Alkylidene fluorene liquid crystalline semiconducting polymers for organic field effect transistor devices

Article abstract of DOI:10.1021/ma049798n

Organic electronic devices comprising arrays of organic field effect transistors (OFETs) are expected to create a range of novel applications for which the ability to be fabricated in large areas, on flexible substrates, with nonconventional shapes, and at low cost are key enabling factors. To improve the electrical performance of such devices, new solution processable organic semiconductors are required with high charge carrier mobilities and environmental stability. This work describes the molecular design of a p-type charge transport liquid crystalline polymer, in an attempt to control the factors responsible for both mobility and stability. Molecules were designed that were able to exhibit closely packed, π stacked morphologies, which can result in efficient intermolecular charge hopping and hence high mobility. Molecular manipulation of the conjugated π electron system was required to optimize the HOMO energy level, to both resist oxidation and be able to readily accept holes from a source electrode.

Full text of DOI:10.1021/ma049798n

5250
Macromolecules 2004, 37, 5250-5256
Alkylidene Fluorene Liquid Crystalline Semiconducting Polymers for
Organic Field Effect Transistor Devices
Ma r tin Heen ey, Cla r e Ba iley, Ma r k Giles, Ma xim Sh k u n ov, Da vid Sp a r r ow e,
Steve Tier n ey, Weim in Zh a n g, a n d Ia in McCu lloch *
Merck Chemicals, Chilworth Science Park, Southampton, SO16 7QD, UK
Received J anuary 30, 2004; Revised Manuscript Received March 24, 2004
ABSTRACT: Organic electronic devices comprising arrays of organic field effect transistors (OFETs) are
expected to create a range of novel applications for which the ability to be fabricated in large areas, on
flexible substrates, with nonconventional shapes, and at low cost are key enabling factors. To improve
the electrical performance of such devices, new solution processable organic semiconductors are required
with high charge carrier mobilities and environmental stability. This work describes the molecular design
of a p-type charge transport liquid crystalline polymer, in an attempt to control the factors responsible
for both mobility and stability. Molecules were designed that were able to exhibit closely packed, π stacked
morphologies, which can result in efficient intermolecular charge hopping and hence high mobility.
Molecular manipulation of the conjugated π electron system was required to optimize the HOMO energy
level, to both resist oxidation and be able to readily accept holes from a source electrode.
In tr od u ction
The development of organic field effect transistors
(OFETs) has generated a great deal of interest in the
generation of solution processable organic semiconduc-
tors, which can combine both oxidative stability and
high charge carrier mobility.1-3 It has been shown that
the charge carrier mobility is strongly dependent on the
macroscopic organization of the molecules.4-7 In par-
ticular, creation of organized macroscopic domains, in
which there is molecular orientation of the π-conjugated
molecular orbitals with respect to the substrate, and
alignment on the macroscale with respect to the source
and drain electrodes facilitate intermolecular charge
transport. We have attempted to create this type of
semiconductor macrostructure through the design of
main chain liquid crystalline polymers, where supramo-
lecular organization and alignment of the polymer
chains can be enhanced through utilization of liquid
crystalline mesophases occurring during the processing
steps. Both lyotropic and thermotropic phases can
induce highly ordered, closely packed structures, leading
to high charge carrier mobilities within the domain
boundaries.8
F igu r e 1. Chemical structure of polyalkylidene fluorene (a)
and polyfluorene (b) (Where R ) C6H13 (P6AF), C8H17 (P8AF),
C
10H21 (P10AF)).
crystalline or liquid crystalline state.11 In comparison,
the carbon at the 9-position of poly(9,9-dialkylfluorene)
is sp3-hybridized, and therefore, the alkyl substituents
at this position cannot extend in the plane of the
fluorene unit, thus limiting the extent of π stacking.12
The planar conformation of the polyalkylidenefluorene
chain, stabilized by the intermolecular interactions, also
enhances the effective conjugation along the length of
the chain, which has been shown to reduce the ioniza-
tion potential13 and thus improve both charge injection,
with respect to gold electrodes, as well as charge carrier
mobility in a transistor device.
Resu lts a n d Discu ssion
Poly(9,9-dialkyl)fluorenes9,10 (PF) have been shown to
be stable semiconductors. The charge carrier mobility
of these polymers are however, limited by their steric
inability to exhibit the two-dimensional lamellar π
stacking morphology that has been shown, in the case
of polyalkylthiophenes,5 to be particularly effective in
promoting intermolecular hopping, leading to high
charge carrier mobilities. To address this limitation, a
new class of semiconducting polymer, polyalkylidene
fluorenes, have been synthesized, as shown in Figure
1. Polyalkylidene fluorenes have an sp2-hybridized
carbon at the 9-position, which permits the alkyl chains
to adopt a coplanar conformation relative to the polymer
backbone, thus facilitating cofacial aggregation. Cofa-
cial, π-π stacking morphology has been shown to lead
to very small intermolecular distances (<4 Å) in the
Syn th esis of Mon om er s. Alkylidene-substituted
fluorenes containing methyl and ethyl side chains have
previously been synthesized by the reaction of fluo-
renones with the appropriate secondary alkyl Grignard
reagent, followed by dehydration of the resulting alco-
hol.14 To provide polymers of good solubility, it was
reasoned that the incorporation of longer alkyl chains
was necessary. The drawbacks of the existing synthesis,
namely the paucity of commercially available long chain
secondary alkyl Grignards or their precursor halides
and the tedious nature of their synthesis, necessitated
the development of a new route to the starting mono-
mers.
As outlined in Scheme 1, the monomers were conve-
niently synthesized in just two steps from commercially
available 2,7-dibromofluorene. The initial step involved
the formation of a ketene dithioacetal by condensation
of a preformed fluorenyl anion with carbon disulfide,
followed by an in situ alkylation of the resultant ketene
* Corresponding author. E-mail: iain.mcculloch@mercknbsc.
co.uk.
10.1021/ma049798n CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/17/2004

Macromolecules, Vol. 37, No. 14, 2004
Alkylidene Fluorene Polymers for OFETs 5251
Sch em e 1. Syn th etic Ap p r oa ch to P oly(a lk ylid en e)flu or en es
dithiolate anion with methyl iodide to give the dimethy-
lated thioacetal in high yield. Treatment of the ketene
dithioacetal with 2 equiv of an alkyl Grignard reagent
in refluxing DME for 12 h initially resulted in moderate
yields (20-25%) of the dialkylated product. This reac-
tion presumably occurs via an addition-elimination
sequence, with the intermediate carbanion at the bridge-
head position stabilized by resonance. After some ex-
perimentation, it was found that the addition of a
catalytic amount of Kuchi’s salt (Li2CuCl4) both lowered
the reaction temperatures and time and improved yields
significantly. Derivatives containing hexyl to decyl side
chains were synthesized in reasonable yields (50-60%).
In contrast to unsubstituted dibenzofulvene, which
readily reacts with itself or amine nucleophiles at room
temperature,15 the present compounds were stable
under ambient conditions and in the presence of amine
nucelophiles such as morpholine or piperidine.
An X-ray crystal structure for monomer C6AF reveals
an essentially planar fluorene ring system, where the
central alkylidene bond (C1-C14) lies in the plane of
the fluorene ring system (Figure 2). There appears to
be no steric strain between the C3, C12 hydrogen atoms
of the fluorene ring and the vinylic hydrogen atoms
(C15, C21), since there is no twist about the central
double bond. Such a twist has been observed in bifluo-
renylidene derivatives.16 The crystal packing indicates
that the molecules pack in a staggered manner, with
three different π-π interactions apparent, ranging in
distance from 3.73 to 3.82 Å. In contrast, the single
crystal of 2,7-dibromo-9,9-dioctylfluorene exhibits no
aromatic stacking because of the disposition of the alkyl
chains.12
Syn t h esis a n d Ch a r a ct er iza t ion of P olym er s.
Polymerizations were performed under Yamamoto con-
ditions.17 The monomers were heated with a nickel(0)
catalyst in a mixed DMF-toluene solvent for 48 h,
followed by in situ end-capping the as-formed polymer
with an excess of bromobenzene to remove any terminal
bromine functionality. For both the hexyl- and octyl-
substituted polymers, precipitation occurs during the
course of the reaction, due to poor solubility of the
growing polymer in the DMF/toluene solvent mixture.
Purification was carried by out by precipitation of the
reaction mixtures into methanol, followed by sequential
Soxhlet extractions with methanol, acetone, and hexane
to remove catalyst residues and low molecular weight
oligomers. Finally, the polymers were dissolved in
chloroform and then precipitated into methanol, afford-
ing yellow powders. Typical polymerization yields were
low (∼40%) for the short side chain (C6) polymers and
improved to over 80% for side chain lengths of eight
carbons and above. The low yield for the short chain
polymer was attributed to the removal during workup
of a high percentage of very low molecular weight
oligomer that was formed due to low polymer solubility.
With the exception of C6PAF, all polymers exhibited
good solubility in relatively nonpolar organic solvents,
such as chloroform, tetrahydrofuran, and toluene. The
structures of the polymers were characterized by spec-
1
troscopic methods. H NMR spectra were obtained for
the polymers at 50 °C in chloroform-d, since room-
temperature measurements showed considerable broad-
ening of the peaks. Figure 3 shows a representative
polymer, C10PAF, in comparison with the respective
monomer, C10AF. The signals for the three different
aromatic protons in the fluorene unit are resolved as
broad signals at δ 8.1, 7.8, and 7.6 ppm, with the
alkylidene protons clearly visible at 2.9 ppm. The FT-
IR spectra for pristine C10PAF is shown in Figure 4
and is consistent with the expected structure. Of note
is the fact that no fluorenone resonance around 1720
cm-1 is observed.18
Molecular masses for the polymers were determined
by GPC against polystyrene standards and are sum-
marized in Table 1. These data should be taken with a
degree of caution, since the values obtained for rigid-
rod polymers are often an overestimation.19,20 The hexyl-
and octyl-substituted polymers both exhibited unimodal
distributions with low molar masses. These low masses
are probably a result of the polymer precipitating from
the reaction mixture. For the more soluble decyl-
substituted polymer, bimodal distributions were ob-
tained with high polydispersities. The measurements
were further complicated by the fact that the mass
distributions for a given polymer were concentration and
solvent dependent (Figure 5). Thus, in a THF solution
of concentration 0.4 mg/mL, the main peak has an
apparent molecular mass around 65 000 (15 min) with
a smaller component centered around 15 000. However,
on increasing the dilution 20-fold, the peak ratios
change dramatically, with the smaller mass peak now
dominating. The trend continues upon increasing dilu-
tion, but the high Mw peak is never completely absent.
Solutions in chloroform, which is a better solvent for
the polymer, exhibit a similar trend, although the high
Mw peak is less prominent, even in the more concen-
trated solution. We attribute this behavior to a high
propensity for the polymer to aggregate in solution,
especially in a Θ solvent such as THF. This is further
demonstrated by the fact that the UV/vis spectra of the
thin film is almost identical to the solution spectra in
THF.
Op tica l P r op er ties. Alkylidene fluorene polymers
have a bathochromic (red) optical absorption maximum
in comparison to polyfluorenes, as illustrated in Figure
6. This reduced band gap is primarily due to the
enhanced planarization of the conjugated polymer back-
bone, which is particularly pronounced in the solid state
spectra. In addition, a shoulder can be clearly seen at
about 420 nm, which is believed to be due to effects
associated with aggregation.11,21 Upon heating this

5252 Heeney et al.
Macromolecules, Vol. 37, No. 14, 2004
F igu r e 2. ORTEP single crystal and crystal packing of C6AF monomer.
shoulder collapses, as shown in Figure 7. The electronic
orbital band structure, as determined by ultraviolet
photoelectron spectroscopy and reported elsewhere,13
confirms that the ionization potential of alkylidene
fluorene polymers has been reduced by about 0.4 eV, to
5.5 eV, as compared to polyfluorene,22 which is high
enough to be stable to oxidation in air.23
The thermal behavior of polyalkylidene fluorenes was
complicated to interpret, due to small entropy differ-
ences on phase changes and overlapping processes. In
general, complimentary techniques of differential scan-
ning calorimetry (DSC) and optical microscopy were
required to identify phases. All polymers exhibited a
nematic mesophase, which can be identified by the
characteristic Schlieren texture observed by polarized
optical microscopy, as shown in Figure 8. The effect of
increasing side chain length on the thermal behavior
of the polymers was not shown to be very significant.
Although it would be expected that longer side chains,
acting like “bound solvent”, would lower the melt point
of the polymer main chains, this was not conclusively
shown. One explanation of this is that the molecular
weight of the short chain polymers (C6 and C8) is not
high enough to have reached their maximum thermal
properties and hence any trend would be suppressed.
All polymers exhibited a glass transition at about 140
°C, believed to be too high to be related to side chain
melting. The sensitivity of the DSC instrument was not
sufficient to identify this transition. Broad melt points
were observed within the temperature range from 240
to 260 °C. Clearing points for all polymers were only
observed by microscopy. The clearing points appear to
be close to the onset of degradation, and some signs of
degradation at temperatures above the clearing point
are evident by microscopy as darkening around the
edges of the slide. On slow cooling through the me-
sophase, crystallization was observed by polarized
microscopy. Rapid cooling from the mesophase quenches
in a thermodynamically unstable “glassy nematic phase”,
which on heating exhibits a more pronounced glass
transition. No evidence of smectic phases could be
observed by optical microscopy, although this may be

Macromolecules, Vol. 37, No. 14, 2004
Alkylidene Fluorene Polymers for OFETs 5253
F igu r e 5. GPC traces for (a) 0.002 mg/mL solution in THF,
(b) 0.4 mg/mL solution in THF, (c) 0.4 mg/mL solution in
chloroform
F igu r e 3. 1H NMR spectra of polymer C10PAF at 50 °C in
comparison to monomer C10AF.
F igu r e 6. Optical absorption as spin cast films. F8 is poly-
(9,9-dioctylfluorene).
F igu r e 4. FTIR of C10AF (top) and C10PAF (bottom).
Ta ble 1. P olym er Molecu la r Weigh t Da ta
a
polymer
Mn
Da
C6PAF
C8PAF
C10PAF
4000
5400
14000
1.2
1.2
2.5
a
Determined by GPC in CHCl3 against polystyrene standards.
due to the nature of the annealing processes and heat
rates used. A summary of the thermal properties of this
polymer series is shown in Table 2.
Tr a n sistor F a br ica tion a n d Mea su r em en t. Thin-
film organic field-effect transistors (OFETs) were fab-
ricated on highly doped silicon substrates with a 230
nm thick thermally grown silicon oxide (SiO2) insulating
layer, where the substrate served as a common gate
electrode. Transistor source-drain gold electrodes were
photolithographically defined on the SiO2 layer. Prior
to organic semiconductor deposition, FET substrates
were treated with a silylating agent hexamethyldisila-
zane (HMDS). Thin semiconductor films were then
deposited by spin-coating polymer solutions in chloro-
form (0.4-1 wt %) on FET substrates. The electrical
characterization of the transistor devices was carried
out in a dry nitrogen atmosphere using a computer-
controlled Agilent 4155C semiconductor parameter
analyzer.
F igu r e 7. Change in absorption upon heating a thin film of
C10PAF.
were heated to the nematic phase in N2 atmosphere,
held at this temperature, and then cooled to room
temperature. Under negative gate bias, devices showed
typical p-type behavior with good current modulation
(on/off ratio of 104-106) and well-defined linear and
saturation regimes, as shown in Figure 9 for C10PAF.
Field effect mobility was calculated in the saturation
regime [Vd > (Vg - V0)] using eq 1
sat
Electr ica l P r op er ties. Transistor characteristics of
C6PAF, C8PAF, and C10PAF were measured on as-
spun films. Thermal treatment followed, when samples
dId
WCi
L
)
µsat(Vg - V0)
(1)
(
)
dVe
Vd

5254 Heeney et al.
Macromolecules, Vol. 37, No. 14, 2004
der Yamamoto conditions, to form a novel class of
soluble, conjugated main chain semiconducting poly-
mers. A series of homologues, differing in the length of
alkyl side chains, were prepared, all of which were found
to both strongly aggregate in solution and exhibit
nematic thermotropic mesophases. Field effect transis-
tors were fabricated, utilizing these polymers as the
semiconducting layer, and on annealing above the glass
transition, field-effect mobilities of up to 2 × 10-3 cm2/V
s were reached. These good charge transport properties,
together with high current modulation (on/off ratio up
to 106), make this material an attractive candidate for
organic electronic applications.
Exp er im en ta l Section
Gen er a l. 1H and 13C NMR spectra were recorded on a
Bruker AV-300 (300 MHz), using the residual solvent reso-
nance of CDCl3 or TMS as an internal reference, and are given
in ppm. IR spectra were obtained on a Perkin-Elmer Spectrum
One FTIR. UV/vis spectra were obtained on a Perkin-Elmer
Lamda 9 spectrometer. Microanalyses were obtained with an
Elementar Vario EL analyzer. Mass spectra were obtained
either from an Agilent GC-MS using a 6890 series GC with
a 5973 MSD (EI) or a Bruker Esquire 3000+ (ESI). Molecular
weight determinations were carried out in chloroform solution
on an Agilent 1100 series HPLC using two Polymer Labora-
tories mixed B columns in series, and the system was
calibrated against narrow weight PL polystyrene calibration
standards. DSC measurements were performed on a Perkin-
Elmer DSC 7 under nitrogen. All starting materials and
reagents were purchased from Aldrich Chemicals or Lancaster
Chemicals and used as received, with the exception of 1,5-bis-
(cyclooctadiene)nickel(0) (Strem Chemicals). Anhydrous sol-
vents were purchased from Romil Ltd and transferred using
standard Schlenk line techniques. Column chromatography
and TLC were performed on silica gel 60 (70-230 mesh,
Merck) and silica gel F254 plates (Merck), respectively. Petrol
refers to the fraction boiling at 40-60 °C.
F igu r e 8. Micrograph under crossed polarizers illustrating
the threaded texture of C10PAF in nematic phase.
Ta ble 2. Th er m a l Beh a vior for P olym er s
polymer
Tg (°C)
Tm (°C)
Tcl (°C)
C6PAF
C8PAF
C10PAF
140
150
140
235-245
230-240
230-240
390
375
380
where W is the channel width, L the channel length, Ci
the capacitance of the insulating layer, Vg the gate
voltage, and V0 the turn-on voltage. Turn-on voltage (V0)
was determined as the onset of source-drain current
(Figure 9a).
Field-effect mobilities for C6PAF, C8PAF, and C10PAF
are summarized in Table 3. In as-spun films, all
polymers showed a field-effect mobility from 1 × 10-4
to 9 × 10-4 cm2/V s resulting from unoptimized film
morphology. The degree of order for the polymers
improved after thermal treatment where samples were
annealed in the nematic phase, and as a result, in-
creased field effect mobilities from 4 × 10-4 to 2 × 10-3
cm2/Vs were observed. Maximum current observed in
annealed C10PAF FETs with channel length L ) 10 µm
and channel width W ) 2 cm reached 0.1 mA and on/
off ratio exceeded 106.
It has been observed that the optimum annealing
temperature was in the range 170-190 °C with a total
annealing time of about 30 min. At lower annealing
temperatures, polymer mobilities did not reach maxi-
mum values, whereas higher temperatures resulted in
reduced charge transport.
Turn-on voltages for all polymer FET samples were
quite high (between -5 and -24 V) with some varia-
tions from batch to batch. Such high turn-on voltages
can be explained by an approximately 0.4 eV mismatch
between the work function of gold electrodes (∼5.1 eV)24
and the polymer HOMO level (∼5.5 eV). This also
resulted in detectable contact resistance, as evidenced
by a slight curvature of source-drain currents in output
characteristics (Figure 9b) at low source-drain voltages
(0 to -3V).
2,7-Dib r om o-9-(b is(m e t h ylsu lfa n yl)m e t h yle n e )flu -
or en e. Sodium tert-butoxide (31.14 g, 0.324 mol) was added
in portions to a mechanically stirred solution of 2,7-dibromo-
fluorene (50.00 g, 0.154 mol) in anhydrous DMSO (1 L) at room
temperature under nitrogen. Carbon disulfide (12.94 g, 0.170
mol) was added via syringe and the reaction mixture was
stirred for 10 min. Methyl iodide (46.00 g, 0.324 mol) was
added via a dropping funnel over 5 min and the reaction
mixture was stirred for 4 h. The reaction mixture was poured
into ice-water (1 L), and concentrated ammonia (50 mL) was
added to quench any remaining methyl iodide. The resulting
precipitate was filtered, washed with water, dried, and re-
crystallized from ethyl acetate:THF (2:1) to afford the product
as bright yellow needles (55.15 g, 83%). Mp: 155-156.5 °C.
3
1H NMR (CDCl3, 300 MHz): δ (ppm) 8.90 (s, 2H), 7.51 (d, J
) 8.2 Hz, 2H), 7.42 (d, 3J ) 8.2 Hz, 2H), 2.57 (s, 6H). 13C NMR
(CDCl3, 75 MHz): δ (ppm) 147.30, 139.40, 137.54, 134.28,
130.33, 129.13, 121.21, 120.41, 19.14. IR 3097 (w), 2921 (w),
1882 (w), 1560 (m), 1517 (s), 1440 (s), 1390 (s), 1065 (m), 943
(m). Anal. Calcd for C16H12Br2S2: C, 44.9; H, 2.8. Found: C,
44.7; H, 3.1. MS (EI): m/z 430 (M+, 50), 428 (M+, 100), 426
(M+, 50).
The general procedure for the synthesis of the alkylidene
monomers is exemplified by the following synthesis:
2,7-Dib r om o-9-(1′-d ecylu n d ecylid en e)flu or en e. To a
stirred solution of 2,7-dibromo-9-(bis(methylsulfanyl)methyl-
ene)fluorene (10.00 g, 23.35 mmol) in anhydrous THF (150 mL)
at -5 °C under nitrogen was added lithium tetrachlorocuprate
(6 mL of a 0.1 M solution in THF, 0.6 mmol), followed by the
addition of decylmagnesium bromide (52 mL of a 1.0 M
solution in diethyl ether, 52 mmol) over 30 min, keeping the
temperature below 0 °C throughout. The reaction was stirred
for a further 4 h at -5 °C and then quenched by the addition
of 10% sodium hydroxide (100 mL). The reaction was stirred
for 10 min and then filtered through Celite, washing through
Su m m a r y
A new methodology for the synthesis of symmetrically
substituted alkylidene fluorenes was demonstrated. The
resultant monomers were successfully polymerized un-

Macromolecules, Vol. 37, No. 14, 2004
Alkylidene Fluorene Polymers for OFETs 5255
F igu r e 9. Transfer (a) and output (b) characteristics of a C10PAF transistor with channel length L ) 10 µm and channel width
W ) 2 cm.
Ta ble 3. Electr on ic P r op er ties for P olym er s
following the procedure described above. Purification by
column chromatography (eluent: petroleum ether 40-60) and
recrystallization from isohexane yielded the product as pale
µsat (cm2/V s)
1
polymer
as-spun
annealed
on/off
yellow needles (3.60 g, 54%). Mp: 34-35 °C. H NMR (CDCl3,
3
3
300 MHz): δ (ppm) 7.86 (s, J ) 1.4 Hz 2H), 7.58 (d, J ) 8.1
C6PAF
C8PAF
C10PAF
1 × 10-4
3 × 10-4
9 × 10-4
4 × 10-4
1 × 10-3
2 × 10-3
104
104
106
Hz, 2H), 7.43 (dd, 3J ) 8.1 & 1.4 Hz, 2H), 2.72 (t, J ) 8.3 Hz,
3
3
4H), 1.68 (m, 4H), 1.54 (m, 4H), 1.32 (m, 8H), 0.90 (t, J ) 6.7
Hz, 6H). 13C NMR (CDCl3, 75 MHz): δ (ppm) 155.31, 139.95,
137.42, 129.80, 129.37, 127.92, 121.15, 120.49, 37.54, 31.85,
30.06, 29.40, 29.30, 27.82, 22.68, 14.14. IR (thin film): 2954
(m), 2922 (s), 2853 (m), 1876 (w), 1611 (m), 1593 (m), 1439
with ethyl acetate. The resulting layers were separated, and
the aqueous layer further extracted with ethyl acetate. The
combined organic extracts were washed 10% aqueous solution
of sodium hydroxide (100 mL), saturated sodium metabisulfite
(100 mL), and brine (100 mL), and then dried over sodium
sulfate and concentrated in vacuo. The residue was filtered
through a layer of silica (5 × 5 × 10 cm2) with a layer of basic
alumina (5 × 5 × 1 cm2) on top and washed through with petrol
(1.5 L). The filtrate was concentrated in vacuo. Recrystalliza-
tion from isohexane at -38 °C yielded the product as pale
yellow needles (7.47 g, 52%). Mp: 35.5-36.5 °C. 1H NMR
(m), 1072 (m), 938 (m), 816 (vs) cm-1. Anal. Calcd for C30H40
-
Br2: C, 64.3; H, 7.2. Found: C, 64.6; H, 6.7. MS (EI): m/z 562
(M+, 10), 560 (M+, 20), 558 (M+, 10).
The general procedure for the synthesis of the alkylidene
polymers is exemplified below:
P o ly [9-(1′-d e c y lu n d e c y lid e n e )flu o r e n e -2,7′-d iy l]
(C10P AF ). A Schlenk tube was charged with bis(1,5-cyclooc-
tadiene)nickel(0) (2.000 g, 7.271 mmol) and 2,2′-bipyridyl
(0.973 g, 6.233 mmol) under nitrogen. 1,5-Cyclooctadiene (0.64
mL, 5.218 mmol) and anhydrous N,N-dimethylformamide (20
mL) were added, and the reaction mixture was stirred at 60
°C for 30 min. A solution of 2,7-dibromo-9-(1′-decylundecyli-
dene)fluorene (3.202 g, 5.194 mmol) in anhydrous toluene (40
mL) was added and the reaction mixture was stirred at 80 °C
for 24 h with the exclusion of light. The reaction mixture was
cooled to room temperature and added to acidic methanol (400
mL). The suspension was stirred for 1 h. The polymer was
filtered off, washed with water and then methanol, and dried
under vacuum. The polymer was washed (via Soxhlet extrac-
tion) with methanol for 24 h, acetone for 24 h, and isohexane
for 24 h. The polymer was dried under vacuum and dissolved
in hot chloroform (100 mL). The hot chloroform solution was
filtered through a sintered funnel and concentrated in vacuo
to a minimum volume. The concentrated chloroform solution
was precipitated from methanol (500 mL). The polymer was
filtered off and dried under vacuum to yield the polymer as a
yellow solid (2.02 g, 85%). 1H NMR (CDCl3, 50 °C, 300
MHz): δ 8.08 (br, 2H), 7.79 (br, 2H), 7.60 (br, 2H), 2.89 (br,
3
(CDCl3, 300 MHz): δ (ppm) 7.85 (d, J ) 1.5 Hz 2H,), 7.56 (d,
3
3
3J ) 8.1 Hz, 2H), 7.42 (dd, J ) 8.1 & 1.5 Hz, 2H), 2.71 (t, J
) 8.3 Hz, 4H), 1.68 (m, 4H), 1.53 (m, 4H), 1.42 (m, 4H2), 1.28
(m, 20H), 0.89 (t, 3J ) 6.7 Hz, 6H). 13C NMR (CDCl3, 75
MHz): δ (ppm) 155.27, 139.93, 137.40, 129.79, 129.34, 127.90,
121.13, 120.46, 37.52, 31.93, 30.06, 29.64, 29.60, 29.43, 29.34,
27.80, 22.71, 14.14. IR (thin film): 2952 (m), 2919 (s), 2849
(m), 1866 (w), 1617 (m), 1595 (m), 1465 (m), 1439 (m), 1072
(m), 932 (m), 816 (s) cm-1. Anal. Calcd for C34H48Br2: C, 66.2;
H, 7.85. Found: C, 66.1; H, 7.3. MS (EI): m/z 618 (M+, 5), 616
(M+, 10), 614 (M+, 5), 476 (M+ - C10H21, 10), 336 (M+ - C20H42
,
100).
2,7-Dibr om o-9-(1′-h exylh ep tylid en e)flu or en e was syn-
thesized from 2,7-dibromo-9-(bis(methylsulfanyl)methylene)-
fluorene (5.20 g, 12 mmol) and hexylmagnesium bromide (15
mL of a 2 M solution in diethyl ether, 30 mmol) following the
procedure described above. Prior to final chromatographic
purification, dodecane (C12H26) byproduct was removed by
Kugelrohr distillation. Recrystallization from isohexane yielded
the product as pale yellow needles (3.20 g, 53%): mp 31-32
1
3
4H), 1.80 (br, 4H), 1.7-0.7 (m, 36H). Anal. Calcd for C34H50
:
°C. H NMR (CDCl3, 300 MHz): δ (ppm) 7.84 (d, J ) 1.5 Hz,
2H), 7.55 (d, 3J ) 8.1 Hz, 2H), 7.41 (dd, 3J ) 8.1 & 1.5 Hz,
2H), 2.70 (t, 3J ) 8.3 Hz, 4H), 1.67 (m, 4H), 1.55 (m, 4H), 1.39
C, 89.0; H, 11.0. Found: C, 89.0; H, 11.4; Br, <0.3. IR (thin
film): 2920 (s), 2850 (s), 1620 (m), 1597 (m), 1455 (s), 1400
(m), 883 (m), 811 (vs). λmax (CHCl3): 409, 360, 344, 280 (film)
428, 406 (sh), 358, 280, 240 nm. GPC (CHCl3): Mn 14 000
g/mol, D ) 2.5.
3
(m, 8H), 0.94 (t, J ) 6.9 Hz, 6H). 13C NMR (CDCl3, 75 MHz):
δ (ppm) 155.24, 139.96, 137.43, 129.82, 129.37, 127.91, 121.16,
120.49, 37.55, 31.66, 29.74, 27.79, 22.69, 14.13. IR (thin film):
2958 (m), 2921 (s), 2854 (s), 1877 (w), 1617 (m), 1595 (m), 1561
(m), 1456 (m), 1398 (m), 1074 (m), 937 (s) cm-1. Anal. Calcd
for C26H32Br2: C, 61.9; H, 6.4. Found: C, 61.8; H, 6.1. MS
P oly[9-(1′-h exylh eptyliden e)flu or en e-2,7′-diyl] (C6P AF).
Polymerization of 2,7-dibromo-9-(1′-hexylheptylidene)fluorene
(0.500 g, 0.991 mmol) by the method described above afforded
(EI): m/z 506 (M+, 10), 504 (M+, 20), 502 (M+, 10), 420 (M+
C6H13, 18), 336 (M+ - C12H26, 100).
-
1
the product as a yellow solid (0.130 g, 38%). H NMR (CDCl3,
50 °C, 300 MHz): δ 8.10 (br. 2H), 7.88 (br d, 2H), 7.63 (br d,
2H), 2.93 (br, 4H), 1.84 (br, 4H), 1.7-1.2 (m, 12H), 0.9 (br t,
6H). IR (thin film): 2921 (s), 2853 (s), 1620 (m), 1597 (m), 1454
(s), 1400 (m), 881 (m), 809 (vs). Anal. Calcd for C26H34: C, 90.1;
H, 9.9. Found: C, 90.0; H, 8.9. λmax (CHCl3): 399, 355, 340
2,7-Dibr om o-9-(1′-octyln on ylid en e)flu or en e was syn-
thesized by reaction of 2,7-dibromo-9-(bis(methylsulfanyl)-
methylene)fluorene (5.20 g, 12 mmol) with octylmagnesium
bromide (13 mL of a 2 M solution in diethyl ether, 26 mmol)

5256 Heeney et al.
Macromolecules, Vol. 37, No. 14, 2004
(7) Chen, X. L.; Lovinger, A. J .; Bao, Z.; Sapjeta, J . Chem. Mater.
2001, 13, 1341-1348.
(8) Sirringhaus, H.; Wilson, R. J .; Friend, R. H.; Inbasekaran,
M.; Wu, W.; Woo, E. P.; Grell, M.; Bradley, D. D. C. Appl.
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(9) Scherf, U.; List, E. J . W. Adv. Mater. 2002, 14, 477-487.
(10) Leclerc, M. Polymer 2001, 39, 2867-2873.
(11) Yamamoto, T.; Komarudin, D.; Arai, M.; Lee, B.-L.; Sug-
anuma, H.; Asakawa, N.; Inoue, Y.; Kubota, K.; Sasaki, S.;
Fukuda, T.; Matsuda, H. J . Am. Chem. Soc. 1998, 120, 2047-
2058.
(sh), 278 (film) 407, 342, 280, 235 nm. GPC (CHCl3): Mn 4000
g/mol, D ) 1.2.
P oly[9-(1′-octyln on ylid en e)flu or en e-2,7′-d iyl] (C8P AF ).
Polymerization of 2,7-dibromo-9-(1′-octylnonylidene)fluorene
(1.00 g, 1.78 mmol) by the method described above afforded
1
the product as a yellow solid (0.600 g, 83%). H NMR (CDCl3,
50 °C, 300 MHz): δ 8.09 (br, 2H), 7.86 (br, 2H), 7.62 (br, 2H),
2.92 (br, 4H), 1.83 (br, 4H), 1.7-0.7 (m, 28H). Anal. Calcd for
C
30H42: C, 89.5; H, 10.5. Found: C, 89.4; H, 11.4. IR (thin
film): 2920 (s), 2850 (s), 1617 (m), 1598 (w), 1455 (s), 1400
(m), 883 (m), 811 (vs). λmax (CHCl3): 409, 360, 340 (sh), 280,
(film) 429, 409 (sh), 358, 280, 238 nm. GPC (CHCl3): Mn 5400
g/mol, D ) 1.2.
(12) Leclerc, M.; Ranger, M.; Belanger-Gariepy, F. Acta Crystal-
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385, 184-188.
Ack n ow led gm en t. The authors would like to thank
Dr. Simon Coles and Prof. Mike Hursthouse of the
University of Southampton for obtaining the X-ray
crystallography data.
(14) Ranger, M.; Leclerc, M. Macromolecules 1999, 32, 3306-3313.
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Su p p or tin g In for m a tion Ava ila ble: Table of X-ray
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material is available free of charge via the Internet at http://
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