Synthesis, light-harvesting and energy-transfer properties of regioregular silylene-spaced alternating [(donor-SiMe2-)n=1-3- (acceptor-SiMe2)] copolymers

Article abstract of DOI:10.1002/chem.200400472

A series of silylene-spaced alternating [(donor-SiMe₂) _n=1-3-(acceptor-SiMe₂)] copolymers 4-6 was synthesized by rhodium-catalyzed hydrosilylation of bisalkynes with bissilyl hydrides. Monomeric reference compounds 7-10 wi

Full text of DOI:10.1002/chem.200400472

FULL PAPER
Synthesis, Light-Harvesting and Energy-Transfer Properties of Regioregular
Silylene-Spaced Alternating [(Donor-SiMe2-)n=1–3-(Acceptor-SiMe2)]
Copolymers
Yen-Ju Cheng and Tien-Yau Luh*[a]
Abstract: A series of silylene-spaced
alternating [(donor-SiMe2)n=1–3-(accept-
or-SiMe2)] copolymers 4–6 was synthe-
sized by rhodium-catalyzed hydrosilyla-
tion of bisalkynes with bissilyl hydrides.
Monomeric reference compounds 7–10
with similar chromophore components
were prepared for comparison. The
ratio of donor to acceptor groups is
well-controlled by the precise regio-
chemistry and nature of the repeat
units. The silylene moieties serve as in-
sulating spacers between chromo-
phores. The polymers exhibit light-har-
vesting abilities, for which the intensity
of the emission enhanced with larger
donor-to-acceptor ratios. No emission
originating from the donors was ob-
served in fluorescence spectra, illustrat-
ing that intrachain energy transfer is
highly efficient along the polymer
chain.
Keywords: chromophores · energy
transfer · hydrosilylation · inorganic
polymers · light harvesting
Introduction
insulating spacers may allow for tuning of the emission
properties of the polymers.[7] The silylene moiety has been
used extensively as an insulating spacer.[8] It is known that
the intramolecular photoinduced charge transfer between
donor and acceptor chromophores, separated by a silylene
moiety, can occur readily.[9] The silylene-spaced copolymers
1 are readily accessible by rhodium-catalyzed hydrosilylation
of bisalkynes 2 with bissilyl hydrides 3 [Eq. 1].[10] In this
regard, two different chromophores, separated by a silylene
group in the polymeric chain, are regioregularly positioned.
It is envisaged that such a strategy may generate a useful va-
riety of fascinating polymers that have different regioselec-
tive combinations of donors and acceptors along the poly-
mer chain.
There has been ever-burgeoning interest in artificial light-
harvesting systems capable of converting solar radiation into
a useful source of energy.[1] Intramolecular energy transfer
in supramolecular,[2,3] polymeric,[4] and dendritic[5] systems
has been studied extensively. Conjugated copolymers with
alternating donor–acceptor repeat units have received much
attention because intramolecular charge transfer within the
chain may result in concomitant changes in band gaps, and
electrochemical and optical properties.[6] Linear polymer
backbones with pendant chromophores provide alternative
models for the investigation of energy-transfer or light-har-
vesting phenomena. Occasionally, moderate energy-transfer
efficiencies are obtained and
aggregation,
resulting
in
quenching of the fluorescence,
may occur. It is known that
well-designed interruptions of
the conjugation along the con-
jugated polymer backbone by
When the Ar groups in Equation (1) have relatively long
conjugation lengths, the emission profiles of these copoly-
mers appear to be similar to those of the corresponding
monomers (having the same chromophores); no excimer-
like emission is observed in their fluorescence spectra. It is
thus believed that through-spaced interactions between
chromophores along these polymeric chains may not take
place.[11] We envision that silylene-spaced copolymers may
serve as a useful model for the study of light harvesting and
energy transfer along the polymeric backbone.[12] By adopt-
[a] Dr. Y.-J. Cheng, Prof. T.-Y. Luh
Department of Chemistry and
Institute of Polymer Science and Engineering
National Taiwan University, Taipei (Taiwan)
and
Institute of Chemistry, Academia Sinica, Taipei (Taiwan)
Fax : (+886)2-2651-1488
E-mail: tyluh@ntu.edu.tw
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2004, 10, 5361 – 5368
DOI: 10.1002/chem.200400472
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5361

FULL PAPER
ing a strategy similar to that shown in Equation (1), differ-
ent ratios of donor-to-acceptor chromophores can be regio-
selectively incorporated into the copolymers. Herein we
report the unprecedented synthesis and photophysical prop-
erties of a series of silylene-spaced alternating [(donor-
SiMe2)n-(acceptor-SiMe2)]m copolymers 4–6, where n=1–3.
Figure 1. Top: absorption (a) and emission spectra (b) of 7, absorption
(c) and emission spectra (d) of 8 in CHCl3. Bottom: absorption spectra
of 9 (a) and 10 (b); emission spectra of 9 (c) and 10 (d) in CHCl3.
Results and Discussion
The synthesis of copolymers 4–6 was based on the strategy
shown in Equation (1). The donor and acceptor chromo-
phores were chosen on the basis of their absorption and
emission profiles. The absorption and fluorescence spectra
of the corresponding monomers 7–10 are shown in Figure 1.
In general, the absorption of the acceptor chromophore
should overlap with the emission maximum of the donor
chromophore.
Accordingly, the divinyldiphenyl oxadiazole chromophore
was paired with the dimethoxyterphenylene tetravinylene
chromophore. Similarly, the divinylbiphenyl chromophore
was used with the diphenylene tervinylene chromophore.
The acceptor chromophore was designed by incorporation
of the silylhydride substituent at the olefinic termini (for ex-
ample 8 and 10). Nickel-catalyzed silyl olefination of the
corresponding dithioacetals with (iPrO)Me2SiCH2MgCl, fol-
Synthesis of the two-donor diyne 12a: Treatment of 4-bro-
mobenzoylhydrazide (15) with 4-iodobenzoyl chloride (14)
afforded the corresponding hydrazine 16 in 81% yield. Ring
closure of 16 (POCl3) furnished oxadiazole 17 in 82% yield.
A double Heck reaction of 17 with 18 gave the correspond-
ing dibromide 19 (46% yield).[14] Unfortunately, we were
unable to couple 19 with trimethylsilylacetylene under vari-
ous Sonogashira reaction conditions. Instead, the
[Pd2(dba)3]/PPh3–catalyzed Kumada–Corriu reaction of 19
À
lowed by the reduction of the corresponding Si O bond,
was employed for the synthesis of 8 and 10.[13]
Silylene-spaced diynes 12 and 13 having different numbers
of donor chromophores were prepared according to
Scheme 1–3.
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Chem. Eur. J. 2004, 10, 5361 – 5368

Light-Harvesting Copolymers
5361 – 5368
with the Grignard reagent 20,
prepared from trimethylacety-
lene and MeMgI, afforded the
corresponding bisalkyne 21 in
47% yield.[15] Removal of the
TMS group from 21 under basic
conditions (KOH, MeOH) af-
forded 12a in 82% yield
(Scheme 1).
Synthesis of the two-donor
diyne 12b: In a similar manner
(Scheme 2), a double Heck re-
action of 22 with 18 gave 23 in
68% yield.[16] The palladium-
catalyzed cross-coupling reac-
tion of 23 with 20 yielded 24.
This was followed by desilyla-
tion to give 12b in 49% yield
(two steps).
Synthesis of the three-donor
diyne 13: In a sequential Sono-
gashira reaction, 22 was first
treated with one equivalent of
triisopropylsilylacetylene
to
yield 25, which was then al-
lowed to react with trimethyla-
cetylene to afford 26 (overall
84%). Selective removal of the
TMS group in 26 (NaOH, Scheme 1. Synthesis of the two-donor diyne 12a.
MeOH) led to 27 (85%). Rho-
dium-catalyzed hydrosilylation
of 28 with two equivalents of 27 resulted in the formation of
29 in 89% yield. Desilylation of the TIPS group in 29 with
TBAF afforded 13 in 82% yield (Scheme 3).
Synthesis of polymers 4–6: A range of silylene-spaced co-
polymers 4–6 was synthesized by rhodium-catalyzed hydrosi-
lylation of bisalkynes 11–13 with bissilyl hydride 8 and 10
according to Equation (1). The results are summarized in
Table 1. The fluorescence quantum yields (F) of the poly-
mers measured in CHCl3 are also summarized in Table 1
Absorption and fluorescence properties: In the beginning of
this investigation, a 1:1 mixture of the monomeric donor 7
and acceptor 8 chromophores was dissolved at different con-
centrations in chloroform. As can be seen from the fluores-
cence spectra in Figure 2, emission profiles from both 7 and
8 were observed upon excitation of 7 at 310 nm. The fluores-
cence spectrum for polymer 4a is also included in Figure 2
for comparison. In contrast, when the solution was excited
at 310 nm, the emission from the donor in 4a was complete-
ly quenched; only fluorescence from the acceptor was ob-
served at 467 nm and 490 nm. The photophysical properties
of polymer 4a were unaffected when the polarity of the sol-
vent was changed (benzene, THF, EtOAc, and CHCl3).[18]
These results suggested that efficient intrachain energy
transfer from the divinyldiphenyl oxadiazole donor moiety
to the terphenylene tetravinylene chromophore can occur in
Scheme 2. Synthesis of the two-donor diyne 12b.
Chem. Eur. J. 2004, 10, 5361 – 5368
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5363

T.-Y. Luh and Y.-J. Cheng
FULL PAPER
polymer 4a and that no photo-
induced electron transfer takes
place. The excitation spectrum,
recorded at the lem of the ac-
ceptor (490 nm), and the ab-
sorption spectrum of 4a are
shown in Figure 3. When these
two spectra are normalized at
the lmax value of the donor
(405nm), the efficiency of the
energy transfer is estimated to
be 87%.
Figure 4 shows the absorption
spectra of the polymers 4a and
5a in chloroform. Two separate
absorption bands, which corre-
spond to the absorptions of the
donor and acceptor, can be dif-
ferentiated. Apparently, the
spectrum of polymer 5a is the
summation of the individual ab-
sorptions of the donor and the
acceptor chromophores. This
observation again not only illus-
trates that the silylene moiety
Scheme 3. Synthesis of the three-donor diyne 13.
Table 1. Reaction of donor with acceptor monomers by [RhCl(PPh3)3]
leading to silylene-spaced copolymers 4–6.
Donor
Acceptor
Polymer
Mn (PDI)[a]
F[b]
11a
11b
12a
12b
13
8
10
8
10
10
4a
4b
5a
5b
6b
7800(2.8)
8600(3.1)
6700(2.9)
9800(3.3)
12100 (3.0)
0.58
0.66
0.52
0.59
0.51
[a] The Mn and PDI values were determined by GPC using polystyrenes
as standard.[17] [b] Measured in CHCl3 using coumarin 1 in EtOAc (F=
0.99) as the standard.
Figure 3. Comparison of the absorption spectrum (solid line) with the ex-
citation spectrum (dashed line) of 4a in CHCl3, monitored at 490 nm.
Figure 2. Concentration-dependent fluorescence spectra (lex: 310 nm) of
an equal molar mixture of 7 and 8 in CHCl3 (a: 1”10À1 gmLÀ1; b: 1”
10À2 gmLÀ1
;
c: 1”10À3 gmLÀ1
)
and fluorescence spectrum (d: lex
:
Figure 4. Absorption spectra of polymer 5a (dashed line) and 4a (solid
310 nm) of 4a in CHCl3.
line) in CHCl3.
5364
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Light-Harvesting Copolymers
5361 – 5368
in these copolymers serves as insulating spacer, but also
demonstrates that there is no interaction in the ground state
between donors and acceptors. As the molar fraction of the
donor in the polymers increases from 50% in 4a to 67% in
5a, the absorbance around 300–350 nm, corresponding to
that of the donor chromophore, is also doubled. As shown
in Figure 5, excitation of the donor chromophores at 310 nm
due to the higher molar fraction of this donor chromophore.
The emission spectra of these polymers upon excitation at
300 nm are shown in Figure 7.
Figure 7. Emission spectra of 4b, 5b, and 6b in CHCl3 (excitation at
300 nm) and 6b (directly excitation at 360 nm of the acceptor chromo-
phore, dashed line).
Figure 5. Emission spectra of 5a (dashed line) and 4a (solid line) in
CHCl3 (excitation at 310 nm).
As expected, polymer 6b exhibits the highest emission in-
tensity in comparison with those of 4b and 5b. In a similar
manner, the intensity of the emission for 5b is doubled in
comparison with that of 4b. However, the intensity of emis-
sion from 6b (molar fraction=0.75) was somewhat less than
triple that from 4b. Although increasing the donor number
allows more light harvesting from donor to acceptor, the dis-
tance between donor and acceptor would not be the same.
In other words, the distance between the donor chromo-
phore at the center and the acceptor chromophore in 6b
would be different from the distance between the other
donor and acceptor chromophores. Accordingly, the efficien-
cies for the energy transfer from different donor chromo-
phores may not be identical.
The emission profile was recorded upon excitation at
360 nm (the lmax of the acceptor chromophore in 6b), and is
also shown in Figure 7 (dashed line). Interestingly, the re-
corded intensity of this spectrum is much lower than that of
6b when the excitation wavelength was 300 nm (the lmax of
the donor chromophore in 6b). These results revealed that
the acceptor can emit stronger through an energy-transfer
mechanism from donors than when it is directly excited at
the acceptor. The ability of the light-harvesting effect, along
with subsequent energy transfer in these polymers, is very
efficient (>88%).[18]
in polymer 4a and 5a resulted in fluorescence from the ac-
ceptor exclusively. It is noteworthy that the emission intensi-
ty of 5a is approximately doubled in comparison with that
of 4a when the intensity of acceptor absorption was kept
the same in both polymers. These results indicated that the
light-harvesting capability is significantly enhanced in 5a.
Again, a comparison of the excitation spectrum with the ab-
sorption spectrum of 5a suggested that the energy-transfer
efficiency is 86%.[18]
The photophysical properties of 4b, 5b, and 6b were also
examined. The normalized absorption spectra of these poly-
mers (normalized at the lmax = 355 nm) are shown in
Figure 6. This maximum originates from the absorption of
the acceptor chromophores in these polymers. The increase
of the absorption from divinylbiphenyl in 5b and 6b was
Conclusion
In summary, we have demonstrated efficient syntheses of
three types of regioregular silylene-spaced copolymers 4–6.
The ratio of donor to acceptor can easily be controlled by
appropriate design of the monomeric precursors. Unlike
most copolymers, our strategy has provided a powerful ar-
Figure 6. Absorption spectra of polymer 4b, 5b, and 6b in CHCl3.
Chem. Eur. J. 2004, 10, 5361 – 5368
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ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5365

T.-Y. Luh and Y.-J. Cheng
FULL PAPER
1487, 1397, 1250, 845 cmÀ1
;
1H NMR (400 MHz, CDCl3): d = 0.25(s,
senal for the construction of copolymers with precise regio-
chemistry and repeating units. In these polymers, the light-
harvesting ability has been shown to increase with an in-
creasing donor-to-acceptor ratio. No emission coming from
the donor was observed in fluorescence spectra, illustrating
that intrachain energy transfer is highly efficient along the
polymer chain. These results suggest that the use of silylene
linkers for the construction of donor–acceptor polymers has
provided a new ideal architecture for light harvesting and
energy transfer.
18H), 0.36 (s, 6H), 6.68 (d, J=19.1 Hz, 2H), 7.00 (d, J=19.1 Hz, 2H),
7.59–7.64 (m, 8H), 8.06 (d, J=8.3 Hz, 4H), 8.09 ppm (d, J=8.3 Hz, 4H);
13C NMR (100 MHz, CDCl3): d À2.8, À0.2, 97.7, 103.9, 123.1, 123.4,
126.6, 127.1, 127.2, 128.3, 130.3, 132.5, 141.3, 143.8, 164.0, 164.5 ppm;
HRMS (FAB) (M++H, C44H44N4O2Si3): calcd: 745.2850, found: 745.2863;
elemental analysis (%) calcd for C44H44N4O2Si3: C 70.93, H 5.95; found:
C 70.56, H 5.61.
Bis{2-[4-(2-[5-(4-ethynylphenyl)[1,3,4]oxadiazolyl])phenyl]vinyl}dime-
thylsilane (12a): A solution of 21 (75mg, 0.1 mmol) in MeOH (10 mL),
THF (40 mL) and 0.1m NaOH solution (2.2 mL) was stirred at room
temperature for 1 h. After removal of the solvent in vacuo, water was
added and the mixture was extracted with CHCl3. The organic layer was
dried (MgSO4), evaporated in vacuo and the residue was purified on a
flash silica gel column (CHCl3) to yield 12a (49 mg, 82%): m.p. 3128C
(decomp); IR (KBr): n˜ 3295, 3273, 3042, 2952, 2912, 2101, 1926, 1612,
Experimental Section
1577, 1543, 1481, 1245, 991, 833, 743 cmÀ1 1H NMR (400 MHz, CDCl3):
;
4-Benzoic acid N’-4-iodobenzoylhydrazide (16): 4-iodobenzoic chloride
14 (13.3 g, 50 mmol) in THF (30 mL) was added dropwise over 30 min to
d=0.37 (s, 6H), 3.24 (s, 2H), 6.68 (d, J=19.1 Hz, 2H), 7.01 (d, J=
19.1 Hz, 2H), 7.61 (d, J=8.5Hz, 4H), 7.63 (d, J=8.5Hz, 4H), 8.09 (d,
J=8.5Hz, 4H), 8.10 ppm (d, J=8.5Hz, 4H); 13C NMR (75MHz,
CDCl3): d À2.8, 80.1, 82.7, 123.1, 123.9, 125.6, 126.7, 127.1, 127.2, 130.4,
132.7, 141.4, 143.9, 164.0, 164.6 ppm; HRMS (FAB) (M++H,
C38H29N4O2Si): calcd: 601.2060, found: 601.2056; elemental analysis (%)
calcd for C38H29N4O2Si: C 75.97, H 4.70; found: C 75.62, H 5.07.
a
solution of 4-bromobenzoic acid hydrazide 15 (10.75g, 50 mmol),
sodium carbonate (5.3 g, 50 mmol) in THF (60 mL), and water (60 mL).
The mixture was stirred at room temperature for 1 h. After removal of
THF in vacuo, the solid was collected by filtration, washed with water,
and dried in vacuo to give 16 as a white solid (18.02 g, 81%): m.p. 320–
3218C; IR (KBr): n˜ 3183, 2997, 1594, 1554, 1498, 1453, 1256, 845,
743 cmÀ1 1H NMR (400 MHz, [D6]DMSO): d=7.69 (d, J=8.3 Hz, 2H),
;
Bis[2-(4’-bromobiphenyl-4-yl)vinyl]dimethylsilane (23): A mixture of 22
(3.59 g, 10 mmol), 18 (0.67 g, 6 mmol), Pd(OAc)2 (0.11 g, 0.5mmol),
Bu4NOAc (6.03 g, 20 mmol), and molecular sieves (4 Š) in dry DMF
(100 mL) was stirred under argon at 808C for 16 h. After filtration over
celite, the filtrate was extracted with CHCl3 and washed with water and
brine, and then dried (MgSO4). After removal of the solvent in vacuo,
the residue was purified by flash chromatography (hexane) to afford 23
(1.95g, 68%); m.p. 233–234 8C; IR (KBr): n˜ 3030, 2985, 2957, 1909, 1605,
7.74 (d, J=8.5Hz, 2H), 7.85(d, J=8.5Hz, 2H), 7.91 (d, J=8.3 Hz, 2H),
10.59 ppm (s, 2H); 13C NMR (100 MHz, [D6]DMSO): d=100.3, 126.3,
129.9, 130.1, 132.2, 132.4, 138.0, 165.5, 165.8 ppm; HRMS (EI)
(C14H10BrIN2O4): calcd: 443.8964; found: 443.8964; elemental analysis
(%) calcd for C14H10BrIN2O4: C 37.78, H 2.26; found: C 37.92, H 2.34.
2-(4-Bromophenyl)-5-(4-iodophenyl)-[1,3,4]oxadiazole (17): A mixture of
16 (8.9 g, 20 mmol) and POCl3 (100 mL) was refluxed for 16 h. Excess
POCl3 was removed by distillation. The residue was washed with water
and collected by filtration and recrystallized from THF to afford 17 as a
white solid (7 g, 82%): m.p. 242–2438C; IR (KBr): n˜ 3076, 1921, 1656,
1481, 1385cm À1 1H NMR (400 MHz, CDCl3): d=0.35(s, 6H), 6.58 (d,
;
J=19.1 Hz, 2H), 7.00 (d, J=19.1 Hz, 2H), 7.47 (d, J=8.4 Hz, 4H), 7.5–
7.6 ppm (m, 12H); 13C NMR (100 MHz, CDCl3): d=À2.4, 121.7, 127.1,
128.0, 128.6, 132.0, 137.8, 139.7, 144.4 ppm; HRMS (EI) (C30H26Br2Si):
calcd: 572.0171, found: 572.0161; elemental analysis (%) calcd for
C30H26Br2Si: C 62.73, H 4.56; found: C 62.91, H 4.37.
1611, 1532, 1481, 1397, 833, 738 cmÀ1 1H NMR (400 MHz, CDCl3): d=
;
7.66 (d, J=8.4 Hz, 2H), 7.83 (d, J=8.4 Hz, 2H), 7.88 (d, J=8.4 Hz, 2H),
7.98 ppm (d, J=8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3): d=98.8,
122.7, 123.2, 126.6, 128.3, 128.4, 132.5, 138.4, 164.1, 164.2 ppm; HRMS
(FAB) (M++H, C14H9BrIN2O): calcd: 426.8943; found: 426.8940; ele-
mental analysis (%) calcd for C14H8BrIN2O: C 39.38, H 1.89; found: C
39.28, H 1.72.
Bis{2-[4’-trimethylsilylethynyl-biphenyl-4-yl]vinyl}dimethylsilane (24): A
freshly prepared 2m solution of methylmagnesium iodine (0.7 mL) was
added to a solution of trimethylacetylene (0.2 mL, 1.4 mmol) in diethyl
ether (2 mL) at room temperature, and the mixture stirred under argon
for 30 min. THF (30 mL) was introduced, followed by the successive ad-
dition of [Pd2(dba)3] (0.025g), PPh 3 (0.025g), and 23 (0.2 g, 0.35mmol).
The mixture was refluxed for 24 h, quenched with NH4Cl, extracted with
CHCl3, and dried (MgSO4). After removal of the solvent in vacuo, the
residue was purified by flash chromatography (hexane) to afford 24
(0.13 g, 61%): m.p. 249–2508C; IR (KBr): n˜ 3036, 2946, 2918, 2839, 2152,
Bis{2-[4-(2-[5-(4-bromophenyl)[1,3,4]oxadiazolyl])phenyl]vinyl}dimethyl-
silane (19): A mixture of 17 (4.27 g 10 mmol), 18 (0.67 g, 6 mmol),
Pd(OAc)2 (0.11 g, 0.5mmol), Bu 4NOAc (6.03 g, 20 mmol), and molecular
sieves (4Š) in dry DMF (150 mL) was stirred at 80oC for 24 h under
argon. After filtration over celite, water was added, and the mixture was
extracted with chloroform. The organic layer was washed with water and
brine, and dried (MgSO4). After removal of the solvent in vacuo, the
crude product was separated on a flash silica gel column (CHCl3) to
afford 19 (1.63 g, 46%): m.p. 247–2488C; IR (KBr): n˜ 2985, 2952, 1926,
1605, 1487, 1245, 997, 833 cmÀ1 1H NMR (400 MHz, CDCl3): d=0.24 (s,
;
18H), 0.3 (s, 6H), 6.56 (d, J=19.1 Hz, 2H), 7.00 (d, J=19.1 Hz, 2H),
7.4–7.6 ppm (m, 16H); 13C NMR (100 MHz, CDCl3): d=À2.4, 0.1, 95.1,
105.1, 122.2, 126.8, 127.1, 127.2, 128.0, 132.5, 137.7, 140.0, 140.7,
144.4 ppm; HRMS (FAB) (M++H, C40H45Si3): calcd: 609.2829; found:
609.2823; elemental analysis (%) calcd for C40H44Si3: C 78.88, H 7.28;
found: C 79.14, H 7.45.
1605, 1577, 1543, 1481, 1076, 839, 738 cmÀ1 1H NMR (400 MHz, CDCl3):
;
d=0.37 (s, 6H), 6.68 (d, J=19.1 Hz, 2H), 7.01 (d, J=19.1 Hz, 2H), 7.60
(d, J=8.4 Hz, 4H), 7.67 (d, J=8.5Hz, 4H), 8.00 (d, J=8.5Hz, 4H),
8.09 ppm (d, J=8.4 Hz, 4H); 13C NMR (100 MHz, CDCl3): d=À2.7,
122.8, 123.1, 126.4, 127.1, 127.3, 128.3, 130.4, 132.5, 141.4, 143.9, 163.9,
164.6 ppm; HRMS (FAB) (M++H, C34H26Br2N4O2Si): calcd: 709.0270;
found: 709.0276; elemental analysis (%) calcd for C34H26Br2N4O2Si: C
57.48, H 3.69; found: C 57.26, H 3.81.
Bis{2-[4’-ethynylbiphenyl-4-yl]vinyl}dimethylsilane (12b): A mixture of
22 (0.12 g, 0.2 mmol) in MeOH (10 mL) and THF (40 mL) and 0.1m
aqueous NaOH solution (4 mL) was stirred at room temperature for 1 h.
After removal of the solvent in vacuo, water was added and the mixture
was extracted with CHCl3 and dried (MgSO4). Removal of the solvent in
vacuo afforded the residue which was purified on a flash silica gel
(CHCl3) to yield 12b (0.075g, 81%): m.p. 241 8C (decomp); IR (KBr): n˜
Bis{2-[4-(2-[5-(4-triisopropylethynylphenyl)[1,3,4]oxadiazolyl])phenyl]vi-
nyl}dimethylsilane (21): A freshly prepared 2m solution of methylmagne-
sium iodine (2.2 mL) was added to a solution of trimethylacetylene
(0.64 mL, 4.48 mmol) in dry diethyl ether (5mL) at room temperature
and the mixture was stirred for 30 min under argon. THF (120 mL) was
introduced, followed by the successive addition of [Pd2(dba)3] (0.08 g),
PPh3 (0.08 g), and 19 (0.8 g, 1.12 mmol). The reaction mixture was re-
fluxed for a further 24 h, quenched with NH4Cl, extracted with CHCl3,
and dried (MgSO4). After removal of the solvent in vacuo, the crude
product was purified by flash chromatography (chloroform) to afford 21
(0.39 g, 47%): m.p. 286–2888C; IR (KBr): n˜ 2952, 2157, 1611, 1566, 1538,
3267, 2969, 2912, 2107, 1909, 1600, 1492, 1397, 1256, 997, 833, 805 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=0.34 (s, 6H), 3.12 (s, 2H), 6.57 (d, J=
19.1 Hz, 2H), 6.98 (d, J=19.1 Hz, 2H), 7.5–7.6 ppm (m, 16H); 13C NMR
(100 MHz, CDCl3): d À2.5, 77.9, 83.6, 121.0, 126.8, 127.0, 127.1, 128.0,
132.6, 137.7, 139.8, 141.0, 144.3 ppm; HRMS (EI) (C34H28Si): calcd:
464.1960; found: 464.1963; elemental analysis (%) calcd for C34H28Si: C
87.88, H 6.07; found: C 87.91, H 6.31.
5366
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 5361 – 5368

Light-Harvesting Copolymers
5361 – 5368
4’-Bromo-4-[(triisopropylsilyl)ethynyl]biphenyl (25):
(3.59 g, 10.0 mmol), (triisopropylsilyl)acetylene (2.5 mL, 11.0 mmol),
[Pd(PPh3)2Cl2] (0.35g, 0.5mmol) and CuI (95mg, 0.5mmol) in NEt
A
mixture of 22
Polymer 4a: A mixture of 11a (54 mg, 0.2 mmol), 8 (102 mg, 0.2 mmol)
and [Rh(PPh3)3Cl] (4.6 mg) in THF (5mL) was refluxed for 4 h under
argon. After the mixture was cooled to room temperature, it was poured
into MeOH. The precipitate was collected and re-dissolved in THF, then
reprecipitated with MeOH. The product 4a was collected by filtration
and washed with MeOH (0.12 g, 77%): Mn =7800, PDI=2.8; IR (KBr):
n˜ 2942, 2864, 1598, 1481, 1462,1410, 1209, 1045, 814, 668; 1H NMR
(400 MHz, CDCl3): d=0.28 (s, 12H), 3.93 (s, 6H), 6.4–6.6 (m, 2H), 6.4–
6.8 (m, 2H), 6.9–7.2 (m, 8H), 7.3–7.7 (m, 14H), 7.8–8.2 ppm (m, 4H); el-
emental analysis (%) calcd for C50H48N2O3Si2: C 76.88, H 6. 19; found: C
75.59; H 5.79.
3
(40 mL) was refluxed under argon for 8 h and then cooled to room tem-
perature. The mixture was filtered and NEt3 was evaporated. The crude
product was purified by silica gel column chromatography (hexane) to
give 25 as a white solid (4 g, 97%): m.p. 37–388C; IR (KBr): n˜ 2942,
2850, 2154, 2064, 1893, 1588, 1481, 1462, 1380, 1221, 1075, 1002, 882, 836,
813, 742, 663 cmÀ1 1H NMR (400 MHz, CDCl3,): d=1.15(s, 21H), 7.44
;
(d, J=8.3 Hz, 2H), 7.49 (d, J=7.7 Hz, 2H), 7.54 (d, J=7.7 Hz, 2H),
7.56 ppm (d, J=8.3 Hz, 2H); 13C NMR (100 MHz, CDCl3): d 11.3, 18.6,
91.7, 106.7, 121.9, 122.9, 126.6, 128.5, 131.9, 132.5, 139.3, 139.7 ppm;
HRMS (FAB) (M++H, C23H29BrSi): calcd: 413.1300; found: 413.1306; el-
emental analysis (%) calcd for C23H29BrSi: C 66.81, H 7.07; found: C
66.89; H 6.99.
Polymer 4b:
A mixture of 11b (0.061 g, 0.3 mmol), 10 (0.105g,
0.3 mmol) and [Rh(PPh3)3Cl] (6.9 mg) in THF (5mL) was refluxed for
4 h under argon. After the mixture was cooled to room temperature, it
was poured into MeOH. The precipitate was collected and re-dissolved
in THF, then reprecipitated with MeOH. The product 4b was collected
by filtration and washed with MeOH (0.13 g, 78%): Mn =8600, PDI=3.1;
IR (KBr): n˜ 3023, 2982, 2952, 1914, 1693, 1600, 1492, 1413, 1040, 1247,
(4’-Triisopropylsilylethynyl-4-trimethylsilylethnyl)biphenyl (26): To a mix-
ture of trimethylsilylacetylene (1.5mL, 7.2 mmol) and 25 (2.0 g,
4.8 mmol) in piperidine (40 mL) was added [Pd(PPh3)2Cl2] (0.1 g,
0.14 mmol) and CuI (30 mg, 0.15mmol). The mixture was refluxed for
12 h under argon and then cooled to room temperature. After filtration,
the solvent was evaporated in vacuo and the residue was purified on
silica gel (hexane) to afford 26 as an oil (1.8 g, 87%). IR (KBr): n˜ 3033,
2957, 2943, 2865, 2156, 1910, 1489, 1462, 1383, 1249, 1221, 995, 840,
1
986, 839, 803; H NMR (400 MHz, CDCl3): d=0.29 (s, 12H), 6.45–6.6 (m,
4H), 6.85–7.03 (m, 4H), 7.11 (s, 2H), 7.35–7.65 ppm (m, 16H); elemental
analysis (%) calcd for C38H38Si2: C 82.85, H 6.95; found: C 81.76; H 6.69.
Polymer 5a: A mixture of 12a (42 mg, 0.07 mmol), 8 (35mg, 0.07 mmol)
and [Rh(PPh3)3Cl] (2 mg) in THF (3 mL) was refluxed for 4 h under
argon. After the mixture was cooled to room temperature, it was poured
into MeOH. The precipitate was collected and re-dissolved in THF, then
reprecipitated with MeOH. The product 5a was collected by filtration
and washed with MeOH (53 mg, 69%): Mn = 6700, PDI = 2.9; IR
(KBr): n˜ 2942, 2863, 1598, 1481, 1461, 1384, 1248, 1210, 1074, 1045, 838,
814; 1H NMR (400 MHz, CDCl3): d=0.33 (s, 18H), 3.91 (s, 6H), 6.4–6.6
(m, 2H), 6.6–6.8 (m, 4H), 6.9–7.05 (m, 6H), 7.05–7.15 (m, 4H), 7.35–7.55
(m, 10H), 7.55–7.7 (m, 8H), 8.00–8.15 ppm (m, 8H); elemental analysis
(%) calcd for C70H66N4Si3: C 75.64, H 5.98; found: C 74.51; H 5.57.
668 cmÀ1 1H NMR (400 MHz, CDCl3): d=0.27 (s, 9H), 1.14 (s, 21H),
;
7.52 ppm (s, 8H); 13C NMR (100 MHz, CDCl3): d À0.03, 11.3, 18.7, 91.7,
95.2, 104.8, 106.8, 122.4, 122.9, 126.7, 132.4, 132.5, 140.1, 140.3 ppm;
HRMS (FAB) (M++H, C28H39Si2): calcd: 430.2512; found: 430.2505; ele-
mental analysis (%) calcd for C28H38Si2: C 78.07, H 8.89; found: C 78.56;
H 8.55.
(4’-Triisopropylsilylethynyl-4-ethnyl)biphenyl (27):
A mixture of 26
(1.5g, 3.5mmol) and NaOH (0.14 g, 3.5mmol) in MeOH (10 mL) and
THF (10 mL) was stirred at room temperature for 1 h. After filtration,
the solvent was evaporated in vacuo. The residue was purified by silica
gel (hexane) to give 27 as a yellowish solid (1.07 g, 85%): m.p. 41–42 8C;
IR (KBr): n˜ 3301, 2942, 2864, 2153, 2101, 1910, 1488, 1463, 1230, 996,
Polymer 5b:
A mixture of 12b (23.1 mg, 0.05mmol), 10 (17.4 mg,
0.05mmol) and [Rh(PPh 3)3Cl] (2 mg) in THF (3 mL) was refluxed for
4 h under argon. After the mixture was cooled to room temperature, it
was poured into MeOH. The precipitate was collected and re-dissolved
in THF, then reprecipitated with MeOH. The product was collected by
filtration and washed with MeOH (33 mg, 81%): Mn =9800, PDI=3.3;
IR (KBr): n˜ 3023, 2954, 2919, 1905, 1684, 1600, 1492, 1396, 1248, 1045,
1
822, 668 cmÀ1; H NMR (400 MHz, CDCl3): d 1.16 (s, 21H), 3.15(s, 1H),
7.5–7.6 ppm (m, 8H); 13C NMR (100 MHz, CDCl3): d=11.3, 18.6, 78.0,
83.4, 91.7, 106.7, 121.3, 122.9, 126.7, 126.8, 132.5, 132.6, 139.9, 140.7 ppm;
HRMS (FAB) (M++H, C25H31Si): calcd: 359.2195; found: 359.2200; ele-
mental analysis (%) calcd for C25H30Si: C 83.74, H 8.43; found: C 83.43;
H 8.31.
1
987, 838, 798; H NMR (400 MHz, CDCl3): d 0.32 (s, 18H), 6.45–6.65 (m,
6H), 6.85–7.05 (m, 6H), 7.11 (s, 2H), 7.35–7.6 ppm (m, 24H); elemental
analysis (%) calcd for C56H56Si3: C 82.70, H 6.94; found: C 81.44; H 6.72.
4,4’-Bis(2-{[2-(4’-trimethylpropylethynyl-biphenyl-4-yl)vinyl]dimethylsi-
lyl}vinly)biphenyl (29): A mixture of 27 (0.66 g, 1.86 mmol), 28 (0.3 g,
0.93 mmol), and [Rh(PPh3)3Cl] (8 mg) in THF (5mL) was refluxed for
2 h under argon. After the mixture was cooled to room temperature, it
was poured into MeOH. The precipitate was collected and recrystallized
from CHCl3 to give 29 (0.79 g, 82%): m.p. 91–928C; IR (KBr): n˜ 3027,
2942, 2864, 2153, 1910, 1603, 1492, 1462, 1247, 987, 830, 795, 706,
Polymer 6b:
A mixture of 13 (0.121 g, 0.166 mmol), 10 (0.058 g,
0.166 mmol) and [Rh(PPh3)3Cl] (3.8 mg) in THF (5mL) was refluxed for
4 h under argon. After the mixture was cooled to room temperature, it
was poured into MeOH. The precipitate was collected and re-dissolved
in THF, then reprecipitated with MeOH. The product 6b was collected
by filtration and washed with MeOH (0.15g, 84%): Mn =12100, PDI=
3.0; IR (KBr): n˜ 3023, 2986, 2954, 2890, 2954, 1905, 1601, 1492, 1400,
676 cmÀ1 1H NMR (400 MHz, CDCl3): d=0.37 (s, 12H), 1.17 (s, 42H),
;
1330, 1247,1196, 1059, 986, 837, 793 cmÀ1 1H NMR (400 MHz, CDCl3):
,
d=0.35(s, 24H), 6.45–6.65(m, 8H), 6.9–7.05(m, 8H), 7.1 (s, 2H), 7.4–
7.65ppm (m, 32H); elemental analysis (%) calcd for C 74H74Si4: C 82.62,
H 6.93; found: C 81.67; H 7.06.
6.59 (d, J=19.1 Hz, 2H), 6.60 (d, J=19.1 Hz, 2H), 7.02 (d, J=19.1 Hz,
4H), 7.5–7.63 ppm (m, 24H); 13C NMR (100 MHz, CDCl3): d=À2.6,
11.3, 18.7, 91.4, 106.9, 122.5, 126.6, 126.7, 126.8, 126.91, 126.94, 126.98,
127.1, 127.5, 127.9, 132.4, 137.6, 139.9, 140.4, 144.3, 144.4 ppm; HRMS
(FAB) (M++H, C70H87Si4): calcd: 1039.5885; found: 1039.5861; elemental
analysis (%) calcd for C70H86Si4: C 80.86, H 8.34; found: C 80.39; H 8.24.
Bis-4–4’-(2-{[2-(4’-ethynyl-biphenyl-4-yl)vinyl]dimethylsilyl}vinyl)biphen-
yl (13): A 1m solution of TBAF (0.5mL, 0.5mmol) was added dropwise
to a solution of 29 (0.208 g, 0.2 mmol) in THF (5mL). The mixture was
stirred at room temperature for 2.5h, 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 which was
recrystallized from CHCl3 to yield 13 (0.78 g, 82%): m.p. 3218C
(decomp); IR (KBr): n˜ 3295, 2982, 2944, 2097, 1918, 1603, 1491, 1246,
Acknowledgments
This work was supported by the Ministry of Education and the National
Science Council of the Republic of China. Y.J.C. thanks the Yen-Chuang
Foundation for a thesis award (2004).
987, 830, 796, 642 cmÀ1 1H NMR (400 MHz, CDCl3): d=0.35(s, 12H),
;
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3.12 (s, 2H), 6.57 (d, J=19.1 Hz, 2H), 6.59 (d, J=19.1 Hz, 2H), 6.99 (d,
J=19.1 Hz, 4H), 7.5–7.7 ppm (m, 24H); 13C NMR (100 MHz, CDCl3):
d=À2.62, 77.7, 83.5, 121.0, 126.7, 126.86, 126.93, 127.0, 127.5, 128.0,
132.5, 137.4, 137.8, 139.8, 140.3, 141.0, 144.2, 144.4 ppm; HRMS (FAB)
(M++H, C52H47Si2): calcd: 727.3216. found: 727.3226; elemental analysis
(%) calcd for C52H46Si2: C 85.90, H 6.38; found: C 85.52; H 6.11.
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Chem. Eur. J. 2004, 10, 5361 – 5368
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5367

T.-Y. Luh and Y.-J. Cheng
FULL PAPER
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Received: May 14, 2004
Published online: September 20, 2004
5368
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www.chemeurj.org
Chem. Eur. J. 2004, 10, 5361 – 5368