Synthesis and characterization of alternating copolymers of fluorene and oxadiazole

Article abstract of DOI:10.1021/ma011093n

Alternating copolymers of 9,9-dioctylfluorene and oxadiazole have been prepared by the tetrazole route or the Suzuki coupling reaction. In the polymers the oxadiazole units were evenly dispersed in the main chain at every one, P(F₁-alt-Ox), three, P(F₃-alt-Ox), or four, P(F₄-alt-Ox), fluorene units. Another copolymer with an asymmetric repeat unit structure, P(F₃-Ox-F₁-Ox) has also been prepared for comparison. In this study, the tetrazole route has been demonstrated to offer several advantages for preparing polyoxadiazole with well-defined structures compared to other oxadiazole ring formation reactions. These advantages include: clean and fast reactions, mild reaction conditions, high yields, and high molecular masses of product. The glass transition temperature of copolymers ranged from 98 to 150 °C, and the copolymers show high thermal stability with decomposition temperatures around 430 °C. The UV-vis absorption and photoluminescence properties of all the copolymers in solutions are similar to those of poly(9,9-dioctylfluorene). All copolymers fluoresce in the blue-light range with quantum yields of ～70% in CH₂Cl₂ solution.

Full text of DOI:10.1021/ma011093n

3474
Macromolecules 2002, 35, 3474-3483
Synthesis and Characterization of Alternating Copolymers of Fluorene
and Oxadiazole
J ia n fu Din g,* Mich a el Da y, Gilles Rober tson , a n d J a cqu es Roover s
Institute for Chemical Process and Environmental Technology, National Research Council Canada,
1200 Montreal Road, Building M-12 Ottawa, Ontario, Canada, K1A 0R6
Received J une 25, 2001; Revised Manuscript Received February 5, 2002
ABSTRACT: Alternating copolymers of 9,9-dioctylfluorene and oxadiazole have been prepared by the
tetrazole route or the Suzuki coupling reaction. In the polymers the oxadiazole units were evenly dispersed
in the main chain at every one, P(F1-alt-Ox), three, P(F3-alt-Ox), or four, P(F4-alt-Ox), fluorene units.
Another copolymer with an asymmetric repeat unit structure, P(F3-Ox-F1-Ox) has also been prepared
for comparison. In this study, the tetrazole route has been demonstrated to offer several advantages for
preparing polyoxadiazole with well-defined structures compared to other oxadiazole ring formation
reactions. These advantages include: clean and fast reactions, mild reaction conditions, high yields, and
high molecular masses of product. The glass transition temperature of copolymers ranged from 98 to 150
°C, and the copolymers show high thermal stability with decomposition temperatures around 430 °C.
The UV-vis absorption and photoluminescence properties of all the copolymers in solutions are similar
to those of poly(9,9-dioctylfluorene). All copolymers fluoresce in the blue-light range with quantum yields
of ∼70% in CH2Cl2 solution.
Sch em e 1. Ch em ica l Str u ctu r e of th e P olym er s
In tr od u ction
The first demonstration of efficient polymer light-
emitting diodes (PLEDs) in 19901 stimulated a great
interest in display applications for conjugated semicon-
ducting polymers.2,3 Compared to conventional LEDs,
PLEDs offer a wide variety of advantages. For instance,
they are much easier to process and can be fabricated
into large flat panel displays.
Among the three primary colors, green4 and red5
PLEDs have been successfully fabricated with high
efficiency. Meanwhile the performance of blue devices
needs to be improved.2e Because blue-light emissions are
associated with higher energy gaps, higher electric field
intensities have to be applied to the light-emitting layer.
Consequently higher thermal and oxidative stabilities
are demanded for the blue light-emitting polymers.
Polymers of fluorene present an interesting approach
to blue-light-emitting polymers due to their high chemi-
cal stability and the versatile chemical structures, which
make them ideal for chemical modification.2a Polymer-
izations of fluorene monomers with various comonomers
by Suzuki coupling3 or Yamamoto coupling6 reactions
have yielded a wide range of copolymers. Many of these
materials show good photoluminescence efficiency and
in some cases high thermal and oxidative stability. The
facile functionallisation at the 9-position of fluorene also
offers the ability to control interchain interaction, cross-
linking ability and electrical and optical properties.
To obtain high efficient PLED devices, a balance in
the injection of holes and electrons into the polymer
emissive layer is necessary. However, for most conju-
gated polymers developed so far, the injection and
transport of electrons are much less efficient than those
of holes. Therefore, attention has been drawn to the
development of polymers with improved electron trans-
porting capability.2b,7,8 Conjugated polymers with high
electron affinities have lower barriers for electron
injection from metal cathodes.2d,9 Polymers containing
electron-withdrawing units in the main chain or at
side groups usually have high electron affinities. Co-
polymers containing 1,3,4-oxadiazole have been found
to be very efficient at increasing electron affinity and
as a result are capable of enhancing their electron
transporting properties.2b,8 In addition by conjugated
with phenyl ring, oxadiazole units show blue-light-
emitting behavior.10b Of equal importance, the presence
of these units in copolymers has been observed to
enhance the thermal and oxidative stability.10
In this work, two types of copolymers of 9,9-dioctyl-
fluorene with oxadiazole have been prepared: one with
a symmetric structure of repeat units and the other with
an asymmetric structure. Their structures are shown
in Scheme 1. In the symmetric polymers, the oxadiazole
units were evenly dispersed in the main chain, at every
one, three, or four fluorene units. In the asymmetrically
structured copolymer the oxadiazole units were dis-
persed in the manner as shown in Scheme 1. Both types
of polymers have well-defined chain structures. The
purpose of this study was to prepare copolymers with
different oxadiazole content and different symmetry in
order to determine the effect of oxadiazole unit and
chain regularity on performance of the polymers includ-
* To whom correspondence should be addressed.
10.1021/ma011093n CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/27/2002

Macromolecules, Vol. 35, No. 9, 2002
Alternating Copolymers of Fluorene and Oxadiazole 3475
Sch em e 2. P r ep a r a tion of Dibor on ic Acid of 9,9-Dioctyflu or en e a n d Bis(9,9-d ioctyl)flu or en e
ing stability, charge transport, and electroluminescent
efficiency.3a For a similar reason, a homopolymer of 9,9-
dioctylfluorene has been also prepared by the Suzuki
coupling reaction using an A-B type monomer.11 Elec-
trochemical characterization as well as photo- and
electroluminescent studies demonstrated excellent sta-
bilities for the majority of the copolymers at both
positive and negative charged states and very stable
blue-light-emitting properties. Electrochemical studies
also showed that the insertion of oxadiazole units into
polyfluorene chain brought the electron affinities of the
copolymers close to the work functions of the cathodes
(Ca, Mg). All the results indicated the copolymers are
good candidate materials for an electron transport layer
in polymer blue-light-emitting diodes. The relevant
results will be published separately.12
material that can be removed by column chromatog-
raphy with hexane. 2,7-Dibromofluorene reacts in a
similar manner to afford 2,7-dibromo-9,9-dioctylfluorene
(5). However a more traditional route involving lithia-
tion was chosen to prepare 5 from fluorene (Scheme
2B).3a-c This reaction affords a product with higher
purity. Because both hydrogens in the 9-position of
fluorene can be completely deprotonated by n-BuLi, only
traces of monosubstituted byproduct are formed in this
reaction. After bromination, the crude product is easily
purified by recrystallization with hexane to produce
white crystals with an overall yield of 85% for this two-
step reaction. The bromination of 4 was catalyzed by
trace I2.3c Some other catalysts such as FeCl3, or Pd/C
were also reported for this reaction.3a,6c,14 However, we
found that I2 gave higher yields and higher purity.
The bromide (1, 5 or 6) was converted to the boronic
acid (2, 7, or 8) by lithiating the compound in diethyl
ether at low temperatures, followed by reaction with
B(OiPr)3.13b,15 The resulting boronate was then hydro-
lyzed with 2 N HCl to give the boronic acid with yields
from 55% to 76%. The low yields associated with this
reaction were due to the loss of product during purifica-
tion. It was for this reason that boronic esters rather
than the acid were used by some other researchers.3a-b
The use of B(OMe)3 was also investigated instead of
B(OiPr)3; however, the yield was much lower (<20%).
Resu lts a n d Discu ssion
Mon om er Syn th esis. The synthetic approach used
in this study started with fluorene and 2-bromofluorene
(Scheme 2). The hydrogens on the 9-position of 2-bromo-
fluorene are sufficiently acidic to react with 1-bromo-
octane when catalyzed by concentrated NaOH aqueous
solution (50% w/w) in the presence of a phase transfer
catalyst, C6H5CH2N(C2H5)3Cl.13 This reaction affords
2-bromo-9,9-dioctylfluorene (1) in a high yield (95%). The
main byproduct of this reaction is the monosubstituted

3476 Ding et al.
Macromolecules, Vol. 35, No. 9, 2002
Sch em e 3. Ch em istr y of 2-Br om o-9,9-d ioctylflu or en e (A) a n d 2,7-Dibr om o-9,9-d ioctylflu or en e (B)
Bis(9,9-dioctylfluorene) (3) was prepared by the Su-
zuki coupling reaction of boronic acid 2 with bromide
1.11,16 Several coupling reactions including Grignard,17
Yamamoto,6 Stille,3c,18 and Negishi19 reactions were
investigated for the formation of the C-C bond between
the aromatic rings in the preparation of the conjugated
oligomers and polymers. In this work, it was found that
the Suzuki coupling reaction was the most favorable.
The advantages associated with this reaction scheme
include20 reactivity less sensitive to steric hindrance,
mild reaction conditions, reactions less sensitive to the
presence of function groups and the environment, less
side reactions, and higher conversions.
easily controlled at the monosubstituted level. There-
fore, the monocarboxylic (13) and dicarboxylic (15)
compounds can be prepared in high yield by controlling
the molar ratio of 5/n-BuLi at 1.0/1.0 and 1.0/2.1,
respectively. However, from a practical point of view, a
molar ratio of 5/n-BuLi of l/0.9 was preferred for
preparing monocarboxylic product since it benefits the
product purification. The unreacted dibromide was
easily removed from the product by column chromatog-
raphy, while the bicarboxylic byproduct, which is formed
when excess n-BuLi was used, was very difficult to
remove.
A different situation arose when carbonitrile deriva-
tives (17 and 19) were prepared from 5. The reactivities
of the first and the second bromo groups in 5 are very
similar for this reaction, and the ratio of monosubsti-
tuted product to disubstituted product was found to be
6/4 (from NMR measurements of the reaction mixture).
Therefore, the yield of monosubstituted product was
Bromides 1 and 5 were also used for the preparation
of the carboxylic chloride and tetrazole (Scheme 3),
which were used as the starting materials in the
oxadiazole ring formation. In the reaction of dibromide
5 with n-BuLi, the first formed C-Li bond deactivates
the second bromo-group, and allows the reaction to be

Macromolecules, Vol. 35, No. 9, 2002
Alternating Copolymers of Fluorene and Oxadiazole 3477
Sch em e 4. F or m a tion of th e Oxa d ia zole Rin g
Sch em e 5. P r ep a r a tion of Cop olym er s Usin g th e
Tetr a zole Rou te (A) a n d by th e Su zu k i Rea ction (B)
always low (<60%). Fortunately, the separation of the
monosubstitute product from disubstituted product was
easily achieved by column chromatography, and both
products are useful materials in this study.
Another important advantage of the tetrazole route
is that the reaction is unaffected by functional groups
such as bromine in the starting material. These features
therefore made this procedure ideal for the preparation
of 1,3,4-oxadiazole containing monomers with versatile
structures, which could be used in subsequent coupling
polymerization reactions such as the Suzuki and Yama-
moto reaction. In this study the dibromide of trimer,
Br-F-Ox-F-Br (22), and pentamer, Br-F-Ox-F-
Ox-F-Br (23), have been prepared.
P olym er iza tion by th e Tetr a zole Rou te (Sch em e
5A). The tetrazole route was first used in polymeriza-
tions in 1961.25a However it was reported that only low
molecular mass polymers were obtained from this
reaction, and therefore, little attention was given to
apply this reaction to prepare polymers in the past few
decades.10b,27 However, this reaction does exhibit several
advantages in comparison to the other two reactions as
mentioned above. The most important advantages are
that side reactions are minimized and high yields are
possible (73-96% in this work). The tetrazole route
was therefore applied to the polycondensation of 9,9-
dioctylfluorene-2,7-ditetrazole (20) with 9,9-dioctyl-
fluorene-2,7-dicarboxylic chloride (16) (see Scheme 5A).
An aromatic polyoxadiazole (PF1-alt-Ox) with well-
defined structure was obtained in a high yield (93%).
Tetrazole compounds (12, 18, and 20) were prepared
from the corresponding carbonitrile derivatives by
reacting with Bu3SnCl and NaN3.21 This reaction route
was chosen due to its low sensitivity to the presence of
functional groups (Br in this work) in comparison to
other synthetic routes.22 For all three products, the
yields were low (35-64%). The reason for the low yields
has been attributed to the product being formed in salt
form that proved difficult to recover during purification.
Oxadiazole formation is described in Scheme 4. Be-
cause of the high thermal and chemical stability associ-
ated with oxadiazole compounds along with their good
electron transporting properties,8,10 a large amount of
work has been devoted to investigating the synthesis
of oxadiazole containing monomers and polymers. Three
reaction schemes have been extensively studied.10b The
first involves the dehydration of hydrazides with phos-
phorus oxychloride or other dehydrating agents.8a-c,10a,23
The second is a one-step polycondensation reaction,
which involves reacting the carboxylic acid and hydra-
zine sulfate in a strong acid.10a,24 The third route
involves the condensation of tetrazole with carboxylic
chloride under mild condition.22,25 Although the first two
reactions have been widely used for preparing oxadia-
zole-containing polymers, they do pose some problems.
The main disadvantages are associated with side
reactions,22b,24c which lead to impurities and end groups
that are covalently bound to the polymer, which cannot
be easily removed during subsequent purification. This
caused the formation of defects in the structure, which
are responsible for poor performance of the product as
a light-emitting material. Essentially, the defects quench
the fluorescence and enhance the polymer degradation.
However, the condensation between tetrazole and car-
boxylic chloride are clean and fast with high yields
under mild reaction conditions.
The molecular mass was also sufficiently high (Mn
)
12.0 kDa), and compared favorably with other well-
developed polycondensation reactions.16-20 The end
group in this polymer could be carboxylic acid or
tetrazole. The resulting polymer was pale yellow in color
and soluble in most common solvent such as toluene,
chloroform and THF. This result demonstrated the high
potential to prepare polyoxadiazoles with high molecular
mass by the tetrazole route.
P olym er iza tion by th e Su zu k i Rea ction (Sch em e
5B). On the other hand, polyoxadiazoles with different
composition were prepared from oxadiazole containing
dibromide 22, which copolymerized with diboronic acid

3478 Ding et al.
Macromolecules, Vol. 35, No. 9, 2002
Ta ble 1. Molecu la r Weigh t of th e P olym er s
Mn
Mw
polymerization
(monomer type)
polymer
(kDa) (kDa) PDI DP
PF
7.9 13.7 1.73 20.3 Suzuki (A-B)
12.0 27.3 2.28 26.3 tetrazole route
(A-A, B-B)
P(F1-alt-Ox)
P(F3-alt-Ox)
P(F4-alt-Ox)
25.1 62.8 2.50 20.4 Suzuki (A-A, B-B)
30.4 82.0 2.70 18.8 Suzuki (A-A, B-B)
P(F3-Ox-F1-Ox) 21.6 56.7 2.63 12.8 Suzuki (A-A, B-B)
7 or 8 by the Suzuki coupling reaction to offer P(F3-alt-
Ox), or P(F4-alt-Ox), respectively. Similarly, P(F3-Ox-
F1-Ox) was prepared from 23 and 7. In all these
reactions, the diboronic acid was carefully dried under
high vacuum (10-3 mmHg) and was correctly weighed
to obtain an equimolar ratio of diboronic acid/dibromide
in the feed. The end group of the polymers was not
controlled in this reaction and therefore it could be
either bromide or boronic acid.
Traces of Pd(II) formed from the Pd(0) catalyst used
in the Suzuki reaction can form a complex with the
oxadiazole units in the resulting polymers26 and cause
the polymers to darken in color. Attempts to remove the
residual catalyst using common extracting methods
recommended for many Suzuki reactions3a-b,16 were
unsuccessful. The polymer was therefore purified by
precipitating the reaction mixture into an acid solution
(concentrated HCl/methanol/acetone, 1:2:2 by volume).
Light colored polymers were obtained using this ap-
proach. The polymers were then washed with water and
methanol and finally extracted with acetone. The re-
sulting polymer was then dried under high vacuum.
So far, alternating copolymers of fluorene and oxa-
diazole with F/Ox ratios of 1/1 have been prepared by
the tetrazole route, the copolymers with 3/1 and 4/1
ratios, and the asymmetric copolymer (F/Ox ) 2) have
been prepared by the Suzuki coupling reaction.
F igu r e 1. 1H NMR spectra of the copolymers of fluorene and
oxadiazole.
Molecu la r Ma ss. Polystyrene equivalent GPC mo-
lecular masses of the polymers prepared using these two
approaches are given in Table 1. All the polymers gave
high quality films by spin-coating from dichloromethane
solution. Table 1 shows that the Mn of the copolymer
prepared by the tetrazole route is slightly lower than
those of the polymers obtained using the Suzuki reac-
tion. Because the formula weights of the repeat units
are different for each polymer, it can be misleading to
use molecular mass alone as an indicator for the extent
of conversion. The degree of polymerization (DP) is
related to the average number of new bonds formed in
each polymer during reaction. For condensation polym-
erization, it is therefore an indicator of the degree of
conversion. The value of DP in Table 1 indicates that
the oxadiazole ring formation from tetrazole has a
higher conversion than that from the Suzuki reaction.
1H NMR a n d 13C NMR of Cop olym er s. The 1H
NMR spectra of the copolymers are presented in Figure
1. Three groups of peaks associated with chemical shifts
at 8.20-8.24 (a), 7.88-7.96 (b), and 7.69 (c) can be
attributed to aromatic protons. The assignment of these
peaks is given in Figure 1. In addition, P(F3-alt-Ox)
displays some small peaks in the same region, which
may originate from end groups or are caused by traces
of residual Pt(II). However, P(F1-alt-Ox) has a quite
clean spectrum, indicating that the tetrazole route is
capable of producing a purer polymer with well-defined
structure.
F igu r e 2. Aromatic region of the 13C NMR spectrum of P(F1-
alt-Ox) in CDCl3.
the second methylene of octyl side group are located on
the top of a conjugated plane of fluorene and are
shielded by the π-electrons of the fluorene ring, and
consequently, their resonance appears at higher field
in the spectrum.3b The chemical shift is 0.60 ppm for
the trimer (21) and 0.61 ppm for the pentamer (23) (see
Experimental Section). However, it increases to 0.66
ppm for P(F1-alt-Ox), and further increases with the
length of fluorene segment in the repeat units of the
polymers. It reaches 0.79 ppm for P(F4-alt-Ox). This
phenomenon was explained by the increased delocal-
ization of π-electron with the increased length of the
oligomer chain and the increased length of the fluorene
segment in the repeat units of the polymers.
In the carbon NMR of P(F1-alt-Ox) (shown in Figure
2), only seven carbon peaks appear in the region related
to 14 aromatic atoms of the symmetric unit. Three
absorptions peaks are at lower field than ordinary
aromatic carbons. One of them, the aromatic carbon of
the oxadiazole ring, is bonded to two electron-withdraw-
ing atoms and is therefore expected to resonate at very
low field. The other two are from the four aromatic
carbons of the cyclopentadiene structure of the fluorene
group. Because of the rigid five-member ring structure,
those four aromatic carbons are subjected to the ring
current effect of the opposite benzene ring and are
An interesting phenomenon is found in the alkyl
region (0.5-2.5 ppm) of the copolymers. The protons on

Macromolecules, Vol. 35, No. 9, 2002
Alternating Copolymers of Fluorene and Oxadiazole 3479
Ta ble 2. Ch a r a cter istics of th e P olym er s
a
b
b
c
polymer
Tg (°C) Td (°C) λabs (nm) λPL (nm) φPL
PF
51
150
114
98
384
415 (439) 0.75
P(F1-alt-Ox)
P(F3-alt-Ox)
P(F4-alt-Ox)
P(F3-Ox-F1-Ox)
439
431
432
430
394 (372) 402 (426) 0.73
396 (380) 420 (442) 0.75
395 (381) 422 (443) 0.72
396 (379) 422 (444) 0.67
127
a
Temperature of 1% weight loss measured by TGA in nitrogen.
Wavelength of maximum absorbance or emission, wavelength
b
of the shoulder peak is in brackets. c Photoluminescence quantum
yield in CH2Cl2 (λexc ) 375 nm).
F igu r e 4. Absorption and emission spectra of trimer (FOxF),
polyfluorene, and the copolymers.
P(F4-alt-Ox) and P(F3-alt-Ox) are almost identical, only
the spectra of P(F3-alt-Ox) have been displayed in
Figure 4, while the data are summarized in Table 2.
The emission spectra for all polymers were measured
in CH2Cl2 solution using excitation at 375 nm, along
with that of 9,10-diphenylanthracene, a standard mate-
rial for quantum yield analysis. The emission spectrum
of trimer 21 was excited at 344 nm, the wavelength of
the maximum absorption.
F igu r e 3. DSC thermograms of copolymers of fluorene and
oxadiazole and polyfluorene. (insert) a plot of Tg vs weight
content of oxadiazole (wOx) of the copolymers.
therefore deshielded and also appear at lower field. With
the help of one-bond and three-bond heteronuclear
correlation, as well as the spectra of the monomer (21),
it is possible to assign the hydrogen and carbon peaks
as shown in the figures. Some small peaks were also
found in the aromatic region of the carbon spectrum.
These may originate from terminal groups. The integra-
tion of these peaks showed the intensity of the small
peaks is only 2-4% of the intensity of the normal peaks.
This information once again confirmed the well-defined
structure of P(F1-alt-Ox).
The UV-vis and PL spectra of the copolymers were
all very similar to those of polyfluorene, except for P(F1-
alt-Ox). From the results it appears that as oxadiazole
units are inserted into the polyfluorene conjugated
chain, there is a 10-12 nm red-shift in the absorption
spectra and 5-7 nm red-shift in emission spectra, and
the extent of the red-shift was not affected by the
oxadiazole content in the chain. This observation sug-
gests that the oxadiazole unit does not cause interrup-
tion of the main chain conjugation as suggested by
Lee for PPV type copolymers.29 This observation also
appears to be applicable to P(F1-alt-Ox). Its absorption
spectrum displays a vibronic fine structure with two
sharp bands at 372 and 394 nm, which are close to those
reported for the other copolymers, once again suggesting
that the conjugate length is not affected by the increased
oxadiazole units in the chain. This hypothesis, was
further examined by comparing the absorption spectrum
of P(F1-alt-Ox) with those of oligomers with analogous
chain structures as shown in Figure 5. In this case, an
increase in chain length caused a bathochromical shift
with a maximum absorption occurring at 345 nm for
FOxF (21), 348 nm for BrFOxFBr (22), 363 nm for
BrFOxFOxFBr (23), and 394 nm for P(F1-alt-Ox). This
result indicates that the conjugate length increased with
the chain length of the oligomers and confirms that the
oxadiazole units in the main chain do not interrupt the
conjugation of the copolymers. A similar phenomenon
was also reported for the oxadiazole containing poly-
(phenylenevinylene).30
Th er m a l P r op er ties. The thermal properties of the
polymers were investigated by DSC and TGA under
flowing nitrogen conditions. The relevant data are
reported in Table 2. The glass transition temperature
(Tg) was measurement on the second heating curve
(Figure 3) after the sample had first been heated to 250
°C and then allowed to slowly cool to room temperature.
No first-order transitions were detected in the DSC
thermograms for all 5 polymers in the region from -20
to +280 °C. The Tg of the copolymer with 1:1 molar ratio
of F/Ox is 150 °C. This value decreased with the
decreasing of oxadiazole content as displayed in the
insert of Figure 3. The decomposition temperatures (Td),
as measured by TGA, were all around 430 °C. The fact
that no obvious difference of Td was noted due to
oxadiazole content, suggests that both fluorene and
oxadiazole units in the polymer are equally thermal
stable and are not subject to neighbor effects.
Op tica l P r op er ties. Figure 4 presents the UV-vis
absorption and photoluminescence (PL) spectra of the
copolymers along with polyfluorene and trimer 21 for
comparison. Because the spectra of P(F3-Ox-F1-Ox),

3480 Ding et al.
Macromolecules, Vol. 35, No. 9, 2002
MgSO4. The solvent was then removed under reduced pressure
followed by the removal of excess of 1-bromooctane by distil-
lation under vacuum (2 mmHg) at 100 °C (bath temperature).
The product (pale yellow oil) was directly used without further
purification. 1H NMR, δ (CDCl3): 7.68 (d, J ) 6.8 Hz, 2H),
7.30 (m, 6H), 1.94 (m, 4H), 0.96-1.24 (m, 20H), 0.81 (t, J )
7.2 Hz, 6H), 0.60 (m, 4H). Anal. Calcd for C29H42: C, 89.16; H,
10.84. Found: C, 88.56; H, 10.38.
2,7-Dibr om o-9,9-d ioctylflu or en e (5).3c Bromine (159.6 g,
660 mmol) in CH2Cl2 (100 mL) was slowly added with stirring
at room temperature to a CH2Cl2 (600 mL) solution of the
above product (4) (300 mmol) containing I2 (0.12 g, 0.47 mmol).
This is an exothermic reaction, and any rapid addition of the
bromine should be avoided. The solution was stirred at room
temperature for 20 h in the dark, and 300 mL of aqueous
NaHSO3 (15%) was added. Vigorous stirring was applied until
the red color disappeared (<30 min). The organic layer was
separated, washed with water and dried over anhydrous
MgSO4. The solvent was removed under reduced pressure and
the product was purified by recrystallization from hexane three
times to yield a white crystalline product. The overall yield of
F igu r e 5. Absorption spectra of trimer 21, dibromotrimer 22,
dibromopentamer 23, and P(F1-alt-Ox).
1
these two reactions was 85.4%. Mp: 51.0-53.7 °C. H NMR,
δ (CDCl3): 7.51 (dd, J ) 7.6 Hz, 1.0 Hz, 2H), 7.44 (dd, J ) 7.6
Hz, 1.6 Hz, 2H), 7.43 (s, 2H), 1.90 (m, 4H), 0.98-1.24, (m, 20H),
Exp er im en ta l Section
In str u m en ta tion . Nuclear magnetic resonance spectra
0.82 (t, J ) 7.2 Hz, 6H), 0.57 (m, 4H). Anal. Calcd for C29H40
Br2: C, 63.51; H, 7.35. Found: C, 62.18; H, 8.07.
-
were recorded on a Varian Unity Inova spectrometer at a
1
2-Br om o-9,9-d ioctylflu or en e (1).13 A mixture of 2-bromo-
fluorene (24.5 g, 100 mmol) and benzyltriethylammonium
chloride (1.36 g) in 80 mL of DMSO and 40 mL of aqueous
NaOH (50%, w/w) was purged with argon. 1-Bromooctane (67.6
g, 350 mmol) was added to the mixture using a syringe. The
resulting solution was stirred at 35 °C for 5 h before 80 mL of
H2O was added. The solution was then extracted twice with
100 mL of diethyl ether. The combined organic layers were
washed with brine and dried over MgSO4. The solvent was
removed under reduced pressure, followed by removal of excess
1-bromooctane by distillation under vacuum. The crude prod-
uct was purified by column chromatography using hexane as
eluent to yield a colorless oil in 95% yield. 1H NMR, δ
(CDCl3): 7.65 (m, 1H), 7.54 (dd, J ) 7.2 Hz, 1.5 Hz, 1H), 7.44
(s, 1H), 7.43 (dd, J ) 7.6 Hz, 1.8 Hz, 1H), 7.31 (m, 3H), 1.92
(m, 4H), 0.97-1.24 (m, 20H), 0.81 (t, J ) 7.2 Hz, 6H), 0.58 (m,
4H). Anal. Calcd for C29H41Br: C, 74.18; H, 8.80. Found: C,
74.56; H, 8.85.
resonance frequency of 399.961 MHz for H and 100.579 MHz
for 13C. Carbon spectra of polymers as well as carbon hydrogen
correlations were obtained using a 10 mm tunable broadband
1
probe with one-bond J C-H set to 120 Hz while long-range
3
three-bond J C-C-C-Hs were set to 7.5 Hz. Molecular masses
[number-average (Mn) and weight-average (Mw)] were deter-
mined by size exclusion chromatography (SEC) with a Waters
515 HPLC pump and a Waters 410 differential refractometer.
The instrument was calibrated with polystyrene standards in
THF (HPLC grade). Thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) were performed using
a purged nitrogen atmosphere at a heating rate of 10 °C/min,
using TA Instruments 951 and 910 modules, respectively,
controlled by a 2100 controller. The glass transition temper-
ature (Tg) was recorded on the second heating curve. The
melting point range (mp) was recorded from the interval
between the onset and the maximum of the endothermic peak
obtained from the first heating curve. Absorption and photo-
luminescence (PL) emission spectra of the polymers were
measured in dichloromethane (HPLC grade) using a Hewlett-
Packard 8453 spectrophotometer and a Spex Fluorolog 3
spectrometer, respectively. The fluorescence analysis was
performed using about 10-6 M solutions. Quantum yields were
determined using argon saturated solutions in dichloromethane
and were calculated by comparing emission with that of a
standard solution of 9,10-diphenylanthracene in cyclohexane
(φPL ) 0.95) at room temperature.28 Elemental analyses were
conducted on a LECO CHNS932 analyzer.
9,9-Dioctylflu or en e-2,7-d ibor on ic Acid (7).11a,b,15a A 2.5
M solution of n-butyllithium (42 mL, 105 mmol) was added to
an argon-purged solution of (5) (27.4 g, 50 mmol) in anhydrous
diethyl ether (300 mL) at -78 °C using a syringe. The solution
was then allowed to slowly warm to room temperature, and
stirred for a further1 h before it was cooled again to -78 °C.
Triisopropyl boronate (39.5 g, 210 mmol) was added with a
syringe. The resulting mixture was once again allowed to
warm to room temperature and was stirred for an additional
20 h (vigorous stirring was required during this step to avoid
gel formation). Then 2 N HCl (200 mL) was added to the
stirred solution while maintaining the solution at room tem-
perature for 1 h. The organic layer was separated and the
water layer was extracted with 200 mL of diethyl ether. The
combined ether layers were washed twice with 200 mL of
water. The solvent was then removed under reduced pressure.
The crude product was purified by Soxhlet extraction with
hexane to give a white powder in a yield of 65%. Mp: >400
Ma ter ia ls. All starting materials and reagents were pur-
chased from Aldrich. All the solvents for characterization were
used as received without further purification. The solvents for
chemical reaction were dried under the protection of argon.
THF was refluxed with K/Na alloy in the presence of benzo-
phenone until a persistent blue color appeared and then
distilled. Diethyl ether and toluene were refluxed with Na for
4 h and then distilled. Dichloromethane was refluxed with
CaH2 and distilled.
1
°C dec. H NMR, δ (CD3OD): 7.74 (m, 4H), 7.59 (s, 2H), 2.00
Syn th esis. 9,9-Dioctylflu or en e (4). This material was
prepared using a method similar to that in ref 3a. A 2.5 M
n-butyllithium solution (264 mL, 660 mmol, in hexane) was
added dropwise to a solution of fluorene (49.9 g, 300 mmol) in
600 mL of anhydrous THF at -78 °C. The mixture was stirred
at -78 °C for 45 min, and then 1-bromooctane (144.8 g, 750
mmol) was added dropwise followed by further stirring at -78
°C for 1 h. The solution was then allowed to slowly warm to
room temperature and stirred for another 1 h. Then 500 mL
aqueous NH4Cl solution (10%, w/w) was added with stirring.
The organic layer was separated and washed twice with 500-
mL aliquots of water before being dried over anhydrous
(m, 4H), 0.94-1.24 (m, 20H) 0.80 (t, J ) 7.2 Hz, 6H), 0.52 (m,
4H). Anal. Calcd for C29H44O4B2: C, 72.83; H, 9.27. Found: C,
73.21; H, 9.87.
9,9-Dioctylflu or en e-2-bor on ic Acid (2). This compound
was prepared using a similar procedure to that used for 7
starting with compound 1. 1 was reacted with n-BuLi, and
then (iPrO)3B, using molar ratios of 1.0:1.1:3.0. The crude
product was purified by column chromatography using AcOEt/
hexane (30/70, v/v) as eluent to yield a white powder in 55%
yield. Mp: 70.1-77.3 °C.1H NMR, δ (CDCl3): 8.31 (dd, J )
7.6 Hz, 1.0 Hz, 1H), 8.22 (s, 1H), 7.89 (d, J ) 7.6 Hz, 1H), 7.81
(m, 1H), 7.38 (m, 3H), 2.09 (m, 4H), 0.97-1.22 (m, 20H), 0.77

Macromolecules, Vol. 35, No. 9, 2002
Alternating Copolymers of Fluorene and Oxadiazole 3481
(t, J ) 7.2 Hz, 6H), 0.68 (m, 4H). Anal. Calcd for C29H43O2B:
C, 80.17; H, 9.98. Found: C, 81.04; H, 9.75.
Anal. Calcd for C30H40BrN: C, 72.86; H, 8.15; N, 2.83. Found:
C, 73.65; H, 8.80; N, 2.55.
2,2′-Bis(9,9-d ioctylflu or en e) (3).11,15 1 (9.36 g, 20.0 mmol)
and 2 (8.68 g, 20.0 mmol) were mixed in toluene (120 mL),
and 2 M Na2CO3 (80 mL) was added. The mixture was purged
with argon. (PPh3)4Pd0 (0.23 g, 0.20 mmol) was then added in
a glovebox. The mixture was refluxed with stirring in the dark
for 48 h under the protection of argon. The organic layer was
then separated and washed with water and dried with MgSO4.
The solution was then filtered through silica gel to remove the
dark color. The solvent was removed under reduced pressure.
The crude product was purified by recrystallization first from
hexane and then from acetone to give pale-green needlelike
crystals in a yield of 81%. Mp: 74.3-79.2 °C. 1H NMR, δ
(CDCl3): 7.76 (d, J ) 7.8 Hz, 2H), 7.73 (dd, J ) 7.8 Hz, 2H),
7.63 (dd, J ) 8.0 Hz, 1.6 Hz, 2H), 7.60 (d, J ) 1.4 Hz, 2H),
7.32 (m,6H), 2.01 (m, 8H), 0.99-1.24 (m, 40H), 0.80 (t, J )
7.2 Hz, 12H), 0.70 (m, 8H). Anal. Calcd for C58H82: C, 89.39;
H, 10.61. Found: C, 89.63; H, 10.27.
2,2′-Bis(7-br om o-9,9-d ioctylflu or en e) (6). This material
was prepared in a manner similar to that used for 5. 3 was
reacted with Br2 using a molar ratio of 3/Br2 of 1.0:2.2. The
resulting product was twice recrystallized from acetone to give
white crystals in a yield of 86.7%. Mp: 58.5-64.9, 74.5-78.8
°C (bimodal), 1H NMR, δ (CDCl3): 7.73, (d, J ) 8.0 Hz 2H),
7.61 (dd, J ) 8.0 Hz, 1.6 Hz, 2H), 7.58 (dd, J ) 7.6 Hz, 1.0 Hz,
2H), 7.47 (s, 2H), 7.46 (dd, J ) 7.6 Hz, 1.6 Hz, 2H), 1.99 (m,
8H), 0.99-1.23 (m, 40H), 0.80 (t, J ) 0.76 Hz, 12H), 0.68 (m,
8H). Anal. Calcd for C58H80Br2: C, 74.34; H, 8.61. Found: C,
72.78; H, 8.88.
9,9-Dioctylflu or en e-2-ca r bon itr ile (11). This material
was prepared using a similar procedure as that used for 19. 1
was reacted with CuCN in a molar ratio of 1:1.8. The crude
product was purified by column chromatography using AcOEt/
hexane (7/93, v/v) as eluent to produce a pale yellow oil in a
yield of 81%. 1H NMR, δ (CDCl3): 7.75 (dd, J ) 8.0 Hz, 0.7
Hz, 1H), 7.73 (m, 1H), 7.62 (dd, J ) 8.0 Hz, 1.5 Hz, 1H), 7.59
(s, 1H), 7.37 (m, 3H), 1,96 (m, 4H), 0.96-1.23 (m, 20H), 0.80
(t, J ) 7.2 Hz, 6H), 0.53 (m, 4H). Anal. Calcd for C30H41N: C,
86.69; H, 9.94; N, 3.37. Found: C, 85.57; H, 9.59; N, 3.23.
9,9-Dioctylflu or en e-2,7-d itetr a zole (20).22 A mixture of
19 (12.0 g, 27.3 mmol) and NaN3 (4.29 g, 65.5 mmol) in
anhydrous toluene (60 mL) was purged with argon. (n-
Bu)3SnCl was added to the mixture using a syringe. The
mixture was refluxed for 24 h. The solution was then acidified
with concentrated HCl, and washed with water (100 mL) three
times. The suspended solid was collected by filtration and
purified by column chromatography using AcOEt/hexane (33/
67,v/v) followed by acetone as eluent. This gave a product in a
yield of 35%. Mp: 120.5-134.0 °C. 1H NMR, δ (CDCl3/acetone-
d6): 8.19 (d, J ) 1.2 Hz, 2H), 8.11 (dd, J ) 8.0 Hz, 1.2 Hz,
2H), 7.93 (d, J ) 8.0 Hz, 2H), 2.09 (m, 4H), 0.89-1.13 (m, 20H),
0.69 (t, J ) 7.2 Hz, 6H), 0.59 (m, 4H). Anal. Calcd for
C
31H42N8: C, 70.69; H, 8.04; N, 21.27. Found: C, 70.03; H,
8.46; N, 20.79.
7-Br om o-9,9-d ioctylflu or en e-2-tetr a zole (18). This com-
pound was prepared using a similar procedure as that for 20.
17 was reacted with NaN3 in a molar ratio of 1:1.2. After the
crude product was recovered from the reaction mixture by
filtration, it was washed with hexane and methanol twice
respectively to give a white powder in a yield of 64%. Mp:
179.9-182.7 °C.1H NMR, δ (CDCl3/acetone-d6): 8.13 (d, J )
1.5 Hz, 1H), 8.06 (d, J ) 8.0 Hz, 1H), 7.83 (d, J ) 8.0 Hz, 1H),
7.65 (d, J ) 8.0 Hz, 1H), 7.50 (d, J ) 1.8 Hz, 1H), 7.45 (dd, J
) 8.0 Hz, 1.8 Hz, 1H), 2.01 (m, 4H), 0.91-1.18 (m, 20H), 0.73
(t, J ) 7.2 Hz, 6H), 0.56 (m, 4H). Anal. Calcd for C30H41BrN4:
C, 67.03; H, 7.69; N, 10.42. Found: C, 68.37; H, 7.86; N, 10.55.
9,9-Dioctylflu or en e-2-tetr a zole (12). This material was
prepared using a similar procedure as that for 20. 11 was
reacted with NaN3 in a molar ratio of 1:1.1. After the reaction
mixture was acidified and washed with water, the solvent was
removed under reduced pressure. The crude product was
purified by column chromatography using a mixture of AcOEt/
hexane (40/60, v/v) as an eluent to give a pure product in a
yield of 58%. 1H NMR, δ (CDCl3): 8.11 (d, J ) 1.4 Hz, 1H),
8.04 (d, J ) 8.0 Hz,1H), 7.79 (dd, J ) 8.0 Hz, 1H), 7.68 (m,
1H), 7.36 (m, 3H), 2.02 (m, 4H), 0.90-1.16 (m, 20H), 0.76 (t, J
) 7.2 Hz, 6H), 0.57 (m, 4H). Anal. Calcd for C30H42N4: C, 78.56;
H, 9.23; N, 12.22. Found: C, 77.63; H, 9.15; N, 12.03.
2,2′-Bis(9,9-dioctyl)flu or en e-7,7′-dibor on ic Acid (8). This
material was prepared in a procedure similar to that used for
7. 6 was reacted with n-BuLi followed by (iPrO)3B using molar
ratios of 1.0:2.1:4.2. The crude product was purified by
recrystallization from hexane twice to give a white powder in
1
76% yield. Mp: 124.9-127.1-136.3 °C (bimodal). H NMR, δ
(CDCl3/acetone-d6): 8.01 (s, 2H), 7.92 (d, J ) 8.0 Hz, 4H), 7.86
(d, J ) 1.7 Hz, 2H), 7.82 (dd, J ) 7.6 Hz, 0.7 Hz, 2H), 7.76
(dd, J ) 7.6 Hz, 1.7 Hz, 2H), 2.14 (m, 8H), 1.00-1.24 (m, 40H),
0.78 (t, J ) 7.2 Hz, 12H), 0.69 (m, 4H). Anal. Calcd for
C
58H84O4B2: C, 80.36; H, 9.98. Found: C, 81.19; H, 9.47.
2,7-Dicya n o-9,9-d ioctylflu or en e (19).20,22a A mixture of
5 (15.0 g, 27.3 mmol) and CuCN (8.58 g, 95.8 mmol) in NMP
(80 mL) was purged with argon and refluxed for 4 h. The hot
reaction mixture (∼120 °C) was then slowly poured into a
stirred acidified aqueous FeCl3 solution (60.0 g of FeCl3 in 15
mL of concentrated HCl and 90 mL of H2O). The mixture was
stirred for a further 20 min at 90 °C. The aqueous layer was
then separated from the organic layer and was extracted with
toluene (120 mL) twice. The combined organic layer was
washed with 100 mL of 6 N HCl until the dark heavy organic
layer disappeared. The organic layer was then washed with
water, 10% NaOH solution, and water again prior to being
dried over MgSO4. The solution was filtered to remove
insoluble particles. The solvent was then removed under
reduced pressure to give a crude product. The crude product
was purified by column chromatography using AcOEt/hexane
(20/80, v/v) as eluent, followed by recrystallization from hexane
to offer colorless crystals in a yield of 73%. Mp: 77.5-79.7 °C,
1H NMR, δ (CDCl3): 7.82 (dd, J ) 8.0 Hz, 0.7 Hz, 2H), 7.68
(dd, J ) 8.0 Hz, 1.4 Hz, 2H), 7.64 (m, 2H), 1.99 (m, 4H), 0.97-
1.26 (m, 20H), 0.82 (t, J ) 7.2 Hz, 6H), 0.51 (m, 4H). Anal.
Calcd for C31H40N2: C, 84.49; H, 9.15; N, 6.36. Found: C, 83.30;
H, 10.23; N, 6.38.
7-Br om o-9,9-d ioct ylflu or en e-2-ca r b on it r ile (17). This
material was prepared using a similar procedure to that used
for 19, starting from 5 using an equimolar ratio of 5/CuCN.
The crude product was purified by column chromatography
using AcOEt/hexane (10/90, v/v) as eluent to give a white
powder with a yield of 45%. Mp: 48.3-52.2 °C, 1H NMR, δ
(CDCl3): 7.72 (dd, J ) 8.0 Hz, 0.6 Hz, 1H), 7.62 (dd, J ) 8.0
Hz, 1.4 Hz, 1H), 7.59 (dd, J ) 7.2 Hz, 1.6 Hz, 1H), 7.57 (m,
1H), 7.50 (dd, 7.2 Hz, 1.8 Hz, 1H), 7.49 (s, 1H), 1.94 (m, 4H),
0.97-1.26 (m, 20 H), 0.81 (t, J ) 7.2 Hz, 6H), 0.53 (m, 4H).
9,9-Dioctylflu or en e-2,2-d ica r boxylic Acid (15). A solu-
tion of n-BuLi (23.5 mL, 58.8 mmol) was added dropwise into
an argon-purged solution of 5 (14.0 g, 25.5 mmol) in anhydrous
diethyl ether (200 mL) at -78 °C. The solution was then
allowed to warm to room temperature with stirring for 1 h
before it was cooled back to -78 °C. CO2 dried with 3 Å
molecular sieves was bubbled into the slurry over a period of
1 h while maintaining the temperature at -78 °C. The slurry
was then allowed to slowly warm to room temperature with
stirring and maintained for a further 1 h before being acidified
with 2 N HCl solution (120 mL). The organic layer was then
separated and washed with water and the solvent removed
under reduced pressure. The crude product was purified by
recrystallization from acetone to give a white powder with a
yield of 90%. Mp: 218.8-222.2 °C. 1H NMR, δ (CDCl3/acetone-
d6): 8.04 (dd, J ) 8.0 Hz, 1.5 Hz, 2H), 8.02 (m, 2H), 7.78 (dd,
J ) 8.0 Hz, 0.7 Hz, 2H), 1.99 (m, 4H), 0.89-1.16 (m, 20 H).
0.72 (t, J ) 7.2 Hz, 6H), 0.49 (m, 4H). Anal. Calcd for
C
31H42O4: C, 77.79; H, 8.84. Found: C, 78.34; H, 8.76.
7-Br om o-9,9-d ioct ylflu or en e-2-ca r boxylic Acid (13).
This material was prepared using a similar procedure to that
used for 15. 5 was reacted with n-BuLi in a molar ratio of 1:0.9.
The resulting crude product was purified by column chroma-
tography using AcOEt/hexane (5/95) followed by AcOEt/hexane

3482 Ding et al.
Macromolecules, Vol. 35, No. 9, 2002
(20/80) to give a white powder with a yield of 65%. Mp: 113.3-
116.4 °C. 1H NMR, δ (CDCl3): 8.13 (dd, J ) 8.0 Hz, 1.6 Hz,
1H), 8.06 (d, J ) 1.6 Hz, 1H). 7.74 (dd, J ) 8.0 Hz, 0.5 Hz,
1H), 7.62 (d, J ) 8.4 Hz, 1H), 7.50 (d, J ) 1.8 Hz, 1H), 7.49
(dd, J ) 8.4 Hz, 1.8 Hz, 1H), 1.98 (m, 4H), 0.97-1.25 (m, 20H),
then dried under high vacuum to give 3.48 g of a pale yellow
powder with a yield of 93%.
(b) By th e Su zu k i Cou p lin g Rea ction . All the other
polymers were prepared using a procedure similar to that used
for preparing 3. The reactions involved starting with 2.00 g of
the relevant dibromide, 22 or 23, and diboronic acid, 7 or 8,
at an equimolar ratio. Once the reaction was completed, the
organic layer was separated, and added dropwise with stirring
to a mixture of concentrated HCl/methanol/acetone (0.5:1:1).
The resulting polymer was recovered by filtration, washed with
methanol, and further purified by dissolving in toluene and
reprecipitating into methanol/acetone (1/1) mixture. The poly-
mer was then extracted with acetone for 48 h and dried under
high vacuum to give the products (pale green in color) with
the following yields: P(F3-alt-Ox), 2.33 g, 95%; P(F4-alt-Ox),
2.90 g, 90%; P(F3-Ox-F-Ox), 2.08 g, 90%.
0.80 (t, J ) 0.72 Hz, 6H), 0.57 (m, 4H). Anal. Calcd for C30H41
-
BrO2: C, 70.16; H, 8.05. Found: C, 71.47; H, 8.04.
9,9-Dioctylflu or en e-2-ca r boxyl Acid (9). This material
was prepared using a similar procedure to that used for 15. 5
was reacted with n-BuLi in a molar ratio of 1:1.1. The crude
product was purified by column chromatography using AcOEt/
hexane (5/95) followed by AcOEt/hexane (20/80), prior to
recrystallization from hexane to give a white powder with a
yield of 73%. Mp: 55.7-61.4 °C. 1H NMR, δ (CDCl3): 8.13 (dd,
J ) 8.0 Hz, 1.5 Hz, 1H), 8.08 (d, J ) 1.5 Hz, 1H), 7.77 (m,
2H), 7.37 (m, 3H), 2.00 (m, 4H), 0.95-1.24 (m, 20H), 0.80 (t, J
) 0.72 Hz, 6H), 0.58 (m, 4H). Anal. Calcd for C30H42O2: C,
82.90; H, 9.74. Found: C, 82.88; H, 9.58.
Con clu sion
Br F -Ox-F Br , Dibr om otr im er 22.22b,c A solution of 13
(8.15 g 16.4 mmol) in SOCl2 (80 mL) was refluxed for 4 h under
argon to convert the acid to the corresponding acid chloride
(14). The excess SOCl2 and other volatile materials were then
distilled off under reduced pressure. Then 20 mL anhydrous
pyridine was added to the green solid to give a solution that
was added dropwise to a solution of 18 (8.00 g, 14.9 mmol) in
anhydrous pyridine (40 mL) using a syringe. The resulting
mixture was refluxed for 2 h under argon and was cooled to
room temperature prior to being poured into methanol with
stirring to precipitate the product. The crude product was
purified by chromatography using AcOEt/hexane (5/95) fol-
lowed by AcOEt/hexane (15/85). White crystals in a yield of
96% were obtained on recrystallization from acetone. Mp:
109.5-113.8, 134.3-136.5 °C (double peak). 1H NMR, δ
(CDCl3): 8.13 (dd, J ) 7.6 Hz, 1.6 Hz, 2H), 8.12 (s, 2H), 7.81
(dd, J ) 7.6 Hz, 1.3 Hz, 2H), 7.63 (d, J ) 8.4 Hz, 2H), 7.51 (d,
J ) 1.8 Hz, 2H), 7.50 (dd, J ) 8.1 Hz, 1.8 Hz, 2H), 2.03 (m,
8H), 0.96-1.23 (m, 40H), 0.78 (t, J ) 7.2 Hz, 12H), 0.60 (m,
8H). Anal. Calcd for C60H80Br2N2O: C, 71.70; H, 8.02; N, 2.79.
Found: C, 72.77; H, 7.98; N, 2.76.
In this paper, we have established synthetic ap-
proaches to the preparation of copolymers of fluorene
and oxadiazole with well-defined structure using the
tetrazole route and the Suzuki coupling reaction. Both
methods yield high molecular mass polymers with
minimum side reactions. All the polymers exhibit good
thermal behavior and stability. The absorption and
emission spectra of the polymer solutions revealed
that the oxadiazole ring in the polymer could form a
good conjugation with fluorene and offer the polymers
excellent fluorescence properties as blue-light-emitting
materials.
Ack n ow led gm en t. The authors thank Mr. Floyd
Toll for microanalysis. Dr. Marie D’Iorio, Dr. Ye Tao,
and Dr. Isabelle Le´vesque (IMS, NRC, Canada) are
acknowledged for the fluorescence measurement and
fruitful discussions.
F -Ox-F , Tr im er 21. This trimer was prepared using a
similar procedure as that for 22 starting from 9 and 12 with
an equimolar ratio of 9/12. The resultant crude product was
purified by recrystallization from hexane to give a white
crystalline product in a yield of 77%. Mp: 128.6-131.3 °C. 1H
NMR, δ (CDCl3): 8.15 (s, 2H), 8.14 (dd, J ) 7.2 Hz, 1.6 Hz,
2H), 7.84 (dd, J ) 7.2 Hz, 1.6 Hz, 2H), 7.77 (m, 2H), 7.38 (m,
6H), 2.05 (m, 8H), 0.96-1.23 (m, 40H), 0.78 (t, J ) 7.2 Hz,
12H), 0.61 (m, 8H). Anal. Calcd for C60H82N2O: C, 85.05; H,
9.76; N, 3.31. Found: C, 85.94; H, 9.76; N, 3.29.
Br F -Ox-F -Ox-F Br , Dibr om op en ta m er 23. This com-
pound was prepared using a similar procedure as that used
for 22 starting from 13 and 20. The molar ratio of 13/20 was
3.0:1.0. The resulting crude product was purified by chroma-
tography using AcOEt/hexane (5/95) followed by AcOEt/hexane
(15/85), Recrystallization from AcOEt/hexane (10/90) gave
white crystals with a yield of 81%. Mp: 110.9-120.9. 1H NMR,
δ (CDCl3): 8.199 (dd, J ) 8.4 Hz, 1.6 Hz, 2H), 8.197 (d, J )
1.6 Hz, 2H), 8.15 (dd, J ) 8.0 Hz, 1.5 Hz, 2H), 8.14 (s, 2H),
7.94 (d, J ) 8.4 Hz, 2H), 7.84 (dd, J ) 8.0 Hz, 0.8 Hz, 2H),
7.64 (d, J ) 8.4 Hz, 2H), 7.513 (d, J ) 1.8 Hz, 2H), 7.509 (dd,
J ) 8.4 Hz, 1.8 Hz, 2H), 2.17 (m, 4H), 2.04 (m, 8H), 0.97-1.23
(m, 60H), 0.79 (t, J ) 7.2 Hz, 12H), 0.75 (t, J ) 7.2 Hz, 6H),
0.61 (m, 12H). Anal. Calcd for C91H120Br2N4O2: C, 74.77; H,
8.28; N, 3.83. Found: C, 75.77; H, 7.96; N, 3.81.
Refer en ces a n d Notes
(1) Burroughes, J . H.; Bradley, D. D. C.; Brown, A. R.; Marks,
R. N.; Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B.
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