Synthesis and efficient energy transfer in a three-chromophore energy gradient of regioregular silylene-spaced divinylarene copolymers

Article abstract of DOI:10.1021/ma050140z

Regioregular silylene-spaced copolymers 1 composed of an energy gradient with three different chromophores have been achieved by rhodium-catalyzed hydrosilylation of bis-vinylsilanes 3 and bis-alkynes 4. Monomeric reference compounds 2 were prepared for c

Full text of DOI:10.1021/ma050140z

Macromolecules 2005, 38, 4563-4568
4563
Articles
Synthesis and Efficient Energy Transfer in a Three-Chromophore
Energy Gradient of Regioregular Silylene-Spaced Divinylarene
Copolymers
Yen-Ju Cheng† and Tien-Yau Luh*,†,‡
Department of Chemistry and Institute of Polymer Science and Engineering, National Taiwan
University, Taipei 106, Taiwan
Received January 21, 2005; Revised Manuscript Received April 13, 2005
ABSTRACT: Regioregular silylene-spaced copolymers 1 composed of an energy gradient with three
different chromophores have been achieved by rhodium-catalyzed hydrosilylation of bis-vinylsilanes 3
and bis-alkynes 4. Monomeric reference compounds 2 were prepared for comparison. The ratio of three
chromophores is 1:2:1, corresponding to D1, D2, and A chromophores, respectively. The dimethylsilylene
(SiMe2) moiety serves as an insulating bridge between chromophores. Upon excitation of the donor
chromophore (D1), only emission from the acceptor (A) was observed. Efficient and sequential energy
transfer across three different chromophores along the polymeric backbone may proceed smoothly in
these silylene-spaced copolymers.
Introduction
of donors and acceptors along the polymeric chain.9-12
Recently, we disclosed that a series of silylene-spaced
copolymers can serve as an ideal architecture for ef-
ficient intrachain energy transfer10,12 and the light-
harvesting ability is enhanced with the increasing ratio
of donor to acceptor chromophore along the polymeric
backbone.10 It is envisaged that introduction of an
energy gradient with three well-designed chromophores
into a silylene-spaced polymeric chain may lead to
sequential energy transfer. Herein, we present the
unprecedented synthesis and photophysical studies of
silylene-spaced regioregular polymers 1 composed of a
In photosynthesis, energy is harvested by antenna
pigments and transferred into a reaction center where
redox reactions take place.1 Morphologically, different
antenna chromophores surrounding the reaction center
are arranged in an order of energy gradient.2-4 Accord-
ingly, energy can be sequentially transferred and ef-
ficiently funneled to the reaction center over nanometer
distances in the direction of decreasing band gaps. Much
effort has been directed toward the development of
sequential multistep energy-transfer systems not only
for mimicking the natural light-harvesting process2,3 but
also for the potential applications in biological systems4
and optoelectronic applications.5 A conjugated polymeric
backbone with well-designed interruptions of conjuga-
tion by insulating spacers may allow for tuning of the
emission properties and provide an alternative model.6
The silylene moiety has been used extensively as an
insulating spacer.7 In general, when the silylene spacer
contains only one silicon atom, no conjugative interac-
tions between the π systems and the silicon moiety is
observed.8 The silylene-spaced divinylarene copolymers
are readily accessible by rhodium-catalyzed hydrosily-
lation of bis-alkynes with bis-vinylsilanes (eq 1).9
Such a protocol may furnish a range of fascinating
polymers that have different regioselective combinations
* Author to whom correspondence should be addressed.
E-mail: tyluh@ntu.edu.tw.
† Department of Chemistry.
‡ Institute of Polymer Science and Engineering.
10.1021/ma050140z CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/05/2005

4564 Cheng and Luh
Macromolecules, Vol. 38, No. 11, 2005
Scheme 1
Scheme 2
well-designed energy gradient of three-chromophore
systems.
Monomeric reference compounds 2a-d were also pre-
pared. Polymer 1a was designed in accordance with the
conjugation length of three chromophores. The divinyl-
benzene chromophore was chosen as the donor with
highest band gap and the divinylstilbene chromophore
acted as the acceptor with lowest band gap, whereas
divinylbiphenyl chromophore served as the intermediate
gradient. Polymer 2b, consisting of a combination of
three chromophores, divinylbiphenyl, divinyldiphenyl
oxadiazole, and dibutoxyterphenylene tetravinylene,
was also designed and synthesized.
Results and Discussion
Synthesis. By adopting rhodium-catalyzed hydro-
silylation of bis-alkynes with bis-vinylsilanes as shown
in eq 1, a combination of three different chromophores
separated by dimethylsilylene moieties (SiMe2) can be
regioregularly incorporated into the polymeric chain.
The molar fraction of each chromophore in polymer 1
is1:2:1, corresponding to D1, D2, and A, respectively.

Macromolecules, Vol. 38, No. 11, 2005
Regioregular Silylene-Spaced Divinylarene Copolymers 4565
The synthesis of acceptor (A) monomers 3 with
dimethylsilyl substituents at the olefinic termini was
based on the nickel-catalyzed silylolefination of the
corresponding dithioacetals with (iPrO)Me2SiCH2MgCl,
followed by reduction of the corresponding Si-O bond,9-13
whereas silylene-spaced diyne monomers 4, which are
readily comprised of two chromophores (D1 and D2),
were prepared according to Schemes 1 and 2.
Figure 1. Fluorescence spectra of 2a (λex ) 280 nm), 2b (λex
) 310 nm) and 3a (λex ) 355 nm) in CHCl3.
Rhodium-catalyzed hydrosilylation of 5 with 2 equiv
of 6 resulted in the formation of 7 in 79% yield. Removal
of the triisopropylsilyl (TIPS) group in 7 by TBAF
afforded diyne 4a in 60% yield. Hydrosilylation of 4a
with 2 equiv of 8 led to the corresponding monomeric
reference 2d containing divinylbenzene and divinylbi-
phenyl chromophores (Scheme 1) in 52% yield. In a
sequential Sonogashira reaction, 9 was first treated with
1 equiv of triisopropylsilylacetylene to yield 10, which
was then allowed to react with trimethylsilylacetylene
to afford 11 in 64% yield. Selective removal of the
trimethylsilyl (TMS) group in 11 (NaOH/MeOH) led to
12 in 84% yield. Rhodium-catalyzed hydrosilylation of
13 with 2 equiv of 12 resulted in the formation of 14 in
25% yield. Desilylation of the TIPS group in 14 with
TBAF furnished 4b in 88% yield. (Scheme 2).
Hydrosilylation of 4a with 3a (4b with 3b) afforded
the first example of silylene-spaced polymers 1 consist-
ing of an energy gradient with three chromophores in a
regioregular arrangement. (Table 1).
Figure 2. Concentration-dependent fluorescence spectra (λex
) 280 nm) of an equal molar mixture of 2d and 3a in CHCl3
Table 1. RhCl(PPh3)3-Catalyzed Reactions of Bis-alkyne 4
and Bis-vinylsilanes 3
(from 10-4 M to 10-6 M) and fluorescence spectrum (λex ) 280
-5
nm) of polymer 1a in CHCl3 (10
M).
bis-alkynes bis-vinylsilanes polymer
Mn (PDI)
Φ
4a
4b
3a
3b
1a
1b
7900 (2.8) 0.45
16300 (3.1) 0.49
from divinylbenzene to divinylbiphenyl chromophore in
2d is highly efficient, resulting in a complete quenching
of the emission of divinylbenzene. At low concentration
(10-6 M), the observed emission mainly originates from
the divinylbiphenyl chromophore in 2d, which indicates
that energy transfer between 2d and 3a is negligibly
weak. With gradually increasing concentration of the
mixture, the intermolecular energy transfer from divi-
nylbiphenyl in 2d to divinylstilbene in 3a becomes
important, leading to a decreasing emission of divinyl-
biphenyl along with an increasing emission of divinyl-
stilbene. Nevertheless, the energy transfer does not
process completely even at a relatively higher concen-
tration (10-4 M). In sharp contrast, when polymer 1a
was excited at 280 nm, complete energy transfer was
observed, resulting in emission only from divinylstilbene
exclusively. No emission arising from divinylbenzene
itself or divinylbiphenyl was observed. Moreover, the
emission profiles of polymer 1a remain unchanged, with
concentrations from 10-4 to 10-6 M,14 which not only
indicates that the energy transfer may take place in an
intramolecular manner but also reveals that undesired
intrachain or interchain aggregation which will cause
Photophysical Properties of Polymers. The ab-
sorption and emission properties of monomeric refer-
ences 2 and 3 in chloroform are given in Table 2. Figure
Table 2. Absorption and Emission Properties of 2 and 3
in Chloroform
substrate
λmax (nm), ꢀmax (M-1 cm-1
)
λem (nm)
2a
2b
2c
3a
3b
290 (35900)
312 (32300)
324 (35100)
355 (55800)
411 (37000)
334, 347
361, 375
363, 384, 401
392, 411
467, 490
1 illustrates the emission spectra of monomeric refer-
ences, 2a, 2b, and 3a, corresponding to component
chromophores in polymer 1a.
Figure 2 shows the concentration-dependent emission
spectra of an equal molar mixture of two-chromophore
monomer 2d and its corresponding acceptor 3a upon
excitation of divinylbenzene chromophore at 280 nm. It
is apparent that the intramolecular energy transfer

4566 Cheng and Luh
Macromolecules, Vol. 38, No. 11, 2005
subsequently to divinylstilbene chromophores.15 In a
similar manner, upon excitation of divinylbiphenyl
chromophore in polymer 1b at 300 nm, the emissions
from divinylbiphenyl or divinyldiphenyloxadiazole in
polymer 1b have been quenched so that a strong
emission at 467 and 490 nm resulting from the acceptor
chromophore was observed. This result indicates that
efficient intrachain energy transfer may occur from
divinylbiphenyl via divinyldiphenyloxadiazole to ter-
phenylene tetravinylene chromophores (Figure 3). The
energy transfer directly from divinylbiphenyl to terphe-
nylene tetravinylene chromophore, if any, would be
relatively unfavorable because of the much longer
distance and poorer spectral overlap.
As shown in Figure 4, the absorption spectra of
polymers 1a and 1b were compared with its excitation
spectra monitored at 411 and 490 nm, respectively, and
the energy-transfer efficiency in 1a was estimated to
be 89% and 1b 86%.
Figure 3. Fluorescence spectrum (λex ) 300 nm) of 1b in
chloroform.
Conclusions
In summary, the first successful example of regio-
regular silylene-spaced polymers 1 composed of three
different chromophores have been designed and syn-
thesized by the rhodium-catalyzed hydrosilylation of bis-
vinylsilanes 3 and bis-alkynes 4. The ratio of three
chromophores was D1/D2/A ) 1:2:1. Our synthetic
protocol has furnished a powerful arsenal for the
construction of copolymers with precise regiochemistry
and structural variety. In the polymeric segments of an
energy gradient, the band gaps of three chromophores
decrease by means of the increasing conjugation lengths.
Upon excitation of the donor chromophores (D1), only
emission from the acceptor (A) was observed. Efficient
and sequential energy transfer across three different
chromophores along the polymeric backbone may pro-
ceed smoothly in these silylene-spaced copolymers.
Experimental Section
The absorption spectra were recorded on a Hitachi U-3310
spectrometer. The photoluminescence and excitation spectra
were measured on a Hitachi F-4500 fluorescence spectrometer.
Gel permeation chromatography (GPC) was performed on a
Waters GPC machine using an isocratic HPLC pump (1515)
and a refractive index detector (2414). THF was used as the
eluent (flow rate ) 1 mL/min). Waters Styragel HR2, HR3,
HR3, and HR4 (7.8 × 300 mm) columns were employed for
molecular weight determination, and polystyrenes were used
as standard (Mn values ranging from 375 to 3.5 × 106).
Quantum yield (Φ) of polymer 1 was measured in CHCl3 using
coumarin 1 in EtOAc (Φ ) 0.99) as the standard. The
ionization method of HRMS for all compounds was FAB using
3-nitrobenzyl alcohol (NBA) matrix.
1,4-Bis{2-{2-[4′-(tri-isopropylsilylethynyl)biphen-4-yl]-
vinyl}dimethylsilylvinyl}benzene (7). Under argon, a mix-
ture of 610 (1.08 g, 3 mmol), 5 (0.37 g, 1.5 mmol), and
Rh(PPh3)3Cl (14 mg, 0.5 mol %) in THF (5 mL) was refluxed
for 2 h. After cooling to room temperature, the mixture was
poured into MeOH. The precipitate was collected and recrys-
tallized from CHCl3 to give 7 (1.1 g, 79%): mp 90-91 °C; IR
(KBr): ν 3019, 2942, 2863, 2153, 1910, 1602, 1491, 1462, 1247,
Figure 4. A comparison of the absorption spectra (solid line)
of (a) 1a and (b) 1b in CHCl3 with the corresponding excitation
spectra (dashed line) monitored at (a) 411 nm and (b) 490 nm,
respectively.
1
985, 832, 731, 706, 676 cm-1; H NMR (400 MHz, CDCl3): δ
0.38 (s, 12 H), 1.19 (s, 42 H), 6.58 (d, J ) 19.1 Hz, 2 H), 6.61
(d, J ) 19.1 Hz, 2 H), 7.00 (d, J ) 19.1 Hz, 2 H), 7.03 (d, J )
19.1 Hz, 2 H), 7.48 (s, 4 H), 7.55-7.65 (m, 16 H); 13C NMR
(100 MHz, CDCl3): δ -2.4, 11.5, 18.8, 91.5, 107.1, 122.7, 126.8,
126.9, 127.1, 127.2, 127.5, 127.6, 128.0, 132.6, 137.8, 140.1,
140.6, 144.4, 144.7; HRMS (FAB) (C64H82Si4) calcd: 962.5494;
found: 962.5488. Anal. Calcd for C64H82Si4: C 79.77, H 8.58;
found: C 79.49, H 8.53.
energy losses may not occur in 1a under the conditions
of measurements.
Because the rate of energy transfer depends strongly
on distance, being inversely proportional to r6, it seems
likely that successive two-step energy transfer might
be first transferred from divinylbenzene chromophores
to the nearest divinylbiphenyl chromophores, then

Macromolecules, Vol. 38, No. 11, 2005
Regioregular Silylene-Spaced Divinylarene Copolymers 4567
1,4-Bis{2-[2-(4′-ethynylbiphen-4-yl)vinyl]dimethyl-
silylvinyl}benzene (4a). To a solution of 7 (0.58 g, 0.6 mmol)
in THF (5 mL) was added dropwise a 1 M solution of TBAF
(1.4 mL, 1.4 mmol). The mixture was stirred at room temper-
ature for 2.5 h, diluted with water, and extracted with CHCl3.
The organic layer was washed with brine and dried (MgSO4).
Solvent was removed in vacuo to give a brown solid that was
recrystallized from CHCl3 to yield 4a (0.23 g, 60%): mp 278-
279 °C (dec); IR (KBr): ν 3295, 2986, 2954, 2010, 1914, 1603,
filtration, the solvent was evaporated in vacuo. The residue
was chromatographed on silica gel (hexane) to give 12 as a
yellowish solid (0.9 g, 84%): mp 173-174 °C; IR (KBr): 3306,
3085, 2950, 2869, 2153, 2101, 1938, 1614, 1580, 1487, 1463,
1417, 1242, 996, 883, 845, 745, 679 cm-1; 1H NMR (400 MHz,
CDCl3): δ 1.15 (s, 21 H), 3.26 (s, 1 H), 7.63 (d, J ) 8.7 Hz, 2
H), 7.65 (d, J ) 8.6 Hz, 2 H), 8.07 (d, J ) 8.7 Hz, 2 H), 8.10 (d,
J ) 8.6 Hz, 2 H); 13C NMR (100 MHz, CDCl3): δ 11.3, 18.6,
80.1, 82.7, 94.6, 105.9, 123.1, 123.8, 125.7, 126.7, 126.8, 127.1,
132.6, 132.8, 164.1, 164.3; HRMS (FAB) (M++ H, C27H31N2-
OSi) calcd: 427.2206; found: 427.2209. Anal. Calcd for C27H30N2-
OSi: C 76.01, H 7.09, N 6.57; found: C 75.82, H 7.15, N 6.52.
4,4′-Bis{2-{2-[4-[5-(4-tri-isopropylsilylethynylphenyl)-
[1,3,4]oxadiazol-2-yl]-â-styryl]dimethylsilyl}vinyl}-
biphenyl (14). Under nitrogen, a mixture of 12 (0.43 g, 1
mmol), 1310b (0.16 g, 0.5 mmol), and Rh(PPh3)3Cl (4.6 mg, 0.5
mol %) in THF (5 mL) was refluxed for 6 h. After removal of
the solvent in vacuo, the residue was chromatographed on
silica gel (CH2Cl2/hexane ) 1:3) to afford a white solid 14 (0.15
g, 25%): mp 120-122 °C; IR (KBr): ν 2954, 2869, 2158, 1931,
1609, 1577, 1548, 1492, 1412, 1252, 1069, 991, 843, 748, 689
cm-1; 1H NMR (400 MHz, CDCl3): δ 0.37 (s, 12 H), 1.15 (s, 42
H), 6.57 (d, J ) 19.1 Hz, 2 H), 6.71 (d, J ) 19.1 Hz, 2 H), 7.02
(d, J ) 19.1 Hz, 4 H), 7.54 (d, J ) 7.7 Hz, 4 H), 7.62 (m, 12 H),
8.09 (d, J ) 8.2 Hz, 4 H), 8.12 (d, J ) 8.2 Hz, 4 H); 13C NMR
(100 MHz, CDCl3): δ -2.6, 11.3, 18.7, 94.5, 106.0, 123.0, 123.3,
126.6, 126.7, 126.99, 127.01, 127.03, 127.06, 127.1, 127.3,
127.6, 131.0, 132.6, 141.5, 143.6, 144.7, 164.1, 164.6; HRMS
(FAB) (M+ + H, C74H87N4O2Si4) calcd: 1175.5906; found:
1175.5887.
4,4′-Bis{2-{2-[4-[5-(4-ethynylphenyl)[1,3,4]oxadiazol-2-
yl]-â-styryl]dimethylsilyl}vinyl}biphenyl (4b). To a solu-
tion of 14 (0.12 g, 0.1 mmol) in THF (5 mL) was added
dropwise a 1 M solution of TBAF in THF (0.25 mL, 0.25 mmol).
The mixture was stirred at room temperature for 2.5 h, diluted
with water, and extracted with CHCl3. The organic layer was
washed with brine and dried (MgSO4). Solvent was removed
in vacuo to give a white solid that was recrystallized from
CHCl3 to yield 4b (75 mg, 88%): mp 267-268 °C; IR (KBr): ν
3300, 2960, 2944, 2860, 2110, 1925, 1608, 1576, 1549, 1493,
1412, 1252, 1065, 989, 846, 799, 745, 659 cm-1; 1H NMR (400
MHz, CDCl3): δ 0.37 (s, 12 H), 3.26 (s, 2 H), 6.57 (d, J ) 19.1
Hz, 2 H), 6.71 (d, J ) 19.1 Hz, 2 H), 7.01 (d, J ) 19.1 Hz, 4 H),
7.54 (d, J ) 7.7 Hz, 4 H), 7.6-7.8 (m, 12 H), 8.11 (d, J ) 7.8
Hz, 8 H); 13C NMR (100 MHz, CDCl3): δ -2.6, 80.1, 82.7, 123.0,
123.9, 125.6, 126.8, 127.0, 127.06, 127.13, 127.3, 131.0, 132.8,
137.2, 140.3, 141.5, 143.6, 144.7, 164.0, 164.7; HRMS (FAB)
(M+ + H, C56H47N2O2Si2) calcd: 863.3238. found: 863.3238.
Anal. Calcd for C56H46N2O2Si2: C 77.92, H 5.37, N 6.49;
found: C 77.72, H 5.37, N 6.21.
1492, 1247, 987, 831, 796, 641 cm-1 1H NMR (400 MHz,
;
CDCl3): δ 0.34 (s, 12 H), 3.13 (s, 2 H), 6.54 (d, J ) 19.1 Hz, 2
H), 6.58 (d, J ) 19.1 Hz, 2 H), 6.95 (d, J ) 19.1 Hz, 2 H), 6.99
(d, J ) 19.1 Hz, 2 H), 7.44 (s, 4 H), 7.5-7.6 (m, 16 H); 13C
NMR (100 MHz, CDCl3): δ -2.6, 77.8, 83.5, 121.0, 126.67,
126.73, 126.9, 126.95, 127.1, 127.4, 128.0, 132.5, 137.7, 139.7,
141.0, 144.2, 144.5; HRMS (FAB) (C46H42Si2) calcd: 650.2825;
found: 650.2828. Anal. Calcd for C46H42Si2: C 84.87, H 6.50;
found: C 84.68, H 6.63.
1,4-Bis{2-{2-[4′-[2-(â-styryldimethylsilyl)vinyl]biphen-
4-yl]vinyl}dimethylsilylvinyl}benzene (2d). Under argon,
a mixture of 8 (65 mg, 0.4 mmol), 4a (0.13 g, 0.2 mmol), and
Rh(PPh3)3Cl (1.9 mg, 0.5 mol %) in THF (3 mL) was refluxed
for 2 h. After cooling to room temperature, the mixture was
poured into MeOH. The precipitate was collected and chro-
matographed on silica gel (CH2Cl2/hexane ) 1:4) to afford a
solid 2d (0.1 g, 52%): mp 231-233 °C; IR (KBr): ν 3029, 2992,
2961, 1912, 1746, 1605, 1514, 1497, 1451, 1334, 1253, 1197,
1
988, 843, 791, 695 cm-1; H NMR (400 MHz, CDCl3): δ 0.33
(s, 24 H), 6.45-6.65 (m, 8 H), 6.85-7.05 (m, 8 H), 7.3-7.7 (m,
30 H); 13C NMR (100 MHz, CDCl3): δ -2.5, 126.4, 126.5, 126.7,
126.9, 127.0, 127.3, 127.50, 127.53, 127.6, 127.8, 128.11,
128.14, 128.26, 128.28, 128.50, 128.52, 137.3, 138.2, 144.33,
144.34, 144.5, 144.9; HRMS (FAB) (C66H70Si4) calcd: 974.4555;
found: 974.4548. Anal. Calcd for C66H70Si4 : C 81.25, H 7.23;
found: C 81.79, H 7.43.
2-(4-Bromophenyl)-5-(4-tri-isopropylsilylethynyl-
phenyl)[1,3,4]oxadiazole (10). A mixture of 910 (2.6 g, 6.0
mmol), tri-isopropylsilylacetylene (1.46 mL, 6.0 mmol), Pd-
(PPh3)2Cl2 (0.23 g, 0.3 mmol) and CuI (57 mg, 0.3 mmol) in
NEt3 (50 mL) and THF (40 mL) was refluxed under nitrogen
for 8 h and then cooled to room temperature. The mixture was
filtered, and the solvent was evaporated in vacuo. The crude
product was purified by column chromatography on silica gel
(hexane) to give 10 as a white solid (2.78 g, 95%): mp 170-
171 °C; IR (KBr): ν 3092, 2947, 2868, 2160, 1918, 1644, 1605,
1489, 1409, 1071, 883, 836, 682 cm-1 1H NMR (400 MHz,
;
CDCl3,): δ 1.15 (s, 21 H), 7.62 (d, J ) 8.6 Hz, 2 H), 7.69 (d, J
) 8.6 Hz, 2 H), 8.01 (d, J ) 8.6 Hz, 2 H), 8.07 (d, J ) 8.6 Hz,
2 H); 13C NMR (100 MHz, CDCl3): δ 11.3, 18.7, 94.6, 105.9,
122.7, 123.1, 126.6, 126.7, 127.2, 128.4, 132.5, 132.7, 164.0,
164.3; HRMS (FAB) (M+ + H, C25H30BrN2OSi) calcd: 481.1311;
found: 481.1315. Anal. Calcd for C25H29BrN2OSi: C 62.36, H
6.07, N 5.82; found: C 62.39, H 6.11, N 5.80.
Polymer 1a. Under argon, a mixture of 4a (0.13 g, 0.2
mmol), 3a12 (0.07 g, 0.2 mmol), and Rh(PPh3)3Cl (2 mg) in THF
(5 mL) was refluxed for 4 h. After cooling to room temperature,
the mixture was poured into MeOH. The precipitate was
collected and redissolved in THF and then reprecipitated with
MeOH. The product 1a was collected by filtration and washed
with MeOH (0.17 g, 85%): Mn ) 7900; PDI ) 2.8; (KBr): ν
3023, 2986, 2954, 2890, 1897, 1601, 1493, 1409, 1330, 1249,
1195, 1045, 985, 838 cm-1; 1H NMR (400 MHz, CDCl3): δ 0.34
(s, 24 H), 6.40-6.65 (m, 8 H), 6.90-7.05 (m, 8 H), 7.11 (s, 2
H), 7.3-7.65 (m, 28 H). Anal. Calcd for C68H70Si4: C 81.70, H
7.06; found: C 80.72, H 7.41.
2-(4-Trimethylsilylethynylphenyl)-5-(4-tri-isopropyl-
silylethynylphenyl)[1,3,4]oxadiazole (11). To a mixture of
trimethylsilylacetylene (1.5 mL, 7.5 mmol) and 10 (2.4 g, 5
mmol) in NEt3 (50 mL) and THF (20 mL) was added Pd(PPh3)2-
Cl2 (0.1 g, 0.14 mmol) and CuI (30 mg, 0.15 mmol). The mixture
was refluxed for 12 h under nitrogen and then cooled to room
temperature. After filtration, the solvent was evaporated in
vacuo, and the residue was chromatographed on silica gel (CH2-
Cl2) to afford 11 as a light-yellow solid (1.6 g, 64%): mp 42-
43 °C; IR (KBr): ν 2953, 2869, 2160, 1612, 1489, 1411, 1252,
Polymer 1b. Under argon, a mixture of 4b (15 mg, 0.017
mmol), 3b (10.34 mg, 0.017 mmol), and Rh(PPh3)3Cl (2 mg) in
THF (5 mL) was refluxed for 4 h. After cooling to room
temperature, the mixture was poured into MeOH. The pre-
cipitate was collected and redissolved in THF and then
reprecipitated with MeOH. The product 1b was collected by
filtration and washed with MeOH (16 mg, 65%): Mn ) 16300;
PDI ) 3.1; (KBr): ν 2943, 2865, 1597, 1481, 1462, 1410, 1209,
1225, 1070, 1017, 864, 749, 694 cm-1 1H NMR (400 MHz,
;
CDCl3): δ 0.28 (s, 9 H), 1.15 (s, 21 H), 7.62 (d, J ) 8.2 Hz, 4
H), 8.07 (d, J ) 8.2 Hz, 2 H), 8.08 (d, J ) 8.2 Hz, 2 H); 13C
NMR (100 MHz, CDCl3): δ -0.2, 11.3, 18.6, 94.6, 97.9, 103.9,
106.0, 123.1, 123.3, 126.68, 126.71, 127.1, 132.6, 132.7, 164.2,
164.3; HRMS (FAB) (M+ + H, C30H39N2OSi2) calcd: 499.2601;
found: 499.2596. Anal. Calcd for C30H38N2OSi2: C 72.24, H
7.68 N 5.62; found: C 72.41, H 7.74, N 5.51.
1
1045, 814, 668; H NMR (400 MHz, CDCl3): δ 0.36 (s, 24 H),
2-[4-Ethynylphenyl)-5-(4-tri-isopropylsilylethynyl-
phenyl)[1,3,4]oxadiazole (12). A mixture of 11 (1.25 g, 2.5
mmol) and KOH (0.14 g, 2.5 mmol) in MeOH (20 mL) and THF
(20 mL) was stirred at room temperature for 1 h. After
0.9-1.1 (m, 6 H), 1.5-1.7 (m, 4 H), 1.8-2.0 (m, 4 H), 3.9-4.1
(m, 4 H), 6.5-6.8 (m, 8 H), 6.9-7.2 (m, 12 H), 7.4-7.7 (m, 26
H), 8.0-8.2 (m, 8 H). Anal. Calcd for C94H96N4O4Si4: C 77.43,
H 6.64, N 3.84; found: C 76.21, H 6.12, N 4.12.

4568 Cheng and Luh
Macromolecules, Vol. 38, No. 11, 2005
(7) (a) For a review see: Ohshita, J.; Kunai, A. Acta Polym. 1998,
49, 379 and references therein. (b) Hu, S. S.; Weber, W. P.
Polym. Bull. 1989, 21, 133. (c) Corriu, R. J. P.; Guerin, C.;
Henner, B.; Kuhlmann, T.; Jean, A.; Garnier, F.; Yassar, A.
Chem. Mater. 1990, 2, 351. (d) Pang, Y.; Ijadi-Maghsoodi, S.;
Barton, T. J. Macromolecules 1993, 26, 5671. (e) Mao, S. S.
H.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 5365. (f)
Brouwer, H. J.; Krasnikov, V. V.; Hilberer, A.; Hadziioannou,
G. Adv. Mater. 1996, 8, 935. (g) Son, D. Y.; Bucca, D.; Keller,
T. M. Tetrahedron Lett. 1996, 37, 1579. (h) Miao, Y.-J.; Bazan,
G. C. Macromolecules 1997, 30, 7414. (i) Jung, S. H.; Kim,
H. K.; Kim, S. H.; Kim, Y. H.; Jeoung, S. C.; Kim, D.
Macromolecules 2000, 33, 9277. (j) Mori, A.; Takahisa, E.;
Kajiro, H.; Nishihara, Y.; Hiyama, T. Macromolecules 2000,
33, 1115 (k) Ohshita, J.; Takata, A.; Kai, H.; Kunai, A.;
Komaguchi, K.; Shiotani, M.; Adachi, A.; Sakamaki, K.; Okita,
K.; Harima, Y.; Kunugi, Y.; Yamashita, K.; Ishikawa, M.
Organometallics 2000, 19, 4492. (l) Luh, T.-Y.; Chen, R.-M.;
Hwu, T.-Y.; Basu, S.; Shiau, C.-W.; Lin, W.-Y.; Jin, B.-Y.; Hsu,
C.-C. Pure Appl. Chem. 2001, 73, 243. (m) Jiang, X.; Harima,
Y.; Yamashita, K.; Naka, A.; Lee, K. K.; Ishikawa, M. J.
Mater. Chem. 2003, 12, 785. (n) Cheng, Y.-J.; Liang, H.; Luh,
T.-Y. Marcomolecules 2003, 36, 5912.
Acknowledgment. We thank the National Science
Council and the Ministry of Education of the Republic
of China for support. Y.J.C. thanks the Yen-Chuang
Foundation for a best thesis award (2004) and the
Chinese Chemical Society, Taipei, for outstanding gradu-
ate research (2004).
References and Notes
(1) (a) Ku¨hlbrandt, W.; Wang, D. N. Nature 1991, 350, 130. (b)
Ku¨hlbrandt, W.; Wang, D. N.; Fujiyoshi, Y. Nature 1994, 367,
614. (c) McDermott, G.; Prince, S. M.; Freer, A. A.; Haw-
thornthwaite-Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.;
Isaacs, N. W. Nature 1995, 374, 517. (d) Ku¨hlbrandt, W.
Nature 1995, 374, 497.
(2) (a) Fleming, G. R.; Scholes, G. D. Nature 2004, 431, 256. (b)
Jang, S.; Newton, M. D.; Silbey, R. J. Phys. Rev. Lett. 2004,
92, 218301.
(3) (a) Devadoss, C.; Bharathi, P.; Moore, J. S. J. Am. Chem. Soc.
1996, 118, 9635. (b) Serin, J. M.; Brousmiche, D. W.; Fre´chet,
J. M. J. Chem. Commun. 2002, 2605. (c) Weil, T.; Reuther,
E.; Mu¨llen, K. Angew. Chem., Int. Ed. 2002, 41, 1900. (d)
Yamazaki, I.; Tamai, N.; Yamazaki, T.; Murakami, A.;
Mimuro, M. Fujita, Y. J. Phys. Chem. 1988, 92, 5035. (e)
Berberan-Santos, M. N.; Martinho, J. M. G. J. Phys. Chem.
1990, 94, 5847.
(4) (a) Kawahara, S.; Uchimaru, T.; Murata, S. Chem. Commun.
1999, 563. (b) Tong, A. K.; Jockusch, S.; Li, Z.; Zhu, H.-R.;
Akins, D. L.; Turro, N. J.; Ju, J. J. Am. Chem. Soc. 2001,
123, 12923. (c) Shchepinov, M. S.; Korshun, V. A. Nucleosides,
Nucleotides Nucleic Acids 2001, 20, 369.
(5) (a) Deshpande, R. S.; Bulovic, V.; Forrest, S. R. Appl. Phys.
Lett. 1999, 75, 888. (b) Peng, K.-Y.; Chen, S.-A.; Fann, W.-S.
J. Am. Chem. Soc. 2001, 123, 11388. (c) Kim, J.; McQuade,
D. T.; Rose, A.; Zhu, Z.; Swager, T. M. J. Am. Chem. Soc.
2001, 123, 11488.
(6) (a) Burn, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D. C.;
Brown, A. R.; Friend, R. H.; Gymer, R. W. Nature 1992, 356,
47. (b) Yang, Z.; Sokolik, I.; Karasz, F. E. Macromolecules
1993, 26, 1188.
(8) Fang, M.-C.; Watanabe, A.; Matsuda, M. Macromolecules
1996, 29, 6807.
(9) (a) Chen, R.-M.; Chien, K.-M.; Wong, K.-T.; Jin, B.-Y, Luh,
T.-Y. J. Am. Chem. Soc. 1997, 119, 11321. (b) Chen, R.-M.;
Luh, T.-Y. Tetrahedron 1998, 54, 1197.
(10) Cheng, Y.-J.; Luh, T.-Y. Chem.sEur. J. 2004, 10, 5361.
(11) (a) Hwu, T.-Y.; Basu, S.; Chen, R.-M.; Cheng, Y.-J.; Hsu, J.-
H.; Fann, W.; Luh, T.-Y. J. Polym. Sci., Part A: Polym. Chem.
2003, 40, 2218. (b) Cheng, Y.-J.; Basu, S.; Luo, S.-J.; Luh,
T.-Y. Macromolecules 2005, 38, 1442.
(12) Cheng, Y.-J.; Hwu, T.-Y.; Hsu, J.-H.; Luh, T.-Y. Chem.
Commun. 2002, 1978.
(13) Ni, Z.-J.; Yang, P.-F.; Ng, D. K. P.; Tzeng, Y.-L.; Luh, T.-Y.
J. Am. Chem. Soc. 1990, 112, 9356.
(14) The concentration here was defined as the concentration of
the repetitive unit of the polymer in solution.
(15) Fo¨rster, T. Ann. Phys. 1948, 2, 55.
MA050140Z