Synthesis and characterization of photorefractive polymers containing transition metal complexes as photosensitizer

Article abstract of DOI:10.1021/ja970048l

This paper reports detailed synthesis and characterization of a hybridized polymer system which combines the ionic transition metal complexes and a conjugated polymer backbone bearing NLO chromophores to manifest a large photorefractive (PR) effect. In th

Full text of DOI:10.1021/ja970048l

4622
J. Am. Chem. Soc. 1997, 119, 4622-4632
Synthesis and Characterization of Photorefractive Polymers
Containing Transition Metal Complexes as Photosensitizer
Zhonghua Peng, Ali R. Gharavi, and Luping Yu*
Contribution from the Department of Chemistry and The James Frank Institute,
The UniVersity of Chicago, 5735 South Ellis AVenue, Chicago, Illinois 60637
ReceiVed January 6, 1997X
Abstract: This paper reports detailed synthesis and characterization of a hybridized polymer system which combines
the ionic transition metal complexes and a conjugated polymer backbone bearing NLO chromophores to manifest a
large photorefractive (PR) effect. In this system, the conjugated polymer backbone was chosen to play the dual role
of a transporting channel for the charge carriers and a macroligand to chelate with the transition metal complex.
Ru(II)-tri(bispyridyl) complexes were chosen as the photocharge generator by utilizing their metal-to-ligand charge
transfer properties. The Heck coupling reaction was applied to synthesize these multifunctional polymers. A large
net optical gain (>200 cm-1) at a zero electric field was observed on poled samples. The synthetic approach is
versatile and was extended to the synthesis of PR polymers containing Os complexes. The resulting polymer showed
photorefractivity at a wavelength in the near IR region (780 nm). This approach also offers the opportunity to
fine-tune the electronic properties of polymers through modification of the polymer structures. Model reactions
were studied to elucidate the structural defects caused by the side reactions in the Heck reaction. The effects of
these defects on the PR performance of these polymers were evaluated. It was demonstrated that eliminating these
defects could enhance the photorefractive response time.
Organic photorefractive (PR) materials have recently attracted
pronounced photorefractive effect, Fe2+/Fe3+ impurities play the
most important role as electron donor and trapping centers. It
attention not only due to their potential for practical applications,
such as in optical signal processing and information storage,
but also due to the fundamental challenge in identifying the
basic principles of the preparation or synthesis of these
materials.1 The photorefractive effect involves the modulation
of the index of refraction of a material by a space charge field
via the electro-optic effect.2 This space charge field arises from
the redistribution of charges in a photoconductor when it is
illuminated with a nonuniform light intensity pattern. Since
the change of the refractive index is proportional to the
magnitude of the space charge field, the generation of a large
space charge field is crucial for a high PR performance. The
formation of a space charge field involves three processes: the
generation of free charge carriers, their transport, and eventually
trapping by a trapping center. Therefore, in order to build up
a large space charge field, the optimization of these three
processes is essential.
is believed that the photoinduced interconversion of Fe2+
T
Fe3+ and the efficient band transporting of the free charge
carriers are responsible for the buildup of space charge fields.
Unlike their inorganic counterparts, organic PR materials lack
such mechanisms for the formation of the photoinduced space
charge field.1a The photogeneration of the charge carriers is
accomplished through exciton dissociation. Free charge carriers
are transported away through a hopping mechanism along a
series of transporting molecules. Because of the low dielectric
constant and numerous channels for the relaxation of excited
states to ground states, the quantum yield for the charge
generation in organic materials is usually low. To address these
problems, we recently designed a new photorefractive polymer
system which contains multivalent transition metal complexes
(Ru2+ or Os2+ complexes) and conjugated polymer backbones.
In this system, the conjugated polymer backbone was chosen
to play the dual role as the transporting channel for the charge
carriers and the macroligand to chelate with the transition metal
complex. It is well-known that doped conjugated polymer
systems have high electrical conductivities, and charge trans-
porting in the polaron or bipolaron states which reside in the
forbidden gap could be also very efficient.5,6 Therefore, a
conjugated backbone could provide an efficient charge trans-
porting pathway and could facilitate the formation of the space
charge field.
The photorefractive effect was discovered in a ferroelectric
inorganic crystal (LiNbO3) 30 years ago.2 Since then, numerous
crystals such as BaTiO3, Bi12SiO20 (BSO), SrxBa1-xNbO3, etc.
have been demonstrated to possess photorefractivity.3,4 In the
majority of these oxygen-octahedral ferroelectrics with a
X Abstract published in AdVance ACS Abstracts, May 1, 1997.
(1) (a) Moerner, W. E.; Silence, S. M. Chem. ReV. 1994, 94, 127. (b)
Meerholz, K.; Volodln, B. L.; Sandalphon; Klppelen, B.; Peyghambarian,
N. Nature 1994, 371, 497. (c) Lundquist, P. M.; Wortmann, R.; Geletneky,
C.; Twieg, R. J.; Jurich, M.; Lee, V. Y.; Moylan, C. R.; Burland, D. M.
Science 1996, 274, 1182. (d) Wiederrecht, G. P.; Yoon, B. A.; Wasielewski,
M. R. AdV. Mater. 1996, 8, 535. (e) Zhang, Y.; Burzynski, R.; Ghosal, S.;
Casstevens, M. K. AdV. Mater. 1996, 8, 111. (f) Yu, L.; Chan, W. K.; Peng,
Z. H.; Gharavi, A. R. Acc. Chem. Res. 1996, 29, 13.
(2) (a) Ashkin, A.; Boyd, G. D.; Dziedzic, J. M.; Smith, R. G.; Ballmann,
A. A.; Nassau, K. Appl. Phys. Lett. 1966, 9, 72. (b) Chen, F. S. J. Appl.
Phys. 1967, 38, 3418. (c) Chen, F. S.; LaMacchia, J. T.; Fraser, D. B. Appl.
Phys. Lett. 1968, 13, 223. (d). Chen, F. S. J. Appl. Phys. 1969, 40, 3389.
(3) (a) PhotorefractiVe Materials and Their Applications; Gunter, P.,
Huignard, J. P., Eds.; Springer-Verlag: Berlin, 1988; Vols. 1 and 2. (b)
Yariv, A. Optical Electronics, 4th ed.; Harcourt Brace Jovanovich: Orlando,
FL, 1991. (c) Yeh, P. Introduction to PhotorefractiVe Nonlinear Optics;
John Wiley: New York, 1993.
Ru(II)-tri(bispyridyl) complexes were chosen as a photo-
charge generator. Ru(bpy)32+; and its derivatives are known
to exhibit interesting metal-to-ligand charge transfer (MLCT)
processes, and their photochemistry, photophysics, electrochem-
istry, and electron/energy transfer properties have been exten-
(4) Petrov, M. P.; Stepanov, S. I.; Khomenko, A. V. PhotorefractiVe
Crystals in Coherent Optical Systems; Springer-Verlag: Berlin, 1991.
(5) Conjugated Polymers; Bredas, J. L., Silbey, R., Eds.; Kluwer
Academic Publishers: The Netherlands, 1991.
(6) Handbook of Conducting Polymers I & II. Skotheim, T. A., Eds.;
M. Dekker: New York, 1986.
S0002-7863(97)00048-6 CCC: $14.00 © 1997 American Chemical Society

Synthesis and Characterization of PhotorefractiVe Polymers
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4623
Scheme 1. Synthesis of Monomers A and B Containing Transition Metal Complexes
sively studied.7 They have also been extensively studied as
light-harvesting materials, materials which can reduce water into
hydrogen when coupled with other components.8 To utilize their
interesting charge transfer properties in the synthesis of PR
polymers, Ru(II) complexes were designed to chelate with the
conjugated polymer backbone. Upon excitation in the region
of the MLCT transition of the Ru complex, electrons would be
injected into the polymer backbone (equivalent to n-doping of
PPV), transported away through either intrachain migration or
interchain hopping and eventually trapped by the trapping
centers which could be impurities or structural defects. We
envision that the combination of the efficient MLCT process
of the ruthenium complexes and the efficient charge transporting
process of the conjugated backbone will lead to a higher charge
separation efficiency and therefore to a better PR performance
in this new PR polymer system than our previous ones.1f
Experimental results confirmed that the incorporation of the Ru
complex into the PR polymers dramatically enhanced the PR
performances of the resulting polymers. This approach is
versatile and has been extended to synthesize PR polymers
containing Os complexes, which have shown photorefractivity
at a wavelength in the near IR region. This paper reports the
detailed synthetic effort and the physical studies of this new
PR polymer system.
condition and tolerance for a variety of functional groups are
especially useful for synthesizing such functional polymers. We
have previously demonstrated that the Heck coupling reaction
can be utilized to synthesize conjugated polymers containing
ionic transition metal complexes, and the resulting polymer
exhibits enhanced photoconductivity.10 That work is the basis
for the design of our new PR polymers.
Synthesis of the Monomers and Polymers. To utilize the
Heck reaction, Ru complexes bearing diiodofunctional groups
were synthesized according to Scheme 1. 5,5′-Dimethyl 2,2′-
bipyridine was synthesized by the Raney nickel catalyzed self-
coupling of 3-picolines.11 Compound 6, a crucial compound
in this approach, was synthesized by reacting compound 5 with
1 equiv of butyllithium and subsequently quenching with DMF.
The reaction of compound 3 with compound 6 under the
Horner-Wittig-Emmons (HWE) reaction condition yielded
compound 7. The final ruthenium (or osmium) complex
(monomers A or B), soluble in common organic solvents, was
prepared after refluxing compound 7 with Ru(bipy)2Cl2 (or
Os(bipy)2Cl2) and was easily purified by recrystalization from
THF/hexane.
Monomer C was synthesized by using the approach outlined
in Scheme 2. This monomer contains an alkoxyl substituent
which was introduced to increase the solubility of the resulting
conjugated polymers: the polymer without this substituent was
insoluble in common organic solvents due to the strong
interchain π-π interactions.12
The polymerization was carried out according to Scheme 3
where Pd(OAc)2/P(o-tolyl)3/NEt3 (0.04:0.2:2.5 mol ratio relative
to divinyl benzene) was applied as the catalytic system.
Results and Discussion
Since the targeted polymer is a multifunctional polymer which
contains conjugated systems, NLO chromophores, and ionic
transition metal complexes, a reaction which can tolerate all of
these functionalities and possesses a high yield should be utilized
for the polymerization. From our previous studies and the work
of other groups,9 the Heck coupling reaction is found to be
versatile in synthesizing conjugated polymers. Its mild reaction
(9) (a) Heitz, W.; Brugging, W.; Freund, L.; Gailberger, M.; Greiner,
A.; Jung, H.; Kampschulte, U.; Niebner, N.; Osan, F. Makromol. Chem.
1991, 192, 967. (b) Suzuki, M.; Lim, J. C.; Saegusa, T. Macromolecules
1990, 23, 1574. (c) Weitzel, H. P.; Mullen, K. Makromol. Chem. 1990,
191, 2837. (d) Bao, Z. N.; Chen, Y. M.; Cai, R. B.; Yu, L. P.
Macromolecules 1993, 26, 5281.
(10) Peng, Z. H.; Yu, L. J. Am. Chem. Soc. 1996, 118, 3777.
(11) Sasse, W. H. F. J. Chem. Soc. 1959, p 3046.
(12) Chan, W. K.; Yu, L. Macromolecules 1995, 28, 6410.
(7) (a) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Hor-
wood: Chichester, U.K., 1991. (b) Juris, A.; Balzani, V.; Barigelletti, F.;
Campagna, S.; Belser, P.; Von Zelewsky, A. Coord. Chem. ReV. 1988, 84,
85. (c) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem.
ReV. 1996, 96, 759.
(8) Pierre-Alain, B. Gratzel, M. J. Am. Chem. Soc. 1980, 102, 2461.

4624 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Peng et al.
Figure 2. UV/vis spectra of monomer A and polymers 1 and 2.
the ruthenium complex into the polymer. Elemental analyses
also support the incorporation of the ruthenium complex.
The UV/vis spectra of the polymers are shown in Figure 2.
Both polymers 1 and 2 exhibit two major peaks: one at 390
nm which is due to the absorption of the NLO chromophore,
the other at 460 nm which is attributed to the absorption of the
conjugated backbone. However, for polymer 2, there is also
an absorption tail extending beyond 600 nm, which can be
assigned to the metal-to-ligand charge transfer absorption of
the ruthenium complexes. This is further evidence of the
incorporation of the ruthenium complex into the polymer. It
also indicates that the introduction of the ruthenium complex
extends the photosensitivity of the polymer to the region of
longer wavelengths. By using a diode laser (i.e., 690 nm), we
can photoexcite the polymer mainly through the MLCT process,
while the absorptions due to the NLO chromophore and the
conjugate backbone are minimized. It can be noted that a small
peak at 290 nm, due to the ligand-centered transition of the
two bipyridyl ligands in the ruthenium complexes, exists for
polymer 2 while polymer 1 does not have this absorption.
DSC studies showed that polymers 1 and 2 have a similar
glass transition temperature at ca. 130 °C. The main chain
melting temperature for polymers 1 and 2 was observed at 215
°C, overlapping with the cross-linking temperature of the
conjugated polymer backbone.13 TGA analysis showed that
polymer 1 was stable up to 350 °C, while polymer 2 showed a
small weight loss starting at 270 °C, caused by the loss of the
bypyridyl ligands in the ruthenium complexes.
Figure 1. 1H NMR spectra of polymers 1 and 2.
Scheme 2. Synthesis of Monomer C
Physical Characterization. The second-order nonlinearity
of the poled polymers was demonstrated by the second harmonic
generation (SHG) measurements. After corona poling, a SHG
coefficient, d33, of 70 pm/V for polymer 2 was obtained at 1064
nm. The poled polymer films also exhibited reasonable thermal
and temporal stabilities in their optical nonlinearity. It was
found that the SHG signal of polymer 2 was stable up to 80
°C. When the poled polymer film was kept at 60 °C, the SHG
signal stabilized at a value of 80% after an initial drop. This
stability of the nonlinearity allowed us to perform the photo-
refractive experiments without applying an external electric field.
To further demonstrate the electro-optic effect, the EO
coefficient of polymer 2 was measured using a reflection
method.14 An E-O coefficient of 7 pm/V was obtained at 690
nm, which is relatively high compared with other photorefractive
polymers.1a This large nonlinearity arises from the large NLO
chromophore concentration in the polymers (∼50 wt %).
The photoconductivity of the polymers, another necessary
condition for PR effect, was also measured at a wavelength of
Polymers soluble in tetrachloroethane, DMF, and NMP were
obtained in excellent yields.
Structural Characterization. Polymers 1 and 2 are in-
soluble in THF and chloroform but soluble in tetrachloroethane
(TCE), DMF, NMP, etc. Their intrinsic viscosities were
measured to be 0.46 and 0.53 dL/g, respectively, in NMP at 30
°C, indicating that reasonably high molecular weights were
obtained. High optical-quality films with thicknesses over 30
µm were cast from their TCE solutions.
1
The H NMR spectra of polymers 1 and 2 in tetrachloro-
ethane-d4 are shown in Figure 1. These two polymers exhibit
1
very similar H NMR spectra. As assigned in Figure 1, the
major peaks correspond to the protons of the chromophore and
the divinyl benzene moieties. However, the chemical shifts due
to the protons of the bipyridyl ligand at 8.0 and 8.5 ppm are
still noticeable for polymer 2, indicating the incorporation of
(13) Bao, Z.; Chen, Y. M.; Cai, R. B.; Yu, L. Macromolecules 1993,
26, 5281.
(14) Teng, C. C.; Man, H. T. Appl. Phys. Lett. 1990, 56, 1734.

Synthesis and Characterization of PhotorefractiVe Polymers
Scheme 3. Synthesis of Polymers 1, 2, and 3
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4625
690 nm. As expected, polymer 2 exhibited large photocon-
ductivity. A photoconductivity of 3 × 10-10 s/cm (laser
intensity 6.17 mW/cm2) and a photocharge generation efficiency
of 0.2% were obtained under an external electric field of 950
kv/cm. This is a significant improvement compared to our
previous polymers.15
To study the PR effect, an effective technique is the two beam
coupling experiment which is regarded as the standard experi-
ment to confirm the PR response. We performed the two beam
coupling experiment at 690 nm (diode laser, s-polarized). The
normal of the sample was rotated 35° with respect to the bisector
of the writing beams to obtain a nonzero projection of the EO
coefficient. The dynamics of the grating formation in poled
polymer 2 at a zero external electric field is shown in Figure 3.
The transmitted beam intensities were measured with lock-in
amplifiers (the time constant of the lock-in amplifiers was set
at 10 ms), and the data were collected by a computer. At the
time of 20 s, the two laser beams were overlapped at a pristine
spot inside the polymer film. Notice that the intensity of one
beam, as a function of time, kept increasing while that of the
other decreasing. The gain and loss was calculated (the ratio
of the two incident beam intensities was 1.12) according to the
equation:
Figure 3. Grating formation dynamics of polymer 2 and polymer 1
(inset) in 2BC experiments.
By utilizing a grating-translation technique, the phase of index
grating can be studied.16 This experiment can furnish further
evidence for the photorefractive effect. After forming the
grating by intersecting the two laser beams inside of the polymer
film for a few minutes, the sample was translated along the
direction parallel to the grating wave vector. The transmitted
intensities of the two beams exhibit an oscillating pattern which
reflects the spacing and phase of grating. It was found that a
90° phase shift of the index grating over the intensity distribution
exists for polymer 2. This result verified the photorefractive
nature of the grating. Since polymer 2 exhibits an absorption
coefficient of 102 cm-1, a large net optical gain is obtained in
this polymer at a zero external electric field.
1
Γ ) ln
L
1 + R
1 - âa
(
)
where R is the ratio of the intensity modulation (∆Is/Is) and â
is the intensity ratio of the two incident laser beams (Is/Iq). It
was found that polymer 2 exhibited an optical gain higher than
300 cm-1. At the time of 700 s, the pump beam b was blocked,
and the transmitted intensity of the other beam returned to the
initial value. When the sample was rotated 180 °C along its
axis, the gain and the loss beams were switched due to the
reversal of the dipole orientation. This is a clear indication that
the grating is indeed of a photorefractive nature, although the
process is rather slow. The deep trap centers might be
responsible for the slow response time.
Polymer 1, without Ru complexes, did not show clear
photorefractivity. As shown in the inset of Figure 3, blocking
beam b had no effect on the transmitted intensity of beam a,
which implies that there was no asymmetric energy exchange
between the two beams.
Synthesis of Near-IR Sensitive PR polymers. The synthetic
approach described above is versatile and can be applied to
(15) (a) Peng, Z. H.; Bao, Z.; Yu, L. J. Am. Chem. Soc. 1994, 116, 6003.
(b) Chen, Y. M.; Peng. Z. H.; Chan, W. K.; Yu, L. Appl. Phys. Lett. 1994,
64, 1195.
(16) (a) Sutter, K.; Gunter, P. J. Opt. Soc. Am. B 1990, 7, 2274. (b)
Wash, C. A.; Moerner, W. E. J. Opt. Soc. Am. B 1992, 9, 1642.

4626 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Peng et al.
Figure 5. Asymmetric energy exchange in the 2BC experiment for
polymer 3 at zero external field (laser wavelength; 780 nm).
Figure 4. UV/vis spectra of monomer B and polymer 3.
Scheme 4. Synthesis of Monomer D
synthesize other metal-containing polymers, such as polymers
containing Os complexes. The advantage of utilizing the Os
complex as a photosensitizer is that the Os complex has a spin-
1
allowed MLCT transition at 450 nm and an extremely broad
(over 200 nm bandwidth) spin-forbidden 3MLCT transitions at
around 640 nm (e.g., see Figure 4, the UV/vis spectrum for
monomer B).7 The broad absorption which extends beyond 750
nm is very useful for the design of IR sensitive materials. If
we polymerize the Os complex into the conjugated PR polymer
system, the resulting polymer could show photorefractivity at
wavelengths in the near-IR regions (for example at 780 nm).
The Os complex (monomer B) was synthesized by reacting
the ligand (compound 7 in Scheme 1) with Os(II)(bpy)2Cl2,
which was prepared according to a literature procedure.17 The
resulting Os complex is a black, shiny powder, soluble in
common organic solvents such as chloroform, THF, methylene
chloride, etc.
For the purpose of comparison, a polymer with the same
molar composition (5 mol % Os complex) as polymer 2 was
synthesized (polymer 3), using the Heck reaction with similar
conditions. Polymer 3 is a dark powder which is soluble in
NMP, DMF, etc. The incorporation of the Os complex into
the polymer backbone can be clearly seen from its UV/vis
spectrum. As shown in Figure 4, there is an absorption tail
extending to 600 nm, which can be assigned to the spin allowed
transition of the Os complex. The inset of Figure 4 is the UV/
vis spectra of the concentrated solution of polymer 3. It clearly
shows that polymer 3 has an absorption tail extending to near
800 nm.
clearly observed and the corresponding optical gain was
calculated to be 80 cm-1. Although net optical gain was not
obtained in this case (R was measured to be 186 cm-1 at 780
nm), the observation of such a photorefractive response at near-
IR region is still very interesting. Net optical gain may be
possible for polymers with lower Os complex concentrations.
PR Polymers Based on Alkyl-Substituted PPV. As men-
tioned earlier, the alkoxy-substituted PPV has a π-π* transition
maximum at 450 nm, overlapping partially with the MLCT
transition of the Ru complex. Absorptions at the working laser
wavelength (690 nm in the case of polymers containing Ru
complex) by the conjugated components will reduce the
quantum efficiency for the charge generation and should be
minimized. It is known that the π-π* transition of alkyl-
substituted PPVs occurs at shorter wavelengths. By changing
the alkoxy substitutes in polymer 2 to alkyls, we should be able
to decrease the absorption of the PPV backbones significantly.
For this purpose, a new chromophore (monomer D) was
synthesized as shown in Scheme 4. The polymer structures are
shown in Scheme 5. Two polymers were synthesized: polymer
4 without a Ru complex and polymer 5 with 5 mol % Ru
complexes.
This polymer has a glass transition temperature of 110 °C
and a cross-linking temperature of 175 °C. TGA analysis
showed two weight losses, one at around 240 °C and the other
at 310 °C. The first weight loss (6%) is due to the decomposi-
tion of the Os complex, supported by the studies on the complex,
while the second one is caused by the decomposition of the
backbone.9d
In order to study the PR effect of polymer 3, we performed
the two beam coupling experiment at 780 nm (30 mW,
s-polarized) on a corona poled polymer film with a thickness
of 5.09 µm. The sample was tilted 30° and the angle between
the two incident laser beams was θ () 46.4°), which gave a
grating spacing (Λ ) λ/4πsin(θ/2)) of 0.24 µm (the polymer
has a refractive index of 1.7486 at 780 nm). The results are
shown in Figure 5 where the data were taken under zero external
field after overlapping the two laser beams inside the sample
for four to five minutes. The asymmetric energy exchange was
Unlike polymers 1 and 2, polymers 4 and 5 are soluble in
chloroform and THF. Their molecular weights were measured
by GPC (polystyrene as standard) to be 21 kdalton (Mn, PD )
2.8) and 18 kdalton (Mn, PD ) 2.25), respectively. The
incorporation of the Ru complex into the polymer backbone
(17) (a) Belser, P.; Zelewsky, A. V.; Frank, M.; Seel, C.; Vogtle, F.;
Cola, L. D.; Barigelletti, F. and Balzani, V. J. Am. Chem. Soc. 1993, 115,
4076. (b) Lay, P. A.; Sargeson, A. M.; Tauber, H.; Chou, M. H.; Creutz,
C. Inorg. Synth. 1986, 24, 294.

Synthesis and Characterization of PhotorefractiVe Polymers
Scheme 5. Synthesis of Polymers 4 and 5
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4627
Figure 6. UV/vis spectra of polymers 4 and 5.
Figure 7. Two beam coupling results for a thick film made from
polymer 5.
was again proved by the 1H NMR spectra typical chemical shifts
at 8.0 and 8.5 ppm due to the bipyridyl ligand protons and at
4.0 ppm due to the -OCH2- protons were observed for polymer
5.
The UV/vis spectra of the polymers are shown in Figure 6.
The absorption due to the PPV backbone overlaps with that of
the chromophores, both systems having a maximum at around
380 nm. Again, polymer 5, unlike polymer 4, has an absorption
tail extending beyond 600 nm. Since both the chromophores
and the PPV backbones essentially have no absorption beyond
500 nm, a much smaller absorption coefficient (21.5 cm-1) was
obtained for polymer 5.
Polymers 4 and 5 have a relatively low glass transition
temperature of 75 °C. Consequently their SHG stability is not
as good as polymers 1 and 2. However, we were able to prepare
thick films sandwiched between two ITO coated glasses. Two
beam coupling experiments were carried out by applying
external fields across the sandwiched sample. As shown in
Figure 7, when an electric field (1000 V over 75 µm thick film)
was applied at 20 s, the transmitted intensity of one beam
increased, while that of the other beam decreased with a
response time of 10 s. Energy exchange of more than 5%
between the two beams was observed, giving an optical gain
of 16 cm-1. When the field was turned off at 60 s, the intensities
of the two beams returned to their original values gradually
during a period of 20 s. Considering the small field applied
(less than 15 V/µm), one would expect higher optical gain values
if higher electric fields could be applied. Further studies are in
progress.
Study of the Structural Defects in the Heck Reaction and
Their Effects on the Photorefractivity. It was found that the
1H NMR spectra of all of our polymers synthesized by the Heck
reaction exhibited small peaks which could not be removed by
any purification process. For example, as shown in Figure 1,
small peaks at 0.82, 1.02, and 5.30 ppm exist. It is known that
the Heck reaction involves many side reactions which clearly
introduces defects into the conjugated backbone.18 These
defects may play the role of deep trapping centers and thus exert
a profound effect on the PR performance of the polymers. To
identify the structural defects in the conjugated polymers
synthesized by the Heck reaction, we carried out model reactions
involving similar monomers and styrene as shown in Scheme
6.
Three diiodo compounds were used to run the model
reactions. After completion of the reactions, the mixtures were
poured into aqueous solution (5% HCl) and extracted with ethyl
1
ether. The H NMR spectra of the mixtures were collected.
Based on the spectra, the relative yields of the products were
calculated. The results are shown in Table 1.
Within 5 h, the coupling reactions were completed for all
three model reactions. No proton peaks corresponding to the
(18) Brenda, M.; Greiner, A. and Heitz, W. Makromol. Chem. 1990, 191,
1083.

4628 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Scheme 6. Model Reactions via the Heck Coupling
Peng et al.
Table 1. Yields of the Products in the Model Reaction
Scheme 7. Synthesis of Monomer E
Figure 8. UV/vis spectra of polymers 6 and 7.
As shown in Scheme 7, we utilized the Heck reaction to
synthesize monomer E from monomer C. Considering the
uncertainty of the Ru complex under the harsh reaction condition
of the HWE reaction (a strong base was used), we chose to
synthesize the conjugate polymer first and then coordinate with
the ruthenium complex. This approach, of course, lacks the
certainty regarding the yield of the coordination of the ruthenium
complexes.
As shown in Scheme 8, polymer 6 was synthesized as a red
powder. THF was found to be the best solvent for the
polymerization, and the polymer precipitated out of the reaction
mixture in several hours. The final coordination step was carried
out in THF. The resulting polymer 7 displayed much better
solubility in THF, chloroform, etc. than polymer 6.
1
diiodo-starting material were observed in the H NMR of the
1
The H NMR spectrum of polymer 7 showed that a linear
reaction mixtures. It was found that a significant amount of
conjugated polymer was obtained. The side peaks correspond-
ing to the R-adducts were not observed. However, the
incorporation of the Ru complex is not evident in the 1H NMR
spectrum. But the UV/vis spectra do provide some structural
information. As shown in Figure 8, polymer 7 showed a
backbone absorption maximum at 474 nm, slightly blue-shifted
compared to polymer 6 (477 nm), and an absorption tail
extending near 600 nm. These results imply that some
coordination of the ruthenium complex indeed occurred. More
evidence of the coordination comes from the elemental analy-
sis: 0.09% ruthenium was found in the polymer, which accounts
for 12% of the dipyridyl site. This low coordination ratio could
be due to the poor solubility of polymer 6.
the R-substituted product 19 was obtained in all three cases.
1
The small peaks mentioned above in the H NMR spectra of
polymers (polymers 1 and 2) correspond well to the R-substi-
tuted structural moieties. These R-substituted units break the
conjugation and therefore form structural defects. However,
the defect densities in the polymers are much smaller than those
observed in the model reactions, as indicated by the integrations
1
of H NMR spectra. The exact reason is not clear.
To study the effects of these defects on the polymer
properties, we synthesized the ruthenium complex-containing
PR polymers via the Horner-Wadsworth-Emmons (HWE)
reaction, by which the R-coupling structures can be avoided. It
is known that tetraethyl xylylenebisphosphonate reacts with
benzaldehyde resulting in only trans-products.19 In addition,
the phosphorus product is a phosphate ester and hence soluble
in water, making it easy to separate it from the olefin product.
We found that the HWE reaction gave all-trans linear conjugated
polymers.20
Preliminary two beam coupling studies gave encouraging
results. As shown in Figure 9, a response time of less than
150 s and an optical gain of 99 cm-1 were obtained. The
photorefractive response time is faster than that of our previous
PR polymers made by the Heck reaction (over 500 s), although
such a comparison should be considered with caution. The
smaller optical gain could be due to the incomplete coordination
of the ruthenium complexes.
(19) Wadsworth, W. S., Jr.; Emmons, W. D. J. Am. Chem. Soc. 1961,
83, 1733.
(20) Deb, S.; Peng, Z.; Yu, L. Manuscript in preparation.

Synthesis and Characterization of PhotorefractiVe Polymers
Scheme 8. Synthesis of Polymers 6 and 7 via HWE Reaction
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4629
approach is promising and warrants further exploration. This
work also revealed a dilemma in choosing polymerization
approaches. The Heck reaction can unambiguously assure the
coordination of the transition metal complex, but it introduces
undesired structural defects in the conjugated backbone. While
HWE reaction minimizes the structural defects in the conjugated
backbone, it cannot guarantee complete coordination. Therefore,
a new polymerization method which not only can tolerate
transition metal complex but also give defect-free linear
conjugate polymer chain is needed.
Experimental Section
THF and ethyl ether were purified by distillation over sodium chips
and benzophenone. Styrene was distilled over calcium hydride. The
p-divinylbenzene was separated from a mixture of p-divinylbenzene
and m-divinylbenzene according to the literature procedure.21 All of
the other chemicals were purchased from Aldrich Chemical Co. and
used as received unless otherwise stated.
Syntheses of Monomers. The following compounds were synthe-
sized according to literature procedures: 5,5′-dimethyl-2,2′-bipyridine
1,11 compound 2,22 compound 5.23
Compound 3. The mixture of compound 2 (3.00 g, 8.77 mmol)
and P(OEt)3 (4.37 g, 26.3 mmol) was stirred at 125 °C for 4 h. The
excess P(OEt)3 was distilled out, and the residual solid was recrystallized
from chloroform/hexane to give 3.50 g of compound 3 (87%, mp 99-
100 °C). 1H NMR (CDCl3, ppm): δ 1.27 (m, 12 H, -CH3), 3.16 (d,
J ) 21.71 Hz, 4 H, -CH2P-), 4.03 (m, 8 H, -OCH2-), 7.73 (d, J )
8.16 Hz, 2 H, aromatic protons), 8.27 (d, 8.07 Hz, 2 H, aromatic
protons), 8.50 (s, 2 H, aromatic protons). Anal. Calcd for C20H30N2-
O6P2: C, 52.63; H, 6.62; N, 6.14. Found: C, 52.44; H, 6.54; N, 6.07.
Compound 6. BuLi (14.33 mL, 2.5 M solution in hexane, 35.82
mmol) in ether (50 mL) was added dropwise into an ether solution
containing 2,5-dialkoxy-1,4-diiodobenzene (R ) C7H15, 20.00 g, 35.82
mmol, 75 mL ether) at 0 °C. After addition of BuLi was completed,
DMF (3.93 g, 53.76 mmol) in 15 mL of ether was added dropwise
into the solution. The resulting mixture was stirred at room temperature
for 2 h and then poured into water (200 mL). The ether layer was
washed three times with water and dried over MgSO4. The ether was
Figure 9. Grating formation dynamics in the 2BC experiment for
polymer 7.
Conclusions
We have demonstrated that the hybridized polymers, which
combine the ionic transition metal complexes and a conjugated
polymer backbone bearing NLO chromophores, exhibited large
photorefractivity. In this system, the conjugated polymer
backbone was designed to play the dual role of both transporting
channel for the charge carriers and the macroligand to chelate
with the transition metal complex. The Ru(II)-tri(bispyridyl)
complex was selected as the photocharge generator because of
its metal-to-ligand charge transfer properties. The Heck cou-
pling reaction was successfully applied to synthesize these
multifunctional polymers. A large net optical gain (>200 cm-1
)
at a zero external electric field was observed. The synthetic
approach is versatile and was extended to the synthesis of PR
polymers containing Os complexes. The resulting polymer
showed photorefractivity at a wavelength in the near IR region.
This approach also offers the opportunity to fine-tune the
electronic properties of polymers through easy modification of
the polymer structures. Model reactions were studied to
elucidate the structural defects caused by the side reactions of
the Heck reaction. The effects of these defects on the PR
performance of these polymers were evaluated. It was dem-
onstrated that elimination of these defects could enhance the
photorefractive response time. These results indicate that this
(21) Strey, B. T. J. Polym. Sci. Part A 1965, 3, 265.
(22) Ebmeyer, F.; Vogtle, F. Chem. Ber. 1989, 122, 1725.
(23) Bao, Z. N.; Chen, Y. M.; Cai, R. B.; Yu, L. P. Macromolecules
1993, 26, 5281.

4630 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Peng et al.
then removed by vacuum evaporation. The resulting liquid was
dissolved in hexane and refrigerated. Compound 6 crystallized out of
the solution (10.70 g, 65% yield, mp 51.5-52 °C). 1H NMR (CDCl3,
ppm): δ 0.89 (t, J ) 6.56 Hz, 6 H, -CH3); 1.31 (m, 8H, -CH2CH2-
CH3); 1.36 (m, 4H, -CH2CH2CH2CH3); 1.46 (m, 4 H, -CH2CH2CH2-
CH2CH3); 1.80 (quartet, J ) 6.89 Hz, 4H, -OCH2CH2-); 3.97 (t, J )
5.47 Hz, 2 H, -OCH2-); 3.99 (t, J ) 5.65 Hz, 2 H, -OCH2-); 7.14
(s, 1 H, aromatic proton, ortho to CHO); 7.4 (s, 1 H, aromatic proton,
meta to CHO); 10.34 (s, 1H, -CHO). 13C NMR (CDCl3, ppm): 14.2,
22.8, 26.1, 29.2, 29.3, 31.9, 69.6, 70.0, 108.9, 124.6, 125.3, 152.3, 155.9,
189.2. Anal. Calcd for C21H33O3I: C, 54.79; H, 7.22; I, 27.56.
Found: C, 54.86; H, 7.21; I, 27.49.
3.88 (t, J ) 6.16 Hz, 2 H, -OCH2-); 4.88 (b, 1 H, -OH); 6.97 (s, 1
H, aromatic protons ortho to OH); 7.35 (s, 1 H, aromatic protons meta
to OH).
Monomer C. Diethyl azodicarboxylate (DEAD) (1.00 g, 5.7 mmol)
in THF (5 mL) was added into a solution of compound 10 (1.70 g, 3.8
mmol), 4-(2-hydroxy ethyl)ethylamino-4′-sulfone stilbene (compound
11, 1.30 g, 3.8 mmol), and triphenylphosphine (1.50 g, 5.7 mmol) in
THF (20 mL). The resulting mixture was stirred overnight and then
concentrated to less than 5 mL. The solution was poured into hot
methanol and filtered while it was still hot. The resulting yellow solid
was purified by chromatography (CH2Cl2 as eluent) and then recrystal-
lized from acetone/methanol. The resulting product was a light yellow-
colored crystal (2.05 g, 70%, mp 145-147 °C). 1H NMR (CDCl3,
ppm): δ 0.90 (m, 3H, -CH3 in alkoxy); 1.23 (t, J ) 7.01 Hz, 3 H,
-CH3 on chromophore), 1.33-1.79 (m, 8H, aliphatic protons), 3.03
(s, 3H, -SO2CH3), 3.56 (m, 2H, NCH2CH3), 3.78 (m, 2H, -CH2CH2N),
3.90 (m, 2H, -OCH2- on alkoxy side chain), 4.07 (t, J ) 5.46 Hz,
2H, -OCH2CH2N-), 6.69 (d, J ) 8.34 Hz, 2H, aromatic protons),
6.86 (d, J ) 16.33 Hz, 1H, vinyl proton), 7.12 (s, 1H, aromatic protons),
7.13 (d, J ) 16.56 Hz, 1H, vinyl proton), 7.37 (d, J ) 8.59 Hz, 2H,
aromatic protons), 7.55 (d, J ) 8.26 Hz, 2H, aromatic protons), 8.01
(d, J ) 7.91 Hz, 2H, aromatic protons). 13C NMR (CDCl3, ppm): 12.6,
14.4, 22.8, 26.2, 29.2, 29.3, 32.0, 44.9, 46.0, 49.6, 68.1, 70.5, 86.2,
86.5, 112.0, 121.8, 122.7, 122.9, 124.3, 126.5, 127.9, 128.8, 132.9,
137.7, 144.0, 148.0, 152.6, 153.5. Anal. Calcd for C31H37NO4SI2: C,
48.13; H, 4.82; N, 1.81. Found: C, 48.22; H, 4.78; N, 1.77.
Monomer B. To a solution of compound 7 (0.20 g, 0.187 mmol)
in ethylene glycol (15 mL) was added at 120 °C cis-dichlorobis(2,2′-
bipyridine)osmium(II) (0.10 g, 0.187 mmol) in 5-10 mL of ethylene
glycol. The resulting solution was stirred at 140 °C for 48 h. After
cooling to room temperature, the solution was concentrated to 10 mL
and then added to a solution of (NH4)PF6 (0.25 g) in 80 mL of water.
A dark solid was collected by filtration and recrystallized from CH2-
Cl2/MeOH to give 0.2 g of product as a black shining crystal (57%).
1H NMR (CDCl3, ppm): d 0.85 (t, J ) 6.56 Hz, 12 H, -CH3); 1.20-
1.55 (m, 32 H, aliphatic protons); 1.73 (m, 8H, -CH2-); 3.86 (t, J )
5.33 hz, 4H, -OCH2-); 3.97 (t, J ) 5.6 Hz, 4H, -OCH2-); 6.90 (d,
J ) 16.40 Hz, 2 H, vinyl protons); 7.04 (s, 2H, aromatic protons meta
to iodo); 7.19 (s, 2H, aromatic protons ortho to iodo); 7.31-7.34 (m,
4H, 2 vinyl protons and 2 ArH); 7.37 (t, J ) 6.82 Hz, 2H, ArH); 7.56
(s, 2H, ArH); 7.66-7.70 (m, 8H, ArH); 7.90 (d, J ) 8.29 Hz, 2H,
ArH); 8.15 (d, J ) 8.34 Hz, 2H, ArH); 8.21 (t, J ) 5.70 Hz, 4H, ArH).
Anal. Calcd for C74H90N6O4I2P2F12Os: C, 47.74; H, 4.87; N, 4.51.
Found: C, 47.67; H, 4.88; N, 4.53.
Compound 12. Mg (1.89 g, 0.0777 mol) and ether (30 mL) were
added to a two-necked flask. Octyl bromide (15.00 g, 0.0777 mol) in
20 mL of ether was then added to the above suspension at such a rate
that the reaction mixture maintained self-refluxing. After the addition
was complete, the mixture was further refluxed in an oil bath for half
an hour. The solution was then transferred to an addition funnel and
added dropwise into a mixture containing 1,4-dibromobenzene (19.73
g, 0.0777 mol), PdCl2(dppf) (0.60 g, 0.7 mmol), and 40 mL of ether.
The resulting mixture was refluxed overnight and then poured into
water. After removal of the catalyst residue (red precipitate) by
filtration, the filtrate was extracted with ethyl ether. The organic layer
was washed with water and dried (MgSO4), and the solvent was
evaporated. The resulting liquid was distilled to give 17 g of product,
a colorless liquid (76%, bp 91-92 °C/0.8 mmHg). 1H NMR (CDCl3,
ppm): δ 0.87 (t, J ) 6.79 Hz, 3H, -CH3), 1.28 (m, 10 H, alkyl protons),
1.56 (m, 2 H, alkyl protons), 2.53 (t, J ) 7.31 Hz, 2 H, benzyl protons),
6.89 (d, J ) 7.63 Hz, 2H, aromatic protons), 7.32 (d, J ) 7.72 Hz, 2
H, aromatic protons).
Compound 7. Sodium hydride (0.24 g, 9.81 mmol) was added to
a solution of compound 6 (3.01 g, 6.65 mmol) in DME (20 mL). The
resulting suspension was stirred for 5 min. Compound 3 (1.49 g, 3.27
mmol) in DME (10 mL) was then added dropwise at room temperature.
The mixture was refluxed overnight. After the solution cooled down
to room temperature, water was added. The resulting mixture was
stirred for 5 min, and the crude product was separated by filtration.
Recrystallization from dichloromethane/methanol gave 2.20 g of pure
compound 7 (83%, mp 84-85 °C). 1H NMR (CDCl3, ppm): d 0.9
(m, 12 H, -CH3); 1.3-1.9 (m, 40H, aliphatic protons); 3.95 (t, J )
6.2 Hz, 4 H, -OCH2-); 4.01 (t, J ) 6.2 Hz, 4 H, -OCH2-); 6.99 (s,
2 H, aromatic protons meta to iodo); 7.10 (d, J ) 16.47, 2 H, vinyl
protons); 7.26 (s, 2 H, aromatic protons ortho to iodo); 7.44 (d, J )
15.56 Hz, 2 H, vinyl protons); 7.92 (dd, J ) 8.42 (1.73) Hz, 2 H,
4-pyridine protons); 8.34 (d, J ) 8.24 Hz, 2 H, 3-pyridine protons);
8.71 (s, 2 H, 2-pyridine protons). 13C NMR (CDCl3, ppm): 14.4, 22.8,
26.3, 29.3, 29.5, 32.0, 69.6, 70.3, 86.9, 110.0, 120.9, 123.7, 125.5, 126.8,
133.4, 148.3, 151.6, 152.3, 154.6. Anal. Calcd for C54H74N2O4I2: C,
60.67; H, 6.98; N, 2.62. Found: C, 60.90; H, 6.93; N, 2.59.
Monomer A. A solution of 0.1500 g of compound 7 (0.14 mmol)
in 10 mL of methoxyethanol was heated to 100 °C. cis-dichlorobis-
(2,2′-bipyridine)ruthenium(II) hydrate (0.0679 g, 0.14 mmol) in ethanol
(10 mL) was added. The ethanol was evaporated, and the resulting
solution was stirred at 140 °C for 3 h. After cooling to room
temperature, the solution was added into a solution of (NH4)PF6 (0.2283
g) in water (50 mL). An orange solid was collected by filtration and
recrystallized from THF/hexane to give 0.1300 g of the desired product.
(53%, mp 234-235 °C). 1H NMR (CDCl3, ppm): d 0.86 (t, J ) 6.56
Hz, 12 H, -CH3); 1.28-1.78 (m, 40 H, aliphatic protons); 3.87-4.01
(m, 8H, -OCH2-); 6.93 (d, J ) 16.45 Hz, 2 H, vinyl protons); 7.07
(s, 2 H, aromatic protons meta to iodo); 7.20 (s, 2 H, aromatic protons
ortho to iodo); 7.38 (d, J ) 16.44 Hz, 2H, vinyl protons); 7.47 (t, J )
6.63 Hz, 2H, aromatic protons on the dipyridine ligand); 7.51 (t, J )
6.22 Hz, 2 H, aromatic protons on the dipyridine ligand); 7.67 (s, 2 H,
aromatic protons); 7.81 (d, J ) 5.28 Hz, 4 H, aromatic protons); 7.91
(m, 4 H, aromatic protons); 8.07 (d, J ) 8.47 Hz, 2 H, aromatic
protons); 8.15 (d, J ) 8.67 Hz, 2 H, aromatic protons); 8.22 (t, 7.82
Hz, 2 H, aromatic protons). Anal. Calcd for C74H90N6O4I2P2F12Ru:
C, 50.14; H, 5.12; N, 4.74; I, 14.32. Found: C, 50.17; H, 5.15; N,
4.73; I, 14.44.
Compound 9. To a solution of 2,5-dimethoxy-1,4-diiodobenzene
(10.00 g, 25.6 mmol) in dichloromethane (50 mL), cooled in dry ice/
acetone, was added dropwise BBr3 (26.50 g, 105.8 mmol) in dichlo-
romethane (15 mL). The resulting solution was stirred at room
temperature overnight and then poured into ice water. A white
precipitate was collected by filtration and recrystallized from THF/
hexane to yield compound 9 (8.1 g, 87%, mp 192-194 °C). 1H NMR
(CDCl3, ppm): δ 7.10 (s, 2 H, aromatic protons); 9.72 (s, 2 H, -OH).
Compound 10. To a solution of compound 9 (7.00 g, 19.34 mmol)
in DMSO (50 mL) was added potassium hydroxide powder (3.25 g,
58.02 mmol). A solution of bromohexane (3.19 g, 19.34 mmol) in
DMSO (10 mL) was then added immediately. The resulting mixture
was stirred at room temperature overnight and then poured into water.
A white solid (mainly dialkoxy side product) was filtered out, and the
filtrate was neutralized by hydrochloric acid. The product was collected
by filtration and recrystallized further from hexane (refrigeration) to
give compound 10 (5.00 g, 56%, mp 48-50 °C). 1H NMR (CDCl3,
ppm): δ 0.91 (m, 3 H, -CH3); 1.34-1.80 (m, 8 H, aliphatic protons);
Compound 13. To a suspension containing Mg (0.90 g, 37.14
mmol) and a small crystal of iodine and THF (10 mL) was added 1
mL of compound 12 (10.00 g, 37.14 mmol). After stirring for a couple
of minutes, the mixture started to reflux. The rest of the compound
12 was then added to the mixture at such a rate as to maintain the
refluxing. After the addition was complete, the mixture was refluxed
for another half an hour. The resulting Grignard reagent was transferred
to an addition funnel and added dropwise into a mixture containing
1,6-dibromohexane (9.06 g, 37.14 mmol), Li2CuCl4 (3.71 mL of 0.1
M THF solution, 37.14 mmol), and 20 mL of THF at 5-10 °C. The

Synthesis and Characterization of PhotorefractiVe Polymers
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4631
resulting mixture was stirred overnight at room temperature and then
poured into water. The mixture was extracted with methylene chloride.
The organic layer was washed with water, aquous NaHCO3 solution,
and water again. It was then dried with MgSO4. After removal of the
solvent, the resulting liquid was purified by passing the solution through
a short filtration column (hexane as the eluent), and 9.02 g of pure
product was obtained as colorless liquid (70%). 1H NMR (CDCl3,
ppm): δ 0.87 (t, J ) 6.79 Hz, 3 H, -CH3), 1.24-1.34 (m, 12 H, alkyl
protons), 1.44 (m, 2 H, alkyl protons), 1.59 (m, 4 H, alkyl protons),
1.83 (m, 2 H, alkyl protons), 2.55 (t, J ) 7.20 Hz, 4 H, benzyl protons),
3.36 (t, J ) 6.34 Hz, 2 H, -CH2Br), 7.02 (s, 4 H, aromatic protons).
Compound 14. A mixture containing compound 13 (9.00 g, 25.47
mmol), iodine (5.19 g, 20.47 mmol), H5IO6 (2.332 g, 10.23 mmol),
acetic acid (17 mL), 30% sulfuric acid (3 mL), and CCl4 (8 mL) was
stirred at 80 °C for 48 h. It was then poured into aqueous solution of
NaHSO3 and extracted with methylene chloride. The organic layer
was washed with water and dried (MgSO4), and the solvent was
evaporated. The resulting liquid was purified by flash chromatogaphy
(hexane as the eluent) to give 11.8 g of product (78%). 1H NMR
(CDCl3, ppm): δ 0.87 (t, J ) 6.79 Hz, 3H, -CH3), 1.24-1.34 (m,
12H, alkyl protons), 1.46-1.59 (m, 6H, alkyl protons), 1.83 (m, 2H,
alkyl protons), 2.55 (t, J ) 7.20 Hz, 4H, benzyl protons), 3.36 (t, J )
6.34 Hz, 2H, -CH2Br), 7.52 (s, 2H, aromatic protons).
Compound 15. A solution of compound 14 (4.00 g, 6.71 mmol),
N-methyl aniline (1.078 g, 10.07 mmol), potassium carbonate (1.85 g,
13.42 mmol), tetrabutylammonium bromide (0.11 g, 0.34 mmol), and
sodium iodide (2.02 mg, 0.013 mmol) in toluene (5 mL) was stirred
under reflux overnight. Diethyl ether (25 mL) and water (25 mL) were
then added. The organic layer was separated and dried over magnesium
sulfate. After removal of the solvent, the residual liquid was purified
by chromatography (methylene chloride as eluent) to give 3.1 g of
product as colorless liquid (73%). 1H NMR (CDCl3, ppm): δ 0.87 (t,
J ) 6.79 Hz, 3H, -CH3), 1.26-1.37 (m, 14H, alkyl protons), 1.51-
1.58 (m, 6H, alkyl protons), 2.56 (t, J ) 6.50 Hz, 4H, benzyl protons),
2.90 (s, 3H, -NCH3), 3.28 (t, J ) 7.15 Hz, 2H, -CH2N), 6.40 (t, J )
7.95 Hz, 3H, aromatic protons), 7.17 (d, J ) 7.08 Hz, 2H, aromatic
protons), 7.52 (s, 2H, aromatic protons).
Compound 16. Phosphorus oxychloride (1.21 g, 7.919 mmol) was
added dropwise to DMF (5 mL, 64.6 mmol) at 0 °C. The solution
was stirred at 0 °C for 1 h and then at 25 °C for another 1 h. Compound
15 (5.00 g, 7.919 mmol) in 5 mL of DMF was then added dropwise to
the mixture. The resultng solution was stirred at 80 °C overnight. After
being cooled to room temperature, the solution was poured into cold
water and neutralized with NaAc. The mixture was extracted with
methylene chloride. The organic layer was washed with water and
then dried. After removal of the solvent, hexane was added to the
liquid residue. The product crystallized and was collected by filtration
as white solid (3.34 g, 64%, mp: 70-71 °C). 1H NMR (CDCl3,
ppm): δ 0.88 (t, J ) 6.48 Hz, 3H, -CH3), 1.27-1.64 (m, 20H, alkyl
protons), 2.55-2.59 (m, 4H, benzyl protons), 3.02 (s, 3H, -NCH3),
3.38 (t, J ) 7.36 Hz, 2H, -CH2N), 6.63 (d, J ) 8.61 Hz, 2H, aromatic
protons), 7.52 (s, 2H, aromatic protons), 7.66 (d, J ) 8.61 Hz, 2H,
aromatic protons), 9.65 (s, 1H, aldehyde proton).
Monomer D. Sodium hydride (0.40 g, 16.51 mmol) was added to
a solution of compound 16 (7.26 g, 11.01 mmol) in 1,2-dimethoxy-
ethane (DME) (10 mL). The suspension was stirred for 5 min and
diethyl 4-(methylsulfonyl)benzyl phosphate (3.37 g, 11.01 mmol) in 5
mL of DME was then added dropwise. The resulting solution was
stirred at 80 °C overnight and then poured into water. The mixture
was extracted with methylene chloride. The organic layer was washed
with water and dried. After removal of the solvent, the resulting mixture
was purified by chromatography (hexane:ethyl acetate ) 2:1 as eluent)
and recrystallization from ether to give 1.8 g of product as greenish
yellow solid (50%, mp: 94-95 °C). 1H NMR (CDCl3, ppm): δ 0.87
(t, J ) 6.48 Hz, 3H, -CH3), 1.23-1.60 (m, 20H, alkyl protons), 2.57-
2.58 (m, 4H, benzyl protons), 2.96 (s, 3H, -SO2CH3), 3.03 (s, 3H,
-NCH3), 3.33 (t, J ) 6.60 Hz, 2H, -CH2N), 6.62 (d, J ) 8.15 Hz, 2
H, aromatic protons), 6.84 (d, J ) 16.13 Hz, 1H, vinyl proton), 7.11
(d, J ) 16.20 Hz, 1 H, vinyl proton), 7.36 (d, J ) 8.39 Hz, 2 H aromatic
protons), 7.53-7.55 (m, 4 H, aromatic protons), 7.80 (d, J ) 7.97 Hz,
2 H, aromatic protons). Anal. Calcd for C36H47SNI2O2: C, 53.27; H,
5.84; N, 1.73. Found: C, 53.21; H, 5.86; N, 1.67.
Polymerization via the Heck Coupling Reaction. A typical
polymerization was exemplified by the synthesis of polymer 2.
Triethylamine (0.19 mL, 1.36 mmol) was added to a solution of
monomer A (0.0458 g, 0.0258 mmol), monomer C (0.4000 g, 0.517
mmol), p-divinylbenzene (0.0707 g, 0.543 mmol), Pd(OAc)2 (4.9 mg,
0.0217 mmol), and tri-o-tolylphospine (32.9 mg, 0.108 mmol) in 5-10
mL of DMF. The resulting mixture was stirred at 80 °C overnight in
a nitrogen atmosphere and was then poured into methanol. The
precipitated polymer was collected by filtration, redissolved in tetra-
chloroethane and reprecipitated in methanol. The polymer was further
purified by extraction in a Soxhlet extractor with methanol for 24 h
and dried under a vacuum at 50 °C for 2 days.
Polymer 1. 1H NMR (CDCl2-CDCl2, ppm): δ 0.88 (broad, 3H,
-CH3 in alkoxyl chain), 1.21 (b, 3H, -CH3 in chromophore), 1.38,
1.49, 1.71, 1.80 (four broad peaks, each has 2H, methylene protons),
2.87 (m, 3H, -SO2Me), 3.48 (b, 2H, -NCH2CH3) 3.79 (b, 2H, -NCH2-
CH2O-), 4.00 (b, 2H, -OCH2- in alkoxyl chain), 4.20 (b, 2H,
-OCH2CH2N-), 6.75 (b, 4H, aromatic protons), 7.02 (b, 5H, vinyl
protons), 7.38 (b, 5H, four aromatic and one vinyl protons), 7.46 (b,
4H, aromatic protons), 7.69 (m, 2H, aromatic protons). Anal. Calcd
for C41H45NO4S: C, 76.04; H, 6.96; S 4.94. Found: C, 74.38; H, 7.00;
S, 5.09
Polymer 2. 1H NMR spectra of polymer 2 is very similar to that of
polymer 1 except for some small peaks due to the ruthenium complex
(8.00, 8.5 ppm). Anal. Calcd for C43.15H47.65N1.25O4S0.95P0.1F0.6Ru0.05
:
C, 74.28; H, 6.83; N, 2.49; Ru, 0.69. Found: C, 73.36; H, 6.98; N,
2.67; Ru, 0.55.
Polymer 3. 1H NMR spectra of polymer 5 is very similar to that of
polymer 3 except for some small peaks due to the osmium complex
(4.0, 8.00, 8.5 ppm). Anal. Calcd for C47.9H57.15N1.25O2.1S0.95P0.1F0.6
-
Os0.05: C, 74.02; H, 6.98; N, 2.38. Found: C, 71.48; H, 6.73; N, 2.36.
Polymer 4. 1H NMR (CDCl3, ppm): δ 0.87 (broad, 3H, -CH3 in
alkyl chain), 1.19-1.16 (b, 20H, aliphatic protons), 2.74 (b, 4H, benzyl
protons), 2.92 (b, 3H, -SO2Me), 2.99 (b, 3H, -NCH3), 3.31 (b, 2H,
-NCH2-), 6.59 (b, 2H, aromatic protons), 6.99 (m, 1H, vinyl protons),
7.02 (b, 2H, aromatic protons), 7.07 (d, J ) 16.85 Hz, 1H, vinyl proton),
7.32 (b, 2H, aromatic protons), 7.40 (b, 4H, vinyl protons), 7.49 (b,
6H, aromatic protons), 7.77 (m, 2H, aromatic protons). Anal. Calcd
for C46H55SNO2: C, 80.54; H, 8.08; N, 2.04. Found: C, 80.50; H,
8.02; N, 2.08.
Polymer 5. 1H NMR spectra of polymer 5 is very similar to that of
polymer 4 except for some small peaks due to the ruthenium complex
(4.0, 8.0, 8.5 ppm). Anal. Calcd for C47.9H57.15N1.25O2.1S0.95P0.1F0.6
-
Ru0.05: C, 78.38; H, 7.85; N, 2.38, Ru, 0.67 Found: C, 76.48; H, 7.72;
N, 2.41, Ru, 0.50
Compound 21. Compound 21 was synthesized from compound 5
by an approach similar to that used in the synthesis of compound 6 (2
equiv of butyllithium was used) mp 74-75 °C. 1H NMR (CDCl3,
ppm): 0.90 (t, J ) 6.50 Hz, 6H, -CH3), 1.33 (m, 8H, methylene
protons), 1.46 (m, 4H, methylene protons), 1.79-1.84 (m, 4H,
methylene protons), 4.05 (t, J ) 6.16 Hz, 4H, -OCH2-), 7.37 (s, 2H,
aromatic protons), 10.44 (s, 2H, aldehyde protons). Anal. Calcd for
C20H30O4: C, 71.82; H, 9.04; O, 19.14. Found: C, 71.69; H, 9.11.
Compound 23. A mixture of compound 6 (0.60 g, 1.388 mmol),
vinyl tributyltin (0.44 g, 1.388 mmol), and Pd(PPh3)4 (0.032 g, 0.0278
mmol) in DMF (8 mL) was stirred at 100 °C for 4 h. After cooling to
room temperature, the mixture was filtered, and the filtrate was poured
into water. After extraction with ethyl ether, the organic layer was
collected and dried over MgSO4. Then, after removal of the solvent,
the crude product was purified by chromatography (hexane:ethyl acetate
) 20:1 as eluent) to give the product (0.24 g, 52%). 1H NMR (CDCl3,
ppm): 0.86-0.93 (m, 6H, -CH3), 1.26-1.46 (m, 12H, methylene
protons), 1.75-1.83 (m, 4H, methylene protons), 3.95 (t, J ) 6.51 Hz,
2H -OCH2-), 4.04 (t, J ) 6.38 Hz, 2H, -OCH2-), 5.38 (d, J )
11.30 Hz, 1H, vinyl proton), 5.80 (d, J ) 17.71 Hz, 1H, vinyl proton),
7.01 (m, 2H, one vinyl and one aromatic protons), 7.24 (s, 1H, aromatic
proton), 10.36 (s, 1H, -CHO).
Monomer E. The typical Heck reaction conditions as for polym-
erization were applied. The product was purified by chromatography
(H:EA)10:1 as eluent) and recrystalized from methylene chloride/
methanol. Yield: 38%, mp 123-124 °C. 1H NMR (CDCl3, ppm): δ
0.87-0.91 (m, 15H, -CH3 in alkoxy); 1.23 (t, J ) 7.08 Hz, 3 H, -CH3

4632 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Peng et al.
on chromophore), 1.27-1.38 (m, 22H, aliphatic protons), 1.47-1.55
(m, 10H, aliphatic protons), 1.80-1.87 (m, 10H, aliphatic protons),
3.04 (s, 3H, -SO2CH3), 3.51 (t, J ) 7.04 Hz, 2H, NCH2CH3), 3.81 (t,
J ) 5.60 Hz, 2H, -CH2CH2N), 3.97-4.08 (m, 10H, -OCH2- on
alkoxy side chain), 4.22 (t, J ) 5.81 Hz, 2H, -OCH2CH2N-), 6.70
(d, J ) 8.57 Hz, 2H, aromatic protons), 6.74 (d, J ) 16.39 Hz, 1H,
vinyl proton), 7.02 (d, J ) 16.23, 1H, vinyl proton), 7.08 (d, J ) 6.56
Hz, 2H, aromatic protons), 7.10 (d, J ) 15.50 Hz, 2H, vinyl protons),
7.25 (s, 1H, aromatic proton), 7.28 (s, 2H, aromatic protons), 7.30 (s,
1H, aromatic proton), 7.39 (d, J ) 16.45 Hz, 1H, vinyl proton), 7.44
(s, 1H, aromatic proton), 7.46 (s, 1H, aromatic proton), 7.49 (d, J )
8.06 Hz, 2H, aromatic protons), 7.52 (d, J ) 16.56 Hz, 1H, vinyl
proton), 7.80 (d, J ) 8.15 Hz, 2H, aromatic protons), 10.33 and 10.34
(s, 2H, -CHO). Anal. Calcd for C74H101NO10S: C, 74.27; H, 8.51;
N, 1.17. Found: C, 74.29; H, 8.47; N, 1.21.
Model Reaction. The reaction conditions were similar to the above.
The reaction mixture was poured into 5% hydrochloric acid solution
and extracted with ethyl ether. The organic layer was washed with
water and dried over MgSO4, and then the solvent was removed. After
collecting the 1H NMR, the residue was separated by chromatography
(hexane:ethyl acetate ) 6:1 as the eluent) to give compounds 18, 19,
and 20. The relative yield was calculated based on the 1H NMR
spectrum. The characterizations of the products were exemplified by
entry a (2,5-dihexoxyl-1,4-diiodobenzene as the reactant) as below.
Compound 18. Purified yield, 78%. 1H NMR (CDCl3, ppm): 0.92
(t, J ) 6.58 Hz, 6H, -CH3), 1.37 (m, 8H, methylene protons), 1.53
(m, 4H, methylene protons), 1.85 (m, 4H, methylene protons), 4.02 (t,
J ) 6.21 Hz, 4H, -OCH2-), 7.07 (s, 2H, aromatic protons), 7.08 (d,
J ) 15.98, 2H, vinyl protons), 7.30 (t, J ) 7.40, 6H, aromatic protons),
7.42 (d, J ) 16.51, 2H, vinyl protons), 7.47 (d, J ) 7.38, 4H, aromatic
protons). 13C NMR (CDCl3, ppm): 14.0, 22.6, 25.9, 29.4, 31.6, 69.4,
110.5, 123.4, 126.4, 126.7, 127.3, 128.6, 137.9, 151.0. Anal. Calcd
for C34H42O2: C, 84.60; H, 8.77. Found: C, 84.72; H, 8.76.
protons), 1.55 (b, 10H, methylene protons), 1.87(m, 10H, methylene
protons), 3.04 (b, 3H, -SO2CH3), 3.55 (b, 2H, NCH2CH3), 3.80 (b,
2H, -CH2CH2N), 4.10 (b, 10H, -OCH2- on alkoxy side chain), 4.22
(b, 2H, -OCH2CH2N-), five broad peaks at 6.70, 7.15, 7.31, 7.48,
7.70 were observed which could not be unambiguously assigned. Anal.
Calcd for C, 74.02; H, 6.89; Ru, 0.72. Found: C, 75.33; H, 8.24; Ru,
0.09.
Characterization. The 1H NMR spectra were collected on a Varian
500-MHz FT NMR spectrometer. The FTIR spectra were recorded
on a Nicole 20 SXB FTIR spectrometer. A Shimadzu UV-2401PC
UV/vis spectrometer was used to record the UV/vis spectra. Thermal
analyses were performed by using the DSC-10 and TGA-50 systems
from TA Instruments under a nitrogen atmosphere. The melting points
were obtained with open capillary tubes on a Mel-Tem apparatus
without corrections. Elemental analyses were performed by Atlantic
Microlab, Inc., except for the ruthenium analyses, which were done
by Galbraith Laboratories, Inc.. Molecular weights were measured with
a Waters RI GPC system using polystyrene as the standard and THF
as the eluent.
The photoconductivity was studied by measuring the voltage across
a 1 MΩ resistor resulting from a photocurrent running through the
sample. A Diode laser (690 nm) with an intensity of 20 mW was used
as the light source.24
Second-order NLO properties of poled polymeric films were
characterized by second harmonic generation measurements. A mode-
lock Nd:YAG laser (Continuum-PY 61 C-10, 10-Hz repetition rate)
was used as the light source. The second harmonic of the fundamental
wave (1064 nm) generated by the polymer sample was detected by a
photomultiplier tube (PMT), then amplified, and averaged in a boxcar
integrator. To measure the temperature dependence of the second order
nonlinearity, a polymer film was mounted to a heating stage. The
transmitted SHG signal was monitored while the sample was heated.
The linear electrooptic coefficient, r33, of the poled polymer films
was measured at 690 nm using a reflection method.14 A Soleil-Babinet
compensator was used to bias the DC intensity at its half maximum
intensity. The phase retardation between the p and s waves was
modulated by an external oscillating field. The amplitude of the
modulation intensity was collected using a lock-in amplifier, which
was then used to calculate the r33 value.
Two-beam coupling experiments were performed using a diode laser
(690 nm, 25 mW, Laser Power Technology, 690-300 or 780 nm, 30
mW) as the light source. The laser beam (s-polarized) was split into
two beams, which were intersected in the polymer film at a geometry
reported before.25 The transmitted intensities of the two beams were
monitored by lock-in amplifiers and collected by a computer.
To measure the phase shift of the refractive index grating over the
intensiy interference pattern, a motor driven pizoelectric translator was
used to move the sample along the grating vector. The transmitted
intensity of the two beams was collected in the same way as in the
two beam coupling experiment.
Compound 19. Purified yield, 11.7%. 1H NMR (CDCl3, ppm):
0.82 (m, 3H, -CH3), 0.92 (m, 3H, -CH3), 1.02 (m, 2H, methylene
protons), 1.10 (m, 2H, methylene protons), 1.18 (m, 2H, methylene
protons), 1.33 (m, 6H, methylene protons), 1.52 (m, 2H, methylene
protons), 1.81 (m, 2H, methylene protons), 3.73 (t, J ) 6.11 Hz, 2H,
-OCH2-), 3.96 (t, J ) 6.03 Hz, 2H, -OCH2-), 5.30 (s, 1H, vinyl
proton), 5.60 (s, 1H, vinyl proton), 6.81 (s, 1H, aromatic proton), 7.04
(s, 1H, aromatic proton), 7.07 (d, J ) 16.30, 1H, vinyl proton), 7.18-
7.31 (m, 8H, aromatic protons), 7.42-7.48 (m, 3H, two aromatic
protons + one vinyl proton). 13C NMR (CDCl3, ppm): δ, 13.99, 22.41,
22.58, 25.29, 25.88, 29.06, 29.39, 31.48, 31.56, 68.96, 69.35, 110.49,
115.27, 115.97, 123.47, 126.40, 126.56, 126.74, 127.16, 127.26, 127.88,
128.51, 128.66, 131.57, 137.88, 141.47, 147.52, 150.63, 150.72. Mass
spectra m+/e ) 482.3 (required 482.32).
Polymerization via the HWE Reaction. Typical polymerization
procedures were exemplified by the synthesis of polymer 6: Monomer
E (0.5680 g, 0.475 mmol) was dissolved in THF (5 mL), and NaH
(0.0340 g, 1.42 mmol) was then added. A solution of compound 22
(0.1710 g, 0.451 mmol) and compound 3 (0.0110 g, 0.024 mmol) in
THF (5 mL) was added into the above solution while stirring. The
resulting mixture was refluxed for 4 h, and the red polymer began to
precipitate out. The reaction was stopped, and the mixture was poured
into methanol. The polymer was collected by filtration and purified
by extraction in a Soxhlet extractor with methanol for 24 h. It was
then dried under a vacuum at 50 °C for 2 days (0.55 g, 91%).
Polymer 6. A similar 1H NMR spectrum as polymer 7 was obtained.
Since the solubility of polymer 7 is much better than that of polymer
Acknowledgment. This work was supported by the National
Science Foundation and Air Force Office of Scientific Research.
Support from the National Science Foundation Young Inves-
tigator program is gratefully acknowledged. This work also
benefitted from the support of the NSF MRSEC program at
the University of Chicago.
JA970048L
1
6 in CDCl3, H NMR data of polymer 7 was presented.
(24) Roncali, J. Chem. ReV. 1992, 92, 711.
(25) Chan, W. K.; Chen, Y. M.; Peng, Z. H.; Yu, L. J. Am. Chem. Soc.
1993, 115, 11735.
Polymer 7. 1H NMR (CDCl3, ppm): δ 0.89 (b, 15H, -CH3 in
alkoxy); 1.25 (b 3H, -CH3 on chromophore), 1.35 (m, 22H, methylene