A facile synthetic route to monodisperse asymmetrical oligo(phenylene- ethynylene)s

Article abstract of DOI:10.1081/SCC-200057287

Monodisperse asymmetrical oligo(phenylene-ethynylene)s were synthesized iteratively by combining the selective deprotection and the Sonogashira coupling. Trimethylsilylethyl ester (TSE) and trimethylsilyl (TMS) were used as protecting groups for carboxyl

Full text of DOI:10.1081/SCC-200057287

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A Facile Synthetic Route to
Monodisperse Asymmetrical
Oligo(phenylene‐ethynylene)s
Jinling Zhao a & Zhishan Bo a
a State Key Laboratory of Polymer Physics and
Chemistry, Institute of Chemistry, Chinese Academy
of Sciences, Beijing, China
Published online: 16 Aug 2006.
To cite this article: Jinling Zhao & Zhishan Bo (2005): A Facile Synthetic
Route to Monodisperse Asymmetrical Oligo(phenylene‐ethynylene)s, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:10, 1391-1402
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Synthetic Communicationsw, 35: 1391–1402, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200057287
A Facile Synthetic Route to
Monodisperse Asymmetrical
Oligo(phenylene-ethynylene)s
Jinling Zhao and Zhishan Bo
State Key Laboratory of Polymer Physics and Chemistry, Institute of
Chemistry, Chinese Academy of Sciences, Beijing, China
Abstract: Monodisperse asymmetrical oligo(phenylene-ethynylene)s were syn-
thesized iteratively by combining the selective deprotection and the Sonogashira
coupling. Trimethylsilylethyl ester (TSE) and trimethylsilyl (TMS) were used as pro-
tecting groups for carboxyl and acetylene, respectively. The acetylenic TMS protecting
group could be removed selectively by the treatment with TBAF in methylene chloride,
whereas both TSE and TMS protecting groups were cleaved in THF.
Keywords: Monodispersed oligo(phenylene-ethynylene)s, selective deprotection,
Sonogashira coupling
INTRODUCTION
There is much growing interest in the field of oligomer chemistry in recent
years because of the fast development of its applications in the areas of
material science and supramolecular science.[1–3] Monodisperse oligomers
are important in that they offer the possibility of inspecting the properties of
corresponding polymers. Particular attention was paid to the preparation of
monodisperse conjugated oligo(p-phenylene-ethynylene)s (OPEs) because
of their potential applications as molecular wires and other molecular elec-
tronic devices.[4–15] In the past few years, Tour et al. used an iterative
divergent/convergent doubling approach to prepare OPEs with one or two
Received in Japan December 8, 2004
Address correspondence to Zhishan Bo, State Key Laboratory of Polymer Physics
and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080,
China. Fax: þ86(10)82618587; E-mail: zsbo@iccas.ac.cn
1391

1392
J. Zhao and Z. Bo
protected thiol endgroups.[9,10] Mu¨llen et al. described an AB-type monomer
approach toward the preparation of a,v-poly(phenylene-ethynylene)s.[11]
Sita and coworkers reported the synthesis of asymmetric ferrocene-terminated
phenylethynyl oligomers.[12,13] Yu et al. also reported the design and synthesis
of the OPEs possessing a ferrocene and a thiol at each terminus.[14] Based on
the bromide-iodide selectivity of the Pd-catalyzed alkyne-aryl-coupling, Godt
et al. developed a new iterative divergent/convergent approach to oligoPPEs,
which allowed them to synthesize substantial amounts of octamers and
carboxyl derivatives.[15] Considering the side reactions under cross-coupling
conditions, Godt et al. also developed an efficient synthetic route, in which
they used the polarity difference of the endgroups for facile purification of
the product with the column chromatography.[16]
In this work, we describe an efficient iterative synthetic approach toward
asymmetrical monodisperse OPEs bearing functional endgroups. A solvent-
dependent deprotection reaction was developed in the synthesis (vide infra).
2-Trimethylsilylethyl (TSE) was chosen as a protective group for the
carboxylic acid because it could be removed under very mild conditions
[tetrabutylammonium fluoride (TBAF), THF as a solvent, and at room
temperature]. Asymmetrical OPEs have the potential to form self-assembled
monolayers on gold substrates and gold nanoparticles. Upon the formation
of self-assembled monolayers, surface ester groups will be easily converted
into free carboxylic acids by the treatment with TBAF in THF. To the best
of our knowledge, this is the first report on synthesis of monodisperse OPEs
bearing a protected carboxylic and a protected thiol endgroup. Additionally,
this selective deprotection method is also used to synthesize porphyrin-
containing oligomers.
RESULTS AND DISCUSSION
Scheme 1 shows the synthetic route of compounds 1, 2, and 3. For the
synthesis of 1, the Sonogashira cross-coupling reaction was carried out in
THF at 508C with diisopropylethylamine as a base and Pd(PPh3)2Cl2/CuI
as cocatalyst precursors. Compound 1 was obtained in a 25% yield after puri-
fication. Using Pd(dba)2, tri-p-tolylphosphine, and CuI as catalyst precursors
in this step was not efficient, and the yield was less than 5%. The synthesis
of 2 was brought by the coupling of asymetrical dimer 6 and monoiodo
porphyrin 7. The yield was 36%. The cleavage of the protecting TSE group
of 2 was achieved by treatment of 2 with TBAF in THF at room temperature.
The yield was 85%.
The key building block 12 was prepared according to the sequence
in Scheme 2. Commercially available 4-iodobenzoic acid was esterified
with 2-trimethylsilylethanol under DCC/DMAP conditions to give the corre-
sponding ester 8 in a 96% yield. Coupling of 8 with 2-trimethylsilylacetylene
afforded compound 9 in a 94% yield. Cleavage of the acetylenic TMS

Scheme 1. Reagents and conditions: (a) Pd(PPh3)2Cl2, CuI, THF, diisopropylethylamine, 508C, 5 d. (b) Pd(PPh3)2Cl2, CuI, THF, diisopropylamine,
room temp., 24 h; (c) TBAF, THF, room temp.

1394
J. Zhao and Z. Bo
Scheme 2. Reagents and conditions: (a) DCC, DMAP, CH2Cl2, room temp., 24 h; (b)
Pd(PPh3)2Cl2, CuI, THF, diisopropylamine, room temp., 24 h; (c) TBAF, CH2Cl2,
room temp., 1 h; (d) TBAF, THF, room temp., 2 h; (e) Pd(PPh3)2Cl2, CuI, THF, tri-
ethylamine, 508C, 24 h.

Oligo(phenylene-ethynylene)s
1395
protecting group was done in CH2Cl2 using 1.5 folds of TBAF (1.0 M in THF)
at room temperature. Compound 10 was obtained in a quantitative yield. This
is a solvent-dependent reaction. When THF was used as a solvent, the ester-
protecting group was also removed during the reaction. Additionally, when
all starting materials were consumed, the entire reaction mixture should
directly be filtered through a short pad of silica gel using CH2Cl2 as an
eluent. In some cases, a partial cleavage of the ester-protecting group was
observed when the solvent was evaporated before the column separation.
Product 10 was then reacted with compound 12 under Sonogashira coupling
conditions. We found that the best result was obtained when the coupling
reaction was performed in THF with diisopropyl amine as a base, 1.0 mol
% Pd(PPh3)2Cl2 and 2.0 mol % CuI as cocatalyst precursors. After the purifi-
cation, dimer 13 was obtained in a yield of 88%. The removal of the protecting
group of 13 proceeded cleanly and gave compound 6 in a yield of 99%. Under
the same conditions as for the synthesis of compound 13, coupling of 6 with 12
afforded trimer 14 in an 84% yield. The treatment of 14 with TBAF in CH2Cl2
afforded 15 in a yield of 98%, whereas treatment of 14 with 2.5 folds of TBAF
in THF afforded trimer 17 with carboxyl endgroup. Tetramer 16 was obtained
in a 60% yield according to the same procedure as applied to 6. The cleavage
of 16 in CH2Cl2 using 1.5 folds of TBAF gave compound 4 in a 99% yield.
Key building block 5 was prepared by the reaction of 18[10] with excess
folds of 11 (Scheme 2). The product was obtained in a yield of 40%. In this
step, triethyl amine was used as a base instead of diisopropyl amine,[17]
because thiol ester is labile to secondary amine. It is interesting to note that
diisopropylethyl amine as a base gave a better result toward the preparation
of compound 1 (25% versus 5% yield of triethyl amine).
Asymetrical porphyrin containing oligomer 2 was prepared by Sonoga-
shira cross-coupling of compound 6 with monoiodo porphyrin 7. The yield
was 36%. The cleavage of the TMS group of 2 with TBAF in THF afforded
the corresponding carboxyl-ended compound 3 in a yield of 85%. All new
compounds were unambiguously characterized with 1H, 13C NMR spec-
troscopy and high-resolution mass spectrometry or MALDI-TOF mass
spectrometry.
Initial photophysical studies were performed on the oligomers with
different conjugation lengths. The electronic absorption and emission
spectra of OPEs 13, 14, 16, 5, 1, 2, and 3 in toluene are shown in Figure 1.
As expected, the absorption and emission maxima are red-shifted with increas-
ing the conjugated lengths. In the absorption spectra, 13, 14, 16, 5, and 1 gave a
single absorption peak at 345, 366, 393, 404, and 412 nm, respectively. In the
emission spectra, only compound 5 gave a single emission peak at 394 nm;
compounds 13, 14, 16, and 1 exhibited structured emissions with two
resolved bands and the emission maxima appeared at 414, 437, 455, and
469 nm, respectively. For compounds 13, 14, and 16, the relative emission
intensity of vibronic bands decreased with increasing conjugated length; for
compound 1, an increasing of vibronic band intensity is observed with

1396
J. Zhao and Z. Bo
Figure 1. (a) Absorption and (b) emission spectra of oligomers 13, 14, 16, 5, 1, 2, and
3 in toluene.
increasing the conjugated length because of the thiol ester endgroup. The
absorption spectra of compounds 2 and 3 are fully superimposed, and they
exhibited typical absorption features of zinc porphyrin with an intense Soret
band at 426 nm and two weak Q-bands at 557 and 597 nm. In the emission
spectra, both 2 and 3 emit in the blue and red regions. The weak emission in
blue region for compound 2 is due to the energy transfer from the
phenylene–ethynylene segment to the porphyrin ring. For compound 3, the
strong emission in blue region indicates that the energy transfer from the
carboxyl-ended phenylene-ethynylene segments to the porphyrin ring is less
efficient. Additionally, the use of compound 1 in preparation of self-
assembled monolayers on gold substrates and nano particles is still in progress.
In summary, monodisperse asymetrical OPEs were synthesized using a
convenient iterative method. A solvent-dependent deprotection method was
developed for the selectively cleavage of TMS protecting group in the

Oligo(phenylene-ethynylene)s
1397
presence of TSE protecting group, which will be of great interest to
synthetic chemists.
EXPERIMENTAL
General Remarks
Unless otherwise noted, all reactions were carried out under a dry nitrogen
atmosphere. All reagents were purchased from commercial suppliers and
used without further purification unless otherwise indicated. Tetrahydrofuran
(THF) was distilled from Na-benzophenone under nitrogen. Diisopropylamine
and triethylamine (TEA) were distilled from CaH2. Compound 18 was
prepared according to published procedures.[10] Thin-layer chromatography
(TLC) analysis was performed using silica gel HSG (F254) plates, and the
eluted plates were observed under a UV detector. Chromatographic purifi-
cations were performed by flash chromatography on silica gel (200–300
1
mesh). H and 13C NMR spectra were recorded at 300 MHz and 75 MHz,
respectively, with choroform-d1 as the solvent. UV-visible spectra were
recorded in toluene solution with a UV-1601pc spectrometer. Emission
spectra were obtained in toluene solution with a F-4500 Fluorescence spec-
trometer. MALDI-TOF mass spectra were recorded on a BIFLEXIV mass
spectrometer. Low-resolution mass spectra were recorded on a MS-50 mass
spectrometer.
General Procedure for the Palladium/Copper-Catalyzed
Coupling Reactions
To a dried Schlenk flask were charged with aryl iodides, terminal acetylenes,
Pd(PPh3)2Cl2 (1 mol%), CuI (2 mol%), and TEA or THF/diisopropylamine or
THF/diisopropylethylamine. The mixture was stirred at 25–608C under N2
for one to several days, depending on the specific reaction performed. After
removal of solvents, the residues were first filtered through a short pad of
silica gel eluting with CH2Cl2. Further purification of crude products was
then achieved by column chromatography on silica gel.
General Procedure for the Desilylation of Alkynes
To a solution of silylated alkyne (1.0 equiv.) in dichloromethane was added
TBAF (1.3 equiv.), and the mixture was stirred at room temperature for 1 h.
The whole reaction mixture was then filtered through a short pad of silica
gel eluting with CH2Cl2. Removal of the solvent afforded desired products.

1398
J. Zhao and Z. Bo
Individual compounds
Compound 12: 11 (5.0 g, 7.2 mmol), 2-trimethylsilylacetylene (0.5 mL,
3.5 mmol), Pd(PPh3)2Cl2 (25 mg, 0.036 mmol), CuI (13 mg, 0.068 mmol),
THF (20 mL), and diisopropylamine (10 mL) were used. The reaction mixture
was stirred at room temperature for 24 h. After removal of the solvent, the
residue was purified by flash chromatography on silica gel eluting with
1
hexane to give 12 as a white solid (1.1 g, 47%). H NMR d 7.28 (s, 2H),
6.85 (s, 2H), 3.95 (t, 4H), 1.83–1.75 (m, 4H), 1.57–1.48 (m, 4H), 1.28
(m, 32H), 0.92–0.87 (m, 6H), 0.27 (s, 9H). 13C NMR d 154.7, 151.5, 123.5,
116.0, 113.1, 100.6, 99.2, 87.7, 69.9, 69.5, 31.8, 29.5, 29.2, 29.1, 29.0, 25.8,
22.5, 14.0, 20.2.
Compound 9: 8 (0.96 g, 2.77 mmol), 2-trimethylsilylacetylene (0.5 mL,
3.6 mmol), Pd(PPh3)2Cl2 (98.5 mg, 0.14 mmol), CuI (54 mg, 0.28 mmol),
THF (20 mL), and diisopropylamine (10 mL) were used. The reaction
mixture was stirred at room temperature for 24 h. After the removal of the
solvent, the residue was purified by flash chromatography on silica gel
eluting with hexane/dichloromethane (3:2, v:v) to give 9 as a white solid
1
(0.83 g, 94%). H NMR d 7.96 (d, 2H), 7.51 (d, 2H), 4.41 (t, 2H), 1.11
(t, 2H), 0.25 (s, 9H), 0.06 (s, 9H). 13C NMR d 166.0, 131.7, 130.1, 129.2,
127.4, 104.0, 97.4, 63.3, 17.3, 20.3, 21.6. C17H26O2Si2: C, 64.03; H, 8.24.
Found: C, 64.10; H, 8.23.
Compound 10: 9 (753 mg, 2.37 mmol), dichloromethane (100 mL), and
TBAF (0.9 mL, 3.0 mmol) were used. 10 was obtained as a colorless oil
1
(520 mg, 89%). H NMR d 7.99 (d, 2H), 7.55 (d, 2H), 4.43 (t, 2H), 3.23
(s, H), 1.15 (t, 2H), 0.09 (s, 9H). 13C NMR d 166.0, 132.0, 130.6, 129.4,
126.5, 82.8, 80.0, 63.5, 17.4, 21.5. MS m/z for C14H18O2Si: 245 (M þ ).
Found: 246.11.
Compound 13: 10 (102 mg, 0.41 mmol), 12 (277 mg, 0.42 mmol),
Pd(PPh3)2Cl2 (3 mg, 0.0047 mmol), CuI (2 mg, 0.011 mmol), THF (14 mL),
and diisopropylamine (7 mL) were used. The reaction mixture was stirred at
room temperature for 24 h. After the removal of the solvent, the residue was
purified by flash chromatography on silica gel eluting with hexane/ethyl
1
acetate (50:1, v:v) to give 13 as a yellowish solid (0.2856 g, 88%). H NMR
d 8.01 (d, 2H), 7.56 (d, 2H), 6.96 (s, 1H), 6.95 (s, 1H), 4.42 (t, 2H), 4.01–
3.95 (m, 4H), 1.85–1.78 (m, 4H), 1.52–1.50 (m, 4H), 1.26–1.14 (m, 32H),
1.11 (t, 2H), 0.89–0.86 (m, 6H), 0.27 (s, 9H), 0.07 (s, 9H). 13C NMR d
166.2, 154.1, 153.6, 131.4, 129.9, 129.4, 127.9, 117.1, 116.8, 114.2, 113.5,
101.0, 100.4, 94.1, 88.8, 69.5, 69.5, 63.4, 31.9, 29.7, 29.5, 29.4, 29.3, 26.1,
22.7, 17.4, 14.2, 0.0, 21.4. MALDI-TOF for C49H78O4Si2: 786.8. Found:
786.54.
Compound 6: 13 (92 mg, 0.12 mmol), dichloromethane (50 mL), and
TBAF (0.045 mL, 0.16 mmol) were used. 6 was obtained as a yellow solid
1
(83 mg, 99.1%). H NMR d 8.02 (d, 2H), 7.57 (d, 2H), 7.00 (s, 1H), 6.99
(s, 1H), 4.43 (t, 2H), 4.03–3.98 (m, 4H), 3.36 (s, H), 1.85–1.81 (m, 4H),

Oligo(phenylene-ethynylene)s
1399
1.50–1.48 (m, 4H), 1.27–1.14 (m, 32H), 1.11 (t, 2H), 0.89–0.86 (m, 6H),
0.08 (s, 9H). 13C NMR d 166.2, 154.1, 153.6, 131.4, 130.0, 129.4, 127.8,
117.6, 116.8, 113.9, 113.1, 94.1, 88.6, 82.5, 79.9, 69.6, 69.5, 63.4, 31.9,
29.6, 29.6, 29.3, 29.2, 29.1, 26.0, 25.9, 22.7, 17.4, 14.1, 21.5. MALDI-
TOF for C46H70O4Si: 714.5. Found: 714.5.
Compound 14:
6 (89 mg, 0.12 mmol), 12 (87 mg, 0.13 mmol),
Pd(PPh3)2Cl2 (0.9 mg, 0.0013 mmol), CuI (0.6 mg, 0.0032 mmol), THF
(8 mL), and diisopropylamine (4 mL) were used. The reaction mixture was
stirred at room temperature for 24 h. After the removal of the solvent, the
residue was purified by flash chromatography on silica gel eluting with
hexane/ethyl acetate (70:1, v:v) to give 14 as a yellow solid (0.13 g, 84%).
1H NMR d 8.01 (d, 2H), 7.57 (d, 2H), 7.00 (s, 1H), 7.00 (s, 1H), 6.95
(s, 1H), 6.94 (s, 1H), 4.42 (t, 2H), 4.04–3.94 (m, 8H), 1.84–1.82 (m, 8H),
1.52–1.50 (m, 8H), 1.25–1.14 (m, 64H), 1.11 (t, 2H), 0.87–0.85 (m, 12H),
0.26 (s, 9H), 0.07 (s, 9H). 13C NMR d 166.3, 154.2, 153.8, 153.4, 153.4,
131.4, 129.9, 129.4, 128.0, 117.4, 117.1, 117.0, 114.9, 114.4, 113.8, 113.3,
101.2, 100.8, 100.2, 94.1, 91.7, 91.4, 89.0, 69.8, 69.7, 69.5, 69.4, 63.5, 32.0,
29.7, 29.5, 29.4, 29.3, 26.1, 26.0, 22.7, 17.5, 14.2, 0.0, 21.4. MALDI-TOF
for C81H130O6Si2: 1255.0. Found: 1254.94.
Compound 15: 14 (0.13 g, 0.10 mmol), dichloromethane (50 mL), and
TBAF (0.042 mL, 0.15 mmol) were used. 15 was obtained as a yellowish
1
solid (0.12 g, 98%). H NMR d 8.01 (d, 2H), 7.57 (d, 2H), 7.00 (s, 1H),
7.00 (s, 1H), 6.99 (s, 1H), 6.97 (s, 1H), 4.43 (t, 2H), 4.06–3.97 (m, 8H),
3.35 (s, 1H), 1.84–1.82 (m, 8H), 1.54–1.48 (m, 8H), 1.26–1.14 (m, 66H),
1.11 (t, 2H), 0.87–0.85 (m, 12H), 0.08 (s, 9H). 13C NMR d 166.2, 154.1,
153.8, 153.4, 153.3, 131.4, 129.9, 129.4, 128.0, 117.9, 117.0, 116.9, 114.8,
114.7, 113.3, 112.6, 94.1, 91.5, 91.4, 89.0, 82.3, 80.0, 69.7, 69.5, 69.4, 63.4,
31.9, 29.7, 29.5, 29.4, 29.3, 29.2, 26.1, 26.0, 22.7, 17.4, 14.2, 21.4.
MALDI-TOF for C78H122O6Si: 1183.0. Found: 1182.9.
Compound 16: Following the general procedure for the palladium-
catalyzed coupling reaction using compound 15 (0.11 g, 0.093 mmol),
compound 12 (0.67 g, 0.10 mmol), Pd(PPh3)2Cl2 (0.8 mg, 0.0011 mmol),
CuI (0.4 mg, 0.0021 mmol) in THF (8 mL) and diisopropylamine (4 mL).
The reaction mixture was stirred at room temperature for 24 h. After
removal of the solvent, the residue was purified by flash chromatography on
silica gel eluting with hexane/ethyl acetate (100:1, v:v) to give 16 as a
yellow solid (97 mg, 60%). 1H NMR d 8.01 (d, 2H), 7.57 (d, 2H),
7.01–6.94 (m, 6H), 4.42 (t, 2H), 4.04–3.96 (m, 10H), 1.84–1.82 (m, 10H),
1.52–1.50 (m, 16H), 1.26–1.14 (m, 96H), 1.11 (t, 2H), 0.88–0.85
(m, 18H), 0.26 (s, 9H), 0.09 (s, 9H). 13C NMR d 166.2, 154.1, 153.8, 153.5,
153.5, 153.5, 153.3, 131.4, 129.9, 129.4, 128.0, 117.3, 117.2, 117.1, 116.9,
114.9, 114.5, 114.3, 114.2, 113.6, 113.2, 101.2, 100.1, 94.1, 91.9, 91.5,
91.4, 89.0, 69.7, 69.6, 69.5, 69.4, 63.4, 31.9, 29.7, 29.5, 29.5, 29.4, 29.3,
26.1, 26.0, 22.7, 17.4, 14.2, 0.0, 21.4. MALDI-TOF for C113H182O8Si2:
1723.6. Found: 1723.34.

1400
J. Zhao and Z. Bo
Compound 4: 16 (95 mg, 0.055 mmol), dichloromethane (50 mL), and
TBAF (0.023 mL, 0.079 mmol) were used. 4 was obtained as a yellow solid
1
(90 mg, 99%). H NMR d 8.01 (d, 2H), 7.57 (d, 2H), 7.01–6.97 (m, 6H),
4.42 (t, 2H), 4.06–3.96 (m, 12H), 3.34 (s, 1H), 1.86–1.77 (m, 12H), 1.51–
1.50 (m, 12H), 1.24–1.14 (m, 98H), 1.11 (t, 2H), 0.87–0.85 (m, 16H), 0.07
(s, 9H). 13C NMR d 166.3, 154.2, 153.8, 153.5, 153.5, 153.3, 131.4, 129.9,
129.4, 128.1, 118.0, 117.2, 117.1, 117.0, 114.9, 114.3, 113.3, 112.5, 94.2,
91.9, 91.6, 91.5, 91.3, 89.0, 82.3, 80.1, 69.7, 69.7, 69.6, 69.5, 63.5, 32.0,
29.7, 29.5, 29.5, 29.4, 29.3, 29.2, 26.2, 26.1, 26.0, 22.7, 17.5, 14.2, 21.4.
MALDI-TOF for C110H174O8Si: 1651.3. Found: 1651.3.
Compound 5: 18 (0.021 g, 0.12 mmol), compound 11 (0.41 g, 0.59 mmol),
Pd(PPh3)2Cl2 (2.5 mg, 0.0036 mmol), CuI (1.4 mg, 0.0074 mmol) in THF
(8 mL) and triethylamine (4 mL) were used. The mixture was stirred at
508C for 24 h. After removal of the solvent, the residue was purified by
flash chromatography on silica gel eluting with hexane/dichloromethane
1
(5:1, v:v) to give 5 as a yellow-orange solid (36 mg, 40%). H NMR d 7.50
(d, 2H), 7.34 (d, 2H), 7.21 (s, H), 6.86 (s, H), 3.96–3.91 (m, 4H), 2.40
(s, 3H), 1.83–1.78 (m, 4H), 1.52–1.43 (m, 4H), 1.23–1.20 (m, 32H), 0.86–
0.81 (m, 6H). 13C NMR d 193.4, 154.4, 151.8, 134.2, 132.1, 124.7, 123.8,
115.9, 113.2, 93.4, 88.0, 87.3, 70.1, 69.8, 31.9, 30.3, 29.7, 29.6, 29.4, 29.3,
29.2, 26.1, 26.0, 22.7, 14.2. MALDI-TOF for C40H59IO3S: 746.8. Found:
746.32.
Compound 1: 5 (22 mg, 0.030 mmol), compound 4 (44 mg, 0.027 mmol),
Pd(PPh3)2Cl2 (0.6 mg, 0.00080 mmol), CuI (0.3 mg, 0.0015 mmol), THF
(3 mL), and diisopropylethylamine (3 mL) were used. The mixture was
stirred at 508C for 5 days. After removal of the solvent, the residue was
purified by flash chromatography on silica gel eluting with hexane/dichloro-
methane (4:5, v:v) changing to hexane/ethyl acetate (20:1, v:v) to give 1 as a
1
yellow solid (15 mg, 25%). H NMR d 8.01 (d, 2H), 7.57 (d, 2H), d 7.54
(d, 2H), 7.39 (d, 2H), 7.01 (m, 8H), 4.42 (t, 2H), 4.04–4.00 (m, 16H), 2.44
(s, 3H), 1.86–1.80 (m, 16H), 1.52–1.47 (m, 18H), 1.25–1.13 (m, 130H),
1.11 (t, 2H), 0.87–0.83 (m, 20H), 0.09 (s, 9H). 13C NMR d 193.5, 166.2,
153.8, 153.5, 134.2, 132.1, 131.4, 129.9, 129.4, 128.0, 124.8, 117.2, 117.1,
117.0, 114.7, 114.4, 114.3, 113.5, 113.2, 94.1, 94.0, 91.7, 91.6, 87.8, 69.7,
69.6, 69.5, 63.4, 32.7, 32.2, 31.9, 30.3, 30.0, 29.7, 29.5, 29.4, 26.4, 26.0,
22.7, 17.4, 14.1, 21.4. MALDI-TOF for C150H232O11SSi: 2269.8. Found:
2269.71.
Compound 2: 6 (25 mg, 0.034 mmol), porphyrin 7 (31 mg, 0.033 mmol),
Pd(PPh3)2Cl2 (0.3 mg, 4.3 ꢀ 1024 mmol), CuI (0.2 mg, 0.0011 mmol), THF
(6 mL), and diisopropylamine (2 mL). The mixture was stirred at room tempe-
rature for 24 h. After removal of the solvent, the residue was purified by flash
chromatography on silica gel eluting with hexane/dichloromethane (3:1, v:v)
to give 2 as a purple solid (18 mg, 36%). 1H NMR d 8.72–8.59 (m, 8H), 8.27
(d, 2H), 8.06 (d, 2H), 7.92 (d, 2H), 7.65 (d, 2H), 7.32 (m, 6H), 7.20 (s, 1H),
7.13 (s, 1H), 4.46 (t, 2H), 4.16 (m, 4H), 2.66 (m, 9H), 1.95–1.87 (m, 18H),

Oligo(phenylene-ethynylene)s
1401
1.64–1.60 (m, 4H), 1.44 (m, 4H),1.27 (m, 32H), 1.17 (t, 2H), 0.91–0.86
(m, 6H), 0.09 (s, 9H).
Compound 3: 2 (10 mg, 0.0066 mmol), THF (20 mL), and TBAF (10 mL,
1
0.0344 mmol) were used. 3 was obtained as a purple solid (8 mg, 85%). H
NMR d 8.89 (m, 2H), 8.80 (m, 2H), 8.73 (m, 4H), 8.24 (d, 2H), 8.12
(d, 2H), 7.94 (d, 2H), 7.68 (d, 2H), 7.30 (m, 6H), 7.21 (s, 1H), 7.14 (s, 1H),
4.16 (m, 4H), 2.65 (m, 9H), 1.98–1.87 (m, 18H), 1.67–1.62 (m, 4H), 1.45
(m, 4H), 1.28 (m, 32H), 0.90–0.83 (m, 6H).
ACKNOWLEDGMENT
Financial support from CAS (KJCX2-SW-H07), the National Natural Science
Foundation of China (20225415, 20374053), and the Major State Basic
Research Development Program (2002CB613400) are greatly acknowledged.
REFERENCES
1. Mu¨llen, K.; Wegner, G. Electronic Materials: The Oligomer Approach. Wiley-
VCH: Weinheim, Germany, 1998.
2. Moore, J. S.; Prince, R. B. Nonbiological sequence-specific oligomers by repetitive
syntheses. In Synthesis of Polymers; Schlu¨ter, A.-D., Ed.; Wiley: Weinheim, 1999;
pp. 11–38.
3. Hensel, V.; Godt, A.; Popvitz-Biro, R.; Cohen, H.; Jensen, T. R.; Kjaer, K.;
Weissbuch, I.; Lifshitz, E.; Lahav, M. Hybrid composites of monodisperse
p-conjugated rodlike organic compounds and semiconductor quantum particles.
Chem. Eur. J. 2002, 8 (6), 1413–1423.
4. Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Polyphenylene nanostructures. Chem.
Rev. 1999, 99 (7), 1747–1786.
5. Tour, J. M. Conjugated macromolecules of precise length and constitution.
Organic synthesis for the construction of nanoarchitectures. Chem. Rev. 1996,
96 (1), 537–553.
6. Tour, J. M. Molecular electronics. Synthesis and testing of components. Acc.
Chem. Res. 2000, 33 (11), 791–804.
7. Briehn, C. A.; Baeuerle, P. From solid-phase synthesis of p-conjugated oligomers
to combinatorial library construction and screening. Chem. Commun. 2002, 10,
1015–1023.
8. Martin, R. E.; Diederich, F. Linear monodisperse n-conjugated oligomers: model
compounds for polymers and more. Angew. Chem., Int. Ed. Engl. 1999, 38 (10),
1350–1377.
9. Jones, L. R.; Schumm, J. S.; Tour, J. M. Rapid solution and solid phase syntheses
of oligo(1,4-phenylene ethynylene)s with thioester termini: molecular scale wires
with alligator clips. Derivation of iterative reaction efficiencies on a polymer
support. J. Org. Chem. 1997, 62 (5), 1388–1410.
10. Pearson, D. L.; Tour, J. M. Rapid syntheses of oligo(2,5-thiophene ethynylene)s
with thioester termini: potential molecular scale wires with alligator clips.
J. Org. Chem. 1997, 62 (5), 1376–1387.

1402
J. Zhao and Z. Bo
11. Francke, V.; Mangel, T.; Mullen, K. Synthesis of a,v-difunctionalized oligo- and
poly(p-phenyleneethynylene)s. Macromolecules 1998, 31 (8), 2447–2453.
12. Hsung, R. P.; Chidsey, C. E. D.; Sita, L. R. Synthesis and characterization of
unsymmetric
ferrocene-terminated
phenylethynyl
oligomers
Cp2Fe-
[C.tplbond.C-C6H4]n-X, (X ¼ SH, SMe, SOMe, and SO2Me). Organometallics
1995, 14 (10), 4808–4815.
13. Zehner, R. W.; Parsons, B. F.; Hsung, R. P.; Sita, L. R. Tuning the work function of
;;
gold with self-assembled monolayers derived from X–[C6H4–C C–]nC6H4–SH
(n ¼ 0, 1, 2; X ¼ H, F, CH3, CF3, and OCH3). Langmuir 1999, 15 (4), 1121–1127.
14. Yu, C. J.; Chong, Y.; Kayyem, J. F.; Gozin, M. Soluble ferrocene conjugates for
incorporation into self-assembled monolayers. J. Org. Chem. 1999, 64 (6),
2070–2079.
15. Ziener, U.; Godt, A. Synthesis and characterization of monodisperse oligo(pheny-
leneethynylene)s. J. Org. Chem. 1997, 62 (18), 6137–6143.
16. Kukula, H.; Veit, S.; Godt, A. Synthesis of monodisperse oligo(para-
phenyleneethynylene)s using orthogonal protecting groups with different
polarity for terminal acetylene units. Eur. J. Org. Chem. 1999 1, 277–286.
17. Hsung, R. P.; Babcock, J. R.; Chidsey, C. E. D.; Sita, L. R. Thiophenol protecting
groups for the palladium-catalyzed heck reaction: Efficient syntheses of conju-
gated arylthoils. Tetrahedren Lett. 1995, 36 (26), 4525–4528.