Preparation and optical investigation of monodisperse oligo(9,9-dioctylfluorene)s containing one fluorenone unit

Article abstract of DOI:10.1002/chem.200500261

A set of monodisperse oligo(9,9-dioctylfuorene)s, each containing only one fluorenone unit, was synthesized by using iterative Suzuki cross-coupling and iododesilylation reactions. Their optical properties were also investigated.

Full text of DOI:10.1002/chem.200500261

DOI: 10.1002/chem.200500261
Preparation and Optical Investigation of Monodisperse Oligo(9,9-
dioctylfluorene)s Containing One Fluorenone Unit**
Jing Li, Ming Li, and Zhishan Bo*[a]
Abstract: Aset of monodisperse oligo(9,9-dioctylfuorene)s, each containing only
one fluorenone unit, was synthesized by using iterative Suzuki cross-coupling and
iododesilylation reactions. Their optical properties were also investigated.
Keywords: conjugation
transfer · fluorenone · oligomers ·
polyfluorenes
·
energy
Introduction
Results and Discussion
Polyfluorenes are a class of promising blue-light-emitting
polymers, which exhibit extremely high solution and solid-
state quantum yields.[1] However, in practical applications,
polyfluorenes exhibited poor color stability. Alow-energy
green emission band is generated during operation or an-
nealing in air. In the earlier literature, the origin of this low-
energy green emission was attributed to the aggregation or
excimer formation in the bulky materials.[2] Recent studies
have proposed that the origin of the green emission band is
rather from fluorenone defects than aggregation or forma-
tion of excimers.[3] However, little is known regarding to
their structure–property relationship.
Monodisperse, p-conjugated oligomers have gained in-
creasing scientific attention in recent years, because they
can be used to better elucidate the structure–property rela-
tionship than the corresponding polymers.[4] Here we de-
signed and synthesized a set of monodisperse oligofluorenes
with only one fluorenone unit in the center of the oligomers,
and also investigated their optical properties. It should be
mentioned that Wegner, Geng, and Miller have recently re-
ported the synthesis, characterization, and optical properties
of monodisperse fluorene oligomers free of ketonic de-
fects.[5]
Repetitive strategies are normally required for the synthesis
of structurally defined and monodisperse oligomers. As de-
fined by Moore, the growth processes can be divided into
three categories, that is, simple repetitive synthesis, orthogo-
nal repetitive synthesis, and divergent/convergent process-
es.[6] Considering the large number of steps required in the
synthesis and purification of longer oligomers, it is desirable
to reduce the number of synthetic steps to simplify their
preparation and to improve the overall yield of the final
product. This may be achieved in a double stage divergent/
convergent growth approach based on the large building
blocks synthesized by either divergent or convergent meth-
ods. The synthetic route leading from compounds 1–8 to the
formation of monodisperse oligomers 9–14 is illustrated in
Schemes 1–3.
Scheme 1 depicts the synthesis of oligomers 3–6, carrying
either trimethylsilyl (TMS) or iodo groups at the two termi-
ni. The chemistry used in the synthesis was iododesilylation
and Suzuki cross-coupling reactions developed by Schlüter
et al. to synthesize the monodisperse oliogophenylene rods
and macrocycles.[7] Starting from TMS-masked 7-trimethyl-
silyl-9,9-dioctylfluorene-2-boronic pinacol ester (1),[4a] cross-
[a] J. Li, M. Li, Prof. Dr. Z. Bo
State Key Laboratory of Polymer Physics and Chemistry
Institute of Chemistry, Chinese Academy of Sciences
Beijing, 100080 (China)
Fax : (+86)10-8261-8587
E-mail: zsbo@iccas.ac.cn
[**] Editorial note: Please also see the following paper, which is on a simi-
lar subject.
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FULL PAPER
and 8c were obtained in yields of 91, 98,
and 63%, respectively.
Scheme 3 shows the synthesis of the
target longer oligomers 9–14. Reaction of
2 and 7c under standard Suzuki cross-
coupling conditions afforded 3-mer 9 in a
61% yield. Coupling 4b with benzene-
boronic acid gave 5-mer 10 in a 50%
yield. Coupling 5b with benzeneboronic
acid afforded 7-mer 11 in an 82% yield
after purification by simple flash chroma-
tography on silica gel column. Coupling
of 6b with benzeneboronic acid, 7c, and
8c gave 9-mer 12, 11-mer 13, and 13-mer
14 in yields of 48, 56, and 27%, respec-
tively. The purification of 12–14 was ac-
complished by combination of flash chro-
matography and preparative SEC (size
elution chromatography). The purity of
9–14 was checked by gel permeation
chromatography (GPC) with THF as an
Scheme 1.
coupling of 1 and 2,7-dibromofluorenone (2)[8] under stan-
dard Suzuki–Miyaura cross-coupling conditions afforded di-
TMS 3-mer 3a in a yield of 95%. Iododesilylation of 3a
with iodine monochloride in CH2Cl2 at 08C gave the corre-
sponding diiodide 3b in a 97% yield. Reaction of 3b with 1
gave the subsequent 5-mer 4a in a 89% yield after purifica-
tion by flash chromatography. Subsequent iodination led to
diiodide 4b in a yield of 91%. Repeating the above reaction
sequence, 7-mers 5a and 5b and 9-mers 6a and 6b were ob-
tained in good to excellent yields (83–98%) after purifica-
tion by simple flash chromatography.
The synthesis of building blocks 7c and 8c are outlined in
Scheme 2. Starting from compound 1, coupling with bromo-
benzene afforded 7a in a 95% yield. Conversion of 7a into
7b was accomplished in 98% yield. Subsequent halo-lithium
exchange and quenching with trimethyl borate gave the cor-
responding boronic acid, the conversion of which into the
cyclic boronic ester was achieved by refluxing with pinacol
in CH2Cl2. Compound 7c was obtained as a colorless oil in a
42% yield. Repeating the above reaction sequence, 8a, 8b,
Scheme 3.
eluent. As shown in Figure 1, all the peaks are symmetrical
and monomodal with a polydispersity index of 1.01–1.04.
Optical properties of fluore-
none and monodisperse oligo-
mers 9–14 were investigated
with UV-absorption and flores-
cence spectroscopy (Figure 2
and Table 1). In toluene, fluore-
none displayed a strong absorp-
tion band below 350 nm and a
weak peak centered at around
400 nm. All the oligomers ex-
hibited an intensive broad ab-
sorption band in the range of
350–400 nm. The absorption
maximum of the oligomers is
red-shifted with increasing the
Scheme 2.
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Z. Bo et al.
none-containing oligomers 9–14 exhibited a large Stokes
shift of up to about 160 nm. This number is much larger
than that of the fluorene oligomers. Compared with the cor-
responding fluorene oligomers, the introduction of an ac-
ceptor group (fluorenone) in the oligomersꢁ main chain
gives rise to intramolecular charge-transfer effect, which is
characterized by the larger Stokes shift and the red-shifted
structureless emission.[10] For the two longest oligomers 13
and 14 (about 10–12 nm in length) the weak blue emission
residues from the fluorene segments were observed.
Solid films on quartz plates used for UV-visible absorp-
tion and fluorescence characterization were prepared by
spin coating with 1% toluene solution at 1500 rpm. The ab-
sorption and emission spectra of the spin-coated films (9–
14) are shown in Figure 3. In film fluorenone exhibited a
Figure 1. GPC elution traces of 9–14 with THF as an eluent.
Figure 2. UV-visible absorption and photoluminescent spectra of oligo-
mers 9–14 in toluene.
Figure 3. UV-visible absorption and photoluminescent spectra of oligom-
ers 9–14 in films.
Table 1. Summary of the absorption and emission spectra (solution and
film) as well as the fluorescence quantum yields (in toluene) of fluore-
none and the fluorenone-containing oligomers.
red-shifted weak emission peak at around 509 nm. The red-
shift and low intensity of fluorenone emission in film are
probably due to the formation of the aggregation and self-
quenching their fluorescence. Compared with their emission
spectra in solution, their film emission spectra were slightly
red-shifted by about 8–10 nm. All polymer films (9–14) dis-
played a structureless green-orange band that peaked at
around 544 nm. In their film emission spectra no blue emis-
sion residue was detected. Slight blue-shift of the emissive
peaks (about 3 nm) was observed with increasing the fluo-
rene segments from one to six on each side of the oligomers.
The quantum yields (FF) of oligomers 9–14 in dilute toluene
was measured to be around 0.19–0.21 in comparison to 9,10-
diphenylanthracene (in cyclohexane, FF =0.9).[11] Due to the
intramolecular charge transfer effects in the fluorenone-con-
taining oligomers, this number is much lower than that of
the fluorene oligomers.
The thermal properties of the oligomers were investigated
by using differential scanning calorimetry (DSC). The DSC
traces of the second heating run are shown in Figure 4. All
oligomers displayed a glass transition and a crystal melting
peak. The results are summarized in Table 2. The glass tran-
sitions and the crystal melting peaks could be easily identi-
fied as the temperature increased, but the transition temper-
UV [nm]
solution
FL [nm]
solution
film
film
FF
fluorenone
9
483
535
535
535
535
535
535
509
557
553
554
554
554
554
0.01
0.19
0.20
0.20
0.19
0.21
0.21
359
370
373
376
379
380
363
374
374
382
385
389
10
11
12
13
14
conjugation length. Fluorenone displayed a blue-green emis-
sion peak at round 483 nm. Compared with fluorenone, the
emission wavelength of the oligomers was red-shifted. All
the oligomers 9–14 showed almost fully superimposed emis-
sion spectra with an intense green to orange emission band
peaked at around 535 nm. This phenomenon indicates that
the emission wavelength is independent of the length of the
conjugated oligomers. The emission state of the oligomers is
only related to the fluorene units adjacent to the central
fluorenone unit. The experimental results we obtained agree
quite well with the theoretical prediction that the emissive
state is strongly confined to the fluorenone unit.[9] Fluore-
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Oligofluorenes
FULL PAPER
tions were carried out under nitrogen. 1H and 13C NMR spectra were re-
corded on Bruker Avance-300 and Avance-400 NMR spectrometers with
CDCl3 as a solvent. UV/Vis absorption spectra were recorded on a Shi-
madzu UV-1601PC. Fluorescence spectra were recorded on a Varian-
FLR025. Elemental analysis was carried out on a Carlo Erba model 1106
elemental analyzer. The molecular weights were determined by using gel
permeation chromatography (Waters 410) against polystyrene standards
with THF as an eluent. Differential scanning calorimetry was measured
on a Mettler DSC 822e with a heating and cooling rate of 108CminÀ1
.
Compound 3a: Amixture of 1 (1.47 g, 2.5 mmol), 2 (0.39 g, 1.0 mmol),
THF (20 mL), water (10 mL), and NaHCO3 (0.35 g, 4 mmol) was careful-
ly degassed before and after [Pd(PPh3)4] (50 mg, 0.04 mmol) was added.
The mixture was stirred and refluxed for 4 days. CH2Cl2 was added, the
organic layer was separated, the aqueous layer was extracted with
CH2Cl2 (3”30 mL), and the combined organic layers were dried over
MgSO4 and evaporated to dryness. Chromatography on silica gel eluting
with CH2Cl2/hexane (1:5, v/v) afforded 3a (1.05 g, 95%) as a light yellow
solid. 1H NMR (400 MHz, CDCl3): d=8.04 (s, 2H), 7.85–7.83 (d, J=
7.6 Hz, 2H), 7.80–7.78 (d, J=7.6 Hz, 2H), 7.73–7.71 (d, J=7.2 Hz, 2H),
7.66–7.64 (d, J=8.0 Hz, 4H), 7.61 (s, 2H), 7.53–7.51 (d, J=8.0 Hz, 2H),
7.49 (s, 2H), 2.04–2.00 (t, J=8.0 Hz, 8H), 1.21–1.07 (br, 40H), 0.82–0.79
(t, J=6.8 Hz, 12H), 0.69–0.68 (br, 8H), 0.33 ppm (s, 18H); 13C NMR
(100 MHz, CDCl3): d=194.1, 151.9, 150.2, 142.9, 142.7, 141.2, 139.4,
138.7, 135.3, 133.4, 131.9, 127.6, 125.6, 123.1, 121.1, 120.7, 120.2, 119.1,
55.2, 40.2, 31.8, 30.0, 29.9, 29.2, 29.1, 29.1, 23.8, 22.6, 14.0, À0.9 ppm; ele-
mental analysis calcd (%) for C77H104OSi2: C 83.94, H 9.51; found: C
83.75, H 9.66.
Figure 4. DSC traces of oligomers 9–14 (second heating at 108CminÀ1).
Table 2. Summary of the glass transition temperatures (Tg), the melting
temperatures (Tm), and the enthalpy of melting of the fluorenone-con-
taining oligomers.
Tg [8C]
Tm [8C]
DHm [JgÀ1
]
9
44
52
54
55
59
63
167
163
162
120
153
173
43.9
5.3
3.1
0.56
0.6
0.65
10
11
12
13
14
Compound 3b: Asolution of ICl (3 mL, 3 mmol) in CH 2Cl2 was added
dropwise to a solution of 3a (1.05 g, 0.95 mmol) in CH2Cl2 (10 mL) at
08C. The reaction mixture was stirred at 08C for 1 h. Then a larger
excess of aqueous NaHSO3 solution was added to destroy the unreacted
ICl. The organic layer was separated, the aqueous layer was extracted
with CH2Cl2 (3”30 mL), and the combined organic layers were dried
over MgSO4 and evaporated to dryness. The residue was purified by
chromatography on silica gel eluting with CH2Cl2 to afford 3b (1.11 g,
97%) as a yellow solid. 1H NMR (300 MHz, CDCl3): d=8.02 (s, 2H),
7.84–7.81 (d, J=10.2 Hz, 2H), 7.77–7.74 (d, J=7.8 Hz, 2H), 7.69 (s, 2H),
7.69–7.61 (br, 6H), 7.58 (s, 2H), 7.49–7.47 (d, J=7.5 Hz, 2H), 2.07–1.87
(t, J=7.5 Hz, 8H), 1.33–1.07 (br, 40H), 0.83–0.79 (t, J=6.3 Hz, 12H),
0.64 ppm (br, 8H); 13C NMR (75 MHz, CDCl3): d=195.6, 155.0, 152.6,
144.6, 144.0, 141.7, 141.7, 140.7, 137.5, 136.8, 134.9, 133.7, 127.4, 124.6,
123.1, 122.5, 122.3, 121.8, 94.4, 57.1, 41.8, 33.3, 31.4, 31.2, 30.7, 25.3, 24.1,
15.6 ppm; elemental analysis calcd (%) for C71H86I2O: C 70.52, H 7.71;
found: C 70.33, H 7.39.
ature from nematic to isotropic was hard to follow due to
the small transition enthalpy. As shown in Table 2, the glass
transition temperature increased as the backbone chain
length increased. Oligomers 9 and 10 showed exothermic
crystallization peaks at around 114 and 798C, respectively.
This peak was not observed for the longer oligomers (11–
14). With the increase of the chain length, the melting tem-
perature first decreased and then increased. The detailed in-
vestigation of the in-situ and in real time crystallization be-
haviors by using hot-stage AFM are undergoing and will be
reported elsewhere.
Compound 4a: The general procedure for synthesis of 3a was followed.
Compound 3b (1.10 g, 0.91 mmol), 1 (1.34 g, 2.3 mmol), THF (20 mL),
water (10 mL), NaHCO3 (0.5 g, 6 mmol), and [Pd(PPh3)4] (45 mg,
0.04 mmol) were used. The crude product was purified by flash chroma-
tography on silica gel eluting with CH2Cl2/hexane (1:5, v/v) to afford 4a
(1.52 g, 89%) as a yellow solid. 1H NMR (300 MHz, CDCl3): d=8.06 (s,
2H), 7.87–7.78 (br, 8H), 7.74–7.65 (br, 16H), 7.53–7.50 (d, J=8.1 Hz,
4H), 2.13–2.07 (br, 16H), 1.25–1.11 (br, 80H), 0.84–0.77 (br, 40H),
0.33 ppm (s, 18H); 13C NMR (75 MHz, CDCl3): d=194.1, 151.8, 151.7,
150.1, 142.9, 142.6, 140.8, 140.7, 140.4, 138.9, 133.3, 131.7, 127.5, 126.1,
125.9, 125.6, 123.0, 121.4, 121.0, 120.7, 120.0, 120.0, 119.9, 118.9, 55.3,
55.0, 40.3, 40.0, 31.7, 29.9, 29.8, 29.1, 23.7, 22.5, 14.0, À1.0 ppm; elemental
analysis calcd (%) for C135H184OSi2: C 86.29, H 9.87; found: C 86.08, H
9.97.
Conclusion
In conclusion, we have synthesized a set of monodisperse
fluorene oligomers (with up to 12 fluorene units) containing
only one fluorenone unit in the center of the molecules by a
double stage divergent/convergent growth approach. Optical
studies revealed that the oligomers have large Stokes shifts
that absorb in ultraviolet region and emit in green-orange
region. The emission wavelength is independent of the con-
jugation length, that is, increasing the conjugation length
does not change their emission spectra. All oligomers exhib-
it relatively low quantum efficient yield.
Compound 4b: The general procedure for synthesis of 3b was followed.
ICl (2 mL, 2 mmol), 4a (1.52 g, 0.81 mmol), and CH2Cl2 (10 mL) were
used. The crude product was purified by flash chromatography on silica
gel eluting with CH2Cl2 to afford 4b (1.47 g, 91%) as a yellow solid.
1H NMR (400 MHz, CDCl3): d=8.07 (s, 2H), 7.88–7.82 (br, 6H), 7.78–
7.75 (d, J=10.4 Hz, 2H), 7.70–7.61 (br, 18H), 7.51–7.49 (d, J=10.4 Hz,
2H), 2.10–2.00 (br, 16H), 1.27–1.11 (br, 80H), 0.85–0.74 ppm (br, 40H);
13C NMR (100 MHz, CDCl3): d=194.1, 153.4, 151.9, 151.8, 150.9, 142.6,
140.8, 140.5, 139.8, 138.5, 135.9, 135.2, 133.3, 132.1, 126.2, 125.7, 123.0,
121.4, 121.3, 121.0, 120.7, 120.2, 120.1, 120.00, 92.4, 55.4, 40.4, 40.2, 31.7,
Experimental Section
All chemicals were purchased from Acros and used without further puri-
fication. Solvents were dried according to standard procedures. All reac-
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Z. Bo et al.
29.9, 29.9, 29.7, 29.1, 23.8, 23.7, 22.5, 22.5, 14.0, 14.0 ppm; elemental anal-
ysis calcd (%) for C129H166I2O: C 78.00, H 8.42; found: C 77.96, H 8.50.
used. The crude product was purified by flash chromatography on silica
gel eluting with CH2Cl2 to give 7b (5.78 g, yield 98%) as a slight pink
solid. 1H NMR (400 MHz, CDCl3): d=7.73–7.71 (d, J=4.8 Hz, 1H),
7.67–7.65 (m, 4H), 7.59–7.56 (d, J=7.2 Hz, 1H), 7.53 (s, 1H), 7.49–7.45
(t, J=7.2 Hz, 3H), 7.39–7.35 (t, J=7.2 Hz, 1H), 2.03–1.90 (m, 4H), 1.23–
1.06 (m, 20H), 0.83–8.00 (t, J=6.8 Hz, 6H), 0.67–0.66 ppm (m, 4H);
13C NMR (75 MHz, CDCl3): d=153.4, 150.8, 141.5, 140.7, 140.4, 139.3,
135.9, 132.1, 128.8, 127.2, 127.2, 126.1, 121.4, 120.0, 92.5, 55.4, 40.2, 31.8,
29.9, 29.1, 23.7, 22.6, 14.0 ppm; elemental analysis calcd (%) for C35H45I:
C 70.93, H 7.65; found: C 70.95, H 7.76.
Compound 5a: The general procedure for synthesis of 3a was followed.
Compound 4b (1.24 g, 0.62 mmol), 1 (0.92 g, 1.6 mmol), THF (20 mL),
water (10 mL), NaHCO3 (0.30 g, 4 mmol), and [Pd(PPh3)4] (50 mg,
0.04 mmol) were used. The crude product was purified by flash chroma-
tography on silica gel eluting with CH2Cl2/hexane (1:4, v/v) to give 5a
(1.37 g, 83%) as a yellow solid. 1H NMR (300 MHz, CDCl3): d=8.08 (s,
2H), 7.86–7.79 (br, 12H), 7.72–7.67 (br, 24H), 7.54–7.52 (br, 4H), 2.13–
2.05 (br, 24H), 1.14 (br, 120H), 0.82 (br, 60H), 0.34 ppm (s, 18H);
13C NMR (75 MHz, CDCl3): d=152.0, 151.8, 151.7, 150.2, 143.0, 141.4,
140.9, 140.6, 140.4, 140.3, 140.1, 140.0, 127.7, 126.2, 126.0, 123.1, 121.5,
121.1, 120.8, 120.2, 120.1, 120.0, 119.0, 55.5, 55.3, 55.1, 40.4, 40.1, 31.8,
30.0, 29.9, 29.2, 23.9, 23.8, 22.6, 14.0, À0.8 ppm; elemental analysis calcd
(%) for C193H264OSi2: C 87.27, H 10.02; found: C 87.47, H 10.00.
Compound 7c: nBuLi (1.5 mL, 4.3 mmol) was added to a solution of 7b
(2.1 g, 3.5 mmol) in diethyl ether (40 mL) at À788C under nitrogen. The
solution was kept at À788C for 0.5 h, and then B(OCH3)3 (1 mL,
9 mmol) added at this temperature. The reaction was stirred over night
and warmed gradually to room temperature. Aqueous hydrochloric acid
(2.0 mL) was added, the organic layer was separated, the aqueous layer
was extracted with diethyl ether (3”30 mL), and the combined organic
layers were dried over anhydrous Na2SO4 and evaporated to dryness. The
residue was purified by flash chromatography on silica gel eluting with
CH2Cl2/ether (1:1, v/v) to afford the crude boronic acid as colorless oil.
Compound 5b: The general procedure for synthesis of 3b was followed.
ICl (2 mL, 2 mmol), 5a (1.37 g, 0.52 mmol), and CH2Cl2 (10 mL) were
used. The crude product was purified by flash chromatography on silica
gel eluting with CH2Cl2 to give 5b (1.37 g, 96%) as a yellow solid.
1H NMR (400 MHz, CDCl3): d=8.07 (s, 2H), 7.85–7.82 (br, 10H), 7.77–
7.61 (br, 28H), 7.51–7.48 (d, J=7.5 Hz, 2H), 2.11–2.03 (br, 24H), 1.13
(br, 120H), 0.82–0.81 ppm (br, 60H); 13C NMR (100 MHz, CDCl3): d=
194.1, 153.4, 151.9, 151.8, 150.9, 142.9, 142.6, 141.1, 140.7, 140.4, 139.2,
138.5, 135.8, 135.3, 133.3, 132.1, 126.1, 123.0, 121.4, 121.3, 121.0, 120.7,
120.1,119.9, 92.4, 55.4, 55.3, 40.4, 40.3, 40.2, 31.7, 30.0, 29.9, 29.2, 23.8,
23.7, 22.5, 14.0 ppm; elemental analysis calcd (%) for C187H246I2O: C
81.27, H 8.97; found: C 81.08, H 9.13.
Amixture of the boronic acid prepared above, pinacol (1.0 g, 8.5 mmol),
and dry CH2Cl2 (20 mL) was refluxed for 10 h. Removal of the solvent,
the crude product was purified by chromatography on silica gel eluting
with ethyl acetate/hexane (1:14, v/v) to afford 7c (0.9 g, 42%) as a color-
less oil. 1H NMR (300 MHz, CDCl3): d=7.85–7.80 (t, J=7.5 Hz, 1H),
7.78 (s, 2H), 7.74–7.72 (d, J=7.5 Hz, 1H), 7.69–7.67 (d, J=7.2 Hz, 2H),
7.60–7.57 (d, J=8.7 Hz, 2H), 7.50–7.45 (t, J=7.5 Hz, 2H), 7.39–7.34 (t,
J=7.5 Hz, 1H), 2.06–2.00 (m, 4H), 1.41 (s, 12H), 1.26–1.05 (m, 20H),
0.83–0.79 (m, 6H), 0.66–0.65 ppm (m, 4H); 13C NMR (100 MHz, CDCl3):
d=150.6, 148.7, 142.3, 140.3, 139.1, 138.8, 132.4, 127.4, 127.3, 125.8, 125.7,
124.5, 120.2, 118.9, 117.6, 82.3, 53.8, 38.8, 30.4, 28.5, 27.8, 23.5, 22.3, 21.1,
12.6 ppm; elemental analysis calcd (%) for C41H57BO2: C 83.08, H 9.69;
found: C 82.85, H 9.72.
Compound 6a: The general procedure for synthesis of 3a was followed.
Compound 5b (0.93 g, 0.34 mmol), 1 (0.49 g, 0.84 mmol), THF (20 mL),
water (10 mL), NaHCO3 (0.3 g, 3 mmol), and [Pd(PPh3)4] (30 mg,
0.026 mmol) were used. The crude product was purified by chromatogra-
phy on silica gel eluting with CH2Cl2/hexane (1:3, v/v) to afford 6a
(1.02 g, 88%) as a yellow solid. 1H NMR (400 MHz, CDCl3): d=8.08 (s,
2H), 7.88–7.79 (br, 16H), 7.75–7.68 (br, 32H), 7.54–7.51 (d, J=7.8 Hz,
4H), 2.12–2.02 (br, 32H), 1.14 (br, 160H), 0.83–0.79 (br, 80H), 0.34 ppm
(s, 18H); 13C NMR (100 MHz, CDCl3): d=194.2, 152.0, 151.8, 151.8,
151.7, 150.2, 141.4, 140.8, 140.6, 140.6, 140.5, 140.1, 140.0, 135.3, 133.4,
127.7, 126.2, 126.0, 123.1, 121.5, 120.8, 120.2, 120.0, 119.0, 55.5, 55.4, 55.3,
55.1, 40.4, 40.2, 31.8, 30.0, 30.0, 29.9, 29.2, 29.2, 29.1, 23.9, 23.8, 22.6, 14.1,
À0.8 ppm; elemental analysis calcd (%) for C251H344OSi2: C 87.80, H
10.10; found: C 87.33, H 9.97.
Compound 8a: The general procedure for synthesis of 3a was followed.
Compound 7b (2.92 g, 4.9 mmol), 1 (3.04 g, 5.2 mmol), THF (50 mL),
water (20 mL), NaHCO3 (1.8 g, 21 mmol), and [Pd(PPh3)4] (121 mg,
0.1 mmol) were used. The crude product was purified by chromatography
on silica gel eluting with hexane to give 8a (4.2 g, 91%) as a colorless oil.
1H NMR (400 MHz, CDCl3): d=7.85–7.82 (d, J=8.0 Hz, 3H), 7.78–7.68
(m, 7H), 7.66–7.63 (m, 2H), 7.57–7.50 (m, 4H), 7.42–7.35 (t, J=7.6 Hz,
1H), 2.14–2.06 (m, 8H), 1.24–1.14 (m, 40H), 0.87–0.82 (m, 20H),
0.38 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=151.8, 151.8, 151.7,
150.2, 141.8, 140.7, 140.6, 140.3, 140.1, 140.0, 131.9, 128.8, 127.7, 127.2,
126.2, 126.1, 126.1, 121.6, 121.5, 121.5, 120.0, 119.1, 55.3, 55.2, 40.5, 40.2,
31.8, 30.1, 30.0, 29.3, 29.2, 29.2, 29.2, 23.9, 23.9, 22.6, 14.1, À0.8 ppm; ele-
mental analysis calcd (%) for C38H54Si: C 86.76, H 10.21; found: C 86.50,
H 10.21.
Compound 6b: The general procedure for synthesis of 3b was followed.
ICl (0.5 mL, 0.5 mmol), 6a (0.64 g, 0.19 mmol), and CH2Cl2 (10 mL) were
used. The crude product was purified by flash chromatography on silica
gel eluting with CH2Cl2 to give 6b (0.64 g, 98%) as a yellow solid.
1H NMR (300 MHz, CDCl3): d=8.08 (s, 2H), 7.86–7.75 (br, 14H), 7.72–
7.62 (br, 36H), 7.51–7.48 (d, J=7.8 Hz, 2H), 2.12–2.01 (br, 32H), 1.14
(br, 160H), 0.85–0.79 ppm (br, 80H); 13C NMR (75 MHz, CDCl3): d=
194.2, 153.5, 152.0, 151.8, 150.9, 142.7, 141.2, 140.9, 140.8, 140.5, 140.3,
140.0, 139.8, 139.3, 138.6, 135.9, 135.3, 133.4, 126.2, 123.1, 121.5, 121.1,
120.8, 120.0, 92.5, 55.5, 55.4, 40.4, 40.3, 31.8, 31.1, 30.3, 30.0, 29.6, 29.2,
23.9, 23.8, 22.6, 14.1 ppm; elemental analysis calcd (%) for C245H326I2O: C
83.10, H 9.28; found: C 83.46, H 9.38.
Compound 8b: The general procedure for synthesis of 3b was followed.
ICl (10 mL, 10 mmol), 8a (4.0 g, 4.3 mmol), and CH2Cl2 (10 mL) were
used. The crude product was purified by chromatography on silica gel
eluting with CH2Cl2 to afford 8b (4.15 g, 98%) as a pink oil. 1H NMR
(300 MHz, CDCl3): d=7.81–7.74 (m, 3H), 7.70–7.67 (m, 5H), 7.63–7.59
(m, 5H), 7.50–7.46 (m, 3H), 7.39–7.35 ppm (t, J=8.1 Hz, 1H); 13C NMR
(75 MHz, CDCl3): d=153.5, 151.8, 151.7, 150.9, 141.7, 140.5, 140.3, 140.1,
140.0, 139.3, 135.9, 132.1, 128.8, 127.2, 127.1, 126.3, 126.2, 126.1, 121.6,
121.4, 121.4, 120.0, 120.0, 92.4, 55.5, 55.3, 40.4, 40.2, 31.8, 30.0, 29.9, 29.2,
23.9, 23.8, 22.6, 22.6, 14.1, 14.0 ppm; elemental analysis calcd (%) for
C64H85I: C 78.34, H 8.73; found: C 78.59, H 8.81.
Compound 7a: The general procedure for synthesis of 3a was followed.
Bromobenzene (2.60 g, 16.6 mmol), 1 (7.48 g, 12.7 mmol), THF (70 mL),
water (30 mL), NaHCO3 (3.0 g, 36 mmol), and [Pd(PPh3)4] (300 mg,
0.26 mmol) were used. The crude product was purified by flash chroma-
tography on silica gel eluting with hexane to give 7a (6.5 g, 95%) as a
colorless oil. 1H NMR (300 MHz, CDCl3): d=7.77–7.75 (d, J=8.1 Hz,
1H), 7.71–7.66 (br, 3H), 7.58–7.55 (d, J=8.1 Hz, 2H), 7.51–7.45 (br, 4H),
7.38–7.33 (t, J=7.2 Hz, 1H), 2.02–1.97 (t, J=8.1 Hz, 4H), 1.21–1.06 (br,
20), 0.83–0.79 (t, J=6.6 Hz, 6H), 0.71–0.69 (br, 4H), 0.32 ppm (s, 9H);
13C NMR (100 MHz, CDCl3): d=151.6, 150.2, 141.8, 141.4, 140.4, 140.2,
139.0, 131.8, 128.8, 127.6, 127.2, 127.1, 125.9, 121.6, 120.0, 119.0, 55.1,
40.4, 40.2, 31.8, 30.0, 29.9, 29.2, 29.1, 23.8, 22.6, 14.1, À0.8 ppm; elemental
analysis calcd (%) for C38H54Si: C 84.69, H 10.10; found: C 84.58, H 9.98.
Compound 8c: The general procedure for synthesis of 7c was followed.
8b (1.2 g, 1.2 mmol), diethyl ether (30 mL), nBuLi (0.5 mL, 1.4 mmol),
and B(OCH3)3 (0.9 mL, 8 mmol) were used to prepare the boronic acid.
The crude boronic acid was purified by chromatography on silica gel
eluting with CH2Cl2/ether (1:1, v/v) to afford the boronic acid as colorless
oil. Pinacol (0.30 g, 2.5 mmol) and CH2Cl2 (20 mL) were used to prepare
the corresponding boronic ester 8c. Compound 8c was obtained as a col-
orless oil (0.76 g, 63%) by chromatography on silica gel eluting with
ethyl acetate/hexane (1:14, v/v). 1H NMR (300 MHz, CDCl3): d=7.87–
7.75 (m, 6H), 7.72–7.60 (m, 8H), 7.52–7.47 (t, J=7.2 Hz, 2H), 7.40–7.35
Compound 7b: The general procedure for synthesis of 3b was followed.
ICl (15 mL, 15 mmol), 7a (5.38 g, 10 mmol), and CH2Cl2 (30 mL) were
6934
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Chem. Eur. J. 2005, 11, 6930 – 6936

Oligofluorenes
FULL PAPER
(t, J=7.2 Hz, 1H), 2.10–2.06 (m, 8H), 1.42 (s, 12H), 1.26–1.11 (m, 40H),
0.82–0.71 ppm (m, 20H); 13C NMR (75 MHz, CDCl3): d=150.7, 150.3,
142.4, 139.6, 139.1, 138.7, 138.6, 132.4, 127.5, 127.3, 125.8, 125.7, 124.7,
124.6, 120.2, 120.1, 118.9, 118.5, 117.6, 82.3, 53.9, 53.8, 39.0, 38.8, 30.4,
28.6, 27.8, 23.5, 22.4, 22.3, 21.2, 12.6 ppm;elemental analysis calcd (%) for
C41H57BO2: C 85.67, H 9.96; found: C 85.55, H 9.72.
size elution chromatography (SEC) on Bio-Beads S-X eluting with THF
to afford 11 (54 mg, 48%) as a yellow solid. H NMR (300 MHz, CDCl3):
1
d=8.08 (s, 2H), 7.86–7.80 (m, 22H), 7.71–7.60 (m, 46H), 7.52–7.47 (t, J=
7.4 Hz, 4H), 7.37 (m, 2H), 2.12 (br, 40H), 1.14 (br, 200H), 0.83–
0.79 ppm (br, 100H); 13C NMR (100 MHz, CDCl3): d=194.1, 152.0,
151.8, 143.0, 142.7, 141.7, 140.8, 140.5, 140.0, 139.7, 139.1, 138.5, 135.3,
133.4, 128.7, 127.2, 126.1, 125.7, 123.1, 121.5, 121.1, 120.7, 119.9, 96.1,
55.4, 55.3, 40.4, 31.7, 30.0, 29,2, 28.8, 23.9, 22.6, 14.0 ppm; elemental anal-
ysis calcd (%) for C315H416O: C 89.68, H 9.94; found: C 88.94, H 10.11.
Compound 9: The general procedure for synthesis of 3a was followed.
Compound 2 (16 mg, 0.047 mmol), 7c (72 mg, 0.12 mmol), THF (20 mL),
water (10 mL), NaHCO3 (0.1 g, 1 mmol), and [Pd(PPh3)4] (3 mg,
0.003 mmol) were used. The crude product was purified by flash chroma-
tography on silica gel eluting with CH2Cl2/hexane (1:4, v/v) to afford 9
(32 mg, 61%) as a yellow solid. 1H NMR (400 MHz, CDCl3): d=8.06 (s,
2H), 7.86–7.80 (m, 6H), 7.71–7.60 (m, 14H), 7.51–7.48 (t, J=7.5 Hz,
4H), 7.40–7.36 (t, J=7.2 Hz, 2H), 2.10–2.06 (br, 8H), 1.18–1.09 (br,
40H), 0.82–0.73 ppm (br, 20H); 13C NMR (100 MHz, CDCl3): d=194.2,
151.9, 151.7, 142.9, 142.6, 141.6, 140.8, 140.3, 139.8, 138.5, 135.2, 133.4,
128.8, 127.2, 127.2, 126.1, 125.7, 123.1, 121.6, 121.0, 120.7, 120.2, 120.1,
55.4, 40.4, 31.7, 30.0, 29.2, 23.8, 22.6, 14.0 ppm; elemental analysis calcd
(%) for C83H96O: C 89.84, H 8.72; found: C 89.63, H 8.91.
Compound 14: The general procedure for synthesis of 3a was followed.
Compound 6b (93 mg, 0.026 mmol), 8c (80 mg, 0.082 mmol), THF
(20 mL), water (10 mL), NaHCO3 (0.1 g, 1 mmol), and [Pd(PPh3)4] (5 mg,
0.004 mmol) were used. The crude product was purified by flash chroma-
tography on silica gel eluting with CH2Cl2/hexane (1:3, v/v) and prepara-
tive size elution chromatography (SEC) on Bio-Beads S-X eluting with
THF to afford 12 (36 mg, 27%) as a yellow solid. 1H NMR (300 MHz,
CDCl3): d=8.07 (s, 2H), 7.93–7.76 (m, 26H), 7.71–7.56 (m, 54H), 7.49–
7.44 (t, J=7.5 Hz, 4H), 7.43–7.34 (m, 2H), 2.22–2.12 (br, 48H), 1.13 (br,
240H), 0.83–0.71 ppm (br, 120H); 13C NMR (100 MHz, CDCl3): d=
196.4, 175.2, 152.0, 151.8, 151.7, 140.9, 140.8, 140.5, 140.0, 139.8, 138.6,
135.3, 128.8, 127.2, 126.2, 126.1, 125.8, 123.1, 121.6, 121.5, 121.1, 120.8,
120.2, 120.1, 120.0, 96.1, 55.5, 55.4, 40.4, 31.8, 30.0, 29.5, 29.4, 29.2, 24.1,
23.9, 22.6, 22.5, 14.1 ppm; elemental analysis calcd (%) for C373H496O: C
89.67, H 10.01; found: C 88.80, H 9.95.
Compound 10: The general procedure for synthesis of 3a was followed.
Compound 4b (32 mg, 0.016 mmol), benzeneboronic acid (6 mg,
0.05 mmol), THF (10 mL), water (5 mL), NaHCO3 (0.02 g, 0.2 mmol),
and [Pd(PPh3)4] (2 mg, 0.002 mmol) were used. The crude product was
purified by flash chromatography on silica gel eluting with CH2Cl2/
hexane (1:4, v/v) to afford 10 (15 mg, 50%) as a yellow solid. 1H NMR
(400 MHz, CDCl3): d=8.06 (s, 2H), 7.85–7.80 (m, 10H), 7.79–7.60 (m,
22H), 7.49 (t, J=7.6 Hz, 4H), 7.39–7.37 (t, J=8.0 Hz, 2H), 2.10–2.06 (br,
16H), 1.20–1.10 (br, 80H), 0.81–0.78 ppm (br, 40H); 13C NMR
(100 MHz, CDCl3): d=196.8, 152.0, 151.8, 151.7, 143.0, 142.6, 140.7,
140.4, 140.0, 135.3, 133.4, 128.8, 127.2, 127.1, 126.1, 126.0, 125.7, 121.6,
121.4, 121.1, 120.8, 120.1, 120.1, 120.0, 107.6, 55.4, 55.3, 45.3, 42.8, 40.4,
31.8, 30.0, 29.5, 29.3, 29.2, 23.8, 22.6, 14.0 ppm; elemental analysis calcd
(%) for C141H176O: C 89.75, H 9.40; found: C 89.44, H 9.52.
Acknowledgements
Financial support from the National Natural Science Foundation of
China (No. 20225415, 20423003 and 20374053), and the Major State
Basic Research Development Program (No. 2002CB613401) is greatly ac-
knowledged.
Compound 11: The general procedure for synthesis of 3a was followed.
Compound 5b (138 mg, 0.05 mmol), benzene boronic acid (15 mg,
0.125 mmol), THF (20 mL), water (10 mL), NaHCO3 (0.1 g, 1 mmol), and
[Pd(PPh3)4] (4 mg, 0.003 mmol) were used. The crude product was puri-
fied by chromatography on silica gel eluting with CH2Cl2/hexane (1:3, v/
v) to afford 11 (109 mg, 82%) as a yellow solid. 1H NMR (300 MHz,
CDCl3): d=8.07 (s, 2H), 7.88–7.80 (br, 14H), 7.71–7.60 (br, 30H), 7.52–
7.47 (t, J=7.5 Hz, 4H), 7.43–7.35 (m, 2H), 2.11–2.10 (br, 24H), 1.26–1.13
(br, 120H), 0.83–0.78 ppm (br, 60H); 13C NMR (100 MHz, CDCl3): d=
194.1, 152.0, 151.8, 151.7, 140.8, 140.5, 140.4, 140.1, 140.0, 139.9, 139.7,
135.3, 128.7, 127.2, 126.1, 126.0, 125.7, 123.1, 121.6, 121.5, 121.1, 120.7,
120.1, 119.9, 96.1, 55.4, 55.3, 40.4, 31.7, 30.0, 29.2, 23.8, 22.6, 14.0 ppm; el-
emental analysis calcd (%) for C199H256O: C 89.71, H 9.69; found: C
88.94, H 9.70.
[1] a) J. H. Burroughes, D. D. C. Bradley, A. B. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Bum, A. B. Holmes, Nature 1990, 347,
539; b) Q. Pei, Y. Yang, J. Am. Chem. Soc. 1996, 118, 7416; c) D. C.
Müller, A. Falcou, N. Reckefuss, M. Rojahn, V. Wlederhirm, P.
Rudati, H. Frohne, O. Nuyken, H. Becker, K. Meerhotz, Nature
2003, 421, 829; d) D. Neher, Macromol. Rapid Commun. 2001, 22,
1365; e) U. Scherf, E. J. W. List, Adv. Mater. 2002, 14, 477; f) M. Le-
clerc, J. Polym. Sci. Part A 2001, 39, 2867.
[2] a) S. A. Jenekhe, J. A. Osaheni, Science, 1994, 265, 765; b) J. A. Teet-
sov, D. A. Vanden Bout, J. Am. Chem. Soc. 2001, 123, 3605; c) J.-I.
Lee, G. Klaerner, R. D. Miller, Synth. Met. 1999, 101, 126.
[3] a) J. M. Lupton, M. R. Craig, E. W. Meijer, Appl. Phys. Lett. 2002,
80, 4489; b) X. Gong, P. K. Iyer, D. Moses, G. C. Bazan, A. J.
Heeger, S. S. Xiao, Adv. Funct. Mater. 2003, 13, 325; c) M. Surin, E.
Hennebicq, C. Ego, D. Marsitzky, A. C. Grimsdale, K. Müllen, J.-L.
BrØdas, R. Lazzaroni, P. Lecl›re, Chem. Mater. 2004, 16, 994;
d) M. R. Craig, M. M. de Kok, J. W. Hofstraat, A. P. H. J. Schenning,
E. W. Meijer, J. Mater. Chem. 2003, 13, 2861; e) L. Romaner, A. Po-
gantsch, P. S. de Freitas, U. Scherf, M. Gaal, E. Zojer, E. J. W. List,
Adv. Funct. Mater. 2003, 13, 597; f) M. Gaal, E. J. W. List, U. Scherf,
Macromolecules 2003, 36, 4236; g) X. Gong, D. Moses, A. J. Heeger,
S. Xiao, Synth. Met. 2001, 141, 17; h) E. J. W. List, R. Guentner, P.
Scanducci de Freitas, U. Scherf, Adv. Mater. 2002, 14, 374; i) A. P.
Kulkarni, X. X. Kong, S. A. Jenekhe, J. Phys. Chem. B 2004, 108,
8689.
[4] a) B. S. Li, J. Li, Y. Q. Fu, Z. S. Bo, J. Am. Chem. Soc. 2004, 126,
3430; b) A. L. Kanibolotsky, R. Berridge, P. J. Skabara, I. F. Pere-
pichka, D. D. C Bradley, M. Koeberg, J. Am. Chem. Soc. 2004, 126,
13695; c) J. M. Tour, Chem. Rev. 1996, 96, 537; d) Electronic Materi-
als: The Oligomeric Approach (Eds.: K. Müllen, G. Wegner), Wiley-
VCH, Weinheim, New York, 1998.
Compound 12: The general procedure for synthesis of 3a was followed.
Compound 6b (124 mg, 0.035 mmol), benzene boronic acid (13 mg,
0.11 mmol), THF (20 mL), water (10 mL), NaHCO3 (0.1 g, 1 mmol), and
[Pd(PPh3)4] (4 mg, 0.003 mmol) were used. The crude product was puri-
fied by chromatography on silica gel eluting with CH2Cl2/hexane (1:3, v/
v) and preparative size elution chromatography (SEC) on Bio-Beads S-X
eluting with THF to afford 12 (48 mg, 56%) as a yellow solid. 1H NMR
(400 MHz, CDCl3): d=8.07 (s, 2H), 7.92–7.80 (m, 18H), 7.70–7.59 (m,
38H), 7.51–7.39 (t, J=7.5 Hz, 4H), 7.37–7.31 (m, 2H), 2.10 (br, 32H),
1.13–0.98 (br, 160H), 0.82–0.78 ppm (br, 80H); 13C NMR (100 MHz,
CDCl3): d=195.1, 170.7, 163.5, 156.9, 151.9, 151.7, 151.6, 141.6, 140.7,
140.4, 140.3, 140.0, 139.9, 135.2, 133.3, 128.6, 127.1, 126.0, 125.9, 125.6,
122.9, 121.5, 121.4, 121.0, 120.7, 120.0, 119.9, 119.8, 94.1, 55.3, 55.2, 40.3,
40.1, 31.7, 31.5, 29.9, 29.8, 29.1, 23.8, 23.5, 22.7, 22.6, 22.5, 13.9 ppm; ele-
mental analysis calcd (%) for C257H336O: C 89.69, H 9.84; found: C 88.97,
H 10.05.
Compound 13: The general procedure for synthesis of 3a was followed.
Compound 6b (95 mg, 0.027 mmol), 7c (60 mg, 0.1 mmol), THF (20 mL),
water (10 mL), NaHCO3 (0.1 g, 1.0 mmol), and [Pd(PPh3)4] (5 mg,
0.004 mmol) were used. The crude product was purified by chromatogra-
phy on silica gel eluting with CH2Cl2/hexane (1:3, v/v) and preparative
[5] a) J. Jo, C. Chi, S. Hoeger, G. Wegner, D. Y. Yoon, Chem. Eur. J.
2004, 10, 2681; b) Y. Geng, A. Trajkovska, D. Katsis, J. J. Ou, S. W.
Chem. Eur. J. 2005, 11, 6930 – 6936
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6935

Z. Bo et al.
Culligan, S. H. Chen, J. Am. Chem. Soc. 2002, 124, 8337; c) G.
Klaerner, R. D. Miller, Macromolecules 1998, 31, 2007.
[8] D. D. Mysky, I. F. Perepichka, N. I. Sokolov, J. Chem. Soc. Perkin
Trans. 2 1997, 537.
[6] “Nonbiological Sequence-Specific Oligomers by Repetitive Synthe-
ses”: J. S. Moore, R. B. Prince, in Materials Science and Technology,
Synthesis of polymers (Ed.: A. D. Schlüter), Wiley-VCH, Weinheim,
1999.
[9] E. Zojer, A. Pogantsch, E. Hennebicq, D. Beljonne, J. L. BrØdas,
E. J. W. List, J. Chem. Phys. 2002, 117, 6794.
[10] S. A. Jenekhe, L. Lu, M. M. Alam, Macromolecules 2001, 34, 7315.
[11] S. Hamai, F. Hirayama, J. Phys. Chem. 1983, 87, 83.
[7] a) P. Liess, V. Hensel, A. D. Schlüter, Liebigs Ann. 1996, 1037; b) V.
Hensel, A. D. Schlüter, Liebigs Ann./Recl. 1997, 303; c) V. Hensel,
K. Lützow, J. Jakob, K. Geßler, W. Saenger, A. D. Schlüter, Angew.
Chem. 1997, 109, 2768; Angew. Chem. Int. Ed. Engl. 1997, 36, 2654;
d) Z. S. Bo, J. Qiu, J. Li, A. D. Schlüter, Org. Lett. 2004, 6, 667.
Received: March 8, 2005
Published online: August 24, 2005
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Chem. Eur. J. 2005, 11, 6930 – 6936