Comparison of the electronic properties of poly[2-(2'-ethylhexyloxy)- 1,4-phenylenevinylene] prepared by different precursor polymer routes

Article abstract of DOI:10.1039/a902602i

The synthesis of poly[2-(2'-ethylhexyloxy)-1,4-phenylenevinylene] 10 via chloro 7, S-methyl xanthate 8, and O-ethyl xanthate 9 precursor polymers has been investigated. We found that the chloro and O-ethyl xanthate precursor polymers could be easily forme

Full text of DOI:10.1039/a902602i

J O U R N A L O F
Comparison of the electronic properties of poly[2-(2∞-ethylhexyloxy)-
1,4-phenylenevinylene] prepared by different precursor polymer routes
Shih-Chun Lo,a Anna K. Sheridan,b Ifor D. W. Samuelb and Paul L. Burn*a
aThe Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford, UK OX1 3QY
bDepartment of Physics, University of Durham, South Road, Durham, UK DH1 3LE
C H E M I S T R Y
Received 31st March 1999, Accepted 6th May 1999
The synthesis of poly[2-(2∞-ethylhexyloxy)-1,4-phenylenevinylene] 10 via chloro 7, S-methyl xanthate 8, and O-ethyl
xanthate 9 precursor polymers has been investigated. We found that the chloro and O-ethyl xanthate precursor
polymers could be easily formed whilst the S-methyl xanthate gave only low molecular weight material. The
observed molecular weights of the chloro and O-ethyl xanthate precursor polymers were found to decrease with
decreased polymer concentration when measured by gel permeation chromatography (GPC) with the decrease
probably being due to the dissociation of polymer aggregates or physical networks. In contrast, no decrease of
molecular weight was observed by GPC for the S-methyl xanthate precursor polymer on dilution. The chloro, S-
methyl xanthate, and O-ethyl xanthate precursor polymers were thermally converted to the conjugated polymer 10.
The UV–visible absorption and photoluminescence quantum yield of 10 was determined to be strongly dependent
on the precursor route used. For 10 formed from the chloro precursor 7 the PL quantum yield was found to be
55 5%.
There has been an increased interest in poly(1,4-phenylenevi-
nylene) (PPV) and its derivatives since it was first shown that
PPV could act as the light-emitting layer in a light-emitting
diode (LED).1 Much effort has gone into determining the
effect of substituents on the electronic properties of and the
synthetic pathways to PPV and its derivatives. The two
main synthetic routes to PPV have involved the synthesis of
soluble conjugated derivatives, which are normally substituted
with long lipophilic groups, or via a precursor polymer route
which generally leads to insoluble polymers.2 Of the two main
synthetic routes, we have concentrated on the latter as it gives
rise to materials which can be easily incorporated into multi-
layer LEDs.3 There are now a number of precursor routes to
PPV and its derivatives including, sulfonium,4 alkoxy,4b
halo,5,3c xanthate (dithiocarbonate),6 and sulfoxide and sul-
fone.7 It is clear that different precursor routes to the same
conjugated polymer can give rise to polymers which have
similar chemical structures but different electronic properties.
Of particular interest to us was the report that the xanthate
precursor to PPV gives higher external quantum efficiencies
when used as the light-emitting layer in an LED than PPV
prepared from the traditional sulfonium route.6 This was
attributed to the introduction of cis linkages which made the
material amorphous and have shorter conjugation lengths.
However, it was not made clear whether the PPV produced
via the O-ethyl xanthate route was itself inherently more
luminescent. We were therefore interested in exploring the
effect of the xanthate leaving group on the photoluminescence
quantum yield of a 2-alkoxyPPV derivative.
the electronic properties of the EHPPV produced by the
different routes.
Results and discussion
Monomer syntheses
The strategy for the syntheses of the monomers for EHPPV
is shown in Scheme 1. The first step in the synthesis of all
three monomers investigated was the activation of the two
methyl groups of 1.5a This was achieved by free radical
bromination using N-bromosuccinimide in carbon tetra-
chloride heated at reflux. Under these conditions an insepar-
able mixture of brominated products was formed. To facilitate
Cl
Cl
O
O
1
3
i
ii
OH
Br
iv
HO
Br
O
O
2
5
2-AlkoxyPPVs have been prepared via sulfonium precursor
polymers8 and even directly providing the alkoxy side chain
was a long lipophilic group.9 Our interest in 2-alkoxyPPVs
arises because we have used a 2-(2∞-ethylhexyloxyphenyl)
group as the basic ‘carrier’ monomer for PPV derivatives
which contain electron-withdrawing groups.5a,d We were there-
fore interested in how the precursor route used could affect
the photophysical properties of the basic unsubstituted poly-
mer. In this paper we describe the synthesis of a new 2-
alkoxyPPV, poly[2-(2∞-ethylhexyloxy)-1,4-phenylenevinylene]
10 (EHPPV) via chloro 7 and O-ethyl xanthate 9 polymers,
and a new S-methyl xanthate 8 precursor polymer. We compare
the syntheses and properties of the precursor polymers and
v
iii
OC(S)SMe
EtO(S)CS
SC(S)OEt
MeS(S)CO
O
O
4
6
Scheme 1 Reagents and conditions: i, NBS, CCl , AIBN, D, then
4
NaOAc, CH COOH, D, then KOH, H O, MeOH, DCM, D; ii,
3
2
DMAP, tosyl chloride, triethylamine, DCM, room temp., Ar; iii,
NaH, THF, room temp., then CS , room temp., then MeI, room
temp., Ar; iv, PBr , DCM, room temp., Ar; v, potassium O-ethyl
2
3
xanthate, (n-Bu) NBr, DCM, Ar, room temp.
4
J. Mater. Chem., 1999, 9, 2165–2170
2165

the separation of the desired di-activated p-xylene from the
mono-activated p-xylenes and other by-products the bromin-
ated mixture was acetylated to form the corresponding acetates
using sodium acetate in glacial acetic acid heated at reflux.
Unfortunately, the acetates were not separable as reported in
another synthesis using this strategy5a and the acetates had to
be hydrolysed with potassium hydroxide in aqueous methanol
to give the crude benzyl alcohols. The desired benzyl alcohol
2 was then separable by chromatography from the other by-
products and could be isolated in a total yield of up to 46%
for the 6 reactions. The chloro monomer 3 was formed from
2 by treatment of 2 with a mixture of tosyl chloride, DMAP,
and triethylamine10 and was isolated in a 58% yield. The bis-
(S-methyl xanthate) monomer 4 was also prepared from 2.
This was achieved by reacting the dialkoxy anion of 2 with
carbon disulfide followed by quenching with methyl iodide.
Under these conditions 4 was formed in a yield of 66%. Finally
the bis-(O-ethyl xanthate) monomer 6 was prepared in 98%
yield from the bromo monomer 5 by reaction with potassium
O-ethyl xanthate in the presence of a phase transfer catalyst.
The bromo monomer 5 was synthesised from 2 by treatment
with phosphorus tribromide in an 84% yield.
Polymerisations and conversions
The polymerisations of all three monomers were carried out
under similar conditions (Scheme 2). The general procedure
involved the addition of approximately 0.9 equivalents of a
solution of potassium tert-butoxide in tetrahydrofuran to a
solution of the monomer in tetrahydrofuran. To compare the
utility of each of the monomers for the preparation of
the precursor polymers the polymerisations were all carried
out at a concentration of 0.13–0.15 M with ice bath cooling.
When these conditions were used 7, 8, and 9 were formed in
~57%, ~38%, and ~68% yields respectively. All three poly-
mers had good solubility in tetrahydrofuran. The molecular
weights of the precursor polymers were studied by gel per-
meation chromatography (GPC) against polystyrene stan-
dards. Both the chloro 7 and O-ethyl xanthate 9 precursor
polymers had molecular weights which appeared to be concen-
tration dependent. If the stock solutions of polymer were
diluted for GPC analysis and run immediately then the chloro
Fig. 1 a) GPC traces of 7; b) GPC traces of 9.
by GPC analysis for 7 and 9 on dilution and equilibration is
similar to that seen for some other precursor polymers which
have been used to prepare PPV derivatives and we believe this
occurs due to the dissociation of polymer aggregates or
physical networks.11,5d In contrast the S-methyl xanthate mon-
omer 4 only gave very low molecular weight 8 which had an
M
9
of 8.5×103 and a polydispersity of 1.8. Attempts at
w
increasing the molecular weight of 8 by employing higher
concentrations of monomer, base, or temperature gave no
improvement. For example, adding 1 M base solution to neat
monomer 4 and carrying out the reaction at 55–60 °C for 1 h
precursor polymer 7 had an initial M of about 1.6×106 and
9
w
a polydispersity of ~4.7 and the O-ethyl xanthate polymer, 9,
had an M =7.7×105 with a polydispersity of 2.4. The inaccur-
9
w
acy in the observed molecular weight of 7 arises because the
gave 8 in a 41% yield which had an M =5.5×103 and a
9
w
high molecular weight component of 7 is above the calibration
limits of the GPC column used (Fig. 1a). On equilibration at
polydispersity of 1.7. However, 1H NMR analysis of 8 pro-
duced at the higher temperature and under more concentrated
conditions indicated that it contained a greater proportion of
conjugation than 8 produced at lower temperatures and
concentrations.
the lower concentrations used for GPC analysis the M s of 7
9
w
and 9 were observed to decrease with a concomitant change
in the polydispersities such that 7 had an M =4.4×105 and
9
w
w
a polydispersity of 1.8 (Fig. 1a) and 9 an M =2.6×105 with
9
Thermogravimetric analysis (TGA) of polymers 7, 8, and 9
was carried out with a heating rate of 5 °C min−1. In each
case we expect that the first weight loss corresponds to the
elimination of the leaving group. For 7, hydrogen chloride
was found to eliminate at 234 °C, with the first weight loss
ocurring at ~205 °C. Similarly, TGA of 9 indicated that the
O-ethyl xanthate group was eliminated at 236 °C with the
elimination beginning at ~213 °C. For both 7 and 9 the weight
loss observed corresponded closely to that expected for the
elimination from a precursor polymer with only low levels of
conjugation. 1H NMR also indicated that there were only low
levels of conjugation in 7 and 9. The amount of conjugation
in these precursor polymers can be determined approximately
by comparing the integration of the benzylic methine proton
a polydispersity of 1.7 (Fig. 1b). The decrease in M observed
9
w
Y
Y
n
Y
n
i
ii
O
O
O
3 Y = Cl
4 Y = OC(S)SMe
6 Y = SC(S)OEt
7 Y = Cl
8 Y = OC(S)SMe
9 Y = SC(S)OEt
10
with the signal due to the OCH protons of the 2-ethylhexyloxy
2
side group. In the case of 8 the elimination process was more
complex. There was an initial elimination at 126 °C which
commenced at ~102 °C and corresponded to a weight loss of
around 12%. After this there was almost a continuous weight
Scheme 2 Reagents and conditions: i, KOBut, THF, Ar; ii, heat,
vacuum.
2166
J. Mater. Chem., 1999, 9, 2165–2170

loss until 425 °C when the polymer decomposed. The weight
loss up to the decomposition point was ~41% which is above
the expected mass loss (32%) of 8 on conversion to 10. This
was clearly different to the thermal properties of 7 and 9 for
which the weight loss was well defined and corresponded
closely to the theoretical loss of weight associated with the
elimination reaction. We are unsure as to why the elimination
process for 8 is so complex but it may be due to the low
molecular weight of the polymer. In addition, it is important
to note that the 1H NMR of 8 was much more complex than
the NMR spectra for 7 and 9 with a large number of signals
in the methine region and signals due to the conjugated units.
The complexity in the 1H NMR spectrum could be due to a
combination of factors including the presence of different
structural isomers, different molecular weight polymers having
different conformations in solution, or different levels of
conjugation in the polymer chains.
Fig. 3 Infrared spectra of 7 and 10 formed from 7.
In the initial report on the O-ethyl xanthate precursor route
to PPV it was noted that the significant levels of cis-vinylene
linkages could be formed during the elimination procedure.
We were therefore interested to compare the properties of the
conjugated polymer 10 that was formed from each of the three
precursor polymers. All three precursor polymers were con-
verted in the range of 209–218 °C under vacuum overnight
and properties of 10 formed from the different precursor
polymers were compared by UV–visible spectroscopy and
infrared spectroscopy. There are usually two main features
observed in the UV–visible spectrum of a conjugated polymer
based on PPV; first, there is an absorption in the visible region
due to delocalised p–p* transitions; and second, there is an
absorption in the UV which corresponds to localised p–p*
transitions. In addition, with PPV based polymers an insight
into the degree of conjugation can be gained by comparing
the ratio of the localised to the delocalised transitions with
the smaller the ratio the better the conjugation. Thermal
conversion of 7 gave 10 which had peaks at 210 nm and
450 nm (localised p–p* and delocalised p–p* absorptions
respectively). As can be seen in Fig. 2 the two peaks are of
similar intensity which indicates that when 10 is produced
from 7 it has good conjugation. In addition, the infrared
spectrum of 10 (Fig. 3) when formed from 7 shows a strong
absorption at 965 cm−1 which is attributed to the trans-
vinylene CH out-of-plane bend. Films of 10 formed from 7
were found to be insoluble in chloroform, tetrahydrofuran,
and toluene. When 10 was formed from 9 a similar result was
observed with the UV–visible absorption spectra having a
peak at 445 nm. As in the case of 10 produced from 7, the
peak at 445 nm for 10 formed from 9 is of similar intensity to
that at 208 nm indicating that the degree of conjugation in the
two materials is essentially the same. The UV–visible spectrum
of 10 produced from 9 therefore suggests that the conversion
has gone basically to completion. The essentially complete
Fig. 4 Infrared spectra of 9 and 10 formed from 9.
conversion of 9 to 10 was confirmed by the comparison of the
infrared spectra of 9 and 10 (Fig. 4). The precursor polymer
9 has strong absorptions at 1219 and 1049 cm−1 which are
due to the O-ethyl xanthate leaving group and it can be clearly
seen that these are absent in the sample of 10 formed from 9.
Instead in the sample of 10 we again see the stretch at 965 cm−1
which corresponds to the trans-vinylene CH out-of-plane bend.
The absorption maximum of 10, which has one alkoxy group,
falls as expected between the absorption maxima for PPV
(427 nm)4b and a dialkoxyPPV such as MEHPPV (492 nm).3c
In contrast, when 10 is prepared from 8 the onset of
absorption and peak (417 nm) are blue shifted compared to
10 prepared from 7 or 9 (Fig. 2). This could be due to a
number of reasons including conformational defects, short
chain length, or incomplete conversion. Determining the extent
of conversion of 8 to 10 by infrared analysis is complicated.
Normally we expect to observe in the conjugated polymer an
absorption at around 965 cm−1 corresponding to the trans-
vinylene CH out-of-plane bend. However, in both the S-
methyl xanthate monomer 4 and precursor polymer 8 there
are already absorptions in this region and in the latter case
this may be due to some conjugation in the polymer.
Nevertheless, for 8 there is an absorption at 1060 cm−1 and a
broad absorption at 1217 cm−1 which we believe are associated
with the S-methyl xanthate leaving group (Fig. 5). Under the
conversion conditions used the absorptions due to the S-
methyl xanthate leaving group are not observed in films of 10
and there is a concommitant increase in the stretch at
966 cm−1. In addition, the infrared spectrum of 10 formed
from 8 (Fig. 5) is similar to 10 formed from 7 or 9 (Fig. 3
and 4). To determine whether the blue shift in the absorption
spectrum is due to short chain lengths is more difficult. GPC
Fig. 2 UV–VIS absorption spectra of 10 formed from 7, 8, and 9.
analysis of 8 gives an M of 8.5×103 and M of 4.7×103
9 9
w
n
J. Mater. Chem., 1999, 9, 2165–2170
2167

precursor polymers. In contrast the PL quantum yield varied
widely for 10 produced via the different precursor polymers.
When 10 was produced from 7 the PL quantum yield was
55 5% and when formed from 8 and 9 was 37 4% and 17 2%
respectively. These values should be compared to the 27%
observed for PPV13 and the 10–15% observed for the
dialkoxyPPV, MEHPPV.13,3c The PL quantum yield of 55 5%
is remarkably high for an alkoxy substituted PPV and is in
marked contrast to the results reported for 2-methoxyPPV and
2-n-butyloxyPPV when they were compared to PPV.8a Although
the absolute quantum efficiencies are not reported the relative
quantum efficiencies of 2-methoxyPPV and 2-n-butyloxyPPV to
PPV, which was taken as 1, were 0.43 and 0.48 respectively at
290 K.8a The difference in the PL quantum yield between 10,
and 2-methoxyPPV and 2-n-butyloxyPPV may be due to the
longer side chain. Therefore, our results clearly show that subtle
changes in the synthesis of 10 can have a strong effect on its PL
quantum yield. The differences in the PL quantum yield may be
due to different sample morphologies which can give rise to
different inter- or intra-chain interactions.
In conclusion, we have prepared a new 2-alkoxyPPV,
EHPPV, via chloro, O-ethyl xanthate, and S-methyl xanthate
precursor polymers. The use of an S-methyl xanthate precursor
polymer has not been reported before for the preparation of
poly(arylenevinylene)s. All three polymers could be thermally
converted to give samples of EHPPV which had similar PL
spectra but remarkably different PL quantum yields with the
chloro precursor polymer 7 giving rise to an alkoxyPPV
derivative with an exceptionally high PL quantum yield. We
plan to incorporate the EHPPV prepared by each of these
routes into light-emitting diodes to compare the external
quantum efficiencies of the devices with the PL quantum yields.
Fig. 5 Infrared spectra of 8 and 10 formed from 8.
which would correspond to approximately 25 or 14 units
respectively assuming that 8 has a similar structure to the
polystyrene standards. Although this may be an over esti-
mation of the number of units, given that the HOMO–LUMO
energy gap of model compounds of PPV decrease quickly as
the number of ‘monomer units’ increases such that after
around six units are in place the HOMO–LUMO energy gap
is similar to PPV12 we would conclude that the blue shift in
absorption is probably not due to excessively short chain
lengths. This is strengthened by the fact that uniform thin
films of 8 can be easily prepared by spin-coating. We therefore
conclude that the blue shift observed in the UV–visible spec-
trum is probably due to conformational effects. The poorer
conjugation is observed not only in the blue shift of the peaks
but also in the ratios of the peaks 205 and 405 nm where the
longer wavelength absorption is of lower intensity.
Experimental
Given the similarities in the UV–visible absorption spectra of
10 produced from 7 and 9 it might be expected that their
photoluminescence (PL) spectra and quantum efficiencies should
be the same, with that of 10 formed from 8 being different. For
the PL studies 7, 8, and 9 were converted to 10 at 220 °C at
<0.001 mBar for 15.5 h. The PL spectra of 10 produced from
each of the precursor polymers are illustrated in Fig. 6. The first
point to note is that each of them shows good vibronic structure
which indicates that the 10 produced in each case has good
intramolecular order. The vibronic structure observed is similar
to that reported for 2-methoxyPPV and 2-n-butyloxyPPV8a and
indicates that the longer 2-ethylhexyloxy group is not adding
any significant disorder to the polymer. As in the case of the
UV–visible spectrum there is a blue shift in the PL of 10 produced
from 8 although it is smaller than that observed in the absorption
spectrum. This is consistent with the singlet excited state migrat-
ing to the regions of lowest HOMO–LUMO energy gap in the
polymer which are similar to 10 produced from the other two
Measurements
NMR spectra were recorded on Bruker AM500, AMX500, or
DPX400 MHz spectrometers. 13C NMR spectra were fully
decoupled. IR spectra were recorded on a Perkin-Elmer
Paragon 1000 Infrared spectrometer. UV–visible spectra were
recorded on Perkin-Elmer UV–Visible (Lambda 14P) and
unless otherwise stated all spectra were recorded as a solution
in distilled dichloromethane. Mass spectra were recorded on
either a VG Autospec or BioQ (Electrospray) spectrometer,
the mode of ionisation being stated in each case. Melting
points were determined on a Buchi 510 melting point apparatus
¨
and are uncorrected. Microanalyses were carried out in the
Inorganic Chemistry Laboratory, Oxford. Gel permeation
chromatography was carried out using PLgel 20 mm Mixed-A
columns (600 mm+300 mm lengths, 7.5 mm diameter) from
Polymer Laboratories calibrated with polystyrene narrow stan-
dards (M =1300–15.4×106) in tetrahydrofuran with toluene
9
p
as flow marker. The samples for GPC were filtered through a
teflon membrane (0.45 mm). The tetrahydrofuran was degassed
with helium and pumped at a rate of 1 mL min−1. The PL
spectra of thin films were measured using a CCD spectrograph
following excitation by an argon ion laser at 476 nm. The
absolute photoluminescence quantum yield was measured in
air using an integrating sphere to collect the light emitted in
all directions13 again with excitation at 476 nm provided by
an argon ion laser. The thermogravimetric analysis was carried
out on a Rheometric Scientific STA 1500. For each run the
sample was held at 25 °C for 30 min and then heated from
25–600 °C at 5 °C min−1. The analysis was done under nitrogen
unless otherwise stated.
1,4-Bis(hydroxymethyl)-2-(2∞-ethylhexyloxy)benzene 2
A mixture of 15a (33.0 g, 141 mmol), carbon tetrachloride
(686 cm3), N-bromosuccinimide (55.2 g, 309 mmol), and
Fig. 6 Photoluminescence spectra of 10 formed from 7, 8, and 9.
2168
J. Mater. Chem., 1999, 9, 2165–2170

AIBN (6.48 g, 39.4 mmol) was heated at reflux for 4 h. The
cooled reaction mixture was filtered through a plug of silica
gel using carbon tetrachloride as eluent. The filtrate was
collected and the solvent completely removed to yield a yellow
oil (59.4 g).
had been cooled in an ice bath under argon. The reaction was
stirred with ice bath cooling for 1 h before being poured into
methanol (60 cm3). The reaction mixture was centrifuged for
10 min at 4500 rpm. The supernatant was removed and the
residue was dissolved in tetrahydrofuran (62 cm3). The poly-
mer solution was then added to propan-2-ol (84 cm3) and the
mixture was centrifuged at 4500 rpm for 10 min. The super-
natant was removed and the yellow precipitate of 7 (~437 mg,
~57%) was dissolved in tetrahydrofuran (93 cm3),
d (400 MHz; CDCl ) 0.91 (3 H, br m, Me), 0.97 (3 H, br t,
A mixture of crude 1,4-bis(bromomethyl)-2-(2∞-ethylhexyl-
oxy)benzene 5 (59.4 g), glacial acetic acid (500 cm3), and
anhydrous sodium acetate (55.9 g, 681 mmol) was heated at
reflux for 5 h under nitrogen. The resultant mixture was
allowed to cool to room temperature and the solvent was
completely removed. The residue was dissolved in dichloro-
methane (400 cm3), washed with water (200 cm3), dried over
anhydrous magnesium sulfate, filtered, and the solvent com-
pletely removed to give a brown oil. A preliminary purification
was carried out using column chromatography over silica
using ethyl acetate–light petroleum (1530) as eluent to give a
fraction which consisted mainly of the bis-acetate which was
recovered as a yellow oil (30.7 g).
H
3
Me), 1.25–1.40 (4 H, br s, 2×CH ), 1.43–1.60 (4 H, br m,
2
2×CH ), 1.72–1.83 (1 H, br m, CH), 3.18–3.30 (1 H, br m,
2
ArCH ), 3.31–3.45 (1 H, br m, ArCH ), 3.82–4.03 (2H, br
m, ArOCH ), 5.15–5.24 (1 H, br s, CHCl), 6.82–6.95 (2 H,
br m, ArH), and 7.01–7.15 (1 H, br m, ArH); GPC
2
2
2
(0.35 mg cm−3, 24.5 °C), M ~3.4×105, M ~1.6×106, poly-
9
9
n
n
w
dispersity index ~4.7 or M 2.5×105, M 4.4×105, polydis-
9
9
w
persity index 1.8 after disaggregation; thermogravimetric
A mixture of the crude 1,4-bis(acetoxymethyl)-2-(2∞-ethyl-
hexyloxy)benzene (30.7 g), methanol (189 cm3), dichloro-
methane (84 cm3), and aqueous potassium hydroxide (10 M,
84 cm3) was stirred at room temperature overnight. The solvent
was completely removed and the residue was added to a
mixture of dichloromethane (450 cm3) and brine (300 cm3).
The organic layer was separated and washed with water
(2×300 cm3). The combined water layers were extracted with
dichloromethane (2×200 cm3). The organic layers were com-
bined, dried over anhydrous magnesium sulfate, filtered, and
solvent completely removed to give an orange oil. The residue
was purified by column chromatography over silica gel using
ethyl acetate–dichloromethane (051 to 155) as eluent to give
a yellow oil of 2 (17.3 g, 46%). (Found: C, 72.2; H, 9.6.
C H O requires C, 72.1; H, 9.8%); n /cm−1 (neat) 3336
analysis: 234 °C (weight loss: 10%; expected: 14%).
1,4-Bis[(methylthio)thiocarbonyloxymethyl]-2-(2∞-
ethylhexyloxy)benzene 4
A mixture of 2 (100 mg, 0.38 mmol) anhydrous tetrahydro-
furan (3 cm3) and sodium hydride (60% dispersion in oil,
45 mg, 1.13 mmol) was stirred at room temperature under
argon for 1.5 h. Carbon disulfide (0.1 cm3, 1.50 mmol) was
added to the reaction mixture which was then stirred for
another 3 h. Iodomethane (0.14 cm3, 2.25 mmol) was added
and the reaction mixture was stirred for a further 4 h. The
reaction mixture was passed through a plug of silica gel using
ether as eluent. The filtrate was collected and the solvent
completely removed to give a yellow oil. The residue was
purified by chromatotron chromatography over silica using
ethyl acetate–light petroleum (051 to 156) giving a pale yellow
oil, which solidified at low temperature, of 4 (110.3 mg, 66%),
16 26 3
max
(OH); l /nm 277sh (e/dm3 mol−1 cm−1 2507) and 283
max
(2664); d (400 MHz; CDCl ) 0.89–0.97 (6 H, m, 2×Me),
H
3
1.31–1.38 (4 H, m, 2×CH ), 1.41–1.54 (4 H, m, 2×CH ),
2
2
1.65–1.82 (2 H, m, OH and CH), 2.35 (1 H, m, OH), 3.94 (2
(mp 33–34 °C) (Found: C, 53.7; H, 7.0. C H O S requires
20 30 3 4
H, m, ArOCH ), 4.68–4.70 (4 H, m, 2×ArCH ), 6.91 (1 H,
C, 53.4; H, 6.8%); n /cm−1 (neat) 965, 1056, and 1195 (br);
2
2
max
d, J 7.5, ArH), 6.95 (1 H, s, ArH), and 7.26 (1 H, d, J 7.5,
ArH); d (100 MHz; CDCl ) 11.1, 14.0, 23.0, 24.1, 29.0, 30.7,
l
/nm 281 (e/dm3 mol−1 cm−1 22384); d (500 MHz;
max
H
CDCl ) 0.89–0.96 (6 H, m, 2×Me), 1.30–1.35 (4 H, m,
C
3
3
39.4, 62.1, 65.3, 70.2, 109.5, 118.6, 128.5, 128.6, 141.9, and
2×CH ), 1.38–1.53 (4 H, m, 2×CH ), 1.69–1.78 (1 H, m,
CH), 2.57 (3 H, s, SMe), 2.60 (3 H, s, SMe), 3.90 (2 H, d, J
2
2
157.3; m/z [CI(NH )] 266 (M+).
3
5.5, ArOCH ), 5.61 (2 H, s, ArCH ), 5.66 (2 H, s, ArCH ),
1,4-Bis(chloromethyl)-2-(2∞-ethylhexyloxy)benzene 3
2
2
2
6.93 (1 H, d, J 1.0, ArH), 6.99 (1 H, dd, J 1.0 and 7.5, ArH),
and 7.37 (1 H, d, J 7.5, ArH); d (100 MHz; CDCl ) 11.2,
DMAP (1.42 g, 11.7 mmol), tosyl chloride (6.05 g,
31.7 mmol), and distilled triethylamine (2.7 cm3, 19.5 mmol)
were added sequentially to a solution of 2 (1.51 g, 5.66 mmol)
in dichloromethane (38 cm3) under argon at room tempera-
ture. The reaction mixture was stirred at room temperature
for 3.5 h and then filtered through a plug of silica gel using
dichloromethane as eluent. The filtrate was collected and
solvent completely removed to give a yellow solid. The residue
was purified by column chromatography over silica using light
petrolum as eluent. The main fraction was collected and the
solvent completely removed to give 3 as a colourless oil, which
solidified at low temperatures (1.00 g, 58%) (Found: C, 63.3;
H, 7.7. C H Cl O requires C, 63.4; H, 8.0%); l /nm 289
C
3
14.1, 19.0 (SMe), 19.2 (SMe), 23.0, 23.9, 29.1, 30.6, 39.4 (CH),
70.3, 70.8, 74.9, 111.2, 120.1, 123.6, 130.4, 136.8, 157.6, 215.6
(CLS), and 215.7 (CLS); m/z [Electrospray (NH )] 465
3
(MNH +) and 339 [M−OC(S)SMe]; HRMS 339.1448
4
[339.1452 calc. mass for M−OC(S)SMe].
Poly([2-(2∞-ethylhexyloxy)-1,4-phenylene]{1-[(methylthio)
thiocarbonyloxy]ethylene}) 8
A mixture of potassium tert-butoxide (45 mg, 0.40 mmol) in
dry tetrahydrofuran (2.5 cm3) was added to a solution of 4
(182 mg, 0.43 mmol) in dry tetrahydrofuran (3 cm3) cooled in
an ice bath under argon. The reaction mixture was stirred
with ice bath cooling for 1 h and then poured onto methanol
(9.6 cm3). The reaction mixture was concentrated to about
two thirds of its original volume under reduced pressure and
then centrifuged for 10 min at 4500 rpm. The supernatant was
removed and the resultant yellow residue of 8 (~53 mg,
16 24
2
max
(e/dm3 mol−1 cm−1 4763); d (400 MHz; CDCl ) 0.91–0.98 (6
H
3
H, m, 2×Me), 1.33–1.39 (4 H, m, 2×CH ), 1.44–1.61 (4 H,
2
m, 2×CH ), 1.76–1.83 (1 H, m, CH), 3.94 (2 H, d, J 5.5,
2
ArOCH ), 4.58 (2 H, s, CH Cl), 4.65 (2 H, s, CH Cl),
2
2
2
6.93–6.96 (2 H, m, ArH), and 7.34 (1 H, d, J 7.5, ArH);
d (100 MHz; CDCl ) 11.2, 14.1, 23.0, 24.0, 29.1, 30.6, 39.5,
41.3, 46.1, 70.3, 111.5, 120.3, 126.2, 130.6, 139.3, and 157.2;
C
3
~38%) was dissolved in tetrahydrofuran (3 cm3), n (film on
max
m/z [CI(NH )] 302, 304, and 306 (M+); HRMS 302.1214
KBr disc)/cm−1 967, 1060 and 1217; d (400 MHz; CDCl )
3
H
3
(302.1204 calc. mass).
0.77–1.03 (3 H, br m, 2×Me), 1.17–1.87 (br m, CH and
CH ), 2.03, 2.20, 2.55, 2.80–3.33, and 3.57–4.04 (SMe, ArCH ,
2
2
Poly{[2-(2∞-ethylhexyloxy)-1,4-phenylene](1-chloroethylene)} 7
OCH ), 4.59–4.70 and 4.87–5.68 (ArCH), and 6.39–7.65
2
(ArH and vinylH); GPC (0.80 mg cm−3, 22.6 °C), M =
A mixture of potassium tert-butoxide (298 mg, 2.65 mmol) in
dry tetrahydrofuran (14 cm3) was added to a solution of 3
(868 mg, 2.86 mmol) in dry tetrahydrofuran (22 cm3) which
9
n
4.7×103, M =8.5×103, polydispersity index=1.6; thermo-
gravimetric analysis: 125 °C (weight loss: 12%; expected: 32%).
9
w
J. Mater. Chem., 1999, 9, 2165–2170
2169

1,4-Bis(bromomethyl)-2-(2∞-ethylhexyloxy)benzene 5
m, ArCH ), 3.18–3.32 (1 H, br m, ArCH ), 3.71–3.98 (2 H,
2
2
br m, ArOCH ), 4.13–4.50 (2 H, br m, OCH Me), 5.07–5.12
2
2
Phosphorus tribromide (0.8 cm3, 8.41 mmol) was added
dropwise to a solution of 2 (852 mg, 3.20 mmol) in dry
dichloromethane (60 cm3) at room temperature under argon.
The reaction mixture was stirred at room temperature for 18 h
and then poured onto an ice–water mixture (30 cm3). The
organic layer was separated, washed with water (2×30 cm3),
brine (1×30 cm3), dried over anhydrous magnesium sulfate,
and the solvent completely removed to give a yellowish oil.
The residue was purified by column chromatography over
silica with ethyl acetate–light petroleum (1530) as eluent to
give a colourless oil, which crystallised at low temperatures,
of 5 (1.05 g, 84%); mp 43–44 °C (Found: C, 49.4; H, 6.5.
(1 H, br m, ArCH), 6.75–6.90 (2 H, br m, ArH), and
7.00–7.09 (1 H, br s, ArH); GPC (0.81 mg cm−3, 27.2 °C)
M =3.2×105, M =7.7×105, polydispersity index 2.4, or
9
9
n
n
w
w
M =1.5×105, M =2.6×105, polydispersity 1.7 after disag-
9
9
gregation; thermogravimetric analysis (air) 236 °C (weight loss:
31%; expected: 34%).
Poly[2-(2∞-ethylhexyloxy)-1,4-phenylenevinylene] 10
Method 1. Thin films of 7 were heated at 213 °C at 0.01
mmHg for 15 h to give 10; n
(film on KBr disc)/cm−1 966
max
and 3056; l (thin film)/nm 210, 256, 328sh, and 450.
max
C H Br O requires C, 49.0; H, 6.2%);
l
/nm 254
16 24
2
max
Method 2. Thin films of 8 were heated at 218 °C at
(e/dm3 mol−1 cm−1 11065) and 301 (5042); d (400 MHz;
H
CDCl ) 0.90–1.01 (6 H, m, 2×Me), 1.32–1.42 (4 H, m,
3
0.01 mmHg for 12 h to give 10; n
(film on KBr disc)/cm−1
max
966 and 3055; l (thin film)/nm 208, 256sh, 335sh, and 417.
2×CH ), 1.43–1.65 (4 H, m, 2×CH ), 1.77–1.84 (1 H, m,
max
2
2
CH), 3.95 (2 H, d, J 5.5, OCH CH), 4.47 (2 H, s, ArCH ),
2
2
Method 3. Thin films of 9 were heated at 209 °C at
4.54 (2 H, s, ArCH ), 6.91 (1 H, d, J 1.5, ArH), 6.93 (1 H,
dd, J 1.5 and 7.5, ArH), and 7.29 (1 H, d, J 7.5, ArH);
2
<0.01 mmHg for 15 h to give 10; n
(film on KBr disc)/cm−1
max
965 and 3054; l (thin film)/nm 210, 258, 332sh, and 445.
d (100 MHz; CDCl ) 11.3, 14.1, 23.0, 24.0, 28.4, 29.1, 30.6,
max
C
3
33.4, 39.5, 70.3, 112.0, 120.8, 126.5, 131.0, 139.8, and 157.2;
m/z [CI(NH )] 408, 410, and 412 (MNH +), and 390, 392,
Acknowledgements
3
4
and 394 (M+).
S.-C.L. is a Swire Scholar and holds an Overseas Research
Student Award. I.D.W.S. is a Royal Society University
Research Fellow. We thank BICC Cables Ltd for provision of
1,4-Bis[ethoxy(thiocarbonyl)thiomethyl]-2-(2∞-
ethylhexyloxy)benzene 6
a studentship (A.K.S.) and Dr M. G. Ruther for helpful
¨
discussions and carrying out the thermogravimetric analyses.
A mixture of 5 (92 mg, 0.23 mmol), potassium O-ethyl xan-
thate (94 mg, 0.59 mmol), tetra-n-butylammonium bromide
(21 mg, 0.07 mmol), and dry dichloromethane (3 cm3) was
stirred at room temperature for 4 h under argon. The reaction
mixture was filtered through a plug of silica gel using dichloro-
methane as eluent. The filtrate was collected and the solvent
completely removed to give a colourless oil. The oil was
purified by chromatotron chromatography over silica using
ethyl acetate–light petroleum (1530) as eluent. The main
fraction was collected and the solvent completely removed to
give 6 as a colourless oil (108 mg, 98%) (Found: C, 55.5; H,
7.7. C H O S requires C, 55.7; H, 7.2%); n /cm−1 (neat)
References
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2
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1049 and 1215; l /nm 286 (e/dm3 mol−1 cm−1 36399);
max
d (500 MHz; CDCl ) 0.92–0.97 (6 H, m, 2×Me), 1.32–1.40
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3
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CH S), 4.64–4.70 (4 H, m, 2×OCH Me), 6.86–6.88 (2 H, m,
ArH), and 7.31 (1 H, m, ArH); d (125 MHz; CDCl ) 11.2,
13.72, 13.75, 14.0, 23.0, 24.0, 29.0, 30.6, 35.2, 39.4, 40.5, 69.7,
70.0, 70.1, 111.7, 120.6, 123.7, 130.5, 136.6, 157.1, 213.8, and
214.8; m/z [Electrospray (NH )] 492 (MNH +).
2
2
2
2
2
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Poly(2-(2∞-ethylhexyloxy)-1,4-phenylene]{1-
[ethoxy(thiocarbonyl)thio]ethylene}) 9
6
7
8
A mixture of potassium tert-butoxide (153 mg, 1.37 mmol)
and dry tetrahydrofuran (7.6 cm3) was added to a solution of
5 (700 mg, 1.47 mmol) in dry tetrahydrofuran (11 cm3) cooled
in an ice bath under argon. The reaction mixture was stirred
with ice bath cooling for 1 h before being poured into methanol
(20 cm3). The mixture was centrifuged for 10 min at 4500 rpm
and the supernatant was removed. The residue was dissolved
in tetrahydrofuran (10 cm3) and then added to propan-2-ol
(20 cm3). The mixture was centrifuged at 4500 rpm for 10 min
and the supernatant removed. The yellow residue of 9
(~354 mg, ~68%) was dissolved in tetrahydrofuran (13 cm3),
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9
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n
(film on KBr disc)/cm−1 1049 and 1219; l /nm (thin
max
max
film) 289; d (400 MHz; CDCl ) 0.85–0.92 (3 H, br m, Me),
0.94–1.01 (3 H, br m, Me), 1.14–1.68 (11 H, 4×CH and
OCH CH ), 1.72–1.83 (1 H, br m, CH), 2.95–3.12 (1 H, br
H
3
2
Paper 9/02602I
2
3
2170
J. Mater. Chem., 1999, 9, 2165–2170