Photorefractive properties of poly(siloxane)-triarylamine-based composites for high-speed applications

Article abstract of DOI:10.1021/jp027456i

The photorefractive properties of the hole-transporting polymer poly(methyl-bis-(3-methoxyphenyl)-(4-propylphenyl)amine)siloxane (MM-PSX-TAA) doped with the photorefractive chromophore 4-di(2-methoxyethyl) aminobenzylidene malononitrile (AODCST) are presented and compared with results obtained on similar composites based on poly(n-vinylcarbazole) (PVK). The low intrinsic T_g of the new polymer allows the preparation of samples without additional plasticizers. These composites exhibit good chromophore orientational mobility and exhibit photorefractive response times in the millisecond range, among the fastest reported to date.

Full text of DOI:10.1021/jp027456i

4732
J. Phys. Chem. B 2003, 107, 4732-4737
Photorefractive Properties of Poly(siloxane)-triarylamine-Based Composites for High-Speed
Applications
Daniel Wright,*,† Ulrich Gubler,‡ and W. E. Moerner
Department of Chemistry, Stanford UniVersity, Stanford, California 94305-5080
Michael S. DeClue§ and Jay S. Siegel
Department of Chemistry, UniVersity of CaliforniasSan Diego, La Jolla, California 92093-0340
ReceiVed: NoVember 13, 2002; In Final Form: March 13, 2003
The photorefractive properties of the hole-transporting polymer poly(methyl-bis-(3-methoxyphenyl)-(4-
propylphenyl)amine)siloxane (MM-PSX-TAA) doped with the photorefractive chromophore 4-di(2-meth-
oxyethyl) aminobenzylidene malononitrile (AODCST) are presented and compared with results obtained on
similar composites based on poly(n-vinylcarbazole) (PVK). The low intrinsic Tg of the new polymer allows
the preparation of samples without additional plasticizers. These composites exhibit good chromophore
orientational mobility and exhibit photorefractive response times in the millisecond range, among the fastest
reported to date.
1. Introduction
the Tg of the composite is close to room temperature. Unfor-
tunately, the intrinsic Tg of PVK is greater than 200 °C. Adding
the high concentration of chromophore needed for an efficient
composite depresses the Tg somewhat, but to obtain a Tg near
room temperature, an additional plasticizer is usually added.
This additional component occupies volume in the sample
without contributing to the photorefractive process directly. It
would be preferable to have this volume occupied by additional
nonlinear or charge-transporting moieties. Additionally, plas-
ticizers can affect the photorefractive dynamics because of
changes in the chromophore orientational mobility, the charge
trapping, or charge transport.6
Photorefractive materials have been studied because of their
potential applications in optical data storage and signal
processing.1-6 Organic photorefractive materials offer several
potential advantages over their inorganic and semiconducting
counterparts because of their low cost, ease of processability,
and chemical tunability. Current synthetic methods offer the
possibility to create a virtually unlimited number of organic
materials with varying properties, making possible the realization
of samples that meet all design requirements for a particular
application. Most of the research carried out in the field of
organic photorefractive materials has employed polymer com-
posites in which molecules incorporating all of the necessary
processes for photorefraction (charge generation, charge trans-
port, charge trapping, and optical nonlinearity) are doped into
a host polymer (which itself may provide one or more of the
aforementioned effects). The most commonly used host polymer
has been PVK, which acts as a host matrix and hole transporter.
PVK has many advantages including its commercial avail-
ability, the depth of study on the polymer, and its ability to
dissolve polar chromophores. Composites made with this
polymer have produced observations of gain coefficients ap-
proaching 400 cm-1,7 refractive index modulations (∆n) ap-
One of the more successful ways around these problems has
been to use a siloxane polymer with pendant carbazole groups,
usually referred to as PSX.10 The main merit of this polymer is
that it has similar hole-transport characteristics to those of
PVK11,12 with a lower intrinsic Tg, allowing the preparation of
samples with a room-temperature Tg without additional
plasticizer.13-15 In addition to enabling highly efficient photo-
refractive polymer composites, bifunctional systems in which
both the nonlinear optical chromophore and the charge-
transporting group are covalently bound to the siloxane back-
bone have been synthesized.16
proaching 10-2 8
, and diffraction efficiencies (η) of nearly
In addition to the plasticizer-related problems, PVK has a
relatively low hole mobility, on the order 10-7 cm2/V‚s.17,18
Organic hole-transporting materials with mobilities many orders
of magnitude larger have been reported in the literature;19 these
include tris-tolylamine (TTA), which when doped into poly-
carbonate yields mobilities up to 10-4 cm2/V‚s.20 Thus, the
possibility of greatly improving the response time of the
photorefractive effect may be possible with the substitution of
a better charge-transport agent. The combination of a better
charge-transport agent with a polymer that does not require
additional plasticizer could lead to an improved composite.
100%.1,4-6 Much of the progress in the field of organic
photorefractive materials has been accomplished with materials
using this polymer, but PVK also has several disadvantages, as
discussed in more detail below.
In light of the discovery of the “orientational enhancement”
effect,9 there is much to be gained in terms of index contrast if
* Corresponding author. E-mail: dan.wright@lpqm.ens-cachan.fr. Tel:
33 01 47 40 55 53. Fax: 33 01 47 40 55 67.
† Present address: Laboratoire de Photonique Quantique et Mole´culaire,
Ecole Normale Supe´rieure de Cachan, 61 avenue du Pre´sident Wilson, 94235
Cachan, France.
‡ Present address: CSEM Alpnach, Untere Gru¨ndlistrasse 1, CH-6055
Alpnach, Switzerland.
In an attempt to improve on the results obtained with PVK
and PSX, we have synthesized a new class of charge-transport
polymers based on a siloxane backbone with pendant triaryl-
§ Present address: Laboratorium fu¨r Organische Chemie, Swiss Federal
Institute of Technology, ETH Ho¨nggerberg, CH-8093, Zu¨rich, Switzerland.
10.1021/jp027456i CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/24/2003

Poly(siloxane)-triarylamine-Based Composites
J. Phys. Chem. B, Vol. 107, No. 20, 2003 4733
SCHEME 1: Synthesis of MM-PSX-TAA
Figure 1. Intensity dependence of the photo (open symbols) and dark
(filled symbols) conductivity for composites of PVK\AODCST\BBP\C60
(circles), MM-PSX-TAA\AODCST\C60 (30 wt % AODCST, triangles),
and MM-PSX-TAA\AODCST\C60 (15 wt % AODCST, squares). E )
20 V/µm, and λ ) 647 nm.
the velocity with which the charges move through the material,
and by trapping effects. Charge generation and transport are
reflected in the value of the photoconductivity σp, which in the
most basic (bulk, and assuming small absorption, RL , 1)
picture can be written as
ΦRIτ
hυ
σp ) neµ )
eµ
(1)
(
)
amine groups. This paper describes measurements made on these
polymers doped with the nonlinear optical chromophore
AODCST.
where n is the density of mobile charge carriers, e is the
elementary charge, µ is the mobility, Φ is the mobile charge
generation quantum efficiency, R is the absorption coefficient,
I is the optical intensity, τ is the lifetime of the carrier (the
length time that a charge moves before being trapped or
recombining), h is Planck’s constant, and ν is the frequency of
the light. In the standard model of photorefractivity,2,3 the rate
of space-charge field formation is governed in part of the
normalized response time tn ) τd, which is in turn proportional
to the dielectric relaxation time
2. Results and Discussion
MM-PSX-TAA (3) was synthesized on a multigram scale by
the method depicted in Scheme 1. A modified Ullmann
reaction21 was used to couple 4-bromoaniline to 3-iodoanisole
to provide the triarylamine core (1). Compound 1 was then
converted to the Grignard followed by a palladium-catalyzed
coupling with allyl bromide to provide compound 2. Compound
2 was then attached to commercially available poly(methylhy-
dro)siloxane using a platinum(II) catalyst to provide MM-PSX-
TAA (3). In addition to MM-PSX-TAA, this synthetic method
was applied to provide a small library of PSX-TAA materials.22
The additional methoxy groups were added to improve the
solubility of the matrix with polar chromophores. Composites
with this class of polymer could be made without the addition
of any plasticizer.
In general, when doped with a plasticizer and other dopants,
the Tg of the resulting composite can often be difficult to
measure.23 By contrast, a large reversible change in heat flow
is easily observed in the MM-PSX-TAA polymer and in
composites made with it. The pure MM-PSX-TAA polymer was
found to have a Tg of 25 °C, which is actually too low to be
used with the concentrations of chromophore normally employed
in photorefractive polymer composites. When 30 wt % of the
chromophore AODCST is doped into this polymer, the resulting
composite has a Tg near 0 °C. This low Tg leads to fast phase
separation of the chromophores in the polymer host and
dielectric breakdown at small electric-field strengths (E < 40
V/µm). To circumvent this problem, only 15 wt % of AODCST
was used in most of the experiments described below, which
results in a composite with a Tg of about 13 °C that has a greater
electric-field stability and shelf lifetime.
ꢀs
τd )
(2)
neµ
where ꢀs is the static dielectric constant of the material. We see
from eqs 1 and 2 that this characteristic time is nothing more
than the photoconductivity scaled by the static dielectric
constant. Thus, we can regard the value of σp as a measure of
the speed of the Esc formation.
The photoconductive properties of the composites made with
MM-PSX-TAA and PVK were examined with an applied field
of 20 V/µm, with the results shown in Figure 1. Composites
made with MM-PSX-TAA have a greater photoconductivity at
all of the intensities used in these experiments even though the
intensity dependence strongly deviates from the expected linear
dependence. One possible explanation for the sublinear intensity
dependence of the photoconductivity is that excess shallow traps
are present in the material.24 The photoconductivity is about 1
order of magnitude larger than the dark conductivity in the range
of intensities used in photorefractive experiments. A difference
of approximately a factor of 10 between the magnitude of the
dark and the photoconductivity is a prerequisite to establishing
the maximum space-charge field possible in response to
inhomogeneous illumination.
The overall speed of the space-charge field formation is
governed by the number of generated charges per unit time,
Transient ellipsometry experiments25 were used to quantify
the orientational characteristics of the chromophore in the new

4734 J. Phys. Chem. B, Vol. 107, No. 20, 2003
Wright et al.
Figure 4. Electric-field dependence of ∆n measured in degenerate four-
wave mixing experiments on composites of PVK\AODCST\BBP\C60
(filled circles) and MM-PSX-TAA\AODCST\C60 (15 wt % AODCST,
open circles). I ) 100 mW/cm2, and λ ) 647 nm.
Figure 2. Normalized transient ellipsometry curves taken at 905 nm
for composites of PVK\AODCST\BBP\C60 (circles), MM-PSX-
TAA\AODCST\C60 (30 wt % AODCST, triangles), and MM-PSX-
TAA\AODCST\C60 (15 wt % AODCST, squares). E ) 25 V/µm.
We examined this possibility by taking data on MM-PSX-TAA
composites doped with 30 wt % AODCST, which can also be
seen in Figure 3. As expected, the nonlinearity doubled
compared to that of the 15 wt % sample. However, the
difference in chromophore weight percent seems to account only
for part of the discrepancy because there still remains a factor
of about 2 compared to the PVK composite. This is particularly
perplexing because the MM-PSX-TAA composites doped with
30 wt % have a much lower Tg than the samples made with
PVK and thus should allow a greater orientation of the
chromophores. We have verified that PVK and BBP do not
significantly contribute to the birefringence in these composites
by performing transient ellipsometry experiments on samples
without nonlinear chromophores composed of only PVK\BBP.26
One possible explanation for the reduction in birefringence
is a reduction in the volume fraction of the chromophore that
could arise if the density of the new polymer were lower than
that of PVK. The reduction can also arise from the tendency of
strongly dipolar chromophores to order antiparallel with respect
to one another, thus forming chromophore aggregates that
provide no nonlinear optical effects.8 This effect will be more
pronounced in composites with lower Tg since the chromophores
have a greater ability to move in the host matrix. Another
possible consequence of the lower Tg is that such materials tend
to have higher dielectric constants because of their increased
ability to change their morphology to compensate a given
electric field.27 The greater electric-field screening in the material
can reduce the effect of the space-charge field on the chro-
mophores and thereby lower the change in refractive index.
The difference in nonlinearity observed in ellipsometric
experiments is also apparent when comparing steady-state
refractive index contrasts measured by degenerate four-wave
mixing. We see in Figure 4 that there is approximately a factor
of 3 difference in the value of ∆n within the field range of these
measurements.
Figure 3. Electric-field dependence of the quasi-steady-state (t ) 100
s) refractive index change as measured by transient ellipsometry taken
at 905 nm for composites of PVK\AODCST\BBP\C60 (circles), MM-
PSX-TAA\AODCST\C60 (30 wt % AODCST, triangles), and MM-PSX-
TAA\AODCST\C60 (15 wt % AODCST, squares).
composite. The results of these measurements are shown in
Figures 2 and 3. In Figure 2, we see the time dependence of
the normalized (to the quasi-steady-state value) ellipsometry
signal for the same samples as in Figure 1. We observe that the
orientation is much less dispersive for the MM-PSX-TAA as
compared to that of composites made with PVK. The chro-
mophores in the MM-PSX-TAA polymer orient in the 100-µs
to 100-ms time range. Chromophores orient faster in the
composite made with 30 wt % AODCST owing to its lower
Tg. These results contrast with those obtained with PVK-based
composite samples in which chromophore orientation takes place
over all of the time scales measurable by our setup.
In Figure 3, we compare the quasi-steady-state values (t )
100 s) of composites of MM-PSX-TAA doped with both 15
and 30 wt % AODCST as well as those for the PVK\AODCST\
BBP\C60 composite. We see that there is a reduction of the
quasi-steady-state magnitude of the nonlinearity by about a
factor of 3 in the MM-PSX-TAA polymer composites doped
with 15 wt % AODCST compared to the composite made with
PVK. These composites show a field dependence of the ∆n
that is close to the quadratic dependence expected for low-Tg
nonlinear optical polymers.
Another difference in the two polymers is the environment
that they provide for the charge generator C60. In both
composites, 0.5 wt % of the sensitizer was doped into the
composites, but the PSX composite had an absorption coefficient
of ∼30 cm-1 as compared to the ∼10 cm-1 value observed for
the PVK composite. The disparity in the absorption coefficient
between the two polymers may be due to a charge complex
between the TAA units and C6028 or the difference in the local
environment (most importantly arising from a variance of the
dielectric constant). The high absorption coefficient for MM-
The first possible explanation for the lower nonlinearity is
that it is simply due to the smaller chromophore concentration.

Poly(siloxane)-triarylamine-Based Composites
J. Phys. Chem. B, Vol. 107, No. 20, 2003 4735
cm2, making this system among the fastest organic photore-
fractive materials reported to date.
When we compare the speeds of the MM-PSX-TAA and PVK
composites, the PSX composite has about a factor of 3 greater
speed in the intensity range studied. In this comparison, it is
important to recall from eq 1 that the photoconductivity (σp)
and therefore the speed are proportional to the rate of generation
of mobile charges in the material and therefore to the absorption.
Consequently, to compare the performance of the different
composites, we normalize both the photoconductivity and speed
by dividing by the absorption coefficient of the sample. This
ensures that the possible differences that are observed are not
due to a different degree of charge generation caused simply
by a different level of absorption of the sensitizer. Since the
absorption is about 3 times larger for the MM-PSX-TAA
samples, the normalization accounts for the factor of 3 difference
in speed described above.
The lack of improvement in normalized speed can be due to
several factors. For one, we assumed that the mobility in the
MM-PSX-TAA system should be large on the basis of the
triphenylamine unit. Direct measurements of the mobility would
be needed to prove this assumption. Such measurements are
normally carried out with a time-of-flight apparatus19 and could
be the goal of future research. If the mobility is indeed found
to be larger, then this would point to a difference in the quantum
efficiency of charge generation or charge-trapping dynamics.
As mentioned above, the local environment of C60 seems to be
quite different in the MM-PSX-TAA polymer as compared to
that in PVK; this difference might also result in a difference in
quantum efficiency. One would need a separate measurement
of the quantum efficiency as well (for example, by xerographic
discharge measurements19) to test this hypothesis.
Figure 5. Electric-field dependence of the gain coefficient of
composites of PVK\AODCST\BBP\C60 (filled circles) and MM-PSX-
TAA\AODCST\C60 (15 wt % AODCST, open circles). I ) 100 mW/
cm2, and λ ) 647 nm. The solid (dotted) line represents the absorption
coefficient of the PVK\AODCST\BBP\C60 (MM-PSX-TAA\AOD-
CST\C60) sample.
3. Conclusions
In conclusion, this new class of polymers has several attractive
features when compared to the standard PVK, including no need
for additional plasticizers and possibly higher intrinsic hole
mobility. When doped with the chromophore AODCST and the
sensitizer C60, these composites exhibit grating growth times
in the millisecond range at moderate fields and intensities,
although the refractive index modulation that is obtained is lower
than with PVK composites with similar amounts of chro-
mophore. These composites could be further improved by using
the synthetic methods described in this work to attach other
moieties to the siloxane backbone. Forming multifunctional
polymers16 based on polysiloxane is another possible future
direction.
Figure 6. Intensity dependence of the two-beam coupling speed at an
applied electric field of 50 V/µm (filled circles) and of the photocon-
ductivity at an applied electric field of 20 V/µm (open squares) in a
MM-PSX-TAA\AODCST\C60 (15 wt % AODCST) composite. λ )
647 nm.
PSX-TAA samples, in conjunction with the lower nonlinearity
mentioned above, pushes the field required for net gain to around
55 V/µm in these samples. The field strength needed for net
gain in MM-PSX-TAA samples is rather high compared with
the field strength of 20 V/µm needed for the PVK composite.
The PR performance of these new materials should be improved
if samples with a higher weight percent of chromophore could
be prepared.
4. Experimental Section
Two-beam coupling measurements were performed over a
range of intensities at a constant applied electric field of 50
V/µm to characterize the gain dynamics. Empirical time
constants were obtained from the geometric average of double
NMR spectroscopy (1H and 13C) was recorded on a Varian
(Mercury 400 MHz) spectrometer. 1H NMR spectra were
referenced to tetramethylsilane (TMS) at 0.00 ppm. 13C NMR
spectra were referenced to 77.0 ppm in chloroform-d (CDCl3).
High-resolution mass spectra (HRMS) were obtained from the
University of California at Riverside’s mass spectrometry facility
in the fast atom bombardment (FAB) mode. Infrared (IR) spectra
were recorded on a Perkin-Elmer 1420 IR spectrophotometer.
Modulated differential scanning calorimetry (MDSC) mea-
surements were recorded using a TA Instruments 2920 MDSC
with a sample size ranging between 5 and 20 mg. The glass-
transition temperature (Tg) was determined from the inflection
point in the plot of heat flow versus temperature. The reversible
heat curves were generated at a temperature-rate increase of 4
°C/min.
a
b
exponential fits, thus τave ) τ1 × τ2 , where a and b are the
factional weights of each time constant. In Figure 6, the intensity
dependence of the geometrically averaged photorefractive speed
(1/τave) and the photoconductivity are compared. Both plots can
be fit well with a power law. The fits give the same exponent
within experimental error, suggesting that the speed is not
hindered by the orientation of the chromophores. This is also
reasonable from the ellipsometry data presented above, which
demonstrated that a significant portion (∼40%) of the orientation
takes place on time scales of less than 10 ms. The average time
constants falls below 10 ms for intensities above ∼600 mW/

4736 J. Phys. Chem. B, Vol. 107, No. 20, 2003
Wright et al.
Gel permeation chromatograph (GPC) was performed using
a Varian 9002 GPC analyzer with Pro Star 310 UV/vis and
Varian RI-4 detectors with Varian Star 5.3 system-control
software. A Phenogel 5µ linear column with 100-10 000K MW
range was used with HPLC-grade tetrahydrofuran (THF) at a
flow rate of 0.5 mL/min. Calibration was made with polystyrene
standards. All standards and samples were prepared at 1 mg/
mL in THF with an injection volume of 20 µL. Data analysis
was preformed using Polymer Laboratories PL Caliber Re-
analysis version 7.04.
phine)palladium(0) (1.0 g, 0.9 mmol) was added followed by
allyl bromide (3.0 mL, 34.8 mmol). This mixture was stirred at
room temperature overnight. Next, the reaction was quenched
by the slow addition of water (50 mL). The mixture was then
extracted using CH2Cl2 (3 × 100 mL). All CH2Cl2 layers were
combined, dried over MgSO4, filtered, and evaporated under
reduced pressure to yield a crude tan oil. Purification via flash
chromatography with silica as the absorbent (100% hexanes,
gradient to a mixture of CH2Cl2/hexanes, 2:3 v/v) yielded a clear
oil. (4.2 g, 70%). 1H NMR (400 MHz, CDCl3): δ 3.35 (d, J )
6.8 Hz, 2H), 3.72 (s, 6H), 5.05-5.13 (m, 2H), 5.92-6.03 (m,
1H), 6.54 (dd, J ) 8.4, 2.0 Hz, 2H), 6.60-6.68 (m, 4H), 6.99-
7.17 (m, 6H). 13C NMR (100 MHz, CDCl3): δ 39.73, 55.26,
107.69. 109.58, 115.60, 116.26, 124.94, 129.19, 129.54, 134.80,
137.35, 145.34, 148.84, 160.11. HRMS-FAB+ m/z: found
345.1742; calcd (C23H23NO2) 345.1729.
Techniques and Materials. All syntheses were carried out
under argon in freshly distilled solvents under anhydrous
conditions unless otherwise noted. Commercial chemicals were
acquired from Sigma-Aldrich with the exception of dichlorodi-
cyclopentadienyl platinum(II) that was obtained from Strem
Chemicals, Inc. All commercial chemicals were used as supplied
unless otherwise stated. Tetrahydrofuran (THF) was distilled
from sodium/benzophenone; toluene was distilled from calcium
hydride. Silica gel (230-425 mesh) for flash chromatography
was purchased from Fisher Scientific Company. Thin-layer
chromatography (TLC) was performed on aluminum-backed
silica gel 250-µm F254 plates from Whatman.
4-Bromophenyl-bis(3-methoxyphenyl) amine (1). The pro-
cedure was adapted from Goodbrand.21 To a 500-mL two-
necked round-bottom flask equipped with a Dean-Stark trap,
condenser, gas inlet, stir bar, and glass stopper was added
toluene (60 mL), 4-bromoaniline (3.8 g, 22.3 mmol), 3-iodoani-
sole (5.85 mL, 49.1 mmol), copper(I) chloride (180 mg, 1.8
mmol), 1,10-phenanthroline (325 mg, 1.8 mmol), and potassium
hydroxide (21.5 g, 385 mmol) under a flow of argon. This
mixture was heated to reflux (125-130 °C) overnight. Then
the reaction was cooled to room temperature. The cooled
reaction was then diluted with water (75 mL) and extracted with
CH2Cl2 (3 × 100 mL). All CH2Cl2 layers were combined, dried
over MgSO4, filtered, and evaporated under reduced pressure
to yield a crude purple oil. The crude purple residue was
dissolved in a mixture of CH2Cl2/hexanes (50 mL, 1:1 v/v) and
filtered through a plug of silica gel. The plug was washed with
CH2Cl2/hexanes (1000 mL, 1:1 v/v). The solvent was evaporated
to yield a brown oil. Further purification via flash chromatog-
raphy with silica as the absorbent (100% hexanes, gradient to
a mixture of CH2Cl2/hexanes, 2:3 v/v) yielded a light-yellow
oil. (6.7 g, 78%). 1H NMR (400 MHz, CDCl3): δ 3.71 (s, 6H),
6.56-6.63 (m, 4H), 6.65 (dd, J ) 8.4, 1.2 Hz, 2H), 6.96 (d, J
) 8.8 Hz, 2H), 7.15 (t, J ) 8.0 Hz, 2H), 7.32 (d, J ) 8.8 Hz,
2H). 13C NMR (100 MHz, CDCl3): δ 55.28, 108.53, 110.11,
115.00, 116.73, 125.44, 129.77, 131.95, 146.53, 148.24, 160.23.
HRMS-FAB+ m/z: found 383.0522; calcd (C20H18NO2Br)
383.0521.
Poly(methyl-bis-(3-methoxyphenyl)-(4-propylphenyl)amine)-
siloxane (3). The procedure was adapted from Stroh-
riegl.10,29 To a 250-mL two-necked round-bottom flask equipped
with a condenser, gas inlet, stir bar, and glass stopper under
argon was added toluene (50.0 mL) and poly(methylhydro)-
siloxane (530 µL, 8.9 mmol). Olefin 2 (4.0 g, 11.6 mmol) was
then added to the mixture followed by dichlorodicyclopenta-
dienyl platinum(II) (1.0 mg, 0.0025 mmol). The mixture was
stirred at elevated temperature (60-65 °C) using an oil bath.
The reaction progress was monitored using IR spectroscopy.
After an initial reaction time of 20 h, an aliquot of the neat
reaction solution was evaporated on NaCl plates, and the IR
spectrum was recorded to follow the disappearance of the Si-H
stretch at 2150 cm-1. Additional dichlorocyclopentadienyl
platinum(II) (ca. 1 mg) was added at regular intervals until the
IR spectrum of an aliquot showed no residual Si-H stretch. If
the reaction was incomplete, then additional dichlorodicyclo-
pentadienyl platinum(II) (ca. 1.0 mg) was added. This cycle
was continued at regular time intervals (ca. 1 h) until the
silicon-hydrogen signal was no longer present in the IR
spectrum. A total of three additions of dichlorodicyclopentadi-
enyl platinum(II) (3.0 mg, 0.008 mmol) in addition to the initial
amount was needed to reach completion. Upon completion, the
reaction was cooled to room temperature. Then the reaction
solution was added dropwise to an excess of hexanes (75 mL).
The precipitate was collected by centrifugation and decanted.
Then the precipitated polymer residue was dissolved in the
minimum amount of THF (10 mL) needed to dissolve the crude
polymer completely. This THF solution was precipitated again
into an excess of hexanes (20 mL). The precipitation process
was continued until the polymer residue was free of monomers
as determined by 1H NMR. A total of three precipitations were
needed for a clean product. The residual solvents were removed
from the polymer residue under reduced pressure to yield a white
solid (2.3 g, 64%). Tg ) 25.0 °C. 1H NMR (400 MHz, CDCl3):
δ -0.10-0.28 (br s, 3H), 0.48-0.72 (br s, 2H), 1.52-1.75 (br
s, 2H), 2.40-2.63 (br s, 2H), 3.41-3.75 (br s, 6H), 6.39-6.52
(br s, 2H), 6.59-6.68 (br s, 4H), 6.85-7.13 (br m, 6H). 13C
NMR (100 MHz, CDCl3): δ 0.01, 17.75, 25.22, 39.05, 55.08,
107.51, 109.46, 116.14, 124.82, 128.99, 129.47, 137.22, 144.92,
148.79, 160.02. Mh p ) 18 000, Mh n ) 25 000, Mh n (theoretical) )
16 000, Mh w ) 93 000, Mh n/Mh w ) 3.81. IR (neat): νSi-O ) 1050
4-Allylphenyl-bis(3-methoxyphenyl) amine (2). To a two-
necked round-bottom flask equipped with a condenser, gas inlet,
stir bar, and glass stopper was added 1 (6.7 g, 17.4 mmol),
tetrahydrofuran (75 mL), and magnesium (635 mg, 26.1 mmol,
50 mesh powder) under a flow of argon. This mixture was
heated to reflux (65-70 °C). After the reaction had begun
refluxing, it was cooled slightly to allow for the addition of
allyl bromide (2-3 drops). The reaction was again heated to
reflux following the addition of the Grignard initiator allyl
bromide. Aliquots of the reaction mixture can be quenched and
analyzed by TLC (SiO2, CH2Cl2/hexanes, 2:3 v/v) to determine
complete Grignard formation. In general, the Grignard was
completely formed after refluxing for 4 h. Then the reaction
was cooled to room temperature, and tetrakis(triphenylphos-
cm-1, νC-H ) 2930 cm-1
.
Secondary standard PVK was purified four to seven times
by dripping a solution of PVK/toluene into boiling ethanol. The
synthesis of AODCST is described in the literature.30 BBP (the
plasticizer butyl benzyl phthalate) and C60 were bought com-
mercially and used as received.

Poly(siloxane)-triarylamine-Based Composites
J. Phys. Chem. B, Vol. 107, No. 20, 2003 4737
Photoconductivity experiments were carried out by a standard
DC technique by measuring the current traversing the sample
at a certain applied voltage with and without uniform illumina-
tion at a given intensity from a Kr+ laser operating at 647 nm.
Steady-state currents were transformed into conductivities using
Ohm’s law.
Ellipsometric measurements were carried out by placing
samples between crossed polarizers at an angle of 51° with
respect to the laser beam from a temperature-stabilized laser
diode operating at 905 nm. A Babinet-Soleil compensator was
used to adjust the phase delay between the two polarizations
such that the transmitted beam was totally extinguished when
zero field was applied. Light transmission through the second
polarizer was measured with a silicon photodiode, and the
voltage was applied with a response time of around 100 ms by
a Trek 10/10 voltage amplifier. Part of the initial beam was
diverted by a beam splitter onto a second silicon photodiode to
normalize the resulting signal with respect to intensity fluctua-
tions. The change in refractive index ∆n was calculated using
AODCST chromophore. This work was supported in part by
the U.S. Air Force Office of Scientific Research Grant No.
F49620-00-1-0038.
References and Notes
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λ cos æ ‚arcsin |S |
x
n
∆n(t) )
2πd sin2 æ
where λ is the laser wavelength, æ is the internal angle of
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Photorefractive measurements were carried out with standard
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In four-wave measurements, a weak (100× less intense with
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π∆nL
λ
η ) sin2
e1‚e2
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(
)
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where λ is the laser wavelength and e1 and e2 are unit vectors
along the electric field of the incident and diffracted beams,
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Acknowledgment. We thank Shaumo Sadhukhan for as-
sisting in sample preparation and R. J. Twieg for providing the