Synthesis and structure/property correlation of fully functionalized photorefractive polymers

Article abstract of DOI:10.1021/ma020078v

This paper describes the synthesis and physical study of several new photorefractive polymers. The Heck reaction was successfully applied in the synthesis of these multifunctional polymers. These polymers are conjugated poly(phenylenevinylene)s copolymerized with a small amount of macrocyclic zinc complexes as the photosensitizers. Nonlinear optical chromophores were incorporated as the pendant groups. Both electron-rich and electron-deficient PPV backbones were synthesized. Experimental results showed that when an electron-rich photosensitizer is used, the electron-deficient component for charge transport (CN-PPV) enhances photorefractive performance and reduces the response time.

Full text of DOI:10.1021/ma020078v

4636
Macromolecules 2002, 35, 4636-4645
Synthesis and Structure/Property Correlation of Fully Functionalized
Photorefractive Polymers
Wei You , Lim in g Wa n g, Qin g Wa n g, a n d Lu p in g Yu *
Department of Chemistry and The J ames Franck Institute, The University of Chicago,
5735 South Ellis Avenue, Chicago, Illinois 60637
Received J anuary 16, 2002; Revised Manuscript Received April 3, 2002
ABSTRACT: This paper describes the synthesis and physical study of several new photorefractive
polymers. The Heck reaction was successfully applied in the synthesis of these multifunctional polymers.
These polymers are conjugated poly(phenylenevinylene)s copolymerized with a small amount of macrocyclic
zinc complexes as the photosensitizers. Nonlinear optical chromophores were incorporated as the pendant
groups. Both electron-rich and electron-deficient PPV backbones were synthesized. Experimental results
showed that when an electron-rich photosensitizer is used, the electron-deficient component for charge
transport (CN-PPV) enhances photorefractive performance and reduces the response time.
In tr od u ction
the backbone under the assistance of a certain electric
field, the generated charge carriers will be electrons that
cannot be effectively transported away along PPV
backbone. Moreover, the HOMO energy of PPV is lower
than that of photosensitizers, which makes the hole
transfer from photosensitizer to PPV backbone very
difficult. However, we reasoned that if the energy level
of LUMO of PPV backbone can be lowered by introduc-
ing electron-deficient groups, the substituted PPV could
be made a good electronic conductor (see Table 1). The
excited electrons in photosensitizers will experience a
stronger driving force for charge migration and separa-
tion. The dominant charge carriers will also become
electrons. Better photorefractive performance could be
achieved by tackling this energy mismatch. As shown
in Figure 1, PPV substituted with cyano groups on the
vinyl position exhibit a lower energy level of both LUMO
and HOMO.20,21 These are also reinforced by theoretical
calculation for energy levels of bother CN-PPV(I) and
CN-PPV(II).22 These are the rationales for the polymers
synthesized in this work, which contain cyano substit-
uents on the PPV backbone. PPV with CN substituents
on vinyl groups is well-known.23 However, the reaction
condition for the preparation of vinyl-CN-PPV(I) is not
compatible with the preparation of our multifunctional
polymer structures.24 Thus, we decided to introduce the
CN groups onto the aromatic rings. Additionally, to
utilize the “orientational enhancement effect”,25 the
polymer was designed to exhibit a low glass transition
temperature (Tg). We have successfully developed such
a polymer system (polymer 4 in Scheme 5), and an
excellent PR performance was observed for this polymer
system as expected. In this paper, we describe the
detailed synthesis of three photorefractive polymers
containing macrocyclic zinc complexes in their backbone
and pendant NLO chromophores. Detailed physical
studies of these polymers yielded very insightful infor-
mation about the design principles of new photorefrac-
tive materials.
The photorefractive (PR) effect refers to reversible,
spatial modulation of the index of refraction due to
photoinduced charge redistribution in an optically non-
linear material.1,2 Photorefractive polymers are multi-
functional materials that combine two distinctive physi-
cal properties, photoconductivity and electrooptic effect,
to manifest the photorefractive effect.3-8 These multi-
functional materials, therefore, must contain the ap-
propriate functional moieties providing photosensitivity,
photoconductivity, and electrooptical (EO) response,
either by means of composite materials or fully func-
tionalized polymers.10-19 Our group has developed a
series of fully functionalized PR materials; typical
resultant PR polymers utilize conjugated polymer back-
bones as the photoconductive component because of
their good photoconductivity and wide range of struc-
tural variation, which permits chemical modification
and functionalization.4,7,8 Numerous novel PR materials
have been synthesized, such as high-Tg conjugated PR
polymers containing transition-metal complexes, low-
Tg PR polymers bearing tris(bipyridyl)ruthenium(II)
complexes as photosensitizers, and low-Tg conjugated
PR polymers containing metalloporphyrin (polymer 1)
or metallophthalocyanine (polymer 2, Scheme 1).9,16-19
Our previous results indicated that, among these poly-
mers, polymers 1 and 2 exhibit the best PR perfor-
mances. However, their performances are still pale
compared with our small molecular systems.19 For
example, a monolithic methine dye PR material exhibits
a net optical gain of larger than 200 cm-1 and a
diffraction efficiency of 80%. These polymers show a net
optical gain of around 80 cm-1 and a diffraction ef-
ficiency of 20%.9
Electrochemical studies found that there is an energy
mismatch between the LUMO of photosensitizers and
the LUMO of poly(phenylenevinylene) (PPV) backbones.
It is well-known that PPV is a good conductor for holes.
To achieve the charge transporting and separation,
electrons in the HOMO of photosensitizers must be
promoted to the LUMO via photoexcitation. If the
excited electrons are then transferred to the LUMO of
Resu lts a n d Discu ssion
Syn th esis of Mon om er s a n d P olym er s. One of the
key monomers for the polymerization is dicyanodivinyl-
benzene (monomer A). Several plausible approaches
* Corresponding author. E-mail: lupingyu@midway.uchicago.edu.
10.1021/ma020078v CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/04/2002

Macromolecules, Vol. 35, No. 12, 2002
Photorefractive Polymers 4637
Sch em e 1
Ta ble 1. En er gy Level for Differ en t P olym er s a n d
P h otosen sitizer s
according to the same scheme (Scheme 3) with moderate
overall yield.
onset
ox
onset
re
E
E
EHOMO
ELUMO
Egap
Zinc porphyrin was synthesized according to the
procedure developed in our group.28 The synthesis of
zinc phthalocyanine was achieved according to a modi-
fied literature approach (Scheme 4). It is known that
phthalocyanine (Pc) has a strong tendency to form
columnar assemblies due to its aromatic planar mac-
rocycle (π-π stacking). To prevent the undesirable
aggregation and enhance its solubility, two spiro centers
with long alkyl chains were introduced into the Pc via
ketal 13 that could undergo further transformation to
afford one of the key molecules 15, 2′,2′-bis(tridecyl)-
5,6-(1′,3′-dioxole)-1,3-diiminoisoindole. Another key mol-
ecule for the formation of Pc ring is compound 11, 6/7-
iodo-1,3,3-trichloroisoindolenine, which was synthesized
by reacting compound 10 with PCl5. The phthalocyanine
ring was formed by the coupling reaction of 11 and 15
in dry THF. Upon oxidation with quinone and metala-
tion with zinc acetate dihydrate in a 1:3 mixture of
methanol and chloroform, zinc Pc, a green compound,
was obtained in moderate yield.
(V)
(V)
(eV)
(eV)
(eV)
PPV(MEH)a
CN-PPV(I)a
CN-PPV(II)b
porphyrinc
0.68
1.24
0.75
0.462
0.425
-1.49
-0.90
-1.26
NA
-5.07d
-5.63d
-5.55e
-4.64
-4.60
-2.90
-3.49
-3.54
-2.57
-2.90
2.17
2.14
2.01
2.07
1.70
phthalocyaninec
NA
The values are referred to Ag.20 The values are based on
a
b
the Fc/Fc+ redox couple as the internal reference. c The values are
based on the Ag/AgCl as the reference and are reported as E1/2
.
onset
ox
d
Calculated from EHOMO ) -(E
+ 4.39) eV and ELUMO
)
+ 4.8)
onset
re
onset
ox
-(E
+ 4.39) eV.20 e Calculated from EHOMO ) -(E
onset
re
eV and ELUMO ) -(E
+ 4.8) eV.29,30
were attempted to synthesize this compound, and the
one outlined in Scheme 2 worked best. The 1,4-dibromo-
p-xylene was oxidized into 2,5-dibromoterephthaldehyde
(2) by using CrO3 and mixed acid.26 Compound 2 was
further transformed to 1,4-dicyano-2,5-dibromobenzene
(compound 3) in high yield. The Stille coupling of 3 with
tributylvinyltin yielded monomer A.27 The reaction
conditions are not optimized, and the overall yield is
rather low. Monomers B and C were synthesized
Polymers were synthesized by utilizing the palladium-
catalyzed Heck polycondensation. The polymerization

4638 You et al.
Macromolecules, Vol. 35, No. 12, 2002
porphyrin. Elemental analysis further confirmed this
observation.
Th er m a l P r op er ties. To exhibit large photorefrac-
tive effect, low-Tg materials are needed in order to
utilize the “orientational enhancement effect”.25 Dif-
ferential scanning calorimetry (DSC) studies indicated
that the four polymers (polymers 1, 2, 3, and 4) exhibit
low glass transition temperatures, 16, 16, 9.8, and 4.8
°C, respectively. These low Tg values are due to incor-
poration of long alkyl chains on both the polymer
backbones and the NLO chromophores. Therefore, the
NLO chromophores in these polymer films can be
reoriented in response to photoinduced space-charge
field under ambient temperature.
Op tica l P r op er ties. The optical properties of these
polymers were studied by UV-vis absorption spectros-
copy (see Figure 3). For polymer 3, which is only
electron-deficient PPV, the maximum absorption λmax
appears at 443 nm, red-shifted from the absorption band
around 400 nm of the conventional alkyl-substituted
PPV without cyano susbtituents. PR polymer 4 shows
a strong absorption at 411 nm of λmax. The strong
intensity at 411 nm can be ascribed to the absorption
of the NLO chromophore incorporated in the polymer
backbone. The shoulder around 440 nm can be at-
tributed to the absorption of polymer backbone. The
Q-band at 574 nm was observed due to the incorporation
of zinc porphyrin. The Q-band is the most interesting
feature for the optical measurement, because it permits
the selective photoexcitation of polymers through the
photosensitizer (zinc porphyrin in polymer 4) by using
a He-Ne laser (632.8 nm), far away from the maximum
absorption of the NLO chromophore and PPV backbone.
Polymers 1 and 2 exhibit typical absorption due to either
porphyrin or phthalocyanine zinc complexes (inset of
Figure 3).
F igu r e 1. Energy diagram for polymer backbones and pho-
tosensitizers (PPV for MEH-PPV, CN-PPV(I) for cyano group
in the double bond, CN-PPV(II) for cyano group in the aromatic
ring, POR for zinc porphyrin, PC for zinc phthalocyanine).9,20,21
was carried out according to Scheme 4, using a cata-
lytic system composed of Pd(OAc)2/P(o-tolyl)3/n-Bu3N
(4%/20%/250%, molar ratio vs monomer). Aprotic polar
solvents, such as DMF and NMP, worked well as the
polymerization solvent. NMP was found to generate
CN-PPV polymers with better yield (polymers 3 and 4).
Initially, PR polymer was synthesized by using mono-
mers A and C (structures shown in Schemes 2 and 3)
and zinc porphyrin monomer. The resulting polymer
exhibited poor solubility in common organic solvents
(such as THF, chloroform, tetrachloroethane, and DMF),
and it is not possible to prepare thick films (>100 µm)
for physical studies. To enhance the solubility, longer
alkyl chains were introduced to the chromophore (mono-
mer B in Scheme 3), which lead to not only enhance-
ment in the solubility but also lowering in glass tran-
sition temperature of resultant polymers. A polymer
bearing no NLO chromophores was also synthesized as
a model polymer to investigate electrical properties.
These polymers now exhibit good solubility in common
solvents, such as chloroform, THF, and DMF. Polymers
1 and 2 were obtained in high yields when divinylben-
zene was used with two different zinc complexes. GPC
measurement in THF with polystyrene standard indi-
cated the relative number-averaged molecular weight
(Mn) of approximately 14 000 and 20 000 for polymers
3 and 4. Polymers 1 and 2 exhibit higher molecular
weights (polymer 1: Mw ) 29 000, PDI ) 1.55; polymer
2: Mw ) 72 000, PDI ) 2.74) than polymers 1 and 2,
probably due to less steric hindrance in the divinyl
monomers than monomer A.
Red ox P r op er ties. The redox properties of polymers
3 and 4 were investigated by using cyclic voltammetry
(CV). Under the assumption that the energy level of
ferrocene/ferrocenium is 4.8 eV below vacuum, we can
calculate the LUMO and HOMO energy levels according
onset
ox
onset
+
re
to EHOMO ) -(E
+ 4.8) eV and ELUMO ) -(E
4.8) eV.29,30 The onset reduction potential for 3 appeared
at -1.27 V (vs Fc/Fc+), which was used to infer the
energy level of LUMO for CN-PPV (-3.53 eV). This
value is more negative than that for the LUMO of MEH-
PPV (-2.90 eV). Clearly, the introduction of cyano
groups lowers the energy level of LUMO of electron-
deficient PPV backbone, which supports our previous
assumption. For the PR polymer 4, the reduction
potential was determined to be -1.26 V (vs Fc/Fc+),
corresponding to a LUMO energy level of -3.54 eV (vs
vacuum). On the basis of these data and the UV/vis
absorption spectroscopic results, an energy diagram can
be drawn (see Figure 1). Figure 1 indicates that there
is driving force for the transfer of electrons from LUMO
of photosensitizer to LUMO of polymer 4, which is
beneficial in terms of improving PR properties.
The structures of polymers 1, 2, and 4 were confirmed
by 1H NMR study, elemental analysis, and UV-vis
spectroscopy. For example, the 1H NMR spectrum of
polymer 4 (Figure 2) shows the characteristic chemical
shifts for the NLO chromophore and the electron-
deficient PPV backbone. For example, chemical shift
around 8.01 ppm corresponds to the hydrogen in the
cyano-substituted aromatic ring (hydrogen 11 in Figure
2). Q-band absorption at 574 nm was observed in
polymer solution, indicating the incorporation of zinc
P h otor efr a ctive P r op er ties. To investigate the
photorefractive properties, thick polymer films (>100
µm) were prepared from concentrated polymer solutions
and were sandwiched between two transparent ITO
glasses. Two-beam coupling (2BC) experiments were
performed to determine the PR nature of the polymers.
Two coherent laser beams with equal intensity (632.8
nm, p-polarized, 2 × 1.6 mW/cm2) were intersected
inside the polymer films. The asymmetric energy change

Macromolecules, Vol. 35, No. 12, 2002
Photorefractive Polymers 4639
Sch em e 2. Syn th esis of 1,4-Dicya n o-2,5-d ivin ylben zen e
Sch em e 3
between the two beams was clearly observed due to the
phase shift between the incident light intensity and the
refractive index modulation. (The refractive index was
measured to be 1.72 for polymer 4.) The 2BC gain
coefficient (Γ) was calculated according to the following
equation:
coefficient of 47.7 cm-1 and polymer 2, 54.2 cm-1. While
the absorption coefficients (R) for polymers 1, 2, and 4
were determined to be 12.4, 37, and 10.3 cm-1, respec-
tively, the net optical gain coefficient (Γ - R) are 35.3,
17.2, and 83.3 cm-1 for polymers 1, 2, and 4, individu-
ally, at this low field. Thus, polymer 4 is superior to
polymers 1 and 2 in terms of both gain coefficient and
net gain coefficient.
1
Γ ) ln
L
1 + R
1 - âR
(
)
To further investigate the PR properties for these
polymers, degenerate four-wave mixing (DFWM) ex-
periments were performed, in which two s-polarized
laser beams were used to write the PR grating and a
weak p-polarized, counterpropagating beam served to
probe the grating. All of these polymers show high
diffraction efficiency between 10 and 23%. However,
polymer 4 consistently shows higher diffraction ef-
ficiency. This provides additional evidence to show that
where R is the intensity modulation of the signal beam,
â is the intensity ratio of the two incident writing beams,
and L is the optical path length of the beam with gain.
As shown in Figure 4, the gain coefficients for all three
polymers (polymers 1, 2, and 4) increase with the
applied field, and polymer 4 shows the highest gain
coefficient with 93.6 cm-1 at a relatively low field of 45
V/mm. At the same field, polymer 1 exhibits a gain

4640 You et al.
Macromolecules, Vol. 35, No. 12, 2002
Sch em e 4
mmol), sodium acetate (11.81 g, 144 mmol), and formic acid
(70 mL, 99%) were mixed into a 250 mL two-necked round-
bottom flask. The mixture was heated to reflux overnight.
Then it was poured into water (250 mL) and extracted with
chloroform. The organic layer was washed with diluted NH3‚
H2O solution and water and dried over MgSO4. After removing
the solvent, compound 3 was obtained as a pale-yellow/brown
our initial design idea works. Because of the favored
charge separation process in these polymer systems, the
response time of the photorefractive effect should also
be shortened. It was determined that the response times
for polymers 1, 2, and 4 were 4.7, 0.45, and 0.094 s,
respectively, at a field strength of about 60 V/µm (Figure
6). Clearly, polymer 4 exhibits the fastest response time
among three polymers.
1
solid (6.00 g, 88%). H NMR (500 MHz, CDCl3, ppm): δ 7.95
(s, 2H, aromatic proton). 13C NMR (125 MHz, CDCl3, ppm): δ
114.53, 121.13, 124.23, 137.87. mp: 234-240 °C.
Con clu sion
Mon om er A. Stille coupling reaction was used to prepare
the final monomer A.27 Compound 3 (2.00 g, 7 mmol), tribu-
tylvinyltin (5.1 mL, 17 mmol), and one portion of the catalyst
Pd(PPh3)4 (0.24 g, 0.2 mmol), plus a few crystals of 2,6-di-tert-
butyl-4-methylphenol, were put into 50 mL two-necked RB
flask. The system was flushed with N2, and dry toluene (20
mL) was then added. The mixture was kept at reflux for 4 h,
and another portion of the same catalyst 0.24 g was then added
into the flask. The solution was kept at reflux for another 4 h.
The mixture was diluted with ether and treated with KF
solution (10%). The resulting solution was stirred and followed
by suction filtration to remove the insoluble solid. The yellow
organic layer was separated and dried. After removing the
solvents, a yellow/orange solid was collected. The solid was
dissolved into 100 mL of hexane followed by suction filtration
to provide the pale-yellow solid (0.72 g). Recrystallization with
hexane/chloroform gave a pure white crystal (0.31 g, 25%). 1H
NMR (500 MHz, CDCl3, ppm): δ 5.68 (d, J ) 11 Hz, 2H), 6.02
(d, J ) 17 Hz, 2H), 7.03 (dd, J 1 ) 17 Hz, J 2 ) 11 Hz, 2H), 7.91
(s, 1H, aromatic proton). 13C NMR (125 MHz, CDCl3, ppm): δ
115.19, 116.17, 121.18, 129.93, 130.89, 139.72. MS m/z calcd
from C12H8N2 (M+): 180.21. Found: 181.1 (M + 1+). Anal.
Calcd for C12H8N2: C, 79.98; H, 4.47; N, 15.54. Found: C,
79.68; H, 4.35; N, 15.29.
Several fully functionalized photorefractive polymers
containing conjugated backbones, and macrocyclic metal
complexes have been synthesized. All of the PR poly-
mers exhibit net optical gain under certain external
field. It was found that, in order to obtain high PR
performance, energy levels between photosensitizers
and transporting moieties should be carefully designed
to optimize the driving force for charge transfer. When
an electron-rich photosensitizer is used, the electron-
deficient charge transporting component both enhances
photorefractive performance and reduces the response
time.
Exp er im en ta l Section
Ma ter ia ls. All chemicals were purchased from commercial
suppliers and used as received unless otherwise specified. All
reactions were carried out under a nitrogen atmosphere unless
otherwise noted. Tetrahydrofuran (THF) was distilled over
sodium and benzophenone. Zinc porphyrin, compound 2, and
compound 5 were synthesized according to the literature.17,26,28
Syn th esis of Mon om er s: Com p ou n d 3. Compound 2
(7.01 g, 24 mmol), hydroxyamine hydrochloride (8.34 g, 120

Macromolecules, Vol. 35, No. 12, 2002
Photorefractive Polymers 4641
Sch em e 5
Com p ou n d 4. A mixture of aniline (9.2 mL, 100 mmol),
1-bromohexadecane (15.5 mL, 50 mmol), tetrabutylammonium
bromide (1.61 g, 5 mmol), sodium iodide (0.075 g, 0.5 mmol),
and potassium carbonate (20.73, 150 mmol) with toluene (100
mL) was kept at reflux for 2 days. The mixture was poured
into water and extracted with ether. The organic layer was
washed with water and dried over MgSO4. After removing the
solvent under reduced pressure, the residue was distilled
under reduced pressure (0.2 mmHg, 130-150 °C) to afford
compound 12 (almost white solid, 9.0 g, 57%). Further puri-
fication could be achieved by recrystallization with ethanol.
1H NMR (500 MHz, CDCl3, ppm): δ 0.88 (t, J ) 7 Hz, 3H,
-CH3), 1.22-1.29 (m, 24H, alkyl protons), 1.59-1.63 (m, 4H,
alkyl protons), 3.09 (t, J ) 7 Hz, 2H, -NCH2-), 6.60 (d, J )
8 Hz, 2H, aromatic protons), 6.68 (t, J ) 7 Hz, 1H, aromatic
protons), 7.17 (m, 2H, aromatic proton). 13C NMR (125 MHz,
CDCl3, ppm): δ 14.11, 22.69, 27.17, 29.36, 29.45, 29.57, 29.60,
29.65, 29.67, 29.68, 31.92, 43.98, 112.66, 117.04, 129.19,
148.53. mp: 45-46 °C.
Com p ou n d 6. A mixture of compound 5 (2.88 g, 3.6 mmol),
compound 12 (2.28 g, 7.2 mmol), tetrabutylammonium bromide
(0.115 g, 0.36 mmol), sodium iodide (0.004 g, 0.024 mmol), and
potassium carbonate (1.50 g, 10.8 mmol) with toluene (10 mL)
was kept at reflux for 2 days. The mixture was poured into
water and extracted with CH2Cl2, and the organic extract was
dried over MgSO4. After removing the solvent under reduced
pressure, the residue was purified by flash chromatography
on silica gel (hexane:CH2Cl2 ) 6:1 v/v) to afford compound 6
1
(white solid, 3.23 g, 86%). H NMR (500 MHz, CDCl3, ppm):
δ 0.88 (t, J ) 7 Hz, 6H, -CH3), 1.26-1.31 (m, 66H, alkyl
protons), 1.50-1.56 (m, 10H, alkyl protons), 2.58 (t, J ) 8 Hz,
4H, benzyl protons), 3.24 (t, J ) 8 Hz, 4H, -CH2NCH2-),
6.60-6.64 (m, 3H, aromatic protons), 7.19 (m, 2H, aromatic
proton), 7.59 (s, 2H, aromatic protons). 13C NMR (125 MHz,
CDCl3, ppm): δ 14.12, 22.69, 27.20, 29.30, 29.36, 29.39, 29.55,
29.69, 30.18, 31.92, 39.82, 51.03, 100.32, 110.60, 114.98,
129.16, 139.27, 144.81, 148.14. mp: 43.5-45.5 °C.
Com p ou n d 7. Phosphorus oxychloride (0.4 mL, 4.3 mmol)
was added dropwise into a flame-dried 50 mL two-necked RB
flask loaded with anhydrous DMF (2 mL) in an ice bath. The
mixture was kept stirring for 1 h at 0 °C and another hour at
room temperature. Then, a mixture of compound 6 (3.08 g,
2.97 mmol) with 8 mL of anhydrous DMF was dropwise added
into the flask. The mixture was then kept at 90 °C overnight.
After cooling to room temperature, the mixture was poured
into water and neutralized with sodium acetate and followed
by extraction with CH2Cl2. The organic extract was washed
with water and dried. After removing the solvent under
reduced pressure, the residue was purified by flash chroma-
tography on a silica gel column (hexane:ether ) 6:1, then 4:1
v/v) to afford compound 7 (pale yellow/white solid, 2.38 g, 75%).
1H NMR (500 MHz, CDCl3, ppm): δ 0.88 (t, J ) 7 Hz, 6H,
-CH3), 1.26-1.33 (m, 66H, alkyl protons), 1.50-1.55 (m, 10H,
alkyl protons), 2.58 (t, J ) 8 Hz, 4H, benzyl protons), 3.33 (t,

4642 You et al.
Macromolecules, Vol. 35, No. 12, 2002
F igu r e 2. 1H NMR spectrum for polymer 4.
F igu r e 3. UV-vis spectra of different polymers in chloroform
(c ) 1 × 10-5 mol L-1). Inset: Q-bands for incorporation of
metal complexes in polymers.
F igu r e 4. Optical gain coefficients of polymers 1, 2, and 4 as
a function of applied field.
100.32, 110.62, 124.43, 132.26, 139.26, 144.80, 152.56, 189.95.
mp: 59.0-62.0 °C.
Mon om er B. Compound 7 (1.99 g, 1.86 mmol) was mixed
with 10 mL of dry DME into 50 mL two-necked RB flask,
followed by adding NaH (0.085 g, 3.52 mmol). The suspension
was stirred at room temperature for 20 min. A solution of
J ) 8 Hz, 4H, -CH2NCH2-), 6.63 (d, J ) 9 Hz, 2H, aromatic
protons), 7.59 (s, 2H, aromatic protons), 7.69 (d, J ) 9 Hz, 2H,
aromatic proton), 9.69 (s, 1H, aldehyde proton). 13C NMR (125
MHz, CDCl3, ppm): δ 14.12, 22.69, 27.08, 29.29, 29.36, 29.45,
29.50, 29.55, 29.58, 29.60, 29.68, 30.18, 31.91, 39.81, 51.10,

Macromolecules, Vol. 35, No. 12, 2002
Photorefractive Polymers 4643
the crude product, which was washed by hot water to afford
compound 9 (1.10 g, 65%). 1H NMR (400 MHz, DMSO-d6,
ppm): δ 6.35 (s, 2H), 6.75 (d, J ) 8 Hz, 1H), 6.82 (s, 1H), 7.38
(d, J ) 8 Hz, 1H).
Com p ou n d 10. Compound 9 (2.0 g, 12.3 mmol) was
dissolved in a solution of concentrated H2SO4 (4 mL) and water
(15 mL) at 0 °C. Then a solution of NaNO2 (1.0 g, 14.5 mmol)
mixed with 3 mL of water was added dropwise into the
mixture. After stirring for 30 min, another solution of KI (3.5
g, 21.1 mmol) dissolved in 15 mL of water was added into the
mixture. After another 1 h, the mixture was poured into ice
water and extracted with CH2Cl2, and the organic layer was
further washed with Na2S2O3 solution. After removing the
solvent at reduced pressure, the crude product was purified
by flash chromatography on silica gel (CH2Cl2: ethyl acetate
) 10:1, then 5:1 v/v) several times to afford compound 10 (1.5
F igu r e 5. Diffraction efficiency of polymers 1, 2, and 4 as a
function of applied field.
1
g, 44%). H NMR (400 MHz, DMSO-d6, ppm): δ 7.54 (d, J )
8 Hz, 1H), 8.08 (s, 1H), 8.15 (d, J ) 8 Hz, 1H).
Com p ou n d 11. Compound 10 (1.7 g, 6.2 mmol) was mixed
with PCl5 (2.6 g, 12.5 mmol) and dry 1,2-dichlorobenzene (20
mL) in a 50 mL two-necked RB flask. The mixture was heated
to 105 °C for 30 min until it was sufficiently liquidified to stir.
The mixture was heated and stirred for a week. The mixture
was cooled to room temperature, and the solvent and the
byproduct were removed by vacuum distillation. The residue
was distilled under high vacuum (bp ca. 140 °C for 0.1 Torr)
to afford compound 11 (0.64 g, 30%, almost a 1:1 mxiture of
1
F igu r e 6. Response time of diffraction signal of polymer 4 at
a field of 61 V/µm and 2 × 1.6 mW/cm2.
two regio isomers). H NMR (400 MHz, CDCl3, ppm): δ 7.28
(d, J ) 8 Hz, 1H), 7.94 (dd, J 1 ) 8 Hz, J 2 ) 1.5 Hz, 1H), 8.17
(d, J ) 1.5 Hz, 1H); 7.56 (d, J ) 8 Hz, 1H), 7.90 (d, J ) 1.5 Hz,
1H), 7.99 (dd, J 1 ) 8 Hz, J 2 ) 1.5 Hz, 1H).
compound 16 (1.45 g, 2.80 mmol) with 10 mL of anhydrous
DME was added dropwise into the flask. The mixture was kept
at 90 °C overnight. After cooling to room temperature, the
mixture was poured into water and extracted with CH2Cl2.
The organic extract was washed with water and dried. After
removing the solvent under reduced pressure, the residue was
purified by flash chromatography on silica gel (hexane:ether
) 8:1 v/v) to afford monomer B (greenish-yellow solid, 2.02 g,
75%). (Some residue of the cis isomer could be transformed to
Com p ou n d 12. 1,2-Dihydroxybenzene (11.0 g, 99.9 mmol)
was dissolved in 100 mL of CCl4 at 0 °C. Then bromine (9.9
mL, 194.0 mmol) dissolved in 15 mL of CCl4 was added
dropwise into the mixture, followed by raising the temperature
to room temperature. After keeping stirring for an hour, the
solvent was removed at reduced pressure, and the residue was
purified by recrystallization with ethanol to afford compound
12 (18.94 g, 70%). 1H NMR (400 MHz, CDCl3, ppm): δ 5.35 (s,
2H, OH), 7.14 (s, 2H, ArH).
1
the trans isomer by iodine-assisted isomerization.) H NMR
(500 MHz, CDCl3, ppm): δ 0.88 (t, J ) 7 Hz, 9H, -CH3), 1.23-
1.33 (m, 90H, alkyl protons), 1.54-1.60 (m, 12H, alkyl protons),
1.68-1.72 (m, 2H, alkyl protons), 2.58 (t, J ) 8 Hz, 4H, benzyl
protons), 3.07 (t, J ) 8 Hz, 2H, -SO2CH2-), 3.29 (t, J ) 8 Hz,
4H, -CH2NCH2-), 6.62 (d, J ) 9 Hz, 2H, aromatic protons),
6.87 (d, J ) 16 Hz, 1H, trans double bond), 7.16 (d, J ) 16 Hz,
1H, trans double bond), 7.39 (d, J ) 8 Hz, 2H, aromatic
protons), 7.58 (m, 4H, aromatic protons), 7.81 (d, J ) 8 Hz,
2H, aromatic proton). 13C NMR (125 MHz, CDCl3, ppm): δ
14.12, 22.69, 27.08, 29.29, 29.36, 29.45, 29.50, 29.55, 29.58,
29.60, 29.68, 30.18, 31.91, 39.81, 51.10, 100.32, 111.48, 121.08,
123.25, 126.12, 128.40, 132.87, 135.88, 139.26, 143.91, 144.77,
Com p ou n d 13. Compound 12 (4.80 g, 17.9 mmol), hepta-
cosanone (4.0 g, 10.2 mmol), and a catalytic amount of
p-toluenesulfonic acid monohydrate (0.5 g, 2.6 mmol) were
dissolved in 100 mL of toluene. The solution was kept at reflux
until TLC showed the completion of reaction. The solvent was
removed at reduced pressure, and the residue was purified
by flash chromatography on silica gel (hexane as eluent) to
afford compound 13 (4.12 g, 63%). 1H NMR (400 MHz, CDCl3,
ppm): δ 0.86 (t, J ) 7 Hz, 6H, -CH3), 1.23-1.33 (m, 44H,
alkyl protons), 1.81 (t, J ) 7 Hz, 4H, O-C-CH2-alkyl), 7.14
(s, 2H, ArH).
Com p ou n d 14. A mixture of compound 13 (7.0 g, 10.9
mmol), CuCN (3.00 g, 33.5 mmol), and DMF (80 mL) was kept
at reflux for several hours until TLC showed the completion
of reaction. The mixture was poured into NH4OH solution (200
mL), followed by filtration, and the collected solid was washed
with NH4OH solution and water. The crude product was
purified with flash chromatography on silica gel several times
(first with CH2Cl2, then with CH2Cl2:hexane ) 1:2 v/v) to afford
144.84. 148.48. mp: 53.0-57.0 °C. MS m/z calcd from C80H135
-
-
SO2NI2 (M+): 1428.82. Found: 1428.5. Anal. Calcd for C80H135
SO2NI2: C, 67.25; H, 9.52; O, 2.24; N, 0.98; S, 2.24; I, 17.76.
Found: C, 67.46; H, 9.56; O, 2.26; N, 0.98; S, 2.24; I, 17.36.
Com p ou n d 8. Fuming H2SO4 (20 mL, 20% SO3) was mixed
with fuming HNO3 (5 mL), followed by adding phthalimide
(4.00 g, 27.2 mmol) in portions over a 15 min interval with
stirring. The temperature was raised slowly to 40-50 °C and
kept at that range for 40 min. Then the mixture was cooled to
0 °C and slowly poured onto ice with stirring, followed by
filtration to afford the crude product. The crude product was
washed with water and purified by recrystallization with
ethanol to afford compound 8 (2.90 g, 56%). 1H NMR (400 MHz,
DMSO-d6, ppm): δ 8.04 (d, J 1 ) 8 Hz, J 2 ) 0.5 Hz, 1H), 8.60
(dd, J 1 ) 8 Hz, J 2 ) 2 Hz, 1H), 8.62 (dd, J 1 ) 2 Hz, J 2 ) 0.5
Hz, 1H).
1
compound 14 (2.7 g, 46%). H NMR (500 MHz, CDCl3, ppm):
δ 0.88 (t, J ) 7 Hz, 6H, -CH3), 1.25-1.35 (m, 44H, alkyl
protons), 1.93 (t, J ) 7 Hz, 4H, O-C-CH2-alkyl), 7.02 (s, 2H,
ArH).
Com p ou n d 15. CH3ONa/CH3OH was prepared by adding
Na (0.1 g, 4.4 mmol) to 40 mL of dry CH3OH. To this solution
was added compound 14 (1.0 g, 1.8 mmol), followed by bubbling
dry NH3 (3 atm) through the solution. The solution was first
kept stirring at room temperature for 1 h and then heated to
reflux for another 3 h. The solution was then cooled and left
overnight. After filtration and washed with cold methanol,
compound 15 could be obtained (0.92 g, 90%). 1H NMR (400
MHz, CDCl3, ppm): δ 0.87 (t, J ) 7 Hz, 6H, -CH3), 1.24-
1.40 (m, 44H, alkyl protons), 1.91 (t, J ) 7 Hz, 4H, O-C-
CH2-alkyl), 6.99 (s, 2H, ArH).
Com p ou n d 9. SnCl2 (8.4 g, 44.3 mmol) was mixed with HCl
(saturated solution, 45 mL) and 15 mL of water to prepare
the SnCl2 solution. To this solution was added compound 8
(2.00 g, 10.4 mmol) slowly with stirring. The mixture was kept
at 50 °C for 2 h until TLC showed completion of reaction. The
mixture was cooled to 0 °C, followed by filtration to provide

4644 You et al.
Macromolecules, Vol. 35, No. 12, 2002
Zin c P h th a locya n in e. In a dried 100 mL RB flask were
loaded compound 15 (0.41 g, 0.74 mmol) and triethylamine
(0.161 g, 1.6 mmol). Dry nitrogen was passed through the flask
by the two-needle method. 50 mL of dry THF was added into
the flask by a syringe to dissolve compound 15. Then the
mixture was cooled to 0 °C by a salt/ice bath. A solution of
compound 11 (0.26 g, 0.74 mmol) in 15 mL of dry THF was
gradually added in the flask by a syringe over a period of 15
min. The reaction mixture was then stirred at 0 °C for about
1 h and allowed to warm to room temperature with stirring
for another 6 h. After removing the salt by filtration, the
reaction mixture was put back to the flask, followed by
addition of hydroquinone (0.082 g, 0.74 mmol) and sodium
methoxide (0.130 g, 2.39 mmol). The reaction mixture was
refluxed under nitrogen for 6 h. After the mixture was cooled
and filtered, the solvent was removed. The residue was washed
with boiling water and filtered until the filtrate was clear and
then washed with ethanol until filtrate was clear. After
purification by flash chromatography with neutral alumina
(column with heating) (first with CH2Cl2:hexane ) 1:6, then
adding some CHCl3 to increase the polarity, until finally using
pure CHCl3), dihydrophthalocyanine (H2Pc) could be obtained
at 40% yield. The H2Pc (0.030 g, 0.019 mmol) and Zn(OAc)2‚
2H2O (0.030 g, 0.14 mmol) were added into a mixed solvent of
15 mL of CHCl3 and 5 mL of CH3OH. The resulting mixture
was heated to reflux for 1 day. After removing the solvent at
reduced pressure, the residue was purified by flash chroma-
tography in a basic alumina column (CH2Cl2:hexane ) 1:6,
then 1:4 v/v) to afford the zinc phthalocyanine (zinc Pc, 0.027
was provided by Hewlett-Packard Agilent 1100 LCMSD.
Elemental analyses were performed by Atlantic Microlab, Inc.,
except for the metal (zinc), which was collected by Galbraith
Laboratories, Inc. Molecular weights and distributions were
measured with a Waters RI and UV GPC system (Waters 410
differential refractometer and Waters 486 tunable absorbance
detector) with polystyrene as the standard and THF as the
eluent.
The films for two-beam coupling and four-wave mixing
experiments were prepared by sandwiching the materials
between two indium-tin oxide (ITO) covered glass substrates.
The thickness of the film was maintained at 125 µm with the
help of a polyimide spacer. Two-beam coupling experiments
were performed using a He-Ne laser (632.8 nm, 30 mW) as
the light source. The two split p-polarized laser beams with
equal intensity (2 × 1.6 mW/cm2) were intersected in the film
with a cross-angle of 7.5° to generate the refractive index
grating. The film normal was tilted an angle of 53° with respect
to the symmetric axis of the two writing beams to provide a
nonzero projection of the grating wave vector along the poling
axis. The transmitted intensities of the two beams were
monitored by two calibrated diode detectors. The diffraction
efficiency was measured by degenerate four-wave mixing
(DFWM) experiment, in which two s-polarized laser beams
(632.8 nm) of equal intensity intersected in the film to write
the index grating and a weak p-polarized beam (probe beam)
counterpropagating to one of the writing beams was used to
read the index grating formed in the material. The diffracted
light intensity of the probe beam was detected by a photodiode
and subsequently amplified with a lock-in amplifier. The
diffraction efficiency η was calculated as the ratio of the
intensities of the diffracted beam to the incident reading beam.
Data were collected by a computer. The refractive indexes of
the polymers were measured by using the Metricon model 2010
prism coupler at 632 and 780 nm. The refractive indexes at
other wavelength were deduced from the corresponding Sell-
myer relationship.
1
g, 86%). H NMR (400 MHz, CDCl3, ppm): δ 0.85 (s, br, 12H,
-CH3), 1.25-1.55 (m, br, 88H, alkyl protons), 1.84 (s, br, 8H),
2.34 (s, br, 8H), 7.50-7.74 (br, 4H), 8.07 (br, 4H), 8.65 (br,
2H).
P olym er iza tion . A typical polymerization procedure is as
follows: A mixture of monomer A (0.0812 g, 0.45 mmol),
monomer B (0.6507 g, 0.455 mmol), and zinc porphyrin (0.0045
g, 0.0046 mmol) in 10 mL of NMP was added with tri-n-
butylamine (0.27 mL, 1.13 mmol), palladium acetate (0.0045
g, 0.02 mmol), and tri-o-tolylphosphine (0.0287, 0.094 mmol).
The mixture was kept stirring at 90 °C overnight and then
poured into methanol. The resulting precipitate was collected,
redissolved into chloroform, and filtered through Celite to
remove the catalyst residue. The filtrate was concentrated and
precipitated into methanol, followed again by redissolving the
collected solid, filtration, and reprecipitation. The resulting
polymer was further purified by extraction in a Soxhlet
extractor with methanol for 24 h and then was dried under
vacuum at 40 °C overnight.
Polymer 1: Anal. Calcd for C66.54H95.68N1.04O2S1Zn0.01: C,
82.04; H, 9.82; N, 1.49; Zn, 0.067. Found: C, 81.27; H, 9.57;
N, 1.52; Zn, 0.071.
Polymer 2: Anal. Calcd for C66.3H95.31N1.07O2.02S0.99Zn0.01: C,
81.98; H, 9.81; N, 1.54; Zn, 0.067. Found: C, 81.04; H, 9.37;
N, 1.49; Zn, 0.070.
Ack n ow led gm en t. This work was supported by the
National Science Foundation and the Air Force Office
of Scientific Research. This work also benefited from the
support of NSF MERSEC program at The University
of Chicago.
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1
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