Efficient fully functionalized photorefractive polymethacrylates with infrared sensitivity and different spacer lengths

Article abstract of DOI:10.1039/b102489m

A series of photorefractive polymethacrylates, containing a Disperse Red type chromophore and carbazole as charge transport agent with various spacer lengths, was synthesized and characterized. The photorefractive effect of these materials was studied by

Full text of DOI:10.1039/b102489m

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Efficient fully functionalized photorefractive polymethacrylates with
infrared sensitivity and different spacer lengths
Christiaan Engels,a David Van Steenwinckel,b Eric Hendrickx,b Mark Schaerlaekens,b
Andre´ Persoonsb and Celest Samyn*a
aLaboratory of Macromolecular and Physical Organic Chemistry, University of Leuven,
Celestijnenlaan 200F, B-3001 Leuven, Belgium. Tel: 132-(0)-16-327438;
Fax: 132-(0)-16-327990; E-mail: celest.samyn@chem.kuleuven.ac.be (C. Samyn).
bLaboratory of Chemical and Biological Dynamics and Center for Research on Molecular
Electronics and Photonics, University of Leuven, Celestijnenlaan 200D, B-3001 Leuven,
Belgium
Received 16th March 2001, Accepted 2nd January 2002
First published as an Advance Article on the web 15th February 2002
A series of photorefractive polymethacrylates, containing a Disperse Red type chromophore and carbazole as
charge transport agent with various spacer lengths, was synthesized and characterized. The photorefractive
effect of these materials was studied by four-wave mixing and two beam-coupling at 780 nm after sensitization
with 1 wt% TNFM. We have found a gain coefficient of C ~ 140 cm21 at an applied electric field of
60 V mm21 and complete internal diffraction at an applied electric field of 52 V mm21. For fully functionalized
photorefractive polymers, these values rank among the highest reported up to date.
temperature, 20 mol% of dodececyl methacrylate was incorpo-
Introduction
rated into the polymer.11,12 This general polymer architecture
is shown in Fig. 1(a). These polymers were the first fully
functionalized polymers to show a net two-beam coupling gain
at the infrared wavelength of 780 nm.
Photorefractive polymers are a recently discovered class of
materials for dynamic holography, that combine the intrinsic
advantages of polymers, such as synthetic flexibility, with
excellent optical characteristics, such as high diffraction
efficiencies and sub-second response times.1–3 In a photo-
refractive polymer, charges that are generated by the absorp-
tion of light from an optical interference pattern, migrate under
the influence of an externally applied electric field, until they
are trapped. The resulting non-uniform charge distribution
produces a so-called space-charge field. This space-charge field,
in combination with the externally applied electric field, then
modulates the polymer refractive index through birefringence
and the Pockels effect. The components of a photorefractive
polymer reflect the stepwise buildup of the index modulation,
and include a small quantity of a charge generator, and large
quantities of a charge transport molecule and a highly polar
chromophore.
Here we report on the synthesis and photorefractive response
of a similar series of copolymers P1–P9, shown in Fig. 1(b),
wherein the spacer length between the pendant carbazole and
dye units and the polymer backbone was varied to optimize the
glass transition temperature and avoid the addition of external
plasticizers. As the chromophore moiety, we have chosen the
traditional azo-dye Disperse Red. The main goal of this new
approach is to further increase the index modulation amplitude
attainable in the copolymers. The elimination of the internal
plasticizer can result in a larger chromophore number density.
Furthermore, the Disperse Red dye has a larger dipole moment
than the previously used 4,4’-dimethylaminonitrostilbene
(DANS) chromophore, 8.1 D versus 6.6 D. We expect both
factors to contribute to a larger dynamic range in this type of
newly synthesized copolymers.
First, we discuss the polymer synthesis, characterization, and
the variation of the polymer glass transition temperature with
spacer length, followed by the sample preparation. Finally,
the experimental setup and the photorefractive parameters of
two of the copolymers, sensitized for infrared wavelengths by
adding 1 wt% of (2,4,7-trinitrofluoren-9-ylidene)malononitrile
(TNFM), are discussed. In these polymers and at a wavelength
of 780 nm, we have observed internal diffraction efficiencies of
100% at applied fields as low as 52 V mm21. This photo-
refractive performance is among the best reported for infrared-
sensitive fully functionalized polymers thus far.
One way to combine all these properties in a single material
is to mix
a hole-transporting polymer, such as poly-
(N-vinylcarbazole), with up to 50 wt% of a highly polar
dye.4 To enable chromophore reorientation, and thereby the
enhancement of the index modulation amplitude via bire-
fringence, the glass transition temperature is then further
lowered to room temperature by the addition of N-ethylcarba-
zole as plasticizer. Such an approach can be convenient, since
all the components can be readily purified and many different
combinations can easily be tested. However, this approach will
mostly produce mixtures that are thermodynamically unstable
and show phase separation upon storage. The phase stability
has been improved by using mixtures of chromophores,5,6 but
it is clear that for the complete elimination of phase separation
fully functionalized polymers are the key to success and several
synthetic approaches have been published in the literature.7–10
In previous work, we have reported on the synthesis and the
photorefractive response of a series of functionalized metha-
crylate copolymers, where the carbazole and polar dye unit
were covalently attached to the polymethacrylate backbone
with n-hexyl spacers. In order to reduce the glass transition
Results and discussion
Synthesis of the photorefractive polymethacrylates
Hydroxyalkylcarbazoles 7–9 and hydroxyalkyl chromophores
12 and 13 were synthesized as presented in Schemes 1 and 2.
They were reacted with methacryloyl chloride to yield the
necessary monomers. Scheme 3 depicts the monomer and
DOI: 10.1039/b102489m
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This journal is # The Royal Society of Chemistry 2002
951

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Fig. 1 Generalized structures of the copolymers previously characterized in ref. 11, P0 (left), and the newly synthesized copolymers P1–P9. Note the
use of a chromophore with higher polarity and the omission of the internal plasticizer and the variable spacer length.
polymer syntheses. The polymers were obtained by radical
copolymerization of a carbazole- and chromophore-meth-
acrylate in a 50 : 50 ratio. The polymerizations were carried
out in N,N-dimethylformamide (DMF) at 65 uC for 24 h using
1 wt% of 2,2’-azobisisobutyronitrile (AIBN) as initiator under
an argon atmosphere.
The compositions of the copolymers were determined by
1H-NMR and are listed in Table 1. The results were consistent
1
with the monomer feed. In Fig. 2, the H-NMR spectrum of
with increasing spacer length. This spacer creates a distance
between the ‘bulky’ carbazole and chromophore groups, and
the polymer backbone. This results in a more flexible polymer
backbone and, hence a lower Tg.
Sample preparation
Samples for photorefractive measurements were prepared by
dissolving the polymer in chloroform, and by adding TNFM
up to 1 wt% concentration. After passing this solution through
a 0.2 mm PTFE membrane filter, the solvent was allowed to
evaporate for 3 hours at 80 uC. The resulting homogeneous
mixture was then molten between two ITO-coated glass slides,
and the thickness of the samples was controlled by glass spacers
of 125 mm diameter.
For our optical experiments, we focus on two of the
copolymers with a low Tg, P6 and P8. Good quality optical
films of these polymers could be prepared without adding
plasticizer. Unfortunately, we were not able to prepare films of
P1–P4 without adding a plasticizer. More work is in progress
to prepare films of good optical quality of the remaining
polymers.
polymer P7 is given. In NMR, it is well known that efficient
relaxation results in broad peaks. This efficient relaxation is
also observed in polymers, because of their high molecular
1
weight compared to small molecules.13 The H-NMR spectra
of P1–P9 show a similar feature: they reflect well the influence
of the spacer length on the mobility of the different moieties. A
short spacer results in broader NMR peaks because of efficient
relaxation. As the spacer length increases, the peaks become
sharper and multiplets are better resolved.
The physical properties of polymers P1–P9 are listed in
Table 2. High yields and reasonable molecular weights were
obtained and the GPC measurements showed a monomodal
distribution for all polymers. As expected, the Tg decreases
Scheme 1 Synthesis of hydroxyalkyl carbazoles 7–9.
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Scheme 2 Synthesis of hydroxyalkyl chromophores 12 and 13.
Scheme 3 Synthesis of monomers 14–19 and copolymers P1–P9.
Photorefractive experiments
wavelength of 780 nm. The angle between the two writing
beams outside the samples was (14 ¡ 1)u, and the angle
between the bisector and the surface normal was (50 ¡ 2)u. For
Two-beam coupling experiments and four-wave mixing
experiments were done with a setup similar to the one
described in reference.14 All data were taken under steady
state conditions and were reproducible within 5% of the
experimental values. The laser was a diode laser operating at a
Table 1 Copolymerization results: composition and yield
Polymer
Spacer a/ba
Composn. x/yb
Yield (%)
P1
P2
P3
P4
P5
P6
P7
P8
P9
2/2
2/6
2/11
6/2
0.46/0.54
0.52/0.48
0.51/0.49
0.45/0.55
0.51/0.49
0.53/0.47
0.48/0.52
0.55/0.45
0.49/0.51
67
95
88
71
91
86
67
91
83
6/6
6/11
11/2
11/6
11/11
aa stands for the spacer length of the carbazole while b indicates the
spacer length of the chromophore groups. bx stands for the mole
fraction of the carbazole groups, while y indicates the chromophore
mole fraction, measured by 1H-NMR.
Fig. 2 1H-NMR of polymer P7 in CDCl3. The chromophore peaks are
broader than the carbazole peaks due to the longer carbazole spacer.
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Table 2 Physical properties of the copolymers P1–P9
21a
21a
b
¯
Mn/g mol
¯
Mw/g mol
¯
Mw/Mn
¯
Polymer
Tg/uC
P1
P2
P3
P4
P5
P6
P7
P8
P9
13 700
19 400
27 000
10 000
21 500
25 000
13 800
32 600
28 500
47 100
78 000
95 700
31 000
56 200
75 500
42 000
72 000
113 000
3.4
4.0
3.5
3.1
2.6
3.0
3.0
2.2
4.0
131 ¡ 2
100 ¡ 2
60 ¡ 2
87 ¡ 2
74 ¡ 2
33 ¡ 2
51 ¡ 2
38 ¡ 2
36 ¡ 2
aApparent molecular weights measured by GPC in THF, polystyrene
standards. Polydispersity.
b
the two-beam coupling experiments, the two beams were
p-polarized, had a power of 2.8 ¡ 0.1 mW each, and were
collimated to (250 ¡ 10) mm diameter in the sample. The
analysis of the data was done using eqn. (1),
ꢀ
ꢁ
ꢀ
ꢁ
I1t(I2=0)
I1t(I2~0)
I2t(I1=0)
I2t(I1~0)
Cd~cosa1 ln
{cosa2 ln
(1)
where It1 and It2 are the transmitted intensities of writing beams
1 and 2. Beam 1 is the beam closest to the surface normal, a1
and a2 are the angles between the writing beams and the surface
normal in the sample, d is the sample thickness, and C is the
gain coefficient.
Four-wave mixing experiments were performed using
s-polarized writing beams, and a p-polarized probe beam,
counterpropagating to writing beam 1. The power of the
writing beams was the same as in the two-beam coupling
experiments, and the probe beam, collimated to (150 ¡ 10) mm,
had a power of (2.0 ¡ 0.1) mW. The internal diffraction
efficiencies were calculated using the formula
Fig. 3 (a): Internal diffraction efficiency as a function of applied
electric field for polymer P6 (filled circles) and the copolymer with
internal plasticizer P0 at Tg 12 uC. Inset: Absorption spectrum of a
sample of polymer P6 with (full lines) and without 1 wt% of TNFM
sensitizer. (b) Internal diffraction efficiency as a function of applied
electric field for polymer P8. Inset: Absorption spectrum of a sample of
polymer P8 with (full lines) and without 1 wt% of TNFM sensitizer. All
samples were 125 mm thick, were measured at Tg 12 uC and at a
wavelength of 780 nm. All curves are fits to the general equation.
Idiff
gint
~
(2)
It
where Idiff is the intensity of the light diffracted upon the
photorefractive grating, and It is the total amount of light
transmitted through the sample, that is, the sum of the
diffracted and transmitted intensities.
more carbazole–TNFM complexes are present than chromo-
phore–TNFM complexes, but because of their higher molar
absorptivity the latter still absorb 50% of the incoming light.
As can be seen from the curve fits in both figures, the internal
diffraction efficiency follows the typical dependence of the
applied field that is expected from the theory of Kogelnik for
slanted gratings:17
Photorefractive parameters
The internal diffraction efficiencies measured for 125 mm thick
samples of polymers P6 and P8 as a function of applied electric
field are shown in Figs. 3a and 3b, respectively. The optical
wavelength was 780 nm, and the experiments were conducted
at Tg 12 uC, or at 35 uC and 40 uC for polymers P6 and P8,
respectively. The insets in Figs. 3a and 3b show the absorption
spectra of 125 mm thick samples of the pure polymers and
the polymers sensitized with 1 wt% of TNFM. For a poly(N-
vinylcarbazole) sample sensitized with TNFM, a charge-
transfer complex is formed between carbazole and TNFM.15
This complex absorbs in the wavelength range of 600–850 nm
and this absorption decreases rapidly beyond 830 nm. The fact
that the absorption in polymers P6 and P8 extends beyond
900 nm is indicative of an additional complexation occurring
between the chromophore and TNFM. We have experimen-
tally determined the stability constants and molar absorption
coefficients of the two complexes by applying the Benesi–
Hildenbrandt equation16 to the optical density changes in a
dilution series of the complex in a poly(methyl methacrylate)
polymer film. N-Ethylcarbazole (ECZ) was used as a model
compound for poly(N-vinylcarbazole). The analysis showed
that the chromophore–TNFM complex has a smaller com-
plexation constant (K ~ 0.30 M21 vs. K ~ 2.6 M21) but a larger
molar absorptivity at 780 nm than the ECZ–TNFM complex
(2100 M21 cm21 vs. 260 M21 cm21). Extrapolation of these
data to the TNFM-sensitized copolymer implies that 10 times
g
int~sin2(CDn)
(3)
where C is a constant that depends on the experimental
geometry (C ~ 564 in our experimental geometry) and the
index modulation amplitude Dn varies with the applied electric
field EExt according to:
Dn~N(Aꢀ2DazBꢀb)EExtESc
(4)
Here various constants are combined in A and B, such as the
local field and geometry factors. m is the molecular dipole
moment, Da the polarizability anisotropy, b the first hyper-
polarizability and N the number density of chromophores. ESc
is the amplitude of the space charge field that is directly
proportional to the amplitude of the applied electric field if the
space-charge field is completely saturated.
In Fig. 3a, the internal diffraction efficiency of P0 (in Fig. 1a)
at Tg 12 uC (open circles) is plotted together with that of
polymer P6 (filled circles). A clear improvement of the internal
diffraction efficiency can be observed. A calculation of the
index modulation amplitude at an applied field of 58 V mm21
954
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using eqn. (3) shows that Dn is three times larger for polymer
P6 (2.8 6 1023 vs. 8.4 6 1024, respectively). According to
eqn. (4), this enhancement can in part be attributed to a
larger chromophore number density and chromophore dipole
moment in polymer P6 (N ~ 7.5 6 1020 cm23 and m ~ 8.1 D
for P6,18 vs. N ~ 5.9 6 1020 cm23 and m ~ 6.6 D for the
polymer with the internal plasticizer). Similar diffraction
efficiencies for polymers P6 and P8 in Figs. 3a and 3b could
be foreseen, since the chromophores, and thus the molecular
dipole moments, are identical and the chromophore number
densities are similar for the two polymers (N ~ 7.1 6
1020 cm23 for P8). It also implies that both the hexyl and
undecyl spacers are flexible enough to allow the chromophores
to reorient to their equilibrium positions within the timescale
of the experiment. The overmodulation of the diffraction
efficiency observed at fields of 58 and 52 V mm21 places these
materials among the most efficient infrared-sensitive functio-
nalized polymers reported to date.
was reached after several tens of seconds. Clearly, the slow
nature of the grating build-up is a drawback of these materials.
Both the diffraction efficiency and gain coefficient of the
two copolymers are significantly larger than the diffraction
efficiency (1% at 100 V mm21) and gain coefficient (7 cm21 at
100 V mm21) reported for a poly([2-(N-ethyl-N-{4-[2-(4’-
nitrophenyl)ethenyl]phenyl}amino)ethyl]-co-[2-(carbazol-9-yl)-
ethyl]-co-[n-octyl]) methacrylate.22 This difference can be
attributed to several factors. First, the chromophore only
constituted 17 mol% of the copolymer units. In addition, the
chromophore was identical to that used in P0, and thus had a
small dipole moment. Finally, in ref. 22 the optical experiments
were done at room temperature, whereas the polymer Tg was
47 uC. In previous work, we have shown that the enhancement
of the index modulation amplitude by birefringence is virtually
absent on the timescale of a photorefractive experiment at
Tg 220 uC, and is fully operational at Tg 25 uC.23 This again
shows the importance of the careful optimization of the
polymer glass transition temperature by adjusting the spacer
length.
The results of the asymmetric two-beam coupling are shown
in Fig. 4. The filled symbols stand for the two-beam coupling
gain coefficients C of polymers P6 and P8 as a function of
applied electric field. This coefficient is related to the index
modulation amplitude by:
Conclusion
4p
C~ (ꢀe1ꢀeÃ2)Dnsinh
In conclusion, we have synthesized a new series of infrared-
sensitive photorefractive polymethacrylates functionalized with
carbazole and a polar chromophore. No internal plasticizer
was used, but the spacer lengths were varied to reduce the glass
transition temperature. A glass transition temperature close to
room temperature was observed for the copolymers with hexyl
and undecyl spacer lengths. Four-wave mixing and two-beam
coupling experiments conducted at 780 nm showed excellent
photorefractive properties, with gain coefficients exceeding
150 cm21 and complete internal diffraction at a field of
52 V mm21. The only drawback here is the slow grating
formation of these materials. The improvement of the
photorefractive response of these polymers compared to a
previously synthesized copolymer with internal plasticizer is
attributed to the higher polarity and number density of the
pendant chromophore.
(5)
l
where l is the optical wavelength, e and e are the polarization
¯ ¯
2
1
vectors of the two writing beams, and h is the photorefractive
phase shift between the space-charge field and the interference
pattern generated by the interacting beams. Since both
polymers P6 and P8 have similar index modulation amplitudes
Dn and gain coefficients, it follows from eqn. (5) that they
also have comparable photorefractive phase shifts. The open
symbols in Fig. 4 are the gain coefficient of P0. Note the
clear improvement in gain coefficient by a factor of y4. From
eqn. (5), and the experimental diffraction efficiencies, it is clear
that the enhancement of the index modulation amplitude by
a factor of 3 is the main factor leading to the improved gain
coefficient. Although higher values of gain coefficients have
been reached for blends19 and guest–host systems,20,21 a value
of 140 cm21 at an applied field of 60 V mm21 and at a
fundamental wavelength of 780 nm ranks among the highest
values reported thus far for fully functionalized polymers
without the addition of external plasticizers.
Experimental
General methods
All data points were taken at steady state conditions, which
All reagents are commercially available and used as received
unless stated otherwise. All synthesized products and polymers
were characterized by a Bruker Avance 300 (300 MHz) 1H-
NMR. The molecular weights were determined by gel
permeation chromatography (Waters HP/GPC), using THF
as eluent and toluene as internal reference; polystyrene
standards were used for calibration. The glass transition
temperatures (Tg) of the polymers were measured by differ-
ential scanning calorimetry (DSC), using a Perkin-Elmer DSC-
7. All samples were heated at a rate of 20 uC min21. The listed
Tg’s were measured after a second heating run.
Silylation of the alcohol group with tert-butyldiphenylsilyl
chloride. General procedure.24
To a mixture of 0.09 mol of the halogenated alcohol and 13.5 g
(0.198 mol) of imidazole in 100 mL of dry DMF, 25.7 mL
(0.099 mol) of tert-butyldiphenylsilyl chloride is added
dropwise and stirred for 4 h at room temperature. The reaction
mixture is poured into water, extracted with diethyl ether, the
organic phase dried (MgSO4) and the solvent removed under
reduced pressure to yield the protected halogenated alcohols
1-3. These products were obtained as a slightly yellow oil and
were pure enough to be used in the next step.
Fig. 4 Gain coefficients as a function of applied electric field for
polymers P6 (filled circles), P8 (filled triangles) and the copolymer with
internal plasticizer (open circles) P0. All samples were 125 mm thick,
were measured at Tg 12 uC and at a wavelength of 780 nm. The solid
lines are guides to the eye.
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2-(tert-Butyldiphenylsilyloxy)ethyl chloride (1). Yield: 27.6 g
(96%). H-NMR (CDCl3, ppm) d ~ 7.7 (d, 4H), 7.4 (m, 6H),
4.0 (t, 2H), 3.6 (t, 2H), 1.1 (s, 9H).
N-Ethyl-N-(6-hydroxyhexyl)aniline (10). Compound 10 was
prepared as described in a previous paper.11 Yield: 26.2 g
(72%), bp 167 uC (1.5 mmHg). 1H-NMR (CDCl3, ppm) d ~ 7.2
(m, 2H), 6.8 (m, 3H), 3.6 (m, 2H), 3.2 (m, 4H), 2.9 (br s, 1H),
1.3 (m, 8H), 1.1 (t, 3H).
1
6-(tert-Butyldiphenylsilyloxy)hexyl chloride (2). Yield: 33.4 g
(99%). H-NMR (CDCl3, ppm) d ~ 7.7 (d, 4H), 7.4 (m, 6H),
1
3.7 (t, 2H), 3.5 (t, 2H), 1.7 (m, 2H), 1.6 (m, 2H), 1.4 (m, 4H), 1.1
(s, 9H).
N-Ethyl-N-(11-hydroxyundecyl)aniline (11). Compound 11
was prepared according to Heldmann and Warner.25 Yield: 9.5
g (79%), bp 183–185 uC (0.1 mmHg). 1H-NMR (CDCl3, ppm) d
~ 7.2 (m, 2H), 6.8 (m, 3H), 3.6 (m, 2H), 3.2 (m, 4H), 1.6 (m,
4H), 1.3 (m, 14H), 1.1 (t, 3H).
11-(tert-butyldiphenylsilyloxy)undecyl bromide (3). Yield:
42.5 g (96%). 1H-NMR (CDCl3, ppm) d ~ 7.7 (d, 4H), 7.4
(m, 6H), 3.7 (t, 2H), 3.5 (t, 2H), 1.75 (m, 2H), 1.55 (m, 2H), 1.4–
1.2 (m, 14H), 1.1 (s, 9H).
Synthesis of the chromophores 12 and 13. General procedure.26
To a cooled (0–5 uC) solution of 16.3 g (0.12 mol) of
p-nitroaniline in 120 mL of a 1 : 2 v/v mixture of HCl–
water, a solution of 9.0 g (0.13 mol) of NaNO2 in 18 mL of
water is added dropwise. After formation of the diazonium salt,
0.12 mol of the aniline derivative (10 and 11) in 25 mL of acetic
acid is added dropwise under stirring. The mixture is stirred for
30 min and a solution of 9.0 g (0.11 mol) of sodium acetate in
20 mL of water is added. After 1 h, another 9.0 g (0.11 mol) of
sodium acetate in 20 mL of water is added. The mixture is then
warmed up to room temperature and neutralized with a NaOH
solution. After filtration, the crude product is purified by
column chromatography (silica gel).
Synthesis of the N-alkylated carbazole derivatives. General
procedure
To a solution of 12 g (0.072 mol) of carbazole and 0.6 g
(4.0 mmol) of NaI in 100 mL of dry DMF, a dispersion of 1.9 g
(0.079 mol) of NaH in 30 mL of dry DMF is added dropwise.
After 1 h of stirring, 0.079 mol of protected halogenated
alcohol 1–3 dissolved in 20 mL of dry DMF is added dropwise.
The reaction mixture is then heated to 65 uC for 24 h, cooled,
poured into water and extracted with CH2Cl2. The organic
layer is dried (MgSO4) and the solvent removed under reduced
pressure. Finally, the products 4–6 are purified by column
chromatography (silica gel).
N-Ethyl-N-[4-(4-nitrophenylazo)phenyl]aminohexanol (12).
Eluent: CHCl3–CH3CN 80 : 20 v/v. Yield: 25.5 g (58%), mp
110.0–110.5 uC. H-NMR (CDCl3, ppm) d ~ 8.3 (d, 2H), 7.9
(m, 4H), 6.7 (d, 2H), 3.6 (m, 2H), 3.5 (q, 2H), 3.4 (t, 2H), 1.7–
1.5 (m, 4H), 1.4–1.2 (m, 7H).
9-[2-(tert-Butyldiphenylsilyloxy)ethyl]carbazole (4). Eluent:
CH2Cl2. Yield: 22.8 g (63%) of a slightly yellow oil. 1H-
NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.6–7.2 (m, 16H), 4.4 (t,
2H), 4.0 (t, 2H), 1.0 (s, 9H).
1
N-Ethyl-N-[4-(4-nitrophenylazo)phenyl]aminoundecanol (13).
Eluent: CH2Cl2–CH3CN 85 : 15 v/v. Yield: 9.2 g (69%), mp
71.5–72.7 uC. 1H-NMR (CDCl3, ppm) d ~ 8.3 (d, 2H), 7.9 (m,
4H), 6.7 (d, 2H), 3.6 (m, 2H), 3.5–3.4 (m, 4H), 1.7–1.5 (m, 4H),
1.4–1.1 (m, 17H).
9-[6-(tert-Butyldiphenylsilyloxy)hexyl]carbazole (5). Eluent:
CH2Cl2–CH3CN 90 : 10 v/v. Yield: 16.4 g (45%) of a slightly
yellow oil. 1H-NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.6 (d, 4H),
7.5–7.3 (m, 10H), 7.2 (m, 2H), 4.3 (t, 2H), 3.6 (t, 2H), 1.8 (m,
2H), 1.5–1.2 (m, 6H), 1.0 (s, 9H).
Monomer synthesis. General procedure.27
9-[11-(tert-Butyldiphenylsilyloxy)undecyl]carbazole (6). Eluent:
CH2Cl2–n-hexane 90 : 10 v/v. Yield: 19.2 g (46%) of a slightly
yellow oil. 1H-NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.6 (d, 4H),
7.5–7.3 (m, 10H), 7.2 (m, 2H), 4.3 (t, 2H), 3.6 (t, 2H), 1.8 (m, 2H),
1.5 (m, 2H), 1.4–1.2 (m, 14H), 1.0 (s, 9H).
A mixture of 0.02 mol of one of the alcohols (7–9, 12, 13 and
Disperse Red 1), 4.0 g (0.04 mol) of triethylamine, 20 mg
(0.18 mmol) of hydroquinone, and 150 mL of dichloromethane
was cooled to 0 uC; 3.1 g (0.03 mol) of methacryloyl chloride in
15 mL of dichloromethane was added dropwise under stirring.
The reaction was kept at 0–5 uC for 48 h under stirring, then
washed with water. The organic layer was dried (MgSO4) and
the solvent removed under reduced pressure. The remaining
reaction product was purified by column chromatography
(silica gel) using dichloromethane as eluent.
Removal of the tert-butyldiphenylsilyl protective group. General
procedure.24
A mixture of 0.032 mol of protected carbazole derivative (4–6)
and 20.2 g (0.064 mol) of tetrabutylammonium fluoride?trihy-
drate in 120 mL of THF is stirred for 24 h at room temperature.
To the concentrated reaction mixture, CH2Cl2 is added, and
washed with water, the organic layer is dried (MgSO4) and the
solvent removed under reduced pressure. The products are then
purified by column chromatography (silica gel).
2-(Carbazol-9-yl)ethyl methacrylate (14). Yield: 5.4 g (96%),
mp 85.5–86.5 uC. 1H-NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.5
(m, 4H), 7.3 (d, 2H), 6.1 (s, 1H), 5.9 (s, 1H), 4.4 (t, 2H), 4.2 (t,
2H), 1.9 (s, 3H).
9-(2-Hydroxyethyl)carbazole (7). Eluent: CH2Cl2. Yield: 4.2 g
1
6-(Carbazol-9-yl)hexyl methacrylate (15). Yield: 5.3 g (80%).
1H-NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.5 (m, 4H), 7.3 (d,
2H), 6.1 (s, 1H), 5.9 (s, 1H), 4.3 (t, 2H), 4.1 (t, 2H), 1.9 (s, 3H),
1.5 (m, 4H), 1.4 (m, 4H).
(62%), mp 85.5–87.3 uC. H-NMR (CDCl3, ppm) d ~ 8.1 (d,
2H), 7.4 (m, 4H), 7.2 (m, 2H), 4.3 (t, 2H), 3.6 (t, 2H)
9-(6-Hydroxyhexyl)carbazole (8). Eluent: CH2Cl2–CH3CN
1
90 : 10 v/v. Yield: 5.4 g (63%), mp 125.7–127.0 uC. H-NMR
(CDCl3, ppm) d ~ 8.1 (d, 2H), 7.4 (m, 4H), 7.2 (m, 2H), 4.3 (t,
2H), 3.6 (t, 2H), 1.8 (m, 2H), 1.5–1.2 (m, 6H).
11-(Carbazol-9-yl)undecyl methacrylate (16). Yield: 7.4 g
1
(90%). H-NMR (CDCl3, ppm) d ~ 8.1 (d, 2H), 7.5 (m, 4H),
7.3 (d, 2H), 6.1 (s, 1H), 5.9 (s, 1H), .4.3 (t, 2H), 4.1 (t, 2H), 1.9
(s, 3H), 1.6–1.5 (m, 4H), 1.4–1.2 (m, 14H).
9-(11-Hydroxyundecyl)carbazole (9). Eluent: CH2Cl2. Yield:
6.9 g (64%), mp 73.8–74.6 uC. 1H-NMR (CDCl3, ppm) d ~ 8.1
(d, 2H), 7.4 (m, 4H), 7.2 (m, 2H), 4.3 (t, 2H), 3.6 (t, 2H), 1.8 (m,
2H), 1.6 (m, 2H), 1.5–1.2 (m, 14H).
2-{N-Ethyl-N-[4-(4-nitrophenylazo)phenyl]amino}ethyl metha-
crylate (17). Disperse Red 1 (DR1) was recrystallized from
956
J. Mater. Chem., 2002, 12, 951–957

View Article Online
ethanol before use. Yield: 6.6 g (87%), mp 103.2–104.0 uC. 1H-
NMR (CDCl3, ppm) d ~ 8.3 (d, 2H), 7.9 (m, 4H), 6.7 (d, 2H),
6.1 (s, 1H), 5.6 (s, 1H), 4.3 (t, 2H), 3.5 (q, 2H), 3.4 (t, 2H), 1.9 (s,
3H), 1.2 (t, 3H).
4
5
K. Meerholz, B. L. Volodin, Sandalphon, B. Kippelen and
N. Peyghambarian, Nature, 1994, 371, 497.
E. Hendrickx, B. L. Volodin, D. D. Steele, J. L. Maldonado,
J. F. Wang, B. Kippelen and N. Peyghambarian, Appl. Phys. Lett.,
1997, 71, 1159.
6
K. Meerholz, R. Bittner, Y. De Nardin, C. Bra¨uchle, E. Hendrickx,
B. L. Volodin, B. Kippelen and N. Peyghambarian, Adv. Mater.,
1997, 9, 1043.
6-{N-Ethyl-N-[4-(4-nitrophenylazo)phenyl]amino}hexyl metha-
crylate (18). Yield: 7.9 g (90%), mp 62.0–62.4 uC. 1H-NMR
(CDCl3, ppm) d ~ 8.3 (d, 2H), 7.9 (m, 4H), 6.7 (d, 2H), 6.1 (s,
1H), 5.6 (s, 1H), 4.2 (t, 2H), 3.5 (q, 2H), 3.4 (t, 2H), 1.9 (s, 3H),
1.7 (m, 4H), 1.4 (m, 4H), 1.2 (t, 3H).
7
8
9
Z. Peng, A. R. Gharavi and L. Yu, J. Am. Chem. Soc., 1997, 119,
4622.
F. Wang, Z. Chen, Q. Gong, Y. Chen and H. Chen, Solid State
Commun., 1998, 108(5), 295.
S.-H. Park, K. Ogino and H. Sato, Polym. Adv. Technol., 2000, 11,
349.
11-{N-Ethyl-N-[4-(4-nitrophenylazo)phenyl]amino}undecyl
methacrylate (19). Yield: 8.3g (82%), mp 58.7–59.0 uC. 1H-
NMR (CDCl3, ppm) d ~ 8.3 (d, 2H), 7.9 (m, 4H), 6.7 (d, 2H),
6.1 (s, 1H), 5.6 (s, 1H), 4.2 (t, 2H), 3.5 (q, 2H), 3.4 (t, 2H), 1.9 (s,
3H), 1.7 (m, 4H), 1.4–1.2 (m, 17H).
10 Y. Chen, Y. He, F. Wang, H. Chen and Q. Gong, Polymer, 2001,
42, 1101.
11 D. Van Steenwinckel, C. Engels, E. Gubbelmans, E. Hendrickx,
C. Samyn and A. Persoons, Macromolecules, 2000, 33, 4074.
12 D. Van Steenwinckel, E. Hendrickx, C. Samyn, C. Engels and
A. Persoons, J. Mater. Chem., 2000, 10, 2692.
13 D. H. Williams and I. Fleming, in Spectroscopic Methods in
Organic Chemistry, (McGraw-Hill, London, 1995), p. 102.
14 B. L. Volodin, Sandalphon, K. Meerholz, B. Kippelen,
N. V. Kukhtarev and N. Peyghambarian, Opt. Eng., 1995, 34,
2213.
15 E. Hendrickx, J. F. Wang, J. L. Maldonado, B. L. Volodin,
Sandalphon, E. A. Mash, A. Persoons, B. Kippelen and
N. Peyghambarian, Macromolecules, 1998, 31, 734.
Polymer synthesis. General procedure.27
The polymerizations were carried out in DMF solution under
argon atmosphere at 65 uC in the presence of 1 wt% AIBN for
24 h. The resulting polymer solution was cooled and poured
into methanol to precipitate the polymer. The precipitated
polymer was filtered, redissolved and reprecipitated, filtered
and finally dried under reduced pressure.
16 R. Foster, in Organic Charge-Transfer Complexes, Academic
Press, London, 1969, p. 124.
17 H. Kogelnik, Bell Syst. Tech. J., 1969, 48, 2909.
18 C. R. Moylan, R. J. Twieg, V. Y. Lee, S. A. Swanson,
K. M. Betterton and R. D. Miller, J. Am. Chem. Soc., 1993,
115, 12599.
19 J.-W. Lee and J.-K. Park, Mol. Cryst. Liq. Cryst., 2000, 349, 131.
20 I. K. Moon, D. Yoo, H. S. Moon, D.-H. Shin, W. S. Jahng,
H. Chun and N. Kim, Mol. Cryst. Liq. Cryst., 2000, 349, 43.
21 D. Wright, M. A. Diaz-Garcia, J. D. Casperson, M. DeClue,
W. E. Moerner and R. J. Twieg, Appl. Phys. Lett., 1998, 73(11),
1490.
Acknowledgements
C. E. is a research assistant of the Flemish Institute for
Promotion of the Scientific-Technological Research in Industry
(IWT), D. V. S. is a research assistant and E. H. is a research
associate of the Fund for Scientific Research-Flanders
(Belgium) (FWO). This research was supported by research
grants from the FWO (G.0338.98 and S 2/5-AV. E 8), the
University of Leuven (GOA/2000/03), and the Belgian
Government (IUAP P4/11).
22 C. Zhao, C.-K. Park, P. Prasad, Y. Zhang, S. Ghosal and
R. Burzynski, Chem. Mater., 1995, 7, 1237.
23 D. Van Steenwinckel, E. Hendrickx, A. Persoons, K. Van den
Broeck and C. Samyn, J. Chem. Phys., 2000, 112, 11030.
24 S. Hanessian and P. Lavallee, Can. J. Chem., 1975, 53, 2975.
25 C. Heldmann and M. Warner, Macromolecules, 1998, 31, 3519.
26 C. Samyn, T. Verbiest, E. Kesters, K. Van den Broeck, M. Van
Beylen and A. Persoons, Polymer, 2000, 41, 6049.
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