Poly(phenylenevinylene) analogs with ring substituted polar side chains and their use in the formation of hydrogen bonding based self-assembled multilayers

Article abstract of DOI:10.1039/a707365h

Poly(arylenevinylene) homopolymers and copolymers with polar hydroxy and carboxy moieties attached to the aromatic phenyl ring were prepared. The copolymers and the related homopolymers are copoly[5-(2-hydroxyethoxy)-2-methoxy-1,4-phenylenevinylene/1,4- phenylenevinylene], co(PHydroxyV-PV), and copoly(5-carboxymethoxy-2-methoxy-1,4-phenylenevinylene/1,4-phenylenevinylene), co(PCarboxyV-PV). For co(PHydroxyV-PV) the photoluminescence and electroluminescence spectra can be adjusted over a range of 100 nm as a function of the percentage of the hydroxy substituted phenyl ring. For co(PCarboxyV-PV) the observed spectral features are a function of the pH from which the final conjugated polymer was prepared. The optical density and photoluminescence of co(PCarboxyV-PV) films prepared from solutions at pH = 12 were significantly blue-shifted compared to polymers prepared from pH = 2 solutions at up to 30% substitution at the phenyl ring. The presence of the polar side chain was used to form self-assembled multilayer films, poly(ethyleneimine)/poly(styrenesulfonate)/co(PHydroxyV-PV), based on hydrogen bonding interactions rather than electrostatic forces. The luminescence spectra in the layered systems were blue-shifted compared to the spin coated films.

Full text of DOI:10.1039/a707365h

J O U R N A L O F
Poly(phenylenevinylene) analogs with ring substituted polar side
chains and their use in the formation of hydrogen bonding based
self-assembled multilayers
Iris Benjamin,a,b Haiping Hong,a,b,c Yair Avny,*b Dan Davidovc and Ronny Neumann*†a
C H E M I S T R Y
aCasali Institute of Applied Chemistry, bDepartment of Organic Chemistry, and cRacach Institute of
Physics, T he Hebrew University of Jerusalem, Jerusalem, Israel, 91904
Poly(arylenevinylene) homopolymers and copolymers with polar hydroxy and carboxy moieties attached to the aromatic phenyl
ring were prepared. The copolymers and the related homopolymers are copoly[5-(2-hydroxyethoxy)-2-methoxy-1,4-
phenylenevinylene/1,4-phenylenevinylene], co(PHydroxyV-PV), and copoly(5-carboxymethoxy-2-methoxy-1,4-
phenylenevinylene/1,4-phenylenevinylene), co(PCarboxyV-PV). For co(PHydroxyV-PV) the photoluminescence and
electroluminescence spectra can be adjusted over a range of 100 nm as a function of the percentage of the hydroxy substituted
phenyl ring. For co(PCarboxyV-PV) the observed spectral features are a function of the pH from which the final conjugated
polymer was prepared. The optical density and photoluminescence of co(PCarboxyV-PV) films prepared from solutions at pH=
12 were significantly blue-shifted compared to polymers prepared from pH=2 solutions at up to 30% substitution at the phenyl
ring. The presence of the polar side chain was used to form self-assembled multilayer films, poly(ethyleneimine)/poly(styrene-
sulfonate)/co(PHydroxyV-PV), based on hydrogen bonding interactions rather than electrostatic forces. The luminescence spectra
in the layered systems were blue-shifted compared to the spin coated films.
Electroluminescent conjugated polymers especially of the poly-
(arylenevinylene) family are leading candidates as active layers
in light emitting diode devices based on organic compounds.
The parent poly(1,4-phenylenevinylene) (PPV) has been the
predominant polymer used for device application;1 however,
much research (both in homopolymers and copolymers) has
been reported on PPV derivatives or analogs. Derivatisation
has been based either on substitution at the aromatic nucleus
or more occasionally at the vinylic carbons. Use of alternative
aromatic moieties instead of phenyl units also leads to com-
pounds analogous to PPV. The major intent in the preparation
of PPV-like compounds has been to improve their performance
in device operation. One direction of research has been to
increase device efficiency or quantum yields by adjustment of
the polymer electron affinity. This has been achieved by
substitution with electron withdrawing groups2 and introduc-
tion of electron deficient aromatic rings containing nitrogen
into the polymer backbone.3 The second research goal has
been to tune the emission spectra by tailoring the p–p* optical
band gap. The strategies used to reach this goal have been
substitution with electron withdrawing or donating groups,4
variation of the polymer building blocks including incorpor-
ation of non-chromophoric segments5 and introduction of
sterically demanding substituents which affect planarity and
the effective conjugation length.6 These types of ‘chemical
tuning’ have been realized in polymer blends, e.g. PPV and
polyvinylcarbazole,7 homopolymers and copolymers. Light
emission ranging from the near infrared through the red, green
and blue to the ultraviolet has been observed.
vinylene/1,4-phenylenevinylene], co(PHydroxyV-PV), and
carboxy moieties as in copoly(5-carboxymethoxy-2-methoxy-
1,4-phenylenevinylene/1,4-phenylenevinylene), co(PCarboxyV-
PV), shown in Scheme 1. The photoluminescence (PL) and
electroluminescence (EL) spectra of co(PHydroxyV-PV)
showed fine tuning of the peak position as a function of the
copolymer composition. Similar UV–VIS, PL and EL spectra
of co(PCarboxyV-PV) showed a strong dependence of the
spectral features as a function of the pH of the precursor
polymer solution.
The self-assembly technique as related to conjugated poly-
mers has recently emerged as an important technique for
processing PPV into ultrathin multilayer films with controlled
thickness and architecture.10 These films have been shown to
enable quantum confinement and blue-shifted spectra. In the
past, however, the self-assembly method has been solely based
on electrostatic forces between the insulating and conjugated
pre-polymer used to build the layer structure. Now, the pres-
ence of the polar side chains on the herein newly described
polymers can be used to fabricate self-assembled multilayer
films based on strong hydrogen bonding between the amine
group of an insulating poly(ethyleneimine) and the hydroxy
group of the co(PHydroxyV-PV) conjugated polymer.
Results and Discussion
Synthesis
The synthetic pathway for the synthesis of co(PHydroxyV-
PV) and co(PCarboxyV-PV) is outlined in Scheme 1.
Alkylation of 4-methoxyphenol by ethyl bromoacetate led to
the dialkoxide 1 with a terminal ester group. This compound
was then reduced either to the corresponding alcohol 2 or
hydrolyzed to the corresponding carboxylic acid 3.
Bromomethylation of 2 and 3 was carried out using paraform-
aldehyde in a HBr–acetic acid solution. During the course of
the bromomethylation reaction the hydroxy group of 2 was
also converted to the corresponding bromide 4 as was proven
by mass spectral analysis. The two bromomethylated products
4 and 5 were then reacted with tetrahydrothiophene (THT) in
An easily accessible group of PPV analogs are those originat-
ing from 1,4-dialkoxybenzene.8 These dialkoxy substituted
homopolymers have absorption peaks at ~470 nm and emis-
sion peaks at 570–590 nm independent of the alkoxy chain
length.9 Building on the successful polymerization of dialkoxy-
phenyl monomers, we presently report on the synthesis of new
PPV based polymers which contain reactive polar functional
side chains. The functional units in this case are hydroxy groups
as in copoly[5-(2-hydroxyethoxy)-2-methoxy-1,4-phenylene-
† E-mail: ronny@vms.huji.ac.il
J. Mater. Chem., 1998, 8(4), 919–924
919

Scheme 1
methanol to form the required monomers, 6 and 7. During
reaction with THT the aliphatic bromide of 4 was reconverted
to the corresponding hydroxy derivative as unequivocally
shown in the mass spectral analysis.
Homopolymers and copolymers, PPV, PPHydroxyV,
PPCarboxyV, co(PHydroxyV-PV) and co(PCarboxyV-PV)
were prepared according to the standard Wessling11 and Lenz12
methods from the water soluble precursors. Conversion of
monomers to polyelectrolyte and the final conjugated polymer
yields were measured by titration and gravimetrically, respect-
ively. The results are shown in Fig. 1. As the mole fraction of
the carboxy monomer 7 was increased in the polymerization
reaction, there was an initial decrease in the conversion, with
a minimum at ~20 mol% of 7, followed by a steady increase
in conversion which was practically quantitative in the homo-
polymerization of carboxy monomer. For copolymerization of
hydroxy monomer 6, the conversion at up to ~30 mol% of 6
was constant at 45–50% and increased steadily, similar to
what was found for 7. Again the homopolymerization was
quantitative. After dialysis to remove low molecular mass
fractions using a cellulose membrane with a 12 000 molecular
mass cutoff, the final polymer yield was measured after the
thermal elimination reaction. It is clear from Fig. 1 that the
final high molecular mass polymer yield decreased as the
relative fraction of the functionalized monomer used increased.
Apparently, the use of both the hydroxy and carboxy mon-
omers led to the formation of lower molecular mass oligomers.
The presence of the functionalized units in the conjugated
polymer was verified with FTIR using the typical carbonyl
Fig. 1 Monomer conversion and final polymer yield for
co(PHydroxyV-PV) and co(PCarboxyV-PV) as a function of the
initial monomer ratio: (&) yield of co(PHydroxyV-PV), (%) conver-
sion of co(PHydroxyV-PV), (+) yield of co(PCarboxyV-PV) and (6)
conversion of co(PCarboxyV-PV)
and hydroxy group absorptions as reference. From the analysis
of the optical densities it was concluded that there is a
reasonable correlation, 5%, between the initial feed ratio
and the final composition of the copolymer.
920
J. Mater. Chem., 1998, 8(4), 919–924

UV–VIS, PL and EL spectra in spin coated films
The PL and EL spectra of PPV and co(PHydroxyV-PV) are
shown in Figs. 2 and 3, respectively. In both cases, there is a
clear pattern of a bathochromic shift as the relative ratio, n/m,
of the functionalized vs. non-functionalized moiety increases.
This attests to a controllable method of chemical tuning of
luminescence for these polymers as has been observed in other
alkoxy substituted PPV type copolymers.13 At low mol frac-
tions (up ~10 mol%) of substituted units there is virtually no
change in the wavelength of the luminescence peak. Above
10% co(PHydroxyV-PV) there is a continuously increasing
red shift proportional to the content of the hydroxy moiety in
the emission spectra for both PL and EL. The spectra of the
homopolymer, PPHydroxyV, are identical to those of 75%
co(PHydroxyV-PV). The internal quantum efficiency of an
indium–tin oxide (ITO)/75% co(PHydroxyV-PV)/Al device
was found to be 0.4% and the threshold voltage from the
current–voltage curve (Fig. 4) was 10 V.
The absorption spectra of co(PHydroxyV-PV) are shown
in Fig. 5. Here one can observe the broadening of the spectra
of co(PHydroxyV-PV) compared to the parent PPV. In fact
this broadening is also observable in both the PL and EL
spectra. The broadening in both the absorption and emission
Fig. 4 Current vs. voltage curve for a ITO/20% co(PCarboxyV-
PV)/Al LED
Fig. 5 UV–VIS spectra of thin films of co(PHydroxy V-PV): (a) PPV,
(b) 5, (c) 20, (d) 50 and (e) 100%
spectra led us to conclude that the larger peak widths in
co(PHydroxyV-PV) vs. PPV are attributable to vibronic side-
bands and/or lack of homogeneity in the copolymers. Also
noticeable is that at low, i.e. 5%, fractions of co(PHydroxyV-
PV), the peak of the absorption spectra is blue shifted relative
to PPV whereas this blue-shifted peak is not evident in the
respective PL and EL spectra. A closer examination of the
absorption spectra reveals that the absorption edge for 5 and
20% co(PHydroxyV-PV) are similar. Thus, since the emission
spectra are influenced by the absorption edge rather than
the absorption peak the absence of a blue-shifted emission
spectrum for 5% co(PHydroxyV-PV) is explainable.
Fig. 2 PL spectra of thin films of co(PHydroxyV-PV): (a) PPV, (b) 5,
(c) 10, (d) 20, (e) 50 and ( f ) 100%
The spectra of co(PCarboxyV-PV) were measured as a func-
tion of the pH of the solution of the precursor polyelectrolyte
solution. It was hypothesized that the spectra of the final
conjugated polymer would be affected by the ionic state of the
carboxy unit. The result of such an experiment carried out on
20% co(PCarboxyV-PV) is presented in Fig. 6. Conjugated
polymers prepared from solutions at pH 12 showed blue shifted
UV–VIS, PL and EL spectra compared with similar spectra from
solutions at pH 2. PPV spectra from solutions of different pH
were unaffected. The ionization state of the carboxy unit was
verified by FTIR with peaks at 1689 and 1715 cm−1 at pH 2
assignable to the COOH moiety and a peak at 1625 cm−1 at
pH 12 assignable to the COO−Na+ group. Therefore, clearly
Fig. 3 EL spectra of thin films of co(PHydroxyV-PV): (a) PPV, (b) 5,
(c) 30, (d) 50 and (e) 100%
J. Mater. Chem., 1998, 8(4), 919–924
921

Fig. 7 Specular X-ray reflectivity spectra of self-assembled multilayer
films based on PEI/SPS/100% co(PHydroxyV-PV): d=(a) 370, (b)
245 and (c) 126 A. Inset: film thickness as a function of the number of
Fig. 6 (a) UV–VIS, (b) PL and (c) EL spectra of 20% co(PCarboxyV-
PV) at (i) pH 2 and (ii) 12
˚
trilayers after annealing to form the conjugated polymer.
the ionic state of the carboxy unit affects the spectra; the anionic
carboxylate moiety leads to a blue shift compared to the non-
ionized carboxylic acid form. This pH dependent method for
control of the p–p* optical band gap is unique and could be due
to conformational or more probably aggregation effects.14
Multilayer structures by hydrogen bonding
In the past, we have demonstrated that multiple bilayers of
the type (SPS/conjugated polymer) where SPS is poly-
(styrenesulfonic acid sodium salt) could be formed with a
n
variety of conjugated polymers including PPV and poly(naph-
thylenevinylene). The bilayer formation was based on the
electrostatic interaction between the sulfonate anion of the
insulating polymer, SPS, and the sulfonium cation of the pre-
PPV. Similar attempted bilayer formation with the precursors
of co(PHydroxyV-PV) and co(PCarboxyV-PV) failed due to
aggregration of the precursor polymer presumably because the
polar side chains in these polymers interact by hydrogen
bonding. This observation, however, has now enabled us to
fabricate multiple trilayers based on PEI/SPS/co(PHydroxyV-
PV) where PEI is poly(ethyleneimine). The amine moieties in
PEI function to hydrogen bond the hydroxy polar side chain
of co(PHydroxyV-PV), thus preventing aggregation. Direct
evidence for hydrogen bonding was obtained by comparison
of the FTIR spectrum of PEI alone and the multiple trilayers.
For PEI the absorption was at 3366 cm−1 and was shifted to
a lower energy peak at 3309 cm−1 in the multilayer system.
This shift in the IR spectrum is very similar to what was
observed in other conjugated polymer multilayers where hydro-
gen bonding interactions are proposed.15 In Fig. 7, one may
observe the typical specular X-ray reflectivity spectra of self-
assembled PEI/SPS/100% co(PHydroxyV-PV) on float glass
after thermal conversion to form the conjuaged polymer.
Kiessig oscillations due to interference of beams reflected from
the upper and lower interfaces are clearly observable and
enable calculation of the total film thickness, d. The linear
correlation between d and the number of trilayers, n, (Fig. 7
Fig. 8 Photoluminescence spectra of [PEI/SPS/co(PHydroxyV-
PV)] : (a) 20, (b) 50 and (c) 100% co(PHydroxy-PV); (i) 2, (ii) 3, (iii)
4 and (iv) 5 trilayers
n
peaks are blue-shifted by 30–45 nm relative to the peaks at
535, 555 and 585 nm, observed in the spin coated films (Fig. 2).
These blue-shifted peaks are best explained by the confinement
of the electron-hole pair in the conjugated polymer layer
between the insulating PEI+SPS layer having a thickness
˚
of 35–40 A.10 Very similar spectra (Fig. 9) are observable
for electroluminescence in the case of seven trilayers of
PEI/SPS/20% co(PHydroxyV-PV) and PEI/SPS/100%
co(PHydroxyV-PV) in a ITO/multilayer/Al configuration.
˚
inset) yields a thickness per trilayer after annealing of ~55 A
for PEI/SPS/100% co(PHydroxyV-PV). Both PEI/SPS/20%
co(PHydroxyV-PV) and PEI/SPS/50% co(PHydroxyV-PV)
gave similar results. The photoluminescence spectrum (Fig. 8)
of the multiple trilayers show peaks at 500, 525 and 540 nm
for 20, 50 and 100% co(PHydroxyV-PV), respectively. The
emission peak is independent of the number of trilayers. These
Experimental section
Materials and instrumentation
Chemicals were obtained from commercial sources of the
highest purity available and used without further purification.
922
J. Mater. Chem., 1998, 8(4), 919–924

4-Methoxyphenoxyacetic acid 3
A sample of 1 (10 g, 0.015 mol) was refluxed in 100 ml of a
2  KOH solution for 12 h. Upon cooling a white precipitate
was formed which was filtered, washed with diethyl ether and
added to a solution of 200 ml of water and 300 ml diethyl
ether. A 5  HCl solution was added slowly until an aqueous
phase pH of 2 was obtained. The organic layer was separated
and the aqueous layer was extracted twice with diethyl ether.
The organic extracts were combined, dried with magnesium
sulfate and solvent removed by evaporation. The yield was
80% (7.25 g). d ([2H ]DMSO): 3.70 (3H, s, OCH ); 4.60 (2H,
H
6
3
s, OCH ); 6.86 (4H, s, Ar); 12.96 (1H, s, COOH).
2
1,4-Bis(bromomethyl)-2-(2-bromoethoxy)-5-methoxybenzene 4
Compound 2 (15 g, 0.096 mol), paraformaldehyde (14.4 g,
0.48 mol) and 136 ml of 5.4  HBr in acetic acid were reacted
in 250 ml of acetic acid for 18 h.18 After formation of a white
precipitate water (300 ml) was added to the reaction mixture.
The solution was filtered and the precipitate was washed with
water until the pH of the filtrate was 6. After drying the
product under vacuum the yield was 73% (23.7 g), mp
102–103 °C. d (CDCl ): 3.85 (3H, s, OCH ); 4.20 (2H, t,
Fig. 9 Electroluminescence spectra of [PEI/SPS/co(PHydroxyV-
PV)] : (a) 20 and (b) 100% co(PHydroxyV-PV)
n
H
3
3
OCH ); 4.44 (2H, t, CH Br); 4.50 (2H, s, CH Br); 4.52 (2H, s,
2
2
2
CH Br); 6.86 (2H, s, Ar); 6.87 (2H, s, Ar). The chemical
ionization mass spectrum (CI-MS) using isobutane showed the
2
Solvents were dried when so noted using the common methods.
1H NMR spectra were measured using a Bruker AMP 300
spectrometer. Mass spectra were measured on a TSQ 70
FinniganMat triple quadrupole spectrometer. UV–VIS spectra
were measured on a Hewlett Packard HP8452A diode array
spectrophotometer. PL spectra were obtained using a JASCO
spectrofluorimeter (FP-770) or a Perkin-Elmer LS-5 spec-
trometer using an excitation wavelength of 375 nm, although
measurements showed PL spectra independent of the excitation
wavelength in the range of 300–400 nm. The EL spectra were
measured using an ITO/polymer/Al configuration and a com-
puter controlled Oriel monochromator in a setup described
previously.16 IR spectra were measured using a Nicolet 510M
instrument. The specular X-ray reflectivity measurements were
molecular ion peak at m/z 472, 474, 476, 478 for
[M+isobutane] at the required peak ratio of 1535351. The
base peak at m/z 314, 316 (151) was attributed to
[M+isobutane−2Br] and smaller peaks at m/z 393, 395, 397
(15251) were assigned to [M+isobutane−Br].
2,5-Bis(bromomethyl)-4-methoxyphenoxyacetic acid 5
Compound 2 (15 g, 0.082 mol), paraformaldehyde (5.19 g,
0.164 mol) and 40.15 ml of 5.4  HBr in acetic acid were
reacted in 150 ml of acetic acid for 8 h at 65 °C. After formation
of a white precipitate water (300 ml) was added to the reaction
mixture and the solution was filtered and the precipitate was
washed with water until the pH of the filtrate was 6. After
drying the product under vacuum the final yield was 63%
(19.0 g), Mp 134 °C. d ([2H ]DMSO): 3.81 (3H, s, OCH );
˚
carried out using a Cu-Ka (l=1.54 A) beam from a narrow
line source of a 12 kW Rigaku rotating anode generator.
H
6
3
4.58 (2H, s, OCH ); 4.65 (2H, s, CH Br); 4.68 (2H, s, CH Br);
2
2
2
Ethyl 4-methoxyphenoxyacetate 1
7.08 (1H, s, Ar); 7.13 (1H, s, Ar). Elemental analysis for
C H Br O ): calc. (found) C, 35.90 (36.43); H, 3.29 (3.33);
Br, 43.42% (42.29).
The compound was prepared by a modification of the pro-
cedure of Neu et al.17 Thus, 4-methoxyphenol (20 g, 0.16 mol)
was dissolved in dry acetone (500 ml), potassium carbonate
(33 g, 0.24 mol) was added and the solution was refluxed for
15 min. After 15 min, ethyl bromoacetate (36 ml, 0.32 mol) was
added in one portion and the reflux was continued for another
4 d. The potassium carbonate and bromide were then filtered
off, and the acetone and the excess ethyl bromoacetate were
removed by evaporation and vacuum distillation, respectively.
The product was obtained in 95% yield (32 g). d (CDCl ):
11 12
2 4
2-[4-Methoxy-2,5-bis(tetrahydrothiophen-1-ium-1-ylmethyl)-
phenoxy]ethanol dibromide 6
Compound 4 (25 g, 0.06 mol) and tetrahydrothiophene (16 ml,
0.18 mol) in 350 ml of methanol were stirred at 50 °C for 48 h.
The solution was concentrated by evaporation at room temp.
and the residue was poured into 250 ml of acetone. The
suspension formed was stirred at 0–5 °C for 1 h and the
product was filtered off. The yield was 63% (20 g). d (D O):
H
3
1.28 (3H, t, CH ); 3.77 (3H, s, OCH ); 4.22 (2H, q, CH ); 4.55
(2H, s, OCH ); 6.82 (2H, d, Ar); 6.84 (2H, d, Ar).
3
3
2
H
2
2.40 (8H, m, SCH CH ); 3.55 (8H, m, SCH CH ); 3.96 (3H, s,
OCH ); 4.15 (2H, t, OCH ); 4.35 (2H, t, CH OH); 4.57 (2H,
2
2
2
2
2
3
2
2
s, Ar-CH ); 4.62 (2H, s, Ar-CH ); 7.26 (2H, s, Ar). Elemental
analysis for C H Br O S ): calc. (found) C, 43.19 (43.33); H,
2-(4-Methoxyphenoxy)ethanol 2
2
2
19 30
2 3 2
A 500 ml three-necked flask was equipped with a dropping
5.34 (5.62); S, 12.14 (11.78); Br, 30.24% (30.02). The negative
ion EI–MS of 6 showed a molecular ion peak at m/z 408, 410,
412 (15251). The base peak was at m/z 273, 275 from
M−[(2THT)+Br], (THT=tetrahydrothiophene) and another
peak at m/z 352, 354, 356 (24) from M-(2THT).
funnel and thermometer. The flask was cooled to 0–5 °C,
charged with 200 ml of dry tetrahydrofuran (THF) and LiAlH
(5.4 g, 0.14 mol) under a nitrogen atmosphere. Then 1 (20 g,
4
(0.095 mol) dissolved in 200 ml of dry THF was added drop-
wise over a period of 1 h and the reaction was continued for
another 6 h. The excess LiAlH was carefully quenched with
4-Methoxy-2,5-bis(tetrahydrothiophen-1-ium-1-ylmethyl)-
phenoxyacetic acid dibromide 7
4
water and the THF was evaporated at the pump. The product
was isolated by extraction with diethyl ether giving 80% of 2
(12.8 g). d (CDCl ): 2.65 (1H, br s, OH); 3.75 (3H, s, OCH );
3.90 (2H, t, OCH ); 4.00 (2H, t, CH O); 6.83 (4H, s, Ar).
Compound 5 (10 g, 0.027 mol) and tetrahydrothiophene
(7.18 ml, 0.081 mol) in 150 ml of methanol were stirred at
H
3
2
3
2
J. Mater. Chem., 1998, 8(4), 919–924
923

50 °C for 48 h. The solution was concentrated by evaporation
at room temp. and the residue was poured into 250 ml of
acetone. The suspension formed was stirred at 0–5 °C for 1 h
ably blue shifted due to an electron-hole confinement within
the conjugated copolymer layer.
We thank the Israel Ministry of Science and the Volkswagen
Foundation for their support of this research and Bat-Ami
Gottlieb for her invaluable help in the syntheses.
and the product was filtered off. The yield was 95% (14 g). d
H
(D O) 2.27–2.37 (8H, m, SCH CH ); 3.47–3.58 (8H, m,
SCH CH ); 3.98 (3H, s, OCH ); 4.53 (2H, s, OCH ); 4.62 (2H,
2
2
2
2
2
3
2
s, ArCH ); 4.96 (2H, s, Ar-CH ); 7.16 (1H, s, Ar); 7.27 (1H, s,
Ar). Elemental analysis for (C H Br O S ·CH OH): calc.
(found). C, 42.86 (42.71); H, 5.71 (5.38); S, 11.44 (11.03).
2
2
References
19 28
2
4 2
3
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6
7
8
Multilayer structures
9
The fabrication of multilayer films via self-assembly for the X-
ray reflectivity and photoluminescence studies was carried out
on a smooth float glass substrate cleaned for 1 h in an
ultrasonic cleaner using a 753 solution of H SO –H O. For
10 H. Hong, D. Davidov, H. Chayet, E. Z. Faraggi, M. Tarabia,
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2
4
2
electroluminescence studies an ITO coated glass was used. The
multilayer films were prepared by sequential treatment of the
substrate with aqueous solutions (using Millipore water) of
poly(ethyleneimine), PEI, poly(styrenesulfonic acid) sodium
salt, SPS, and co(PHydroxyV-PV). Thus, the substrate was
first dipped into a solution of 0.1 vol% PEI in water at pH 7–8
for 10 min, followed by dipping into an aqueous 0.01  solution
of SPS, also for 10 min, and finally dipped into a solution of
precursor co(PHydroxyV-PV). This sequence was repeated
until the desired number of trilayers were built up. The
conjugated co(PHydroxyV-PV) was formed in the assembled
structure by heating at 250 °C at 10−6 Torr for 10 h.
Conclusion
The synthesis and characterization of new poly(phenylenevinyl-
ene) type conjugated copolymers with polar side chains has
been presented. The luminescence spectra can be tuned by
control of the copolymer composition. Furthermore, in the
case of the carboxylated copolymer the luminescence spectra
were found to be a function of the pH of the precursor solution.
The copolymer with the hydroxy containing moiety can be
used to self-assemble multiple trilayers based for the first time
on hydrogen bonding rather than electrostatic interactions.
Luminescence spectra of such multiple trilayers are consider-
17 F. A. Neu, E. M. Collins, M. Deasy, G. Ferguson, S. J. Harris,
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18 A. W. van der Made and R. H. van der Made, J. Org. Chem., 1993,
58, 1262.
Paper 7/07365H; Received 13th October, 1997
924
J. Mater. Chem., 1998, 8(4), 919–924