.9 27.5, 25.3, 23.3, 14.5 14.4, 10.9 10.6 ppm; MS (FD): m/z: 904.2
[M+].
[M+], 973.3 [M2+]; elemental analysis: calcd for C145H202 (1945.1): C
89.53, H 10.47; found: C 89.41, H 10.35.
9,9,9’,9’,9’’,9’’,9’’’,9’’’,9’’’’,9’’’’,9’’’’’,9’’’’’-Dodecakis(2-ethylhexyl)-2,2’-7’,2’’-
7’’,2’’’-7’’’,2’’’’-7’’’’,2’’’’’-hexafluorene (15): Compound 15 was prepared ac-
cording to the method used for 13 by using 11 (370.0 mg, 0.300 mmol) in
toluene (10.0 mL) and Ni(COD)2 (82.5 mg, 0.45 mmol), 2,2’-bipyridine
(46.8 mg, 0.45 mmol), 1,5-COD (32.4 mg, 0.45 mmol), and DMF
(2.5 mL). After cooling to room temperature, the mixture was diluted
with diethyl ether and the organic layer was washed with diluted HCl
and brine, then dried over MgSO4. The solvent was removed under
vacuum and the residue was purified by column chromatography over
silica gel with hexane/dichloromethane (10/0.8) as the eluent (Rf =0.24)
to afford 15 as a white solid (183.0 mg, 52.4%): 1H NMR (250 MHz,
CD2Cl2): d=7.86 7.68 (m, 32H), 7.45 7.26 (m, 6H), 2.14 2.06 (m, 24H),
0.90 0.50 (m, 180H) ppm; 13C NMR (62.5 MHz, CDCl3): d=151.2, 150.9,
150.6, 141.1, 140.4, 140.2, 126.8, 126.3, 126.2, 124.1, 122.9, 119.8, 55.1,
44.6, 34.7, 34.0, 28.3, 27.1, 22.8, 14.0, 10.3 ppm; MS (FD): m/z: 2335.9
[M+], 1166.9 [M2+], 777.5 [M3+]; elemental analysis: calcd for C174H242
(2333.8): C 89.55, H 10.45; found: C 89.32, H 10.36.
7-Bromo-9,9,9’,9’,9’’,9’’-hexakis(2-ethylhexyl)-2,2’-7’,2’’-terfluorene (11):
Method A: Compound 11 was prepared according to the method used
for 9 by using 10 (160 mg, 0.18 mmol), 8 (155 mg, 0.26 mmol), and
Pd(OAc)2 (4 mg, 0.018 mmol) in ethanol (10 mL). Column chromatogra-
phy over silica gel with n-hexane as the eluent (Rf =0.16) gave 11 as a
slightly yellowoily product (106 mg, 48%): 1H NMR (250 MHz, CD2Cl2):
d=7.84 7.73 (m, 5H), 7.64 7.57 (m, 10H), 7.50 7.26 (m, 4H), 2.12 2.05
(m, 12H), 0.90 0.53 (brm, 90H) ppm; 13C NMR (62.5 MHz, CDCl3): d=
153.0, 151.2, 150.9, 150.6, 141.1, 140.8, 140.3, 140.1, 139.2, 129.9, 127.4,
126.8, 126.4, 126.1, 124.0, 123.0, 120.9, 120.3, 119.8, 55.0, 44.5, 34.7, 33.8,
28.2, 27.1, 22.7, 14.0, 10.3 ppm; MS (FD): m/z: 1248.4 [M+].
Method B: Compound 11 was also prepared according to the method
used for 5 by using 12 (4.9 g, 5.24 mmol), 4 (1.69 g, 3.27 mmol), and
[Pd(PPh3)4] (0.189 g, 0.15 mmol) in toluene (16 mL) and 2m aqueous
Na2CO3 (15 mmol, 8.2 mL). The reaction took 16 h. After cooling to
room temperature, the mixture was diluted with diethyl ether (200 mL)
and the organic layer was washed with diluted HCl, brine, and water,
then dried over MgSO4. The solvent was removed under vacuum and the
residue was purified by column chromatography over silica gel with
hexane/dichloromethane (10:0.5) as the eluent (Rf =0.42) to give 11
(1.83 g, 45.0%).
7,7’’-Dibromo-9,9,9’,9’,9’’,9’’-hexakis(2-ethylhexyl)-2,2’-7’,2’’-terfluorene
(16): Compound 16 was prepared according to the method used for 9 by
using 2 (0.80 g, 1.25 mmol), 8 (1.82 g, 3.13 mmol), and Pd(OAc)2 (56 mg,
0.25 mmol) in ethanol (40 mL) at 608C for 2 h (no additional base was
added). After cooling to room temperature, the mixture was diluted with
diethyl ether and the organic layer was washed with brine and dried over
MgSO4. The solvent was removed under vacuum and the residue was pu-
rified by column chromatography over silica gel with n-hexane as the
eluent (Rf =0.16) to give 16 as an oily product (0.90 g, 54.4%): 1H NMR
(300 MHz, CD2Cl2): d=7.84 7.76 (m, 4H), 7.64 7.51 (m, 12H), 7.48 (m,
2H), 2.12 2.05 (m, 12H), 0.90 0.54 (m, 90H) ppm; 13C NMR (75 MHz,
CD2Cl2): d=154.9, 153.1, 152.5, 142.4 141.7, 141.1, 131.6, 129.3 129.1,
128.2 127.9, 124.7 124.5, 122.8, 122.3 122.1, 121.7, 57.1 56.9, 46.2 25.9,
36.5 36.4, 35.8 25.3, 30.0 29.7, 28.9, 24.6, 15.7 15.6, 12.0 11.9 ppm; MS
(FD): m/z: 1324.2 [M+].
7,7’-Dibromo-9,9,9’,9’-tetrakis(2-ethylhexyl)-2,2’-bifluorene
(12):
Br2
(3.15 g, 19.71 mmol) in CH2Cl2 (5 mL) was added to a solution of 5
(7.67 g, 9.85 mmol) in CH2Cl2 (20 mL) at room temperature. The solution
was heated to reflux for 1.5 h. After the reaction mixture was cooled to
room temperature, water and diethyl ether were added. The organic
layer was washed with Na2S2O3 solution, brine, and water, then dried
over MgSO4. The solvent was removed under vacuum and the residue
was recrystallized from ethanol to give 12 as a white solid (8.24 g,
89.5%): M.p. 71.5 72.88C; 1H NMR (250 MHz, CD2Cl2): d=7.78 7.46
(m, 12H), 2.08 2.03 (m, 8H), 0.88 0.55 (m, 60H) ppm; 13C NMR
(62.5 MHz, CDCl3): d=153.0, 150.6, 140.6, 140.0, 139.4, 130.0, 127.4,
126.2, 123.0, 121.0, 120.4, 119.9, 55.2, 44.5, 34.7, 33.7, 28.1, 27.1, 22.7, 14.0,
10.3 ppm; MS (FD): m/z: 939.2 [M+].
9,9,9’,9’,9’’,9’’,9’’’,9’’’,9’’’’,9’’’’,9’’’’’,9’’’’’,9’’’’’’,9’’’’’’-Tetradecakis(2-ethylhexyl)-
2,2’-7’,2’’-7’’,2’’’-7’’’,2’’’’-7’’’’,2’’’’’-7’’’’’,2’’’’’’-heptafluorene (17): Compound
17 was prepared according to the method used for 5 by using 16
(369.0 mg, 0.278 mmol), 10 (756.0 mg, 0.835 mmol), and [Pd(PPh3)4]
(10 mg, 0.0087 mmol) in toluene (10 mL) and 2m aqueous Na2CO3
(5.0 mL, 10.0 mmol). The reaction took 24 h. After cooling to room tem-
perature, the mixture was diluted with diethyl ether and the organic layer
was washed with diluted HCl and brine, then dried over MgSO4. The sol-
vent was removed under vacuum and the residue was purified by column
chromatography over silica gel with n-hexane/CH2Cl2 (95:5) as the eluent
(Rf =0.1) to afford 17 as a pale yellowsolid (287.0 mg, 38.0%): 1H NMR
(250 MHz, CD2Cl2): d=7.86 7.69 (m, 38H), 7.45 7.26 (m, 6H), 2.15 2.06
(m, 28H), 0.92 0.50 (m, 210H) ppm; 13C NMR (62.5 MHz, CDCl3): d=
151.2, 150.9, 150.6, 141.1, 140.4, 140.2, 126.8, 126.1, 124.1, 123.0, 119.8,
119.6, 55.1, 44.5, 34.7, 34.1, 28.3, 27.1, 22.8, 14.0, 10.4 ppm; MS (FD): m/
z: 2724 [M+], 1362 [M2+], 907 [M3+]; elemental analysis: calcd for
C203H282 (2722.4): C 89.56, H 10.44; found: C 89.43, H 10.38.
9,9,9’,9’,9’’,9’’,9’’’,9’’’-Octakis(2-ethylhexyl)-2,2’-7’,2’’-7’’,2’’’-tetrafluorene
(13): A schlenk tube was charged with Ni(COD)2 (101.2 mg, 0.55 mmol),
2,2’-bipyridine (57.5 mg, 0.55 mmol), 1,5-COD (39.8 mg, 0.55 mmol), and
DMF (3.0 mL) in a glove box. The mixture was stirred at 808C for 0.5 h
and then 9 (0.32 g, 0.37 mmol) in toluene (11 mL) was added to the blue
solution and stirred at 808C for 8 h. After cooling to room temperature,
the mixture was diluted with diethyl ether. The organic layer was washed
with diluted HCl, brine, and water, then dried over MgSO4. The solvent
was removed under vacuum and the residue was purified by column
chromatography over silica gel with petroleum ether/dichloromethane
(20:1) as the eluent (Rf =0.61) to afford 13 as a white waxy solid
(151 mg, 52.6%): 1H NMR (250 MHz, CD2Cl2): d=7.85 7.75 (m, 8H),
7.67 7.63 (m, 12H), 7.45 7.26 (m, 6H), 2.14 2.06 (m, 16H), 0.90 0.50 (m,
120H) ppm; 13C NMR (62.5 MHz, CDCl3): d=151.2, 150.9, 150.6, 141.1,
140.36, 140.1, 126.8, 126.4, 126.1, 124.1, 122.9, 119.7, 54.9, 44.4, 34.7, 34.0,
28.2, 27.1, 22.8, 14.0, 10.3 ppm; MS (FD): m/z: 1556.4 [M+], 778.2 [M2+];
elemental analysis: calcd for C116H162 (1556.5): C 89.51, H 10.49; found: C
89.22, H 10.35.
Synthesis of poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl): The polymer
was prepared according to the well-known Yamamoto polycondensa-
tion[18] by using Ni(COD)2 (1.1 g, 4 mmol), 2,2’-bipyridine (623 mg,
4 mmol), and 1,5-COD (441 mg, 4 mmol) as the coupling agents for diha-
loaromatic compound 1 (953 mg, 1.74 mmol). The polymer was precipi-
tated by adding the reaction mixture into a mixture of methanol/acetone/
HCl (concentrated). The isolated polymer was dissolved in chloroform
and reprecipitated in methanol. This procedure was repeated twice to
give the polymer (480 mg, 75%): GPC (polystyrene internal standard,
THF): Mn 42000, Mw 84000.
9,9,9’,9’,9’’,9’’,9’’’,9’’’,9’’’’,9’’’’-Decakis(2-ethylhexyl)-2,2’-7’,2’’-7’’,2’’’-7’’’,2’’’’-
pentafluorene (14): Compound 14 was prepared according to the method
used for 5 by using 2 (124.5 mg, 0.194 mmol), 9 (664.7 mg, 0.776 mmol),
and Pd(PPh3)4 (22.4 mg, 0.0194 mmol) in toluene (4 mL) and 1m aqueous
Na2CO3 (2.0 mL, 2.0 mmol). The reaction took 16 h. After cooling to
room temperature, the mixture was diluted with diethyl ether and the or-
ganic layer was washed with diluted HCl and brine, then dried over
MgSO4. The solvent was removed under vacuum and the residue was pu-
rified by column chromatography over silica gel with petroleum ether/di-
chloromethane (10:0.8) as the eluent (Rf =0.31) to afford 14 as a white
waxy solid (176.5 mg, 46.8%): 1H NMR (250 MHz, CD2Cl2):d=7.85 7.74
(m, 10H), 7.67 (brm, 16H), 7.45 7.26 (m, 6H), 2.14 2.06 (m, 20H), 0.92
0.50 (m, 150H) ppm; 13C NMR (62.5 MHz, CDCl3): d=151.2, 150.9,
150.6, 141.1, 140.3, 140.1, 126.8, 126.3, 126.1, 124.1, 123.0, 119.8, 55.1,
44.5, 34.7, 34.0, 28.3, 27.1, 22.7, 14.0, 10.3 ppm; MS (FD): m/z: 1946.2
Acknowledgements
We sincerely thank the Alexander von Humboldt Foundation for grant-
ing a Senior Scientist Research Award to D.Y.Y. to enable this interna-
tional collaboration. This work was also partly supported by the Chemis-
try and Molecular Engineering Program of the Brain Korea 21 Project
and grants from the Korea Research Foundation and the Korea Science
2687
Chem. Eur. J. 2004, 10, 2681 2688
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

G. Wegner, D. Y. Yoon et al.
FULL PAPER
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Menges in taking the fluorescence spectra.
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Received: October 24, 2003
Published online: April 15, 2004
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