Synthesis, characterization, and photoluminescence properties of asymmetrically substituted functional polysilanes bearing carbosilyl side chains, -[R(Me)Si]n- and -[R(Ph)Si]n- [R = (CH 2)xSiR′3; x =

Article abstract of DOI:10.1021/ma047847q

New unsymmetrical polysilanes, -[R¹(Me)Si]_n- (1-3), -[R²(Me)Si]_n- (4-6), and -[R²(Ph)-Si] _n- (7-9), bearing pendant sila-substituted alkyl groups of varying chain length [R¹: (CH

Full text of DOI:10.1021/ma047847q

4176
Macromolecules 2005, 38, 4176-4182
Synthesis, Characterization, and Photoluminescence Properties of
Asymmetrically Substituted Functional Polysilanes Bearing Carbosilyl
Side Chains, -[R(Me)Si]n- and -[R(Ph)Si]n- [R ) (CH2)xSiR′3;
x ) 2 or 3]
Ravi Shankar* and Arti Joshi
Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
Received October 18, 2004; Revised Manuscript Received March 2, 2005
ABSTRACT: New unsymmetrical polysilanes, -[R1(Me)Si]n- (1-3), -[R2(Me)Si]n- (4-6), and -[R2(Ph)-
Si]n- (7-9), bearing pendant sila-substituted alkyl groups of varying chain length [R1: (CH2)3Si≡; R2:
(CH2)2Si≡] have been synthesized by Wurtz coupling reaction. These polysilanes reveal a monomodal
molecular weight distribution with Mw in the range (237-31) × 103 for 1-6 and (2.9-2.3) × 103 for 7-9.
Stereochemical configuration of polysilane 2 has been deduced from a detailed analysis of 13C{1H} NMR
resonances of backbone Si-Me groups and suggests a predominantly atactic microstructure. UV absorption
spectra of polysilanes 1-3 (λmax: 303-317 nm; ꢀ: 2800-5900 (Si repeat unit)-1 dm3 cm-1) feature a
discernible bathochromic shift and higher extinction coefficient values in comparison to those observed
for analogous polysilanes 4-6 (λmax: 296-305 nm; ꢀ: 2000-3000 (Si repeat unit)-1 dm3 cm-1). These
results coupled with photoluminescence (PL) spectra indicate that electronic properties of these polysilanes
are influenced by the pendant sila-alkyl chain length as well as by steric effect of substituents on a silicon
atom. UV and PL emission and excitation spectral characteristics of phenyl-substituted polysilanes 7-9
1
provide evidence in favor of (σ-π*)CT charge-transfer phenomenon.
Introduction
The quasi-one-dimensional nature of polysilanes with
delocalized σ-conjugated electrons imparts photolumi-
nescence (PL) properties with high quantum efficiency,
usually in near-UV or UV region.1a,5d,8 In this respect,
poly(alkyl-arylsilane)s are found to differ from those
of poly(di-n-alkylsilane)s. For example, poly(methylphe-
nylsilane) exhibits a broad photoluminescent band in
the visible region (VPL), in addition to a strong excitonic
UV photoluminescence (UPL) at ca. 320 nm associated
with the σ-σ* transition.9,10 The origin of VPL is
generally ascribed to branching defects in the polymer
chain which can be caused by photodecomposition of the
polymer and insertion of silyl radicals in the backbone.
However, a detailed study of temperature-dependent
photoluminescence spectra of poly(methylphenylsilane)
has shown that the emission band in the visible region
During the past two decades, research interest in the
domain of polysilane chemistry has been largely focused
to understand their unique electronic and optical prop-
erties associated with σ conjugation in the catenated
silicon backbone.1 These intrinsic properties make pol-
ysilanes promising candidates for various applications
such as photoresists,2 optoelectronic devices,3 and non-
linear optical materials.4
The occurrence of σ-σ* electronic transition in pol-
ysilanes is manifested by an intense absorption in the
UV region (270-400 nm). It is now well established that
the energy of this electronic absorption has a strong
dependence on the conformational characteristics of
catenated silicon backbone. Significant influence of side-
chain alkyl/aryl substituents in tailoring conformational
features of the backbone structure and consequently its
optoelectronic properties are also well documented.1,5,9d
A distinct manifestation of this structure-property
relation appears from a number of interesting thermo-
chromic studies in symmetrically and asymmetrically
substituted poly(di-n-alkylsilane)s1,6 representing com-
positional formulas -[R2Si]n- and -[RR′Si]n- (R * R′
) alkyl), respectively. These polysilanes undergo either
a gradual (continuous) or an abrupt (discontinuous) shift
of the absorption band to longer wavelength as temper-
ature is lowered. A theoretical explanation of thermo-
chromic behavior in polysilanes has been put forth by
Schweizer.7 It has been suggested that dispersive
interactions of σ-delocalized electrons along the back-
bone with pendant side chains induce conformational
changes at variable temperatures, and the magnitude
of these interactions triggers a bathochromic shift in the
UV spectra.6d,g
1
(VPL) is attributed to polymer branching as well as -
(σ-π*)CT charge-transfer transitions.10 The disappear-
ance of the VPL band is executed in poly(alkylarylsi-
lane)s, -[R(Ph)Si]n- (R ) pentyl or higher alkyls) with
long chain alkyl substituents.9b,c It has been proposed
that steric effect of these groups favors decomposition
at the branching sites as a result of thermal reactions
and leads to linear polysilanes with minimal branching
defects.
Although extensive studies related to structure and
electronic properties of poly(di-n-alkylsilane)s have been
reported, much less attention has been devoted to
address the influence of heteroatom-substituted alkyl
chains bonded to skeletal silicon backbone. There are a
few previous reports that describe the synthesis of
polysilanes bearing polar ether linkage in the pendant
alkyl groups.11 These polysilanes exhibit interesting
physical and electronic properties which differ from
those of n-alkyl-substituted polysilane analogues. The
present paper describes synthesis and characterization
of new unsymmetrical polysilanes, -[R1(Me)Si]n- (1-
* Corresponding author. E-mail: shankar@netearth.iitd.ac.in.
10.1021/ma047847q CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/06/2005

Macromolecules, Vol. 38, No. 10, 2005
Polysilanes Bearing Carbosilyl Side Chains 4177
Scheme 1
are not discernible in the spectra of polysilanes 1-6 due
to their high molecular weights. The 1H NMR spectrum
(CDCl3, RT) of each polysilane reveals broad and
featureless signals associated with side chain methylene
protons while resonances due to silyl-substituted meth-
yl, ethyl, or phenyl groups are well resolved. A similar
spectral behavior is also observed in 13C{1H} NMR
spectra with the pendant silyl substituents featuring
relatively sharp resonances (see Experimental Section).
The spectral behavior shows a close analogy with those
of poly(methyl-n-alkylsilane)s,15 and the unresolved 1H
and 13C{1H} resonances of methylene groups may
accordingly be attributed to short spin-spin relaxation
time of these nuclei. 13C{1H} NMR spectra of polysilanes
2, 3, 6, and 7 reveal overlapped or closely spaced signals
for methylene carbons as well as for pendant and
backbone Si-Me groups. Unequivocal assignments of
these signals are made from DEPT-135 13C{1H} and
HSQC (1H-13C) NMR spectra, and the results are
summarized in the Experimental Section. A common
feature in the 29Si{1H} NMR spectra of polysilanes 1-3
and 6-9 is the appearance of a sharp singlet at δ 8.68
to -7.93 and a broad featureless signal at -25.89 to
-31.71. By analogy with the spectral data of the
precursor carbosilanes as well as related poly(methyl/
phenyl-n-alkylsilane)s,9c,15,16 the former chemical shift
value is ascribed to the carbosilyl side groups and the
latter to silicon backbone. For polysilanes 4 and 5, two
distinct 29Si{1H} NMR signals appear in the carbosilyl
region at δ 8.48, 7.84 and 0.42, -1.32, respectively, and
are corroborated with the presence of both R (minor) and
â (major) isomers in the precursor dichlorocarbosilanes.
The NMR spectral data coupled with GPC results
clearly indicate that all the polysilanes are devoid of
oligomeric/cyclic products.
Configurational Studies. In principle, unsymmetri-
cal polysilanes may adopt the isotactic (all meso, mm),
syndiotactic (all racemic, rr), or atactic (random, rm/
mr) configuration.17 It has been reported by Schilling
et al.15 that the stereochemical configuration of poly-
(methyl-n-alkylsilane)s can be estimated using 13C{1H}
NMR spectroscopy, since methyl groups bonded to the
skeletal backbone respond to configurational charac-
teristics. In the 13C{1H} NMR spectrum of polysilane
2, three closely spaced resonances at δ -3.62, -3.74,
and -3.92 due to Si-Me (backbone) are distinctly
observed and suggest the sensitivity of the nuclei toward
configurational sequence. Therefore, a detailed micro-
structure analysis of the polymer has been performed
by deconvolution of the spectral region (Figure 2). The
difference between actual and calculated spectra matched
within 1% error. The signal at δ -3.62 was tentatively
assigned to the rr stereodomain while the high field
resonances at δ -3.74 and -3.92 were subscribed to rm/
mr and mm stereodomains, respectively. On the basis
of deconvolution studies, the signal intensity of each
chemical shift region was deduced, and the intensity of
the triad domain (rr:rm/mr:mm) has been evaluated as
0.44:0.45:0.10. A good agreement between these values
and those predicted by Bernoullian statistics18 (0.46:
0.43:0.10) is observed with Pm ) 0.32 and Pr ) 0.68.
These results suggest that the polysilane adopts a
predominantly atactic configuration with a syndiotactic
bias. It is however imperative to mention that the
interchange in δ 13C assignments of rr and mm config-
uration will not affect the Bernoullian statistics but will
result in isotactic preference of the configuration. The
3), -[R2(Me)Si]n- (4-6), and -[R2(Ph)Si]n- (7-9) [
R1: (CH2)3Si≡; R2: (CH2)2Si≡] bearing pendant car-
bosilyl groups of varying alkyl chain length (Scheme 1).
These polymers can be regarded as analogues of exten-
sively studied poly(methyl-n-alkylsilane)s or poly(phe-
nyl-n-alkylsilane)s with the exception that the â- or
γ-carbon of the alkyl chains possesses sterically de-
manding sila-substituted groups. Since structural char-
acteristics of silaalkanes are known to differ from those
of corresponding n-alkanes,12 it was of interest to
examine the influence of pendant carbosilyl groups on
the electronic properties of these new polysilanes. The
results obtained from these studies are reported herein.
Results and Discussion
Synthesis and Characterization of Poly-
silanes, 1-9. Following the classical Wurtz coupling
method,1 reactions of dichlorocarbosilane precursors,
Me(RR2′SiCH2CH2CH2)SiCl2 (1a-3a), Me(RR2′SiCH2-
CH2)SiCl2 (4a-6a), or Ph(RR2′SiCH2CH2)SiCl2 (7a-9a)
[R, R′ ) Et, Me, or Ph], with sodium dispersion in
refluxing toluene afford a crude polymer in each case
having both low and high molecular weight fractions.
Effective separation of the corresponding high molecular
weight polysilanes 1-9 (Scheme 1) from the crude
mixture is accomplished by repeated fractional precipi-
tation using a toluene/2-propanol mixture. The forma-
tion of these polysilanes in low yield (5-15%) is not
unusual in view of the known limitations of the Wurtz
coupling method. Using this approach, it is generally
observed that sterically demanding monomers afford
low molecular weight polysilanes with poor yields.1a,9c,13
All the polysilanes obtained herein are either viscous
gums (1-6) or solids (7-9) and are soluble in common
organic solvents such as toluene, THF, hexane, chloro-
form, dichloromethane, benzene, etc. Thermogravimet-
ric analysis (TGA) reveals that these are stable up to
370-400 °C. However, subsequent weight loss is ob-
served in a continuous manner up to 500 °C, leaving a
residual yield of 7-18%. GPC analysis of these polysi-
lanes (Table 1) reveals a monomodal molecular weight
distribution in each case with Mw ranging between
(237-31) × 103 for 1-6 and (2.9-2.3) × 103 for 7-9. A
representative GPC profile of polysilane 2 is shown in
Figure 1. The chemical composition of each polymer has
been elucidated by IR and multinuclear NMR studies.
A notable feature in the IR spectra of polysilanes 7-9
is the appearance of a weak intensity band at 2083-
2090 cm-1 due to νSiH end groups. By analogy with
earlier reports,14 the formation of Si-H groups during
Wurtz coupling is attributed to abstraction of hydrogen
from the solvent by silyl radicals. However, these groups

4178 Shankar and Joshi
Macromolecules, Vol. 38, No. 10, 2005
Table 1. UV/Photoluminescent Spectral Data and GPC Characteristics of Polysilanes 1-9
d
polysilane
UVa λmax/ꢀ/fwhm
PL(emission)b λmax(nm)/fwhm
PL(excitation)cλmax(nm)
Mw × 10-3
PDIe
yield (%)f
1
2
3
4
5
6
7
303/2800/34
314/5900/36
317/5800/34
296/2000/38
304/3000/30
305/2500/30
325/1900/26
265
321/2400/24
262
325/2100/29
265
336/22
336/22
85
237
119
1.76
123
146
2.8
1.64
1.82
1.57
5.1
1.77
1.55
1.30
6.3
7.2
10
31
336/25
330/25
354/28
368/30
354/28
358/30
360/34
370/36
9.8
11.7
8.8
(258, 285, 324)cx
(260, 298)cy
8
9
(256, 280, 331)cx
(258, 280, 320)cy
(260, 283, 322)cx
(262, 290)cy
2.9
2.3
1.30
1.18
5.8
12.5
a ꢀ units: (Si repeat unit)-l dm3 cm-1; λmax units: nm; fwhm ) full width (nm) at half-maximum of λmax b Peak position in emission
.
spectrum. c Peak position in excitation spectrum (cxmonitored at 370 nm; cy470 nm). d Molecular weights determined by GPC relative to
polystyrene standards; eluant: THF; 25 °C. e PDI ) polydispersity index (Mw/Mn). f Isolated yield of high molecular weight fraction.
Figure 1. GPC profile of -[Ph2MeSiCH2CH2CH2SiMe]n- (3).
Figure 3. UV spectra (THF, RT) of polysilanes 1-6.
quite typical of poly(methyl-n-alkylsilane)s.1,5b,6c How-
ever, a close examination of these results reveal a few
notable features. The spectra of polysilanes 2 and 3
bearing a PhMe2Si/Ph2MeSi group on the pendant alkyl
chains exhibit λmax values at higher wavelengths (314,
317 nm) with considerable increase in UV absorptivity
(ꢀ: 5900, 5800 (Si repeat unit)-1 dm3 cm-1) when
compared with similar parameters of the corresponding
Et3Si-substituted polysilane 1 (λmax: 303 nm; ꢀ: 2800
(Si repeat unit)-1 dm3 cm-1). A similar dependence of
the spectral properties on the sila substituents is also
seen in polysilanes 4-6, though the effect appears to
be much less pronounced. A plausible explanation for
this apparently low response of substituent effect on the
spectral variations can be made by a close inspection of
the spectral data of analogous polysilanes 1, 4, 2, 5, and
3, 6 which possess identical silyl groups but differ with
respect to the pendant alkyl chain length. Interestingly,
a considerable increase in the absorption maxima and
absorptivity values is observed in polysilanes 1-3
bearing pendant CH2CH2CH2 groups in comparison to
those observed for corresponding polysilanes 4-6 which
possess CH2CH2 groups in the carbosilyl chain. On the
basis of these results, it is thus reasonable to conclude
that the electronic properties of these polysilanes are
sensitive not only to steric influence of the pendant sila
substituents but also to the alkyl chain length of
carbosilyl groups.
Figure 2. Partial 13C{1H}NMR spectrum of -[PhMe2SiCH2-
CH2CH2SiMe]n- (2) depicting Si-Me (backbone) region: (a)
spectrum (solid line) and calculated spectrum (dotted line); (b)
difference between actual and calculated spectrum.
results are in accord with those observed earlier for
poly(di-n-alkylsilane)s prepared by Wurtz coupling
method.15,19 Unfortunately, configurational analysis for
polysilanes 1, 3, and 6 could not be made due to either
broadening or overlapping of signals associated with
pendant and/or backbone Si-Me groups, while similar
studies for 4 and 5 are precluded due to presence of R
and â isomeric mixtures.
UV and Photoluminescence Spectra. UV and
photoluminescence spectral studies of polysilanes 1-6
have been performed to gain insight into the electronic
properties associated with σ-delocalized silicon back-
bone. The UV absorption spectra (THF, RT) of these
polysilanes are shown in Figure 3, and the relevant data
are summarized in Table 1. As expected, the observed
spectral characteristics such as absorption maxima,
absorptivity, and full width at half-maxima values are
The UV spectral behavior of a number of polysilanes
bearing linear and/or branched alkyl chains have been
extensively studied in the past. It has been observed

Macromolecules, Vol. 38, No. 10, 2005
Polysilanes Bearing Carbosilyl Side Chains 4179
Figure 4. UV and PL spectra (THF, RT) of -[PhMe2SiCH2-
CH2CH2SiMe]n- (2).
that the absorption maxima are quite sensitive to
distinguish low molecular weight linear/cyclic oligomers
from high molecular weight polysilanes. Nevertheless,
the spectral parameter remains almost constant as the
degree of polymerization attains a critical value.1a In
polysilanes 1-6, this effect appears to be of much less
significance in view of their high molecular weights. In
addition, there exists a significant correlation between
the global conformations of polysilanes and their UV
absorption behavior. Depending on the nature of pen-
dant substituents, poly(di-n-alkylsilane)s are known to
adopt varying conformations which are generally clas-
sified as shrink coil, flexible coil, stiff, or rigid-rod-like
structures.5b This substituent effect is apparently due
to steric interference between pendant groups either 1,2
or 1,3 to each other which can result in the change of
equilibrium content of trans and gauche conformations
in the silicon backbone. In accordance with these trends,
the spectral behavior of polysilanes 1-6 appear to
correspond to a more likely random coil conformation.
For polysilanes 2 and 3, the higher values of absorption
maxima and increased absorptivity may result from a
cumulative effect of the long alkyl chain and steric
influence of the silyl substituents which impart more
extended trans conformation to the silicon backbone in
solution. Further elaboration of the electronic behavior
of polysilanes 1-6 has been made from photolumines-
cence spectra. The UV and PL spectra (THF, RT) for
polysilane 2 are shown in Figure 4 as an illustration.
As evident from Table 1, PL spectral characteristics of
the polysilanes 1, 2 and 5, 6 are quite similar and are
reminiscent of the Stokes shift of 22-33 nm with full
width at half-maxima corresponding to 22-25 nm. In
addition, the observed emission profiles are not mirror
images of the corresponding UV absorption spectra.
These results resemble closely with those of unsym-
metrical poly(methyl-n-alkylsilane)s5b,d which are known
to adopt random coil conformational features in solution.
The UV and PL spectra of polysilanes 7-9 bearing
phenyl groups on the silicon backbone differ signifi-
cantly from those of methyl-substituted polysilane
analogues, 4-6. The UV spectrum of each polymer
typically shows two absorptions with λmax at 321-325
and 262-265 nm which are attributed to σ-σ* transi-
tion of silicon backbone and π-π* transition of phenyl
Figure 5. UV and PL spectra (THF, RT) of -[PhMe2SiCH2-
CH2SiPh]n- (8): (a) excitation λmax ) 315 nm; (b) excitation
λmax ) 260 nm.
ring, respectively. The photoluminescence spectra reveal
a narrow band at 354-370 nm, which tails in the visible
region (VPL) with an edge at ca. 500 nm (Figure 5). It
is noteworthy that intensity of the VPL band is weak-
ened upon using 315 nm as the excitation wavelength
(σ-σ* transition) in comparison to that obtained with
the excitation at λex ) 260 nm (π-π*). Similar results
have been reported earlier for a number of poly(phenyl-
n-alkylsilane)s, and the origin of the VPL band has been
correlated with the presence of branching defects caused
by photodecomposition of the polymer and insertion of
resulting silylene radicals into the backbone.9,10 Such
structural defects in the silicon chain have also been
substantiated by the appearance of additional 29Si NMR
signals around δ -35 and -45. However, an examina-
tion of 29Si{1H} NMR spectra of polysilanes 7-9 does
not reveal additional signals associated with branched
chains. It is believed that the low concentration of
branching defects, if present in these polysilanes, may
have eluded detection on the NMR scale.
An alternate explanation for the origin of VPL band
involving charge transfer state 1(σ-π*)CT has also been
put forth by a detailed study of the excitation spectra

4180 Shankar and Joshi
Macromolecules, Vol. 38, No. 10, 2005
branching defects in the backbone has not been com-
pletely ruled out. These polysilanes are interesting
candidates to explore the functional group chemistry
since silicon atoms associated with backbone as well as
pendant carbosilyl chain can be utilized for chemical
modification. This aspect is currently being investigated.
Experimental Section
General Comments. All operations were carried out using
standard Schlenk line techniques under a dry nitrogen atmo-
sphere. Solvents were freshly distilled under inert atmosphere
over sodium benzophenone (tetrahydrofuran, toluene) or mag-
nesium (alcohols) before use. Glasswares were dried in an oven
at 100-120 °C and further flame-dried under vacuum prior
to use. Dichloromethylvinylsilane and allyldichloromethylsi-
lane (Aldrich) were freshly distilled over magnesium. Karstedt’s
catalyst (platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisilox-
ane complex), triethylsilane, phenyldimethylsilane, and diphe-
nylmethylsilane (Aldrich) were used as received. Literature
method was used to prepare PhVinSiCl2.20
Infrared spectra were obtained as thin films on KBr pellets
on a Nicolet FT-IR (Prote´ge´) spectrophotometer. UV and
photoluminescence spectra were recorded on a Perkin-Elmer
(Lambada Bio 20) spectrophotometer and a Hitachi F-850
spectrofluorometer, respectively. Molecular weights of the
polysilanes were estimated using a Waters 510 liquid chro-
matograph equipped with a Varian 400 refractive index
detector and a Waters Styragel HR3 and HR4 column in series.
The chromatograph was calibrated with polystyrene stan-
dards, and THF was used as eluent. 1H, 13C{1H}, and 29Si-
{1H} NMR spectra were recorded in CDCl3 on a Bruker
spectrospin DPX 300 MHz instrument at frequency 300, 75.5,
and 59.6 MHz, respectively, and chemical shifts are quoted
relative to Me4Si. 13C{1H} NMR spectra in DEPT-135 mode
were obtained using a standard pulse sequence with J
modulation time 3.7 ms and 2 s delay time. HSQC (1H-13C)
spectra were recorded using a standard pulse sequence with
a relaxation delay of 2 s for each of the 512t1 experiments.
Deconvolution was done using the peak fitting module of X
Win NMR 1.3 by a Bruker spectrospin. Thermogravimetric
analysis of polysilanes 1-9 was carried out in a N2 atmosphere
between 30 and 800 °C at a heating rate of 10 °C/min on a
Perkin-Elmer thermal analysis system.
Figure 6. Excitation spectra of -[PhMe2SiCH2CH2SiPh]n-
(8) monitored for UPL at 370 nm (solid line) and VPL at 470
nm (dotted line).
of poly(methylphenylsilane) thin films monitored at low
temperatures.10 In line with these findings, the excita-
tion spectra of polysilanes 7-9 have been studied to
further elaborate the results of PL spectra. As shown
in Figure 6, the excitation spectrum of polysilane 8
monitored at λmax ) 370 nm (UPL) reveals three distinct
optical transitions at 256, 280, and 331 nm. While the
peaks at 256 and 331 nm are similar to those observed
in the absorption spectrum, the band at 280 nm shows
a new appearance. Significantly, the excitation spectrum
of VPL monitored at λmax ) 470 nm also exhibits these
transitions. The spectra of polysilanes 7 and 9 reveal a
similar profile as that of 8 except that the excitation
monitored at 470 nm shows a considerable broadening
of the band at 290-298 nm. The appearance of new
band at 280-298 nm in both the UPL and VPL has not
been clearly understood, although the results are in
accord with recent photoluminescence studies of poly-
(methylphenylsilane) by Nesˇpu˚rek et al.10 These authors
have proposed that the origin of the new band can be
associated with the formation of interchain charge
Synthesis of the Carbosilane Precursors 1a-9a. These
carbosilanes were prepared by following the hydrosilylation
approach.21 To a stirred solution of allyldichloromethylsilane
(11.71 g, 11 mL, 75.5 mmol) containing a catalytic amount of
Karstedt’s catalyst (10-7 Pt/mol of silane), triethyl/phenyldim-
ethyl/diphenylmethylsilane (75 mmol) was added dropwise at
room temperature. Though the reaction mixture turned pale
yellow after a few milliliters of hydrosilane was added, no
induction period was observed during the complete addition.
The reaction mixture was heated at 100 °C for 12 h, and the
product obtained in each case was fractionally distilled to
obtain the corresponding carbosilanes 1a-3a. The carbosilanes
4a-6a and 7a-9a are obtained by following a similar proce-
dure by reacting equimolar quantities of dichloromethylvinyl-
silane or dichlorophenylvinylsilane with the corresponding
hydrosilanes. These carbosilanes are hitherto unknown and
have been characterized by IR and multinuclear NMR studies.
The relevant spectroscopic data are presented below. For
assigning the NMR spectral data, the methylene group at-
tached to the SiCl2 moiety is represented with the notation
R-, and subsequent groups are designated with â- and γ-
notations.
1
transfer state (σ-σ*)CT which is located at a higher
energy than Frenkel exciton and its relaxation to
1
intermolecular (σ-π*)CT charge transfer state.
Conclusions
Synthesis of unsymmetrical polysilanes of the com-
position -[R1(Me)Si]n- (1-3), -[R2(Me)Si]n- (4-6), and
-[R2(Ph)Si]n- (7-9), bearing sila-substituted alkyl
chains (R1: (CH2)3Si≡; R2: (CH2)2Si≡), has been achieved
using Wurtz coupling reaction of the corresponding
dichlorocarbosilane precursors. UV and photolumines-
cence (emission) spectral studies of polysilanes 1-6
reveal a marked dependence of σ-σ* electronic transi-
tion on the steric effect of silyl groups as well as alkyl
chain length associated with pendant carbosilyl moiety.
A detailed examination of UV and PL (emission and
excitation) spectra of phenyl-substituted polysilanes
7-9 indicates that the origin of photoluminescent band
in the visible region (VPL) can result from the 1(σ-π*)CT
charge-transfer state, although the contribution of
Et3SiCH2CH2CH2SiMeCl2 (1a) (bp 104-106 °C/5 mmHg,
1
yield 60%). H NMR: δ 1.52-1.41 (m, 2H, â-CH2), 1.17-1.11
(m, 2H, R-CH2), 0.86 (t, 3JH-H ) 7.6 Hz, 9H, CH3-Et), 0.70 (s,
3
3H, SiMeCl2), 0.59-0.53 (m, 2H, γ-CH2), 0.45 (q, JH-H ) 7.9
Hz, 6H, CH2-Et). 13C{1H} DEPT-135 NMR: δ 26.31 (â-CH2),
17.50 (R-CH2), 15.31 (γ-CH2), 7.65 (CH3-Et), 5.63 (SiMeCl2),
3.45 (CH2-Et). 29Si{1H} NMR: δ 7.17 (Et3Si), 32.69 (SiMeCl2).
PhMe2SiCH2CH2CH2SiMeCl2 (2a) (bp 140-142 °C/5
mmHg, yield 83%). 1H NMR: δ 7.41-7.27 (m, 5H, SiPh), 1.49-

Macromolecules, Vol. 38, No. 10, 2005
Polysilanes Bearing Carbosilyl Side Chains 4181
1.43 (m, 2H, â-CH2), 1.14-1.06 (m, 2H, R-CH2), 0.82-0.76 (m,
2H, γ-CH2), 0.65 (s, 3H, SiMeCl2), 0.20 (s, 6H, PhMe2Si). 13C-
{1H} DEPT-135 NMR: δ 134.15, 129.34, 128.59 (SiPh), 26.36
(â-CH2), 19.12 (R-CH2), 17.61 (γ-CH2), 5.68 (SiMeCl2), -3.48
(PhMe2Si). 29Si{1H} NMR: δ -2.73 (PhMe2Si), 32.80 (SiMeCl2).
Ph2MeSiCH2CH2CH2SiMeCl2 (3a) (bp 160-165 °C/
-[PhMe2SiCH2CH2CH2SiMe]n- (2). 1H NMR: δ 7.34, 7.17
(br, 5H, SiPh), 1.25 (br, 2H, â-CH2), 0.70 (br, 4H, R- and γ-CH2),
0.13 (s, 6H, PhMe2Si), 0.03 (s, 3H, SiMe). 13C{1H} DEPT-135
NMR: δ 134.94, 129.27, 128.22 (SiPh), 21.84 (â- and γ-CH2),
20.16 (R-CH2), -2.62 (PhMe2Si), -3.62, -3.74, -3.92 (SiMe).
29Si{1H} NMR: δ -1.18 (s, PhMe2Si), -26.31 (br, SiMe).
-[Ph2MeSiCH2CH2CH2SiMe]n- (3). 1H NMR: δ 7.47, 7.26
(br, 10H, SiPh), 1.40 (br, 2H, â-CH2), 1.10 (br, 2H, γ-CH2), 0.82
(br, 2H, R-CH2), 0.53 (s, 3H, Ph2MeSi), 0.02 (br, 3H, SiMe).
13C{1H} DEPT-135 NMR: δ 134.57, 129.32, 128.03 (SiPh),
21.66 (â-CH2), 19.97 (R- and γ-CH2), -3.96 (Ph2MeSi), -4.12
(SiMe). 29Si{1H} NMR: δ -7.93 (s, Ph2MeSi), -25.89 (br,
SiMe).
1
5 mmHg, yield 75%). H NMR: δ 7.61-7.40 (m, 10H, SiPh),
1.79-1.62 (m, 2H, â-CH2), 1.31-1.24 (m, 4H, R- and γ-CH2),
0.77 (s, 3H, SiMeCl2), 0.65 (s, 3H, Ph2MeSi). 13C{1H} DEPT-
135 NMR: δ 134.75, 129.39, 128.23 (SiPh), 25.97 (â-CH2),
17.95 (R-CH2), 17.61 (γ-CH2), 5.70 (SiMeCl2), -4.10 (Ph2MeSi).
29Si{1H} NMR: δ -6.92 (Ph2MeSi), 32.79 (SiMeCl2).
Et3SiXSiMeCl2 (4a) [X ) CH2CH2; CHCH3] (bp 95-100
°C/5 mmHg, yield 85%; product obtained as isomeric mixture
in the ratio 92:8%). 1H NMR: δ 1.24 (d, CH-CH3), 1.03-0.94
-[Et3SiXSiMe]n- (4) [X ) CH2CH2; CHCH3]. The CHCH3
1
group has eluded detection in H and 13C{1H } NMR spectra.
(m, CH3-Et + R-CH2 + SiMeCl2), 0.66-0.52 (m, â-CH2
+
However, its presence in the polymer is reminiscent of the 29
-
CH2-Et), 0.84 (s, SiMeCl2), 0.40 (m, Si-CHCH3). 13C{1H}
DEPT-135 NMR: δ 15.68 (CH-CH3), 14.69 (R-CH2), 13.43 (â-
CH2), 7.58 (C-CH3), 7.52 (CH3-Et), 4.38, 4.67 (SiMeCl2), 2.91,
2.27 (CH2-Et). 29Si{1H} NMR: δ 8.84, 7.88 (Et3Si), 33.15,
32.58 (SiMeCl2).
Si{1H} NMR studies. 1H NMR: δ 0.95 (t, 3JH-H ) 7.7 Hz, 9H,
CH3-Et), 0.42-0.57 (br, 10H, R- and â-CH2 + CH2-Et), 0.06
(s, 3H, Si-Me). 13C{1H} DEPT-135 NMR: δ 9.91 (R-CH2), 8.98
(â-CH2), 7.63 (CH3-Et), 4.24 (CH2-Et), -4.85 (Si-Me). 29Si-
{1H} NMR: δ 8.48, 7.84 (s, Et3Si), -27.82 (br, Si-Me).
-[PhMe2SiXSi]n- (5) [X ) CH2CH2; CHCH3]. The CHCH3
PhMe2SiXSiMeCl2 (5a) [X ) CH2CH2 ; CHCH3] (bp 95-
97 °C/5 mmHg, yield 75%, product obtained as isomeric
mixture in the ratio 93:7%). 1H NMR: δ 7.49-7.33 (m, SiPh),
1.19 (d, CHCH3), 1.00-0.95 (m, R-CH2), 0.82-0.78 (m, â-CH2),
0.71, 0.64 (s, SiMeCl2), 0.28, 0.22 (s, PhMe2Si), 0.13 (m,
CHCH3).13C{1H} DEPT-135 NMR: δ 134.32, 129.87, 128.65
(Si-Ph), 15.32 (R-CH2), 14.27 (CH-CH3), 7.51 (â-CH2), 6.69
(C-CH3), 5.12, 4.97 (SiMeCl2), -2.51, -2.86 (PhMe2Si). 29Si-
{1H} NMR: δ -0.76, -1.20 (PhMe2Si), 33.64, 32.33 (SiMeCl2).
Ph2MeSiCH2CH2SiMeCl2 (6a) (bp 140-145 °C/5 mmHg,
1
group has eluded detection in H and 13C{1H} NMR spectra.
However, its presence in the polymer is reminiscent of the 29
-
Si{1H} NMR studies. 1H NMR: δ 7.49, 7.28 (br, 5H, SiPh),
0.85 (br, 4H, R- and â-CH2), 0.26 (s, 6H, PhMe2Si), 0.03 (s, 3H,
SiMe). 13C{1H} DEPT-135 NMR: δ 134.23, 128.68, 127.46 (Si-
Ph), 10.48 (â-CH2), 9.23 (R-CH2), 2.95 (PhMe2Si), -5.12 (Si-
Me). 29Si{1H} NMR: δ 0.42, -1.32 (s, PhMe2Si), -27.75 (br,
SiMe).
-[Ph2MeSiCH2CH2SiMe]n- (6). 1H NMR: δ 7.39, 7.21 (br,
10H, SiPh), 0.88 (br, 2H, â-CH2), 0.72 (br, 2H, R-CH2), 0.43 (s,
3H, Ph2MeSi), 0.06 (br, 3H, SiMe). 13C{1H} DEPT-135 NMR:
δ 134.29, 128.95, 127.63 (Si-Ph), 9.66 (â-CH2), 6.94 (R-CH2),
-4.72 (Ph2MeSi), -5.06 (SiMe). 29Si{1H} NMR: δ -6.53 (s, Ph2-
MeSi), -27.65 (br, SiMe).
1
yield 70%). H NMR: δ 7.57-7.28 (m, 10H, SiPh), 1.24-1.15
(m, 2H, R-CH2), 1.12-1.03 (m, 2H, â-CH2), 0.67 (s, 3H,
SiMeCl2), 0.49 (s, 3H, Ph2MeSi). 13C{1H} DEPT-135 NMR: δ
134.63, 129.61, 128.65 (Si-Ph), 14.72 (R-CH2), 5.61 (â-CH2),
4.57 (SiMeCl2), -4.78 (Ph2MeSi). 29Si{1H} NMR: δ -5.35 (Ph2-
MeSi), 33.56 (SiMeCl2).
-[Et3SiCH2CH2SiPh]n- (7). 1H NMR: δ 7.19 (br, 5H, Si-
Ph), 0.96-0.62 (br, 10H, R- and â-CH2 + CH2-Et), 0.53 (br,
9H, CH3-Et). 13C{1H} DEPT-135 NMR: δ 135.37, 127.31 (br,
Si-Ph), 7.94 (CH3-Et), 2.51 (R- and â-CH2 + CH2-Et). 29Si-
{1H} NMR: δ 8.68 (s, Et3Si), -31.36 (br, SiPh).
Et3SiCH2CH2SiPhCl2 (7a) (bp 145-147 °C/5 mmHg, yield
53%). 1H NMR: δ 7.77-7.49 (m, 5H, SiPh), 1.28-1.22 (m, 2H,
R-CH2), 0.98-0.93 (t, 3JH-H ) 7.7 Hz, 9H, CH3-Et), 0.72-0.66
3
(m, 2H, â-CH2), 0.61-0.53 (q, JH-H ) 7.3 Hz, 6H, CH2-Et).
13C{1H} DEPT-135 NMR: δ 133.70, 131.73, 128.52 (Si-Ph),
-[PhMe2SiCH2CH2SiPh]n- (8). 1H NMR: δ 7.50 (br, 10H,
SiPh), 0.78 (br, 4H, R- and â-CH2), 0.32 (s, 6H PhMe2Si). 13C-
{1H} DEPT-135 NMR: δ 136.22, 134.16, 129.19, 128.14 (SiPh),
13.64 (â-CH2), 7.82 (R-CH2), -3.14 (PhMe2Si). 29Si{1H} NMR:
δ -1.48 (s, PhMe2Si), -30.72 (br, SiPh).
13.86 (R-CH2), 7.50 (CH3-Et), 3.04 (CH2-Et), 2.42 (â-CH2). 29
-
Si{1H} NMR: δ 9.73 (Et3Si), 20.21 (SiPhCl2).
PhMe2SiCH2CH2SiPhCl2 (8a) (bp 176-180 °C/5 mmHg,
1
yield 67%). H NMR: δ 7.73-7.39 (m, 10H, SiPh), 1.29-1.23
-[Ph2MeSiCH2CH2SiPh]n- (9). 1H NMR: δ 7.55 (br, 15H,
SiPh), 0.75 (br, 4H, R- and â-CH2), 0.40 (s, 3H, Ph2MeSi). 13C-
{1H} DEPT-135 NMR: δ 135.48, 129.91, 127.46 (Si-Ph), 13.73
(m, 2H, R-CH2), 0.94-0.89 (m, 2H, â-CH2), 0.33 (s, 6H, PhMe2-
Si). 13C{1H} DEPT-135 NMR: δ 133.81, 133.69, 131.75, 129.34,
128.51, 128.10 (SiPh), 13.86 (R-CH2), 7.06 (â-CH2), -3.31
(PhMe2Si). 29Si{1H} NMR: δ 0.11 (PhMe2Si), 20.34 (SiPhCl2).
Ph2MeSiCH2CH2SiPhCl2 (9a) (bp 190-195 °C/5 mmHg,
(â-CH2), 7.02 (R-CH2), -3.67 (Ph2MeSi). 29Si{1H} NMR:
-5.63 (s, Ph2MeSi), -31.71 (br, SiPh).
δ
1
yield 70%). H NMR: δ 7.61-7.29 (m, 15H, SiPh), 1.21-1.10
(m, 4H, R- and â-CH2), 0.49 (s, 3H, Ph2MeSi). 13C{1H} DEPT-
135 NMR: δ 134.23, 133.16, 131.42, 130.03, 128.58, 128.16
(Si-Ph), 13.90 (R-CH2), 7.10 (â-CH2), -4.03 (Ph2MeSi). 29Si-
{1H} NMR: δ -6.94 (Ph2MeSi), 20.32 (SiPhCl2).
Acknowledgment. The authors are grateful to
C.S.I.R. (India) for financial support and S.R.F to A.J.
We thank Professor M. Fujiki and Dr. A. Saxena for
providing photoluminescence spectra as well as RSIC
(Chandigarh) and SIF Bangalore for 29Si{1H} NMR
data.
Preparation of Polysilanes 1-9. In a typical procedure,
freshly weighed sodium (1.00 g, 43.4 mmol) was transformed
to a fine dispersion in refluxing toluene under a dry nitrogen
atmosphere, and the dichlorocarbosilane precursors 1a-9a
(19.0 mmol) were added separately into it with the help of a
hypodermic syringe. The reaction mixture in each case turned
deep blue in color, and the contents were allowed to reflux at
110 °C for 4 h. The resulting solution was then filtered under
nitrogen, and the solvent was stripped of from the filtrate to
afford a crude polymer in each case. The corresponding high
molecular weight polysilanes were obtained as viscous gum
(1-6) or solid (7-9) by careful centrifugation of the crude
products using a toluene/2-propanol mixture.
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