Silole-containing polyacetylenes. Synthesis, thermal stability, light emission, nanodimensional aggregation, and restricted intramolecular rotation

Article abstract of DOI:10.1021/ma0213504

We synthesized three substituted polyacetylenes carrying 1,2,3,4,5-pentaphenylsilolyl (PS) pendants, i.e., -[HC=C(PS)]_n - (1), -{HC=C[(CH₂)₉OPS]}°_n - (2) and -{(C₆H₅)C=C[(CH₂)

Full text of DOI:10.1021/ma0213504

1108
Macromolecules 2003, 36, 1108-1117
Silole-Containing Polyacetylenes. Synthesis, Thermal Stability, Light
Emission, Nanodimensional Aggregation, and Restricted Intramolecular
Rotation
J u n w u Ch en , Zh ilia n g Xie, J a ck y W. Y. La m , Ch a r les C. W. La w , a n d
Ben Zh on g Ta n g*
Department of Chemistry, Center for Display Research, Institute of Nano Science and Technology, and
Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and
Synthesis,† Hong Kong University of Science & Technology, Clear Water Bay,
Kowloon, Hong Kong, China
Received August 19, 2002; Revised Manuscript Received December 10, 2002
ABSTRACT: We synthesized three substituted polyacetylenes carrying 1,2,3,4,5-pentaphenylsilolyl (PS)
pendants, i.e., -[HCdC(PS)]n- (1), -{HCdC[(CH2)9OPS]}n- (2) and -{(C6H5)CdC[(CH2)9OPS]}n- (3),
and succeeded in turning polymers 2 and 3 from weak luminophors into strong emitters by external
stimuli of aggregation and cooling. The silolylacetylene monomers HCtCPS (10), HCtC(CH2)9OPS (11),
and C6H5CtC(CH2)9OPS (12) were polymerized by NbCl5- and WCl6-Ph4Sn catalysts, which gave high
molecular weight polymers in high yields (Mw up to ∼70 × 103 Da and yield up to ∼80%). The structures
and properties of the polymers were characterized and evaluated by IR, UV, NMR, DSC, TGA, PL, EL,
and nanoparticle size analyses. The polymers were thermally stable and lost little weights when heated
to ∼350 °C. Whereas all the polymers were practically nonluminescent when molecularly dissolved,
polymers 2 and 3 became emissive when aggregated in poor solvents or when cooled to low temperatures.
Restricted intramolecular rotation or twisting of the silole chromophores in the solid nanoaggregates or
at the low temperatures may be responsible for the aggregation- or cooling-induced emission. A multilayer
electroluminescence device using 3 as an active layer emitted a blue light of 496 nm with maximum
brightness, current efficiency, and external quantum yield of 1118 cd/m2, 1.45 cd/A, and 0.55%, respectively.
In tr od u ction
and its highest external quantum efficiency (ηEL) was
8%,5,7 approaching the limit of the possible.8,9 An LED
device of 1,1,2,3,4,5-hexaphenylsilole (HPS),6 a struc-
tural congener of MPS, was turned on at a low voltage
(∼4 V), emitted intensely at a moderate bias (55 880 cd/
m2 at 16 V), and showed high EL efficiencies of 15 cd/A
(CE), 10 lm/W (PE), and 7% (ηEL).10 An LED device of
yet another silole compound, 1-(8-phenyl-1,7-octadiyn-
yl)-1,2,3,4,5-pentaphenylsilole (PPS), also worked well
and exhibited maximum EL efficiencies of 8.5 cd/A (CE),
3.8 lm/W (PE), and 3.9% (ηEL). Similarly impressive
device performances have been reported by other re-
search groups for other silole molecules, examples of
which include 2,5-bis(2,2′-bipyridin-6-yl)-1,1-dimethyl-
3,4-diphenylsilole,3 1,2-bis(1-methyl-2,3,4,5-tetraphenyl-
silolyl)ethane,3 and dithienosilole and dithienodisilacy-
clohexadiene derivatives.11
Silole is a five-membered silacycle, which may struc-
turally be viewed as a cyclopentadiene derivative with
its carbon bridge replaced by a silicon atom, hence the
name silacyclopentadiene. Silole enjoys a unique σ*-
π* conjugation arising from the orbital interaction of
the σ* orbital of its silylene moiety with the π* orbital
of its butadiene fragment, which significantly lowers its
LUMO energy level and increases its electron affinity.1
As a matter of fact, silole has the highest electron-
accepting ability, in comparison to other conjugated five-
membered heterocycles such as pyrrole, thiophene, and
furan.2 Thanks to its fast electron mobility,3 silole has
been used as an electron-transporting and light-emitting
material in the construction of electroluminescence (EL)
devices.4
We have recently observed an intriguing phenomenon
of aggregation-induced emission (AIE) in a silole sys-
tem.5 1-Methyl-1,2,3,4,5-pentaphenylsilole6 (MPS, Chart
1) is practically nonluminescent in solutions but its films
are highly emissive: the photoluminescence (PL) quan-
tum yield (ΦPL) of the silole aggregates can differ from
that of its molecularly dissolved species by 2 orders of
magnitude (>300).5 We fabricated a light-emitting diode
(LED) using a thin solid film of MPS as an active layer,
which luminesced strongly upon application of a low
voltage. Its maximum current efficiency (CE) and power
efficiency (PE) were 20 cd/A and 14 lm/W, respectively,
Siloles are thus a group of excellent organometallic
molecules for LED applications. Low molecular weight
compounds, however, have to be fabricated into thin
films by relatively expensive techniques such as vacuum
sublimation and vapor deposition, which are not well
suited to the manufacture of large area devices.12 One
way to overcome this processing disadvantage is to
make high molecular weight polymers, which can be
readily processed from their solutions into thin solid
films over large areas by simple spin coating or doctor’s
blade techniques. Several research groups have worked
on the preparation of silole-containing polymers.13 Most
of the methods used for the preparation of the silole
polymers are based on polycoupling or polycondensation
reactions. This method enjoys an advantage of versatil-
ity because of its “universal” applicability to multifunc-
tional monomers: any pairs of monomers with two or
* To whom all correspondence should be addressed at the
Department of Chemistry, Hong Kong University of Science &
Technology. Telephone: +852-2358-7375. Fax: +852-2358-1594.
E-mail: tangbenz@ust.hk.
† An Area of Excellence (AoE) Scheme administrated by the
University Grants Committee of Hong Kong.
10.1021/ma0213504 CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/22/2003

Macromolecules, Vol. 36, No. 4, 2003
Silole-Containing Polyacetylenes 1109
Ch a r t 1
Sch em e 1
Ch a r t 2
acetylene) {-[HCdC(Ar-Ch)]n-} is almost nonlumi-
nescent, a monosubstituted poly(1-alkyne) (-{HCdC-
[(CH2)m-Ch]}n-) can be emissive, and a disubstituted
poly(1-aryl-1-alkyne) (-{(Ar)CdC[(CH2)m-Ch]}n-) is
often radiantly glowing.16 We varied the substitution
patterns of the silolylacetylene monomers, i.e., from
monosubstituted 1-silolylacetylene (10) and ω-silolyloxy-
1-alkyne (11) to disubstituted 1-aryl-1-(ω-silolyloxy)-
alkyne (12), in an effort to evaluate how the structural
change will affect the light-emitting behaviors of the
substituted polysilolylacetylenes (1-3, Chart 2).
Aggregation of conjugated polymer chains in the solid
state often causes the formation of less-emissive or
nonemissive species such as excimers and exciplexes,
which partially or sometimes even completely quench
the emission of the polymers.17 This aggregation-
induced quenching has been a thorny problem in the
development of efficient LED systems because conju-
gated polymers are commonly used as thin solid films
in the EL devices. In this regard, the AIE feature of the
silole molecules is an invaluable property because
aggregation is an inherent process accompanying film
formation.18 Will the silolylacetylene polymers still
retain the AIE characteristics of their silole moieties or
will their aggregates be emissive? How will the conju-
gated polyacetylene backbone affect the emission of the
silole aggregates? What is the cause or mechanism for
the AIE process? Can this process be controlled or tuned
by simple external stimuli? In this paper, we will
provide our answers to these questions.
more mutually reacting functional groups can, in prin-
ciple, be polymerized by this reaction route. This
synthetic route suffers, however, an operational dis-
advantage: it demands a stoichiometric balance of the
comonomer feed if one wishes to prepare a soluble
polymer of high molecular weight. This technical dif-
ficulty has made the preparation of high molecular
weight polysiloles a challenging task. Indeed, the pol-
ysiloles prepared by the polycondensation reactions have
molecular weights normally on the order of 103 Da.13
In this work, we attempted to synthesize silole
polymers through a different approach. We tried to knit
the silole molecules together by a technique of acetylene
metathesis polymerization,14 which is, in terms of
reaction mechanism, an addition or chain reaction but
not a condensation or step reaction. To make the silole
molecule metathesis-active, we attached an acetylene
triple bond to the silolyl ring directly without a spacer
(10, Scheme 1) or indirectly through a flexible nonanyl-
oxy spacer (11 and 12). This structural design enables
us to investigate the electronic communication of the
polyacetylene backbone with the functional pendants
and the effect of the flexible spacer on the interaction
of the backbone with the pendants, both of which have
been found to play important roles in the formation of
mesomorphic aggregates in our liquid crystalline poly-
acetylene systems.15 It is known that luminescence
efficiency of a substituted polyacetylene carrying chro-
mophoric pendants (Ch) varies significantly with its
molecular structure: a monosubstituted poly(1-aryl-
Exp er im en ta l Section
The details about the reagents (materials), instrumentation
procedures, device fabrications, monomer syntheses, and po-
lymerization reactions are given in the Supporting Informa-
tion, in which the detailed characterization data for all the
new monomers and polymers, including their isolation yields,
physical forms (colors), molecular weights, and spectroscopic
1
data (IR, H and 13C NMR, MS, and UV) are also listed.
Resu lts a n d Discu ssion
Mon om er Syn th esis. We synthesized three silolyl-
acetylenes (10-12) by nucleophilic substitutions of
1-chloro-1,2,3,4,5-pentaphenylsilole (6) with a Grignard

1110 Chen et al.
Macromolecules, Vol. 36, No. 4, 2003
Ta ble 1. P olym er iza tion of Silolyla cetylen e 10a ,b
reagent of ethynylmagnesium bromide (9)13f and two
alkynyl alcohols (7 and 8, Scheme 1). The chlorosilole 6
is an important intermediate for silole derivatizations,
whose synthesis has, however, been difficult. Curtis
prepared the compound19 according to Braye’s proce-
dure20 by first reacting tolane (4) with an excessive
amount of lithium metal and then treating the resultant
1,4-dilithiotetraphenylbutadiene (5) with trichlorophe-
nylsilane. This synthetic route has, however, several
drawbacks. The use of an excess amount of lithium in
the preparation of 5 can easily cause side reactions,
leading to the formation of byproducts such as 1,2,3-
triphenylnaphthalene, as signaled by the color change
of the reaction mixture from dark green to brownish-
violet when the reaction time is prolonged.20 To avoid
the side reactions, a short reaction time is necessary
(<2 h as advised by Curtis19); doing so, however, results
in a low conversion of tolane to 5. The existence of the
unreacted lithium metal in the reaction mixture can
cause further complications when the mixture is added
into a chlorosilane solution. Gilman et al. thus recom-
mended that excessive lithium should be carefully
avoided even in the reactions of 5 with dichlorosilanes,21
not to mention its reactions with trichlorosilanes.
temp yield
c
c
no.
catalyst
solvent
(°C)
(%)
Mw
Mw/Mn
1
2
3
4
5
6
[Rh(nbd)Cl]2
WCl6-Ph4Sn
MoCl5-Ph4Sn toluene
TaCl5-Ph4Sn toluene
NbCl5-Ph4Sn toluene
NbCl5-Ph4Sn toluene
THF/Et3N
toluene
rt
60
60
60
60
80
0
0
0
0
60.0 46 400
78.0 68 800
1.7
1.8
a
Carried out under nitrogen for 24 h; [M]0 ) 0.1 M; [cat.] )
b
[cocat.] ) 10 mM. Abbreviations: nbd ) 2,5-norbornadiene; rt
) room temperature. c Estimated by GPC in THF on the basis of
a polystyrene calibration.
however, yielded no polymeric product (Table 1, no. 1).
Changing the solvent to dichloromethane (DCM) did not
help. Disappointed by the Rh results, we turned our
attention to metathesis catalysts. The mixtures of
WCl6- and MoCl5-Ph4Sn are known to be active
catalysts for the metathesis polymerizations of silicon-
containing acetylenes of general structure HCtC-
SiMe2R.26,27 Neither the W nor the Mo mixtures were,
however, capable of polymerizing 10. Attachment of the
bulky silole group to the triple bond may have lowered
the polymerizability of the acetylene monomer, prevent-
ing it from being polymerized by the W and Mo
catalysts. The TaCl5- and NbCl5-Ph4Sn mixtures are
known to be more tolerant of bulky groups and can
polymerize sterically very crowded diphenylacetylene
derivatives such as 1-phenyl-2-[(p-triphenylsilyl)phenyl]-
acetylene.27 Unfortunately, our attempt to polymerize
10 by TaCl5-Ph4Sn mixture also failed. Delightfully,
however, the reaction catalyzed by NbCl5-Ph4Sn in
toluene at 60 °C produced red powdery polymer in a
satisfactory yield (60%; Table 1, no. 5). The polymeri-
zation proceeded even more smoothly at a higher
temperature (80 °C) and a polymer with a molecular
weight of ∼69 kDa was obtained in a high yield (78%).
Monosubstituted acetylenes normally undergo cyclotri-
merizations in the presence of NbCl5-Ph4Sn mix-
ture,27,28 and the polymerization of 10, a monosubsti-
tuted acetylene, into high molecular weight polymers
by the Nb catalyst is thus somewhat surprising. While
a couple of silicon-containing alkynes and phenylacety-
lenes have been polymerized by NbCl5-Ph4Sn,29 10 is
the first example of a monosubstituted silylacetylene
with the silicon atom directly attached to the triple bond
that can be successfully polymerized by the Nb cata-
lyst. While poly(trimethylsilylacetylene), -{HCdC[Si-
(CH3)3]}n-, is only partially soluble,26,27 the polymers
of 10 were completely soluble in common solvents such
as chloroform, DCM, toluene, THF, and dioxane. The
excellent solubility is probably due to the large free
volumes created by the bulky silolyl pendants.
We followed Curtis’ procedure but encountered great
difficulty in obtaining our desired products. We thus
modified the reaction procedure and used an excessive
amount of tolane, instead of lithium, in the preparation
of 5. This allowed the lithiation reaction to be carried
out in an extended time frame to afford 5 in a high yield
(∼90%; estimated by a quenching reaction of 5 by
water6). Little, if any, lithium metal was left in the
mixture, and the side reactions were thus suppressed.
The green color of the reaction mixture did not change
for as long as 18 h, so the solution of 5 could be added
with ease in a dropwise fashion to the phenyltrichloro-
silane solution. After the addition, the mixture was
allowed to reflux for 3-5 h, which gave a dark yellow
solution of chlorosilole intermediate 6. Upon cooling to
room temperature, the chlorosilole was readily trans-
formed to 1,2,3,4,5-pentaphenylsilolylacetylene (10), 11-
[(1,2,3,4,5-pentaphenylsilolyl)oxy]-1-undecyne (11), and
11-[(1,2,3,4,5-pentaphenylsilolyl)oxy]-1-phenyl-1-unde-
cyne (12) by the reactions with ethynylmagnesium
bromide (9), 10-undecyn-1-ol (7), and 11-phenyl-10-
undecyn-1-ol (8), respectively. The unreacted tolane was
easily separated from the silole products by column
chromatography22 and could be recycled or reused.
Monomers 10-12 were prepared in 25-35% yields,
based on the amount of trichlorophenylsilane used,
which were far better than what we could achieve with
the Curtis procedure. All the purified monomers were
fully characterized by standard spectroscopic methods,
from which, satisfactory analysis data corresponding to
their expected molecular structures were obtained (see
Supporting Information for details). Single-crystal analy-
sis of monomer 10 revealed that the silolylacetylene
molecules were packed in a regular columnar structure,
details of which will be published in a separate paper.23
The polymerization behaviors of 11, a monomer with
the silolyl moiety separated from the triple bond by a
long nonanyloxy spacer, were distinctly different from
that of 10. While WCl6-Ph4Sn was inactive in polymer-
izing 10, the W catalyst effectively initiated the polym-
erization of 11 in toluene at 60 °C (Table 2, no. 1), giving
a polymer with an Mw of ∼12 kDa in ∼60% yield. The
polymerization in dioxane proceeded to produce a high
molecular weight polymer, albeit in a low yield. The
polymerization was initiated by MoCl5-Ph4Sn catalyst
but the result was much poorer than those from the W
system. Like 11, 12 was also polymerized by WCl6-Ph4-
Sn, giving a polymer with a high molecular weight (∼33
kDa) in a high yield (∼80%). Our attempts to polymerize
P olym er iza tion Rea ction s. Silolylacetylene 10, a
monomer with the silolyl moiety directly attached to the
acetylene triple bond without a spacer, showed interest-
ing polymerization behaviors. Since 10 structurally
somewhat resembles phenylacetylene, we first tried to
polymerize it by [Rh(nbd)Cl]2, an effective catalyst for
the insertion polymerizations of phenylacetylenes.24,25
The reaction catalyzed by the Rh complex in THF/Et3N,

Macromolecules, Vol. 36, No. 4, 2003
Silole-Containing Polyacetylenes 1111
Ta ble 2. P olym er iza tion of Siloxya cetylen es 11 a n d 12a
yield
solvent (%)
b
b
no. monomer
catalyst
Mw
Mw/Mn
1
2
3
4
5
6
11
11
11
12
12
12
WCl6-Ph4Sn toluene 60.3 11 500
WCl6-Ph4Sn dioxane 29.0 33 900
MoCl5-Ph4Sn toluene 11.7 10 600
WCl6-Ph4Sn toluene 80.5 33 400
3.5
2.6
3.4
2.2
TaCl5-Ph4Sn toluene
NbCl5-Ph4Sn toluene
0
0
a
Carried out under nitrogen at 60 °C for 24 h; [M]0 ) 0.1 M;
b
[cat.] ) [cocat.] ) 10 mM. Estimated by GPC in THF on the basis
of a polystyrene calibration.
12 by TaCl5- and NbCl5-Ph4Sn catalysts were, how-
ever, unsuccessful. The polymerizations of the acetylene
monomers with siloxy (Si-O) moieties (or siloxyacety-
lenes) seemed to be sensitive to not only the catalyst
but also the substrate. We tried, for example, to
polymerize a congener of 12 with a short ethyloxy spacer
HCtC(CH2)2OPS using the W and Mo catalysts under
various reaction conditions, but our efforts all ended in
failure. This may account for the rarity of reports on
the polymerizations of siloxyacetylenes in the litera-
ture.27 The only example known to us is the MoCl5-
catalyzed polymerizations of dimethylalkoxysilylacety-
lenes HCtCSi(CH3)2OCmH2m+1 (m ) 2, 3), which gave
insoluble gels of low stability.26a The intractability not
only poses an obstacle to purifying and characterizing
the polymers but also renders the polymers practically
useless in terms of finding practical applications as
plastic materials. The polymers of 11 and 12 were,
however, completely soluble in common organic sol-
vents. These polymers thus represent the first examples
of completely soluble substituted polyacetylenes with
polar siloxy moieties.
F igu r e 1. 1H NMR spectra of (A) 11 and (B) its polymer 2
(Table 2, no. 1) in CDCl3. The solvent peak is marked with an
asterisk. The silolyl moiety in the molecular structure of the
polymer is represented by an Si ring in order to save space.
Str u ctu r a l Ch a r a cter iza tion . All the polymers
gave satisfactory spectroscopic data corresponding to
their expected molecular structures (see Supporting
Information for detailed analysis data). An example of
the IR spectrum of polymer 2 is shown in Figure s1
(Supporting Information); the spectrum of its monomer
11 is also shown in the same figure for the purpose of
comparison. As can be seen from the spectrum of 11,
its tC-H stretching and CtC bending vibrations
occurred at 3297 and 637 cm-1, respectively.16a These
absorption bands disappeared in the spectrum of its
polymer, 2, indicating that the triple bond has been
consumed by the polymerization reaction.
The NMR analysis proved that the acetylene triple
bonds had been transformed to polyene double bonds.
Figure 1 shows the 1H NMR spectra of 11 and its
polymer 2 in CDCl3. There was no acetylene absorption
at δ 1.9 in the spectrum of the polymer. It is known that
the cis olefin proton of the poly(1-alkyne) backbone
absorbs at δ 6.5-5.6.14-16 The spectrum of 2, however,
exhibited no resonance peak in this region, suggesting
that the polymer chains are trans-rich in stereostruc-
ture. Figure s2 (Supporting Information) shows the 13C
NMR spectra of the polymer and its monomer. While
the acetylenic carbon atoms of 11 absorbed at δ 84.7
and 68.1, these absorption peaks disappeared in the
spectrum of 2. The absorption of the propargyl carbon
atom of 11 at δ 18.4 also disappeared owing to its
transformation to the allylic structure by the acetylene
polymerization.16a The absorption peaks of the olefinic
carbon atoms of the polyacetylene backbone were not
easily identifiable, due to their overlapping with the
resonance peaks of the silole pendants.
F igu r e 2. DSC thermograms of 1 (Table 1, no. 6), 2 (Table 2,
no. 1), and 3 (Table 2, no. 4) recorded under nitrogen at a
heating rate of 10 °C/min.
Th er m a l P r op er ties. Figure 2 shows the DSC
thermograms of polymers 1-3. No peaks associated
with crystallization/melting transitions of the polymers
were detected by the DSC analyses. The glass transition
temperatures (Tg’s) of 2 and 3 were observed at 56 and
82 °C, respectively, while 1 exhibited a virtually flat line
with no changes in the measured temperature region,
suggesting that this polymer has a very high Tg. The
bulky pentaphenylsilolyl pendants directly attached to
the polyacetylene backbone make the polymer chain
very rigid, whose segmental movements are signifi-
cantly restricted and cannot occur at low temperatures.
The higher Tg of 3, in comparison to that of 2, should
be due to its more rigid disubstituted polyacetylene
backbone.30
The TGA thermograms of the polymers are shown in
Figure s3 (Supporting Information). All the polymers
were thermally stable and lost little of their weights at
a temperature as high as ∼350 °C. The decomposition
temperatures for poly(dimethylalkoxysilylacetylene)s
-{HCdC[Si(CH3)2OCmH2m+1]}n- are 280 (m ) 2) and

1112 Chen et al.
Macromolecules, Vol. 36, No. 4, 2003
F igu r e 3. UV absorption spectra of chloroform solutions of 1
(Table 1, no. 6), 2 (Table 2, no. 1), and 3 (Table 2, no. 4).
270 °C (m ) 3), respectively;26a the higher stability of
our polysilolyloxyacetylenes 2 and 3 are probably due
to the “jacket effect”15,16 of the bulky silolyl pendants.
Wrapping of the polyacetylene backbone in the silole
rings may have shielded the double bonds from the
chemical and thermal attacks. It has been reported that
the siloxy bonds have been cleaved during the MoCl5-
catalyzed polymerizations of dimethylalkoxysilyl-
acetylenes.26a Such detrimental cleavage reaction did
not occur in the polymerizations of our silolyloxyacety-
lene monomers 11 and 12, demonstrative of the multi-
faceted protective functions of the bulky silole rings.
Electr on ic Tr a n sition s. Polymer 1 exhibited a
strong peak at 376 nm due to the absorption of its silole
pendants, and the absorption of its polyacetylene back-
bone occurred at wavelengths beyond 450 nm, which
well extended into to the visible spectral region (Figure
3). The silole pendants may have conjugated with the
polyacetylene backbone, which increased the effective
conjugation length of the polymer chain,31 hence making
the polymer absorptive in the long wavelength region.32
Little absorption was, however, observed in the long
wavelength region of the spectra of 2 and 3, suggesting
that these polymers possess shorter persistence lengths
of backbone conjugations, in comparison to their struc-
tural congener 1. This difference was reflected in the
colors of the polymers: while 1 was red-colored, 2 and
3 were yellow-greenish solids. Compared to 2, 3 ab-
sorbed more strongly in the short wavelength region
(<380 nm). This enhanced absorption is probably due
to the additional contribution from the phenyl rings
directly attached to the polymer backbone.
Figure 4 shows the absorption spectra of the polymers
in methanol/chloroform mixtures. The mixtures were
prepared by adding methanol into dilute chloroform
solutions of the polymers with vigorous shaking, the
concentrations of all the resultant mixtures being kept
fixed at 10 µM for the purpose of comparison. One can
immediately notice, by comparing the spectra in Figure
4, that there are practically no shifts in the peak
positions for all the three polymers, no matter how the
solvent composition changes. The absorptivity of the
mixtures, however, did change, although in a mixed
manner. With an increase in methanol content in the
mixture, the spectrum of 1 was vertically lifted up, little
change was observed in the absorption spectra of 2, and
the spectra of 3 was somewhat elevated. What is the
cause for this kind of spectral variation? Nanoparticles
are known to vertically raise absorption spectra due to
F igu r e 4. Absorption spectra of (A) 1 (Table 1, no. 6), (B) 2
(Table 2, no. 1), and (C) 3 (Table 2, no. 4) in methanol/
chloroform mixtures with different volume fractions of metha-
nol.
the optical loss caused by light scattering.33,34 Since
methanol is a poor solvent of the polymers, it is likely
that the polymers have formed nanosized aggregates in
the methanol/chloroform mixtures with high contents
of methanol. We thus checked whether there were really
nanoparticles in such mixtures.
We carried out particle size analysis, which proved
that the polymers did form nanoaggregates in the
methanol/chloroform mixtures. Examples of the particle
size histograms are shown in Figure 5. In the mixture
with 90% methanol, 1 clustered into large particles with
a broad size distribution and a large average size (174
nm). Polymer 2 also formed nanoaggregates, whose size
distribution was, however, much narrower and whose
average size was much smaller (34 nm). The size
distribution and average size (112 nm) of 3 were
between those of 1 and 2. The differences in the size
distribution and average size are probably due to the
difference in the solubility of the polymers in the solvent
mixture. Polymer 1 is very hydrophobic and rigid and
will easily associate into large nanoaggregates in the
polar mixture. Polymer 2 possesses polar siloxy moieties
with a better miscibility with the polar solvent and
hence forms smaller aggregates under comparable
conditions. Polymer 3 is a disubstituted polyacetylene
with a more rigid backbone structure30 and its ag-
gregates are thus understandably bigger than those of
2. With the nanoparticle data on hand, we now may
understand why the absorption spectra of the polymers
have changed in a seemingly confusing manner with the
progressive addition of methanol into the chloroform
solutions. The formation of nanoaggregates may have
not appreciably perturbed the electronic structures of
the polymers and has hence caused practically no red

Macromolecules, Vol. 36, No. 4, 2003
Silole-Containing Polyacetylenes 1113
F igu r e 6. (A) Photoluminescence spectra of 3 (Table 2, no. 4)
in chloroform solution, methanol/chloroform mixture (9:1 by
volume), and solid state (thin film). Concentration of 3 in the
solution and the mixture: 10 µM. Excitation wavelength
(nm): 400 (solution/mixture); 325 (thin film). (B) Quantum
yield (ΦF) of 3 vs solvent composition of methanol/chloroform
mixture.
F igu r e 5. Particle size distributions of (A) 1 (Table 1, no. 6),
(B) 2 (Table 2, no. 1), and (C) 3 (Table 2, no. 4) in methanol/
chloroform mixtures (9:1 by volume). Concentration of poly-
mers: 10 µM.
shifts in the peak positions of their absorption spectra.
The optical losses caused by the light scattering from
the nanoparticles of 1 and 3 vertically upraise the levels
of spectra, albeit in a nonlinear fashion due partly to
the size distribution of the nanoparticles.33 The sizes of
the nanoparticles of 2 are too small to induce noticeable
scattering loss,35 and hence, its spectra did not change
much with the solvent composition.
chloroform mixture and the thin film both located at
512 nm, which is close to the emission maximum of the
silole ring, suggesting that the emission of 2 is by its
silole pendants. We estimated the quantum yield (ΦF)
of 2 using 9,10-diphenylanthracene as reference.5 Its
chloroform solution showed a ΦF value as low as 0.15%.
The ΦF value of the mixture remained almost un-
changed when up to ∼40% methanol was added to the
solution but started to swiftly increase afterward (Fig-
ure 4B). When the methanol fraction was increased to
90%, ΦF rose to 2.95%, which was ∼20 times higher
than the solution value. The trajectory of the ΦF change
suggests that the silole pendants of 2 started to ag-
gregate at a methanol fraction of ∼50% and that the
size and population of the nanoaggregates continue to
increase as the methanol fraction increases. Similarly,
polymer 3 was also AIE-active: its solution was almost
nonradiative, but its aggregates luminesced intensely
at 512 nm (Figure 6A). The emission efficiency of 3 (ΦF
) 9.25%) was >3 times higher than that of 2, probably
due to the additional contribution of the backbone
emission: the poly(1-phenyl-1-alkyne) main chain of 3
is known to luminesce in the similar spectral region.16,37
The AIE effect was more striking in this system: the
emission of the nanoaggregates of 3 was ∼46 times more
efficient than that of its molecularly dissolved species.
The picture now becomes clear: in the aggregation
state, 1 is virtually nonluminescent, 2 emits moderately,
and 3 is a most efficient emitter. It is well-known that
a stiff polymer backbone distorts the packing of its
mesogenic pendants.15,16,25,38,39 The rigid polyacetylene
backbone of 1 may not allow its directly attached silole
pendants to pack well in the aggregation state, thus
Ligh t Em ission . Silole’s emission is characterized by
its AIE feature:5 it is practically nonluminescent when
molecularly dissolved in solutions but is highly emissive
when aggregated in poor solvents or fabricated into thin
solid films. Do the silole polymers behave in a similar
way? The answer to this question is yes or no, depending
on the molecular structure of the polymer. A chloroform
solution of 1 with a concentration of 10 µM emitted a
faint red light of 652 nm. It is known that the silole ring
emits blue-green light5-8 while the (unsubstituted)
polyacetylene chain emits weak infrared light.36 The
emission of the dim red light of 652 nm thus should be
associated with the inefficient radiative decay of the
somewhat twisted polyacetylene backbone of 1. We
added methanol into the chloroform solution, while
keeping the concentrations of the resultant mixtures
unchanged. Only very slightly could the light emission
of 1 be enhanced by the addition of the poor solvent;
that is, this polymer does not show the AIE effect.
Polymer 2, on the other hand, exhibited a pronounced
AIE effect. While the PL spectrum of its dilute chloro-
form solution was almost a flat line, intense emission
was observed when a large amount (90 vol %) of
methanol was added into the chloroform solution (Fig-
ure s4A, Supporting Information). Its thin solid film was
also highly emissive. The emission peaks of the methanol/

1114 Chen et al.
Macromolecules, Vol. 36, No. 4, 2003
F igu r e 8. Current efficiency vs. applied bias in a multilayer
electroluminescence device of 3 (sample from Table 2, no. 4)
with a device configuration of ITO/(3:PVK)(1:4)/BCP/Al(q)3/LiF/
Al, where PVK ) poly(9-vinylcarbazole), BCP ) bathocuproine,
and Al(q)3 ) tris(8-hydroxyquinolinato)aluminum.
F igu r e 7. Electroluminescence spectra of single-layer devices
of 1 (Table 1, no. 6), 2 (Table 2, no. 1), and 3 (Table 2, no. 4)
with a device configuration of ITO/polymer/LiF/Al.
making the polymer AIE-inactive. The long flexible
spacer of nonanyloxy group decouples the silole pen-
dants of 2 and 3 from their polyacetylene backbone and
enables the silole groups to pack in a more regular
fashion, hence making the polymers AIE-active. The
emitting center changes with the molecular structure
of the polymer: 1 emits from its polyacetylene backbone,
2 from its silole pendants, and 3 from its backbone and
pendants. This double emission makes 3 the best
emitter among the three polymers.
We checked the EL performances of the polymer thin
films, using a single-layer device configuration. The EL
spectrum of 1 peaked at 664 nm, while the emission
maxima of 2 and 3 were at ∼512 nm (Figure 7). All the
EL devices exhibited similarly low current efficiencies:
0.014 (1), 0.013 (2), and 0.013 cd/A (3). The EL data
clearly contradict with the PL data discussed above,
suggesting that the device configuration is far from
optimized. One possible cause for the inferior perfor-
mance is the unbalanced charge injection and transport
in the single-layer EL devices. We thus tried to modify
the device configuration, using 3, the most PL-active
polymer, as the emitting material. We added PVK, one
of the best-known hole-transport polymers, and Al(q)3,
a very widely used electron-transport material, on the
anode and cathode sides, respectively, to facilitate the
charge injection and to enhance the charge-transport
efficiencies in the EL device. Between the PVK and Al-
(q)3 layers, we added a layer of BCP, a hole-blocking
material, to prevent the holes from traveling through
to reach the cathode. With these modifications, an EL
device with a configuration of ITO/(3:PVK)(1:4)/BCP/
Al(q)3/LiF/Al was fabricated, whose performance was
greatly improved, in comparison to its single-layer
counterpart. The multilayer device emitted a blue light
of 496 nm with a maximum brightness of 1118 cd/m2.
The emission peak is 16 nm blue-shifted from its PL
maximum, probably due to the dilution effect by the
polymer matrix, as reported in our early communica-
tion,5 and/or by the microcavity effect proposed by other
researchers.40 The maximum CE and ηEL of the device
were 1.45 cd/A (Figure 8) and 0.55%, respectively, which
are comparable to some of the best results reported by
other research groups for blue-emitting LEDs.41
F igu r e 9. Photoluminescence spectra of a dioxane solution
of 3 (Table 2, no. 4) with a concentration of 10 µM at different
temperatures. Excitation wavelength: 407 nm.
all organic and polymeric light-emitting materials are
used as solid films in their LED applications. Aggrega-
tion normally quenches light emission;17 what is then
the cause for this “abnormal” AIE phenomenon? To
address this mechanistic question, we designed and
carried out more experiments. We chose dioxane, a
common solvent with a “high” melting point (mp ) 11.8
°C) that readily solidifies with a small extent of cooling
from room temperature. When a dilute dioxane solution
of 3 (10 µM) was cooled, the intensity of its PL spectrum
was increased (Figure 9). The spectral profile hardly
changed with temperature, suggesting that the emission
is still associated with the radiative decay of the singlet
excitons7a but not their triplet cousins. The peak inten-
sity of the PL spectrum changed with temperature in a
nonlinear fashion (Figure 10). When cooled from 23 °C
(room temperature) to below the mp of the solvent, the
liquid solution changed to a solid “glass”. The intra-
molecular rotations or twistings of the peripheral phenyl
rings upon the axes of the single bonds linked to the
central silacyclopentadiene cores may be physically
restricted by the solid environmental surroundings. This
restricted rotation in some sense rigidifies the chro-
mophoric molecule as a whole, thus making the silole
pendant more emissive. The PL intensity was progres-
Restr icted In tr a m olecu la r Tw istin g. The AIE
effect is of technological implications, considering that

Macromolecules, Vol. 36, No. 4, 2003
Silole-Containing Polyacetylenes 1115
solution were lower than those of the 3/DCM solution
with the same concentration; this may be partially
caused by the even higher solvating power of the solvent
to the low molecular weight silole compound.
Twisted intramolecular charge transfer (TICT) has
been found to greatly alter luminescence properties of
some chromophoric molecules containing donor and
acceptor groups, with off-on manipulations of light
emission (from nonluminescent “off” to luminescent “on”
state) achieved in certain systems.42,43 Since silole is not
such a push-pull chromophore, the TICT effect may not
be at play in our system. It is known that torsional or
rotational energy relaxation can nonradiatively deacti-
vate excited molecules.44,45 Restriction of the rotational
or twisting movement will block the radiationless chan-
nel and populate the radiative decay of the excitons. The
rigid chain of 1 may not allow its silole pendants to pack
well and the large free volumes in the nanoaggregates
may still enable the intramolecular rotations of the
phenyl-silole single bonds to occur; the polymer thus
remained nonemissive even in its aggregation state. We
have recently found that the aggregates of our hyper-
branched silole polymers are also nonluminescent, prob-
ably due to the same reasons: the poor packing of the
silole groups in the nanoaggregates and the easy in-
tramolecular rotation or twisting in the large void
spaces in the hyperbranched polymers. Cooling the
polymer solutions can, however, enhance their emission
efficiencies.46 This further supports our hypothesis that
the underlying reason for the AIE phenomenon observed
in linear silole polymers 2 and 3 is the restricted
intramolecular rotation or twisting in the well packed
silole nanoaggregates. A recent paper reported that
restricting the rotation or twisting of the single bond
between two neighboring thienyl rings could lead to a
big increase (up to 12 times) in the emission efficiency
of polythiophenes.47 Thus, the restricted intramolecular
rotation does not only work for our linear silole polymers
but also may find applications in enhancing light
emissions of other chromophoric systems.
F igu r e 10. Effect of temperature on peak intensity of the
photoluminescence spectra of 3 in dioxane and DCM. Data for
HPS are shown for comparison. Excitation wavelength: 407
nm. All the solutions have a concentration of 10 µM except
for the one marked with an asterisk, whose concentration is
20 µM.
sively increased when the temperature was successively
decreased from +23 to -78 °C, indicating that the
cooling is gradually limiting the thermally induced or
activated intramolecular rotations. Further decreasing
the temperature from -78 to -196 °C caused little
change in the peak intensity, implying that the in-
tramolecular rotations have almost completely frozen
at -78 °C.
To separate the cooling effect from the “glass” effect,
we chose DCM, a liquid with a high solvation power but
a low melting point, which can keep both the solvent
and the solute in the solution state during the cooling
process. The peak intensity of the PL spectrum of a
dilute DCM solution of 3 (10 µM) at room temperature
was weaker than that of the dioxane solution, due to
the stronger solvating power of DCM to the polymer.
The PL intensity of the solution increased with a
decrease in temperature in a nearly “linear” fashion (in
the semilog plot). This enhancement in emission must
be due to the restricted intramolecular rotation caused
by cooling-induced conformation freezing because the
melting point of the solvent (-95 °C) is lower than the
lowest temperature we tested for this solution (-78 °C).
The solvent should be in the liquid state, and the solute
should be molecularly dissolved at all the temperatures
tested. We doubled the solution concentration to 20 µM
and found that the emission enhancements were also
roughly doubled at all the temperatures (data marked
with an asterisk in Figure 10). This once again proves
that the solute has indeed remained molecularly dis-
solved at the low temperatures because if the solute
aggregates, it should evoke a clear “nonlinear” response
(in the semilog scale) to the concentration change. We
used a dilute DCM solution of HPS (10 µM) as a control
and found that the silole compound also exhibited an
approximately linear semilog relationship between the
increase in PL intensity and the decrease in tempera-
ture. Noting that HPS is highly soluble in DCM, the
high PL intensities at the low temperatures should be
beyond doubt caused by the restricted intramolecular
rotation or twisting. The PL intensities of the HPS/DCM
Con clu d in g Rem a r k s
In this work, we synthesized a group of new silolyl-
acetylene polymers and studied their light-emitting
properties. Our main results and key findings can be
summarized as follows:
We successfully developed a new synthetic route for
the preparation of silole polymers, which produced high
molecular weight polysilolylacetylenes in high yields.
Overcoming the involved synthetic difficulties, we ac-
complished the polymerizations of silolylacetylene mono-
mers 10-12 using NbCl5- and WCl6-Ph4Sn as cata-
lysts. Monomer 10 is the first example of a monosub-
stituted acetylene with a directly attached silyl group
that can be successfully polymerized by the Nb catalyst,
while 11 and 12 represent the first siloxyacetylenes that
can be polymerized by the W catalyst. All the polymer-
izations yielded completely soluble polymers of high
thermal stability.
The molecular structures of the polymers greatly
affected their optical properties. The direct electronic
communication between the polyacetylene backbone and
the silole pendants of 1 provided the polymer with a
better conjugation and enabled efficient energy transfer
from the side groups to the main chain. The polyacety-
lene backbone of 1 emitted faintly in the red spectral
region, in agreement with the early finding that (un-

1116 Chen et al.
Macromolecules, Vol. 36, No. 4, 2003
1999, 81-102. (c) Yamaguchi, S.; Tamao, K. J . Chem. Soc.,
Dalton Trans. 1998, 3693-3702.
(2) (a) Yamaguchi, S.; Tamao, K. Bull. Chem. Soc. J pn. 1996,
69, 2327-2334. (b) Chuit, C.; Corriu, R. J . P.; Reye, C.; Young,
J . C. Chem. Rev. 1993, 93, 1371-1448.
substituted) polyacetylene is virtually nonluminescent.
The long nonanyloxy spacers electronically decoupled
the silole pendants of 2 from its polyacetylene backbone
and the segregated silole rings acted as the emitting
centers in the polymer nanoaggregates because the poly-
(1-alkyne) backbone is not an active chromophore.15,16
Polymer 3 was more emissive because the excitons of
the silole pendants and the poly(phenylalkyne) back-
bone both undergo radiative transitions in the similar
spectral region.37-39
(3) An electron mobility as high as 2 × 10-4 cm2/(V s) has been
reported for a silole molecule 2,5-bis(2, 2′-bipyridin-6-yl)-1,1-
dimethyl-3,4-diphenylsilole at an electrical strength of 640
kV/cm: (a) Murata, H.; Malliaras, G. G.; Uchida, M.; Shen,
Y.; Kafafi, Z. H. Chem. Phys. Lett. 2001, 339, 161-166. (b)
Murata; H.; Kafafi; Z. H.; Uchida; M. Appl. Phys. Lett. 2002,
80, 189-191.
(4) (a) Ohshita, J .; Kai, H.; Takata, A.; Iida, T.; Kunai, A.; Ohta,
N.; Komaguchi, K.; Shiotani, M.; Adachi, A.; Sakamaki, K.;
Okita, K. Organometallics 2001, 20, 4800-4805. (b) Yama-
guchi, S.; Endo, T.; Uchida, M.; Izumizawa, T.; Furukawa,
K.; Tamao, K. Chem.sEur. J . 2000, 6, 1683-1692.
(5) (a) Luo, J .; Xie, Z.; Lam, J . W. Y.; Cheng, L.; Chen, H.; Qiu,
C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem.
Commun. 2001, 1740-1741. (b) Freemantle, M. Chem. Eng.
News 2001, 79 (41), 29.
(6) Tang, B. Z.; Zhan, X.; Yu, G.; Lee, P. P. S.; Liu, Y.; Zhu, D. J .
Mater. Chem. 2001, 11, 2874-2978.
(7) Chen, H. Y.; Lam, J . W. Y.; Luo, J . D.; Ho, Y. L.; Tang, B. Z.;
Zhu, D. B.; Wong, M.; Kwok, H. S. Appl. Phys. Lett. 2002,
81, 774-576.
(8) The highest ηEL possible for a singlet emitter has been
theoretically predicted to be ∼5.5%, but recent research in
the area suggests that this limit may be uplifted to ∼9%.9.
(9) (a) Cao, Y.; Parker, I. D.; Yu, G.; Zhang, C.; Heeger, A. J .
Nature (London) 1999, 397, 414-417. (b) Kim, J . S.; Ho, P.
K.; Greenham, N. C.; Friend, R. H. J . Appl. Phys. 2000, 88,
1073-1081.
(10) Configuration of the EL device: ITO/CuPc/TPD/HPS/Al(q)3/
LiF/Al, where ITO ) indium tin oxide, CuPc ) copper
phthalocyanine, TPD ) N,N′-diphenyl-N,N′-bis(3-methyl-
phenyl)-1,1′-diphenyl-4,4′-diamine, and Al(q)3 ) tris(8-hy-
droxyquinolinato)aluminum.
The AIE effect was not operative in polymer 1 because
the silole pendants directly attached to the rigid poly-
acetylene backbone cannot pack well in the aggregation
state and the large free volumes still permit the phen-
yl-silole bonds to undergo intramolecular rotation. The
decoupling of the silole pendants of 2 and 3 from their
polyacetylene backbones by the flexible nonanyloxy
spacers allowed the pendants to pack well in the
aggregation state, enabling the AIE effect to function
in the nanoaggregates and solid films. Up to ∼46 times
enhancement in the emission efficiency was induced by
the aggregate formation.
The light emission could be enhanced not only by
adding poor solvents to induce nanoaggregate formation
but also by cooling the molecularly dissolved solutions
to restrict the intramolecular rotation. The changes in
the emission efficiency caused by changing solvent and
temperature may respectively be regarded as special
kinds of solvato- and thermochromisms,5,48 offering
versatile means to manipulate the light emission of the
conjugated polymers by simple external stimuli.
The EL performance of 3 was improved by modifying
its device configuration. Its multilayer device emitted
a blue light of 496 nm with a maximum brightness of
1118 cd/m2. The device efficiencies of 1.45 cd/A (CE) and
0.55% (ηEL) are the best results reported so far for
polyacetylene-based EL devices,37 which may be further
improved by modifying the molecular structure of the
polymers and by optimizing the configuration of the EL
devices. Work along this line is currently in progress in
our laboratories.
(11) Ohshita, J .; Kai, H.; Sumida, T.; Kunai, A.; Adachi, A.;
Sakamaki, K.; Okita, K. J . Organomet. Chem. 2002, 642,
137-142.
(12) Ktaft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. 1998, 37, 402-428.
(13) (a) Adachi, A.; Yasuda, H.; Sanji, T.; Sakurai, H.; Okita, K.
J . Lumin. 2000, 87-9, 1174-1176. (b) Woo, H. G.; Song, S.
J .; Kim, B. H.; Yun, S. S. Mol. Cryst. Liq. Cryst. 2000, 349,
87-90. (c) Tamao, K.; Yamaguchi, S.; Shiozaki, M.; Naka-
gawa, Y.; Ito, Y. J . Am. Chem. Soc. 1992, 114, 5867-5869.
(d) Yamaguchi, S.; Goto, T.; Tamao, K. Angew. Chem., Int.
Ed. 2000, 39, 1695-1697. (e) Lee, Y.; Sadki, S.; Tsuie, B.;
Reynolds, J . R. Chem. Mater. 2001, 13, 2234-2236. (f) Corriu,
R. J .-P.; Douglas, W. E.; Yang, Z.-X. J . Organomet. Chem.
1993, 456, 35-39. (g) Oshita, J .; Hamaguchi, T.; Toyoda, E.;
Kunai, A.; Ishikawa, M.; Naka, A. Organometallics 1999, 18,
1717-1723. (h) Toyoda, E.; Kunai, A.; Ishikawa, M. Orga-
nometallics 1995, 14, 1089-1091. (i) Sanji, T.; Sakai, T.;
Kabuto, C.; Sakurai, H. J . Am. Chem. Soc. 1998, 120, 4552-
4553. (j) Yamaguchi, S.; J in, R.-Z.; Itami, Y.; Goto, T.; Tamao,
K. J . Am. Chem. Soc. 1999, 121, 10420-10421.
(14) Ivin, K. J .; Mol, J . C.Olefin Metathesis and Metathesis
Polymerization; Academic Press: San Diego, CA, 1997.
(15) (a) Mi, Y.; Tang, B. Z. Polym. News 2001, 26, 170-176. (b)
Lam, J . W. Y.; Kong, X.; Dong, Y. P.; Cheuk, K. K. L.; Xu,
K.; Tang, B. Z. Macromolecules 2000, 33, 5027-5040. (c)
Kong, X.; Tang, B. Z. Chem. Mater. 1998, 10, 3352-3363.
(d) Tang, B. Z.; Kong, X.; Wan, X.; Peng, H.; Lam, W. Y.; Feng,
X.; Kwok, H. S. Macromolecules 1998, 31, 2419-2432.
(16) (a) Lam, J . W. Y.; Dong, Y. P.; Cheuk, K. K. L.; Luo, J . D.;
Xie, Z. L.; Kwok, H. S.; Mo, Z. S.; Tang, B. Z. Macromolecules
2002, 35, 1229-1240. (b) Huang, Y. M.; Ge, W.; Lam, J . W.
Y.; Tang, B. Z. Appl. Phys. Lett. 2001, 78, 1652-1654. (c)
Tang, B. Z. Xu, H.; Lam, J . W. Y.; Lee, P. P. S.; Xu, K.; Sun,
Q.; Cheuk, K. K. L. Chem. Mater. 2000, 12, 1446-1455. (d)
Huang, Y. M.; Lam, J . W. Y.; Cheuk, K. K. L.; Ge, W.; Tang,
B. Z. Macromolecules 1999, 32, 5976-5978.
Ack n ow led gm en t. The work described in this paper
was partially supported by the Research Grants Council
of Hong Kong through Grants HKUST 6187/99P, 6121/
01P, and 6085/02P. This project also benefited from the
financial support of the University Grants Committee
(Hong Kong) under an Area of Excellence Scheme
(Project No. AoE/P-10/01-1-A). We sincerely thank Prof.
K. S. Wong of the Department of Physics of our
University for his helpful discussions.
Su p p or tin g In for m a tion Ava ila ble: Text giving details
about the reagents (materials), instrumentation procedures,
device fabrications, monomer syntheses, and polymerization
reactions and detailed characterization data for all the new
monomers and polymers, including their isolation yields,
physical forms (colors), molecular weights, and spectroscopic
data (IR, 1H and 13C NMR, MS, and UV), and figures showing
IR and 13C NMR spectra of 11 and 2, TGA thermograms of
1-3, photoluminescence spectra of 2, and a plot of the
quantum yield of 2. This material is available free of charge
via the Internet at http://pubs.acs.org.
(17) (a) An, B.-K.; Kwon, S.-K.; J ung, S.-D.; Park, S. Y. J . Am.
Chem. Soc. 2002, 124, 14410-14415. (b) Chen, S. H.; Su, A.
C.; Huang, Y. F.; Su, C. H.; Peng, G. Y.; Chen, S. A.
Macromolecules 2002, 35, 4229-4232. (c) Deans, R.; Kim, J .;
Machacek, M. R.; Swager, T. M. J . Am. Chem. Soc. 2000, 122,
8565-8566. (d) Zhang, X. J .; Shetty, A. S.; J enekhe, S. A.
Macromolecules 1999, 32, 7422-7429.
Refer en ces a n d Notes
(1) For reviews, see: (a) Lee, V. Y.; Sekiguchi, A.; Ichinohe, M.;
Fukaya, N. J . Organomet. Chem. 2000, 611, 228-235. (b)
Hermanns, J .; Schmidt. B. J . Chem. Soc., Perkin Trans. 1

Macromolecules, Vol. 36, No. 4, 2003
Silole-Containing Polyacetylenes 1117
(18) Thin Films: Structure and Morphology; Moss, S. C., Ed.;
Materials Research Society: Pittsburgh, PA, 1997.
(19) Curtis, M. D. J . Am. Chem. Soc. 1969, 91, 6011-6018.
(20) Braye, E. H.; Hubel, W.; Caplier, I. J . Am. Chem. Soc. 1961,
83, 4406-4413.
(21) Gilman, H.; Cottis, S. G.; Atwell, W. H. J . Am. Chem. Soc.
1964, 86, 1596-1599.
B.; J ing, X.; Wang, X.; Wang, F.; Pakhomov, A. B.; Zhang, X.
X. Chem. Mater. 1999, 11, 1581-1589. (b) Tang, B. Z.
CHEMTECH 1999, 29 (11), 7-12. (c) Tang, B. Z.; Geng, Y.;
Sun, Q.; Zhang, X. X.; J ing, X. Pure Appl. Chem. 2000, 72,
157-162.
(36) Huang, Y. M.; Ge, W.; Lam, J . W. Y.; Tang, B. Z. Appl. Phys.
Lett. 1999, 75, 4094-4096.
(22) Tolane could be eluted much faster than the siloles using
hexane/chloroform or chloroform/acetone mixtures as eluents.
(23) Chen, J .; Law, C. C. W.; Lam, J . W. Y.; Dong, Y.; Lo, S. M.
F.; Williams, I. D.; Tang, B. Z. Unpublished results.
(24) For selected recent reviews, see: (a) Yashima, E. Anal. Sci.
2002, 18, 3-6. (b) Tang, B. Z. Polym. News 2001, 26, 262-
272. (c) Nagai, K.; Masuda, T.; Nakagawa, T.; Freeman, B.
D.; Pinnau, Z. Prog. Polym. Sci. 2001, 26, 721-798. (d) Tang,
B. Z.; Cheuk, K. K. L.; Salhi, F.; Li, B. S.; Lam, J . W. Y.;
Cha, J . A. K.; Xiao, X. D. ACS Symp. Ser. 2001, 812, 133-
148. (e) Choi, S. K.; Gal, Y. S.; J in, S. H.; Kim, H. K. Chem.
Rev. 2000, 100, 1645-1681. (f) Tang, B. Z.; Xu, K.; Sun, Q.;
Lee, P. P. S.; Peng, H.; Salhi, F.; Dong, Y. ACS Symp. Ser.
2000, 760, 146-164.
(25) (a) Tang, B. Z.; Poon, W. H.; Leung, S. M.; Leung, W. H.;
Peng, H. Macromolecules 1997, 30, 2209-2212. (b) Tang, B.
Z.; Kong, X.; Wan, X.; Feng, X.-D. Macromolecules 1998, 31,
7118. (c) Tang, B. Z.; Kong, X.; Wan, X.; Feng, X.-D.
Macromolecules 1997, 30, 5620-5628. (d) Kong, X.; Lam, J .
W. Y.; Tang, B. Z. Macromolecules 1999, 32, 1722-1730.
(26) (a) Voronkov, M. G.; Pukhnarevich, V. B.; Sushchinskaya,
S. P.; Annenkova, V. Z.; Annenkova, V. M.; Andreeva, N. J .
J . Polym. Sci., Polym. Chem. Ed. 1980, 18, 53-57. (b) Liaw,
D. J .; Soum, A.; Fontanille, M.; Parlier, A.; Rudler, H.
Makromol. Chem. Rapid Commun. 1985, 6, 309-313.
(27) Masuda, T.; Higashimura, T. Adv. Polym. Sci. 1987, 81, 121-
165.
(28) Xu, K.; Peng, H.; Sun, Q.; Dong, Y.; Salhi, F.; Luo, J .; Chen,
J .; Huang, Y.; Zhang, D.; Xu, Z.; Tang, B. Z. Macromolecules
2002, 35, 5821-5834 and references therein.
(29) Masuda, T.; Hamano, T.; Tsuchihara, K.; Higashimura, T.
Macromolecules 1990, 23, 1374-1380.
(30) (a) Masuda, T.; Tang, B. Z.; Tanaka, T.; Higashimura, T.
Macromolecules 1986, 19, 1459-1464. (b) Seki, H.; Tang, B.
Z.; Tanaka, A.; Masuda, T. Polymer 1994, 35, 3456-3462.
(31) Ginsburg, E. J .; Gorman, C. B.; Grubbs, R. H. In Modern
Acetylene Chemistry; Stang, P. J ., Diederich, F., Eds.; VCH:
New York, 1995; Chapter 10, pp 353-383.
(37) (a) Hidayat, R.; Fujii, A.; Ozaki, M.; Teraguchi, M.; Masuda,
T.; Yoshino, K. Synth. Met. 2001, 119, 597-598. (b) Sun, R.
G.; Zheng, Q. B.; Zhang, X. M.; Masuda, T.; Kobayashi, T.
J pn. J . Appl. Phys. 1999, 38, 2017-2023. (c) Wang, Y. Z.;
Sun, R. G.; Wang, D. K.; Swager, T. M.; Epstein, A. J . Appl.
Phys. Lett. 1999, 74, 2593-2595.
(38) (a) Lam, J . W. Y.; Luo, J .; Dong, D.; Cheuk, K. K. L.; Tang,
B. Z. Macromolecules 2002, 35, 8288-8299. (b) Tang, B. Z.;
Chen, H. Z.; Xu, R. S.; Lam, J . W. Y.; Cheuk, K. K. L.; Wong,
H. N. C.; Wang, M. Chem. Mater. 2000, 12, 213-221. (c)
Kong, X.; Wan, X.; Kwok, H. S.; Feng, X.-D.; Tang, B. Z. Chin.
J . Polym. Sci. 1998, 16, 185-192.
(39) (a) Tang, B. Z.; Lam, J . W. Y.; Luo, J , D.; Dong, Y.; Cheuk,
K. K. L.; Xie, Z.; Kwok, H.-S. Proc. SPIE 2001, 4463, 132-
138. (b) Tang, B. Z.; Lam, J . W. Y.; Kong, X.; Salhi, F.; Cheuk,
K. K. L.; Kwok, H. S.; Huang, Y. M.; Ge, W. Proc. SPIE 2000,
4107, 24-30. (c) Tang, B. Z.; Lam, J . W. Y.; Kong, X.; Lee, P.
P. S.; Wan, X.; Kwok, H. S.; Huang, Y. M.; Ge, W.; Chen, H.;
Xu, R.; Wang, M. Proc. SPIE 1999, 3800, 62-71.
(40) Bulovic, V.; Khalfin, V. B.; Gu, G.; Burrows, P. E.; Garbuzov,
D. Z.; Forrest, S. R. Phys. Rev. B 1998, 58, 3730-3740.
(41) Some of the best blue-emitting LEDs have exhibited maxi-
mum CE and ηEL values of 2.1 cd/A and 1.3%, respectively:
(a) Rees, I. D.; Robinson, K. L.; Holmes, A. B.; Towns, C. R.;
O’Dell, R. MRS Bull. 2002, 27, 451. (b) Palilis, L. C.; Lidzey,
D. G.; Redecker, M.; Bradley, D. D. C.; Inbasekaran, M.; Woo,
E. P.; Wu, W. W. Synth. Met. 2001, 121, 1729-1730. (c) J iang,
X. Z.; Liu, S.; Ma, H.; J en, A. K. Y. Appl. Phys. Lett. 2000,
76, 1813-1815.
(42) Rettig, W.; Baumann, W. In Progress in Photochemistry and
Photophysics; Rabek, J . F., Ed.; CRC Press: Boca Raton, FL,
1990; Vol. 6, Chapter 3, pp 79-134.
(43) (a) Morozumi, T.; Anada, T.; Nakamura, H. J . Phys. Chem.
B 2001, 105, 2923-2931. (b) Soujanya, T.; Fessenden, R. W.;
Samanta, A. J . Phys. Chem. 1996, 100, 3507-3512.
(44) (a) Rabek, J . F. Mechanisms of Photophysical Processes and
Photochemical Reactions in Polymers: Theory and Applica-
tions; Wiley: New York, 1987. (b) Photonic Polymer Systems;
Wise, D. L., Wnek, G. E., Trantolo, D. J ., Cooper, T. M.,
Gresser, J . D., Eds.; Marcel Dekker: New York, 1998.
(45) (a) Wang, P. F.; Wu, S. K. J . Lumin. 1994, 62, 33-39. (b)
Wong, K. S.; Wang, H.; Lanzani, G. Chem. Phys. Lett. 1998,
288, 59-64. (c) Wong, K. S. Personal communication.
(46) Chen, J .; Law, C. C. W.; Lam, J . W. Y.; Tang, B. Z.
Unpublished results.
(32) Kunzler, J .; Percec, V. J . Polym. Sci., Polym. Chem. Ed. 1990,
28, 1221-1236.
(33) Optical Properties of Nanoparticles; Trager, F., Ed.; Springer-
Verlag: Berlin, 2001.
(34) (a) Tang, B. Z.; Xu, H. Macromolecules 1999, 32, 2569-2576.
(b) Tang, B. Z.; Peng, H.; Leung, S. M.; Au, C. F.; Poon, W.
H.; Chen, H.; Wu, X.; Fok, M. W.; Yu, N.-T.; Hiraoka, H.;
Song, C.; Fu, J .; Ge, W.; Wong, K. L. G.; Monde, T.; Nemoto,
F.; Su, K. C. Macromolecules 1998, 31, 103-108. (c) Tang,
B. Z.; Leung, S. M.; Peng, H.; Yu, N.-T.; Su, K. C. Macro-
molecules 1997, 30, 2848-2852.
(35) Suspensions of maghemite particles with sizes of a few tens
of nanometers in chloroform and water exhibited little
scattering-induced optical losses and showed “normal” ab-
sorption spectra. (a) Tang, B. Z.; Geng, Y.; Lam, J . W. Y.; Li,
(47) Li, Y.; Vamvounis, G.; Holdcroft, S. Macromolecules 2002,
35, 6900-6906.
(48) For a multigraph, see: An Introduction to Molecular Elec-
tronics; Petty, M. C., Bryce, M. R., Bloor, D., Eds.; Edward
Arnold: London, 1995.
MA0213504