Polyfluorenes with phosphonate groups in the side chains as chemosensors and electroluminescent materials

Article abstract of DOI:10.1021/ma050807h

Polyfluorenes (P1 and P2) with phosphonate groups in the side chains were designed and synthesized. Their absorption and photoluminescence spectra in solutions are solvent dependent and exhibit a red shift up to 14 and 6 nm, respectively, with increasing solvent polarity. The polymers are highly soluble in ethanol with a solution photoluminescence quantum yield of 0.74. Polymer P2 in thin film cast from ethanol shows high intrachain order as revealed by red-shifted absorption spectrum and emission spectrum along with well-resolved vibronic structure. Both P1 and P2 are highly sensitive and selective Fe ³⁺ sensory materials, and the sensitivity is much higher than that of model compounds 3 and 4. The highest sensitivity was observed with polymer P1, and a 210-fold fluorescence quenching in dichloromethane was achieved. Polymer light-emitting diodes (PLEDs) were also fabricated to investigate the electroluminescent properties. A luminous efficiency of 1.49 cd/A with Commission Internationale de L'Eclairage (CIE) coordinates of (0.171, 0.131) at 100 cd/m² and a maximum brightness of 1750 cd/m² have been demonstrated.

Full text of DOI:10.1021/ma050807h

5416
Macromolecules 2005, 38, 5416-5424
Polyfluorenes with Phosphonate Groups in the Side Chains as
Chemosensors and Electroluminescent Materials
Gang Zhou, Gang Qian, Liang Ma, Yanxiang Cheng, Zhiyuan Xie, Lixiang Wang,*
Xiabin Jing, and Fosong Wang
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022,
P. R. China
Received April 17, 2005; Revised Manuscript Received May 2, 2005
ABSTRACT: Polyfluorenes (P1 and P2) with phosphonate groups in the side chains were designed and
synthesized. Their absorption and photoluminescence spectra in solutions are solvent dependent and
exhibit a red shift up to 14 and 6 nm, respectively, with increasing solvent polarity. The polymers are
highly soluble in ethanol with a solution photoluminescence quantum yield of 0.74. Polymer P2 in thin
film cast from ethanol shows high intrachain order as revealed by red-shifted absorption spectrum and
emission spectrum along with well-resolved vibronic structure. Both P1 and P2 are highly sensitive and
3
+
selective Fe sensory materials, and the sensitivity is much higher than that of model compounds 3 and
4
. The highest sensitivity was observed with polymer P1, and a 210-fold fluorescence quenching in
dichloromethane was achieved. Polymer light-emitting diodes (PLEDs) were also fabricated to investigate
the electroluminescent properties. A luminous efficiency of 1.49 cd/A with Commission Internationale de
2
2
L’Eclairage (CIE) coordinates of (0.171, 0.131) at 100 cd/m and a maximum brightness of 1750 cd/m
have been demonstrated.
Introduction
fluorene homopolymers with phosphonate groups in the
side chains, and their optical properties, sensing proper-
ties, and electroluminescent properties are investigated.
Fluorescent conjugated polymers (CPs) have attracted
much attention because of their potential optoelectronic
and biological applications, such as light-emitting di-
Results and Discussion
odes, photovoltaic devices, field-effect transistors,3
1
2
4
5
nonlinear optics, and chemical and biological sensors.
Synthesis and Structure Characterization. Struc-
tures of the polymers and model compounds are depicted
in Chart 1. The syntheses of monomers, polymers, and
model compounds 3 and 4 are shown in Scheme 1. Our
synthesis began with 2,7-dibromofluorene as described
Of all CPs, polyfluorenes (PFs) are one class of the most
promising materials due to their high photolumines-
cence quantum yield, high thermal and chemical stabil-
ity, and facile modification at the side chains without
affecting main-chain conjugation.6-11 CPs carrying ionic
groups or special receptors can be used in detecting
35
by Xia et al. The reaction of 2,7-dibromofluorene with
1,3-dibromopropane in the presence of NaOH aqueous
solution afforded 2,7-dibromo-9,9-bis(3′-bromopropyl)-
fluorene in a yield of 62% after purification with
columnar chromatography. The main byproduct was
2,7-dibromo-9-cyclobutylfluorene in a yield of 21%.
Then 2,7-dibromo-9,9-bis(3′-diethoxylphosphorylpropyl)-
fluorene (1) was obtained as white crystal in a yield of
91% by refluxing 2,7-dibromo-9,9-bis(3′-bromopropyl)-
fluorene in triethyl phosphite. The monomer 2,7-
dibromo-9,9-bis(6′-diethoxylphosphorylhexyl)fluorene (2)
was obtained in the same way as colorless oil in a yield
of 83%. The polymerization reactions of monomers 1 and
2 via the Yamamoto polycondensation36 reaction with
Ni(0) as the catalyst produced light-yellow fibers of P1
and P2 after repeated dissolution in chloroform and
precipitation in n-hexane in the yields of both over 50%.
Models 3 and 4 were prepared through Suzuki coupling
reaction between monomers 1 and 2 and 2-(9,9-dioctyl-
fluoren-2-yl)-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane with
Pd(PPh3)4 as the catalyst. They were both obtained as
yellowish oil in a yield of over 60%.
1
2-18
bioactive species
in optoelectronics
or offer some new opportunities
and supramolecular chemistry.
1
9-23
24
Polyfluorenes with various functional groups, such as
ammonium groups,25 sulfonic groups, phenol groups,
26
27
and imidazole groups,28 have been reported. Among
those the polymers with phenol groups and imidazole
groups are highly sensitive and selective chemosensors
-
2+
for F and Cu , respectively. PFs carrying ionic groups
are soluble in alcohol or water and have been used to
fabricate multilayer PLEDs or as the electron injection
layer to improve the performance of PLEDs.19-21
The phosphine oxide groups are widely used in the
preparation of quantum dots due to their strong affinity
for inorganic nanocrystals.29 While the amphiphilic
3
0
phosphonate groups have been studied as surfactants
and receptors,31,32 they have also successfully been
introduced into the CPs, such as poly(p-phenylene
2
4,33
34
ethynylene)
and polythiophene, as the precursor
for polymers with phosphonic acid groups. Introduction
of the phosphonate groups into PFs may endow the
polymers unique properties, for example, high solubility
in polar solvents and sensing properties to certain metal
ions. In current paper, we design and synthesize novel
Structures of polymers P1 and P2 were verified by
1
FT-IR, H NMR, and elemental analysis. We could not
measure the molecular weight of P1 and P2 by normal
gel permeation chromatography (GPC) method due to
strong absorption of the polymers on the column fillers
possibly induced by the high polarity of the phosphonate
*
Corresponding author: lixiang@ciac.jl.cn, Fax: 0086-431-
5
685653.
1
0.1021/ma050807h CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/27/2005

Macromolecules, Vol. 38, No. 13, 2005
Polyfluorenes with Phosphonate Groups 5417
Chart 1. Structures of Polymers and Model Compounds
Scheme 1. General Synthetic Scheme for the Preparation of Compounds 1-4 and Polymers P1 and P2a
a
(
a) 1,3-Dibromopropane or 1,6-dibromohexane, NaOH/H
2
O, 60 °C, 4 h; (b) triethyl phosphite, 140 °C, 16 h; (c) Ni(0), toluene/
DMF, 80 °C, 96 h; (d) Pd(PPh , Na CO , toluene/H O, 80 °C, 24 h.
3
)
4
2
3
2
groups. Then the molecular weights of P1 and P2 were
estimated to be 25-35 kDa by comparing their viscos-
vacuum at 100 °C for 1 day before the measurements.
In a nitrogen atmosphere, polymers P1 and P2 exhibit
a degradation onset at 225 and 194 °C, respectively,
which are contributed to the decomposition of phos-
phonate groups. Another significant degradation starts
over 300 °C, corresponding to the cleavage of alkyl side
chains. Unlike typical poly(9,9-dialkylfluorene)s (PAFs),38
differential scanning calorimetry (DSC) measurements
did not show any phase transition, and no clear meso-
phase was observed under polarizing optical microscopy
(POM).
3
7
ity in chloroform with poly(9,9-dioctylfluorene) (PF8,
Mn ) 32 kDa); however, the error may be significant
due to the different polarity between these polymers and
PF8.
The thermal properties of polymers P1 and P2 were
studied by thermogravimetric analysis (TGA) (Figure
1
). A moderate weight loss (about 3%-4%) starts from
1
00 °C, which is obviously due to releasing the associ-
2
0,23
ated water,
although the polymers were dried in a

5418 Zhou et al.
Macromolecules, Vol. 38, No. 13, 2005
Figure 1. Thermalgravimetric analysis curves of polymers
P1 and P2.
Optical Properties. Polymers P1 and P2 are soluble
in most of common organic solvents, such as tetrahy-
drofuran (THF), toluene, dimethylformamide (DMF),
chloroform (CHCl3), and dimethyl sulfoxide (DMSO).
Especially, they are also highly soluble in methanol,
ethanol, and acetone. The solubility of either P1 or P2
in ethanol is over 10 mg/mL. The quantum yield of P1
-
6
and P2 in dilute solution (ca. 10 M of repeat unit) is
almost the same. With 9,10-diphenylanthracene as a
standard, the quantum yields of P2 in ethanol and
chloroform are 74% and 93%, respectively. These values
are significantly higher than the photoluminescence
(
PL) quantum yield of fluorene derived polyelectro-
20,23
Figure 2. UV-vis absorption and PL spectra of P1 (a) and
lytes.
The absorption and photoluminescence spectra
-5
3
P2 (b) in CHCl , EtOH, DMF, and DMSO.
in solution were measured at a concentration of ca. 10
M of repeat unit. Like fluorene derived polyelectro-
2
0,23
to that cast from chloroform solution, whereas that of
P2 cast from ethanol solution shows a 3-9 nm further
red shift with major peak at 437 nm and two clear
vibronic shoulders at 460 and 490 nm. Obviously, the
PL spectrum of P2 is better resolved. All these indicate
that polymer chain of P2 is well ordered in film cast
from ethanol. Similar PL spectral features are also
observed in annealed or solvent vapor-treated PFO
films39 and a rod-coil fluorene copolymer. The authors
attributed this spectral red shift to improved intrachain
order or longer effective conjugation length. Figure 4
shows absorption and PL spectra of P2 cast from
chloroform solution before and after annealing at 100
lytes,
the solution absorption and PL spectra of P1
and P2 are dependent on the solvent. P1 shows the
absorption maximum at 382 nm in chloroform, 388 nm
in ethanol, 391 nm in DMF, and 392 nm in DMSO,
while the corresponding PL spectra of P1 are peaked
at 417, 418, 422, and 423 nm with the vibronic shoulder
around 438, 440, 443, and 444 nm, respectively (Figure
2
a). The absorption maximum of P2 in chloroform,
40
ethanol, DMF, and DMSO is at 392, 401, 400, and 406
nm, respectively, while the emission bands are peaked
at 418, 422, 423, and 424 nm with vibronic shoulder
around 442, 436, 445, and 438 nm, respectively (Figure
2
b). Since no aggregation absorption or excimer emis-
°C. After annealing, a 12 nm red shift for absorption
sion was observed, we attribute this red shift to en-
hanced chain conjugation driven by strong interaction
between phosphonate groups and solvent molecules in
polar solvents. Absence of aggregation is also evidenced
by relatively high photoluminescence quantum yield of
both polymers in ethanol.
The thin films of P1 and P2 were fabricated by spin-
casting their chloroform or ethanol solutions (10 mg/
mL) onto quartz substrates. The films from DMF and
DMSO solutions were not studied here due to the high
boiling point of the solvents. The absorption maxima of
the thin films of P1 and P2 cast from chloroform
solutions are at 381 and 388 nm, respectively, while the
PL spectra have two peaks at 428 and 450 nm for P1
and 434 and 453 nm for P2 (Figure 3). Thin film
absorption maxima of P1 and P2 cast from ethanol
solutions further red-shift to 388 and 403 nm, but
almost the same as solution spectra. Thin film PL
spectrum of P1 cast from ethanol solution is identical
maximum and a 6 nm red shift for PL spectrum with
better-resolved peaks were observed, indicating that
polymer chains of P2 prefer higher intrachain order in
solid state.3
9,40
Under the same treatment, P1 exhibits
a 3 nm red shift for absorption maximum and a 5 nm
red shift for PL spectrum. The sky blue emission color
of the films cast from ethanol solutions of polymer P1
or P2 is almost unchanged with a less than 15%
reduction of PL intensity after heat treatment at 100
°
C for 1 h in a vacuum. Compared with the PL spectra
in dilute solutions, film PL spectra show a red shift up
to 16 nm with slightly changed absorption maximum.
The optical change from a dilute solution to thin film
have also been observed in Yang’s BDOH-PF.41
Sensing Properties. The sensing properties of poly-
mers P1 and P2 to different metal ions were character-
ized in 5 µM dichloromethane (CH2Cl2) solutions. Upon
+
+
+
2+
2+
addition of metal ions, i.e., Li , Na , K , Mg , Ca
,

Macromolecules, Vol. 38, No. 13, 2005
Polyfluorenes with Phosphonate Groups 5419
Figure 3. UV-vis absorption and PL spectra of P1 (a) and
P2 (b) films cast from chloroform and ethanol solutions.
Figure 5. Absorption (a) and fluorescence (b) spectra of P1
3
+
2 2
in CH Cl solution upon addition of Fe . The Stern-Volmer
plots are shown as an inset.
Fe3 to the CH2Cl2 solution of P2 also led to a 130-fold
reduction in emission intensity. From the Stern-Volmer
plots as an inset of Figure 5b, the corresponding Stern-
+
6
Volmer constants (Ksv) were calculated to be 4.05 × 10
6
and 2.24 × 10 for P1 and P2, respectively. Since adding
3+
Fe ion into poly(9,9-dioctylfluorene) (PF8) solution
only led to an emission reduction less than 5-fold, we
tentatively attribute the high sensitivity of polymers P1
3+
and P2 to Fe to the formation of certain complex
between Fe3 ions and phosphonate groups, which can
quench the emission from the polymers. The different
sensitivity between P1 and P2 is probably due to the
different length of the alkyl chains, which results in
different distance between Fe3 -phosphonate group
quencher and the polymer backbone.42
+
+
Figure 4. UV-vis absorption and PL spectra of P2 film cast
from chloroform solution before and after annealing at 100 °C
for 1 h.
Fluorescence emission response profiles of polymers
P1 and P2 in CH2Cl2 solution upon addition of other
metal ions were also investigated, as shown in Figure
6. Almost all the metal ions have no effects on the
fluorescence spectra of polymers P1 and P2, except that
Sr2 , Cd2+, Mn2+, Fe2+, Cu2+, Co2+, Ni2+, Ag , Zn2+, and
+
+
2
+
Pb , no obvious changes of absorption spectra were
2+
2+
3
+
Cu and Mg result in slight fluorescence quenching
of less than 15-fold and 5-fold, respectively. These
results indicate that polymers P1 and P2 are both
highly sensitive and selective chemosensors for the Fe3
ion.
observed, while the addition of Fe caused an obvious
enhancement of the molar extinction coefficient (ꢀ) of
P1 at short wavelength along with a slight increase
around main absorption band, as shown in Figure 5a.
P2 showed identical behavior. In contrast, the response
of fluorescence spectra of the polymers to the addition
+
Sensing properties of the polymers to Fe3 ion were
also studied in different solvents. As shown in Figure
7, the fluorescence intensity of P1 in tetrahydrofuran
(THF) solution (5 µM) was almost quenched after the
addition of 100 µM Fe3 ion. However, when a drop of
+
of Fe ion was much remarkable. When the Fe3+ ion
was added into the CH2Cl2 solution of P1 (Figure 5b),
the emission intensity decreased dramatically with a
fluorescence quenching up to 210-fold. The addition of
3+
+

5420 Zhou et al.
Macromolecules, Vol. 38, No. 13, 2005
Figure 8. Fluorescence response profiles of P1 and P2 in
ethanol upon addition of different metal ions.
Figure 6. Fluorescence response profiles of P1, P2 and 3, 4
in CH Cl upon addition of different metal ions.
2
2
Figure 9. Cyclic voltammograms of the P1 and P2 films
coated on platinum electrodes in 0.1 M Bu
solution.
4 4 3
ClO CH CN
To investigate the amplification effect43 of conjugated
polymer chain, model compounds 3 and 4 were synthe-
sized and studied. Upon addition of excess Fe3 (1 mM)
to the CH2Cl2 solution of 3 and 4, the fluorescence
intensity only quenched up to 12-fold and 6-fold, re-
spectively (Figure 6). The corresponding Ksv values were
+
Figure 7. Fluorescence spectra of polymer P1 in THF with
3
+
3 2
or without presence of Fe and NH ‚H O.
ammonia solution (14 M concentration) was added to
the solution, the fluorescence spectrum was recovered
to that before adding analyte. When the experiment was
performed with polymer P2, a similar phenomenon was
also observed. This result indicates that the sensing
properties of the polymers are originated from the
5
4
determined to be 1.14 × 10 and 5.83 × 10 , respectively.
Both the quenching effects and Ksv values are much
lower than those of polymers, which once more proves
signal amplification ability of conjugated polymers due5
to facile energy migration along the polymer backbone.
Electrochemical Properties. The electrochemical
behaviors of the polymers P1 and P2 were investigated
by cyclic voltammetry (CV), as shown in Figure 9. The
CV was performed in a solution of Bu4NClO4 (0.1 M) in
acetonitrile at a scan rate of 50 mV/s at room temper-
3
+
certain interaction between Fe ions and the phos-
phonate groups, and polymer P1 and P2 can act as
3
+
reversible chemosensors for the Fe ion.
Fluorescence emission response profiles of polymers
P1 and P2 in ethanol solution upon addition of various
metal ions are exhibited in Figure 8. Similar to the case
in CH2Cl2, sensitivity of the polymers to the most of
+
ature under argon with an Ag/Ag electrode as the
reference electrode. A platinum electrode coated with a
thin polymer film was used as the working electrode.
According to the onset potential of the oxidation process
and reduction process, we estimate the highest occupied
molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) energy levels of the polymer
P1 to be -5.5 and -2.2 eV with the formula (EHOMO )
3
+
metal ions is very low except for Fe . When excess
3
+
Fe (100 µM) was added into the ethanol solution of
polymers P1 and P2, the fluorescence intensity of
polymers P1 and P2 only drop 18-fold and 14-fold,
respectively. The corresponding Ksv values were deter-
5
5
ox
red
5
44
mined to be 3.55 × 10 and 2.71 × 10 , respectively. The
decreased quenching effect should be attributed to the
hydrogen-bonding interactions between the ethanol
molecules and the phosphonate groups, which weakens
the interactions between the receptors and the an-
alytes. This behavior was also observed in PFs for
-(E + 4.34) eV and ELUMO ) -(E4
+ 4.34) eV).
Compared with the HOMO (-5.8 eV) level of PAF, 0.3
eV reduced HOMO level of P1 should be attributed to
the effect of phosphonate groups on the polymer side
chains. This phenomenon was also observed in fluorene-
based polyelectrolytes.20 There are no obvious differ-
ences in the HOMO and LUMO levels between polymer
-
27
sensing F .

Macromolecules, Vol. 38, No. 13, 2005
Polyfluorenes with Phosphonate Groups 5421
Table 1. EL Emission Maximum (λmax), Turn-On Voltage (VT), Maximum Brightness (Bmax), Luminous Efficiency (ηc), and
CIE Coordinates of the Polymers P1 and P2 with a Device Structure of ITO/HTL/P1 or P2/Ca/Al
Bmax (cd/m2)
ηc (cd/A)
a
CIEa
device
polymers/solutions
HTL
λmax (nm)
VT (V)
1
2
P1/CHCl3
P2/CHCl3
P1/CHCl3
P2/CHCl3
P1/EtOH
P2/EtOH
P1/EtOH
P2/EtOH
PEDOT
PEDOT
PEDOT
PEDOT
PEDOT
PEDOT
PVK
424, 448 (sh)b
428, 452 (sh)
424, 448 (sh)
436, 460 (sh)
424, 448 (sh)
436, 460 (sh)
420, 448 (sh)
436, 460 (sh)
6.0
4.5
5.0
4.0
4.5
5.0
6.0
7.5
901
2779
1279
4101
520
1160
883
1750
0.22
1.25
0.19
0.34
0.10
0.63
0.29
1.49
0.172, 0.167
0.177, 0.230
0.173, 0.099
0.158, 0.074
0.167, 0.138
0.164, 0.088
0.175, 0.142
0.171, 0.131
c
3
c
4
5
6
7
8
PVK
a
At a brightness of 100 cd/m2. b Shoulder peak. c After heat treatment at 100 °C for 1 h in a vacuum.
P1 and P2 due to the same main-chain structure and
the same end phosphonate side groups. From the
electrochemical data we estimate that the band gap is
around 3.3 eV, which is significantly larger than the
optical band gap 2.8 eV estimated from absorption onset
at 430 nm. The band gap difference of PAFs measured
by optical and electrochemical methods was previously
reported by Janietz et al.;45 no detailed explanation
about the discrepancy was provided in their paper.
Electroluminescent Properties. To test electro-
luminescent properties of polymers P1 and P2, devices
with two different configurations were fabricated, i.e.,
ITO/poly(3,4-ethylenedioxythiophene)-poly(styrene-
sulfonic acid) (PEDOT-PSS, 50 nm)/polymer (50 nm)/
Ca (10 nm)/Al (100 nm) and ITO/poly(vinylcarbazole)
(PVK, 50 nm)/polymer (50 nm)/Ca(10 nm)/Al(100 nm).
Ethanol was chosen as the spin-coating solvent for P1
and P2 in all devices, except that chloroform was also
used in fabrication of the first type of devices for
comparison. High solubility of the polymers P1 and P2
in alcohol makes the preparation of the second type of
devices possible by means of spin-coating without
interface interference. The device performance mea-
sured under ambient conditions is listed in Table 1. The
EL maxima of both P1 and P2 are identical to those of
PL spectra. With PVK as the hole-transporting layer
Figure 10. Electroluminescence spectra of P2 with PEDOT-
PSS and PVK as hole-transporting layer at a driving voltage
of 10 V.
(
HTL), the diodes with P1 and P2 as emitting layer
show the luminous efficiencies of 0.29 and 1.49 cd/A
with the Commission Internationale de L’Eclairage
(
CIE) coordinates of (0.175, 0.142) and (0.171, 0.131) at
2
1
00 cd/m and the maximum brightness of 883 and 1750
2
cd/m , respectively. With PEDOT-PSS as the HTL, the
devices fabricated from ethanol exhibit the poorest
efficiency, but the better color purity, indicated by CIE
coordinates of (0.167, 0.138) for P1 and (0.164, 0.088)
for P2. The devices with PEDOT-PSS as the HTL
fabricated from chloroform exhibit the luminous ef-
ficiency close to that of the devices with PVK as the
HTL; however, the color purity is very poor. The EL
spectra of P2 with different fabrication conditions at the
driving voltage of 10 V are shown in Figure 10. For all
spectra, a well-resolved emission structure with peaks
at 436, 460, and 490 nm, assigned to the 0-0, 0-1, and
Figure 11. EL spectra of device ITO/PEDOT/P2(chloroform)/
Ca/Al after heat treatment at 100 °C for 1 h in a vacuum under
different driving voltages.
purity was significantly improved, as indicated by the
CIE coordinates in Table 1. Moreover, the EL spectra
are insensitive to driving voltage. As shown in Figure
11, with increasing the driving voltage from 8 to 12 V,
the EL spectra are almost same. The CIE coordinates
under driving voltages of 8, 10, and 12 V are (0.158,
0.079), (0.159, 0.090), and (0.161, 0.103), respectively,
corresponding to the brightness of 433, 741, and 1082
4
6
0
-2 intrachain singlet transitions, respectively, was
observed. Both types of devices with ethanol as the
device fabrication solvent afford clean and typical EL
spectra of PFs. The poorest color purity of P2 with
PEDOT-PSS as the HTL and chloroform as the spin-
coating solvent, indicated by CIE coordinates, is at-
tributed to the more pronounced emission from 0-2 and
2
cd/m . We did not observe a featureless green emission
0
-3 transitions. However, after heat treatment of this
band in the EL spectra of P1 and P2, which often
appears in PFs EL devices. We speculate that phos-
phonate groups surrounding the main chain might be
able to suppress the interchain interaction of the current
polymers and therefore to prevent the formation of
device at 100 °C for 1 h in a vacuum, a red shift for EL
spectra was observed, like that occurring in PL spectra
(
Figure 11). Most importantly, the emission from 0-2
and 0-3 transitions was depressed, and then the color

5422 Zhou et al.
Macromolecules, Vol. 38, No. 13, 2005
nescence quantum yield in ethanol. The polymers are
highly sensitive and selective chemosensory materials
for Fe3 with an emission quenching up to 210-fold upon
+
3+
addition of Fe . Blue PLEDs was successfully fabri-
cated with PVK as the HTL through solution process.
A luminous efficiency of 1.49 cd/A with the CIE coor-
2
dinates of (0.171, 0.131) at 100 cd/m has been demon-
strated. In addition to the sensing properties, the
polymers with phosphonate groups may also provide the
possibility for selecting wide range of hole-transporting
materials in PLEDs fabrication.
Experimental Section
Measurement and Characterization. H and 13C NMR
spectra were recorded with Varian XL-300 NMR chloroform-d
as solvents and tetramethylsilane as internal standard. The
elemental analysis was performed on a Bio-Rad elemental
analysis system. Mass spectroscopic analysis was recorded on
a matrix-assisted laser desorption ionization time-of-flight
mass spectrometer LDI-1700 (American Linear Scientific Inc.).
Differential scanning calorimetry (DSC) and thermal gravi-
metric analysis (TGA) were performed under a nitrogen
1
-
1
atmosphere at a heating rate of 10 °C min through the use
of Perkin-Elmer-DSC 7. Polarizing optical microscopy (POM)
measurements were performed with a Leica optical microscope
(
Leica Microsystems, Germany) in reflection mode with a CCD
camera attachment. Cyclic voltammograms of polymer films
were recorded on an EG&G 283 (Princeton Applied Research)
at room temperature.
Fluorescence Titration Procedure. Fluorescence spectra
were obtained on a Perkin-Elmer LS 50B luminescence
spectrometer with xenon discharge lamp excitation. Measure-
ments of UV-vis absorption spectra were carried out on a
Perkin-Elmer Lambda 35 UV-vis spectrometer. Solutions of
polymers P1, P2 and models 3, 4 were dilute at a concentration
Figure 12. I-V and L-V curves of device from P2 with
PEDOT (a) and PVK (b) as the HTL.
-
6
of 5 × 10 M (the concentration of polymers is based on the
moles of the repeated unit) in CH Cl . Solutions of cationic
2
2
perchlorate salts or cationic nitrate salts with the concentra-
excimer or aggregation. Figure 12a,b shows the I-V and
L-V curves of devices from P2 with PEDOT-PSS and
PVK as the HTL and ethanol as the solvent. The
relatively higher turn-on voltage of the devices with
PVK as the HTL should be attributed to the large hole-
injection barrier owing to the low HOMO level of PVK,
which should be improved by choosing appropriate
triarylamine compounds as the HTL or inserting a hole
injection layer. In PLEDs fabrication, the polymer layers
are generally deposited through the solution process;
thus, the hole-transporting materials need to be solvent
resistant to enable the fabrication of the subsequent
layer. As the dominant hole-transporting materials
nowadays, PEDOT-PSS involves over amount of sul-
fonic acid groups and is strongly hydrophilic, which
might be disadvantageous in terms of device sta-
bility. Several cross-linkable hole-transporting materials
based on triarylamine have been developed to replace
-
4
tion of typically 5 × 10 M were prepared by successive
dilution. Fluorescence titration was carried out by sequentially
adding 0.1 mL aliquots of cation solutions in CH
2
Cl
was added to acquire
0.00 mL of solutions. The solutions were stirred for 5 min
prior to obtaining fluorescence spectra.
2
to 5.00
2 2
mL of the polymer solutions, and CH Cl
1
PLED Fabrication and Characterization. Polymers P1
and P2 were dissolved in ethanol and filtered through a 0.45
µm filter. Patterned indium tin oxide (ITO)-coated glass
substrates were cleaned with ethanol, detergent, distilled
water, and ethanol. After dried at 110 °C for half an hour,
poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly-
(
styrenesulfonic acid) (PSS) (Baytron-P 4083, Bayer AG) was
spin-coated onto the anode followed by drying at 110 °C for
half an hour. Poly(vinylcarbazole) (PVK) (Acros) and electro-
luminescent polymers P1 and P2 are successively coated onto
the substrate. Film thickness was determined by ellipsometry
(
AUEL-III, Xi’an, China) as well as by applying a scratch to
the polymer film and subsequent atomic force microscopy
(AFM) (SPI3800N, Seiko Instruments Inc., Japan) imaging in
the vicinity of the scratch. Ca and Al layers were thermally
evaporated onto the emissive layer under a vacuum at a base
4
7,48
PEDOT-PSS.
Since most of triarylamine hole-
transporting materials are insoluble in alcoholic sol-
vents and water, the development of the emitting
polymers soluble in these solvents should provide the
other approach to avoid the disadvantages of PEDOT-
PSS.
-4
pressure of 3 × 10 Pa. The electroluminescence (EL) spectra
and current-voltage and brightness-voltage curves of devices
were recorded using a Keithley 2400/2000 current/voltage
source unit with a calibrated silicon photodiode under ambient
conditions.
In summary, we have successfully synthesized poly-
fluorenes with phosphonate polar groups in the side
chains. A red shift of the absorption and PL spectra in
solutions was distinctly observed with increasing solvent
polarity. Polymer P2 shows high intrachain order in
film spin-cast from ethanol, revealed by both red-shifted
absorption and emission along with better-resolved
emission spectra. Both polymers show high photolumi-
Material Synthesis. All chemicals and reagents were used
as received from commercial sources without further purifica-
tion. Solvents for chemical synthesis were purified according
to standard procedures. All chemical reactions were carried
out under an inert atmosphere. Intermediate 2-(9,9-dioctyl-
49
fluoren-2-yl)-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane and 2,7-
3
5
dibromofluorene were synthesized as previously described.

Macromolecules, Vol. 38, No. 13, 2005
,7-Dibromo-9,9-bis(3′-bromopropyl)fluorene. A two-
Polyfluorenes with Phosphonate Groups 5423
2
(0.25 g, 2.2 mmol), cyclooctadiene (0.35 g, 2.2 mmol), and DMF
(5 mL) was heated to 80 °C for half an hour. Then a solution
of 1 (0.34 g, 0.50 mmol) in 5 mL of toluene was added, and
the reaction mixture was stirred at 80 °C for 4 days. After
cooling to room temperature, the reaction mixture was poured
into chloroform and washed with dilute HCl, water, and brine.
The separated organic layer was dried over magnesium sulfate,
and the solvent was evaporated. The product was obtained as
phase mixture of 2,7-dibromofluorene (5.0 g, 15 mmol), 1,3-
dibromopropane (30 mL), tetrabutylammonium bromide (0.1
g), and sodium hydroxide (50% w/w) aqueous solution (30 mL)
was stirred at 60 °C for 4 h under nitrogen. After diluting the
reaction mixture with dichloromethane, the organic layer was
washed with water and brine. The separated organic layer was
dried over magnesium sulfate, and dichloromethane was
evaporated. The nonreacted 1,3-dibromopropane was distilled
in a vacuum, and 2,7-dibromo-9,9-bis(3′-bromopropyl)fluorene
a yellowish fiber (150 mg, 58%) after precipitation from
1
hexane. H NMR (300 MHz, CDCl
3
) δ (ppm): 7.81 (b, 2H), 7.68
(
5.4 g, 62%) was obtained as a white crystal by chromatogra-
(b, 4H), 3.91 (b, 8H), 2.31 (b, 4H), 1.55 (b, 4H), 1.14 (b, 16H).
1
-1
phy with petroleum ether as the eluent; mp 149-150 °C. H
NMR (300 MHz, CDCl
IR (CaF
(w), 1459 (m), 1243 (s), 1055 (sh), 1027 (s), 957 (s), 816 (m).
Anal. Calcd for C27 ‚H O (the amounts of water is based
): C, 60.22; H, 7.49; P, 11.49. Found:
2
), cm : 2980 (m), 2938 (m), 2906 (m), 1738 (w), 1610
3
) δ (ppm): 7.57 (d, 2H, J ) 5.0 Hz),
.52 (d, 2H, J ) 4.6 Hz), 7.50 (s, 2H), 3.14 (t, 4H, J ) 8.7 Hz),
.15 (t, 4H, J ) 8.2 Hz), 1.18 (m, 4H, J ) 15.1 Hz). 13C NMR
) δ (ppm): 144.96, 133.22, 125.23, 120.45,
16.24, 115.73, 48.75, 32.76, 27.87, 21.24. The compound 2,7-
7
2
(
H
38
20,23
O
6
P
2
2
on the TGA analysis
75 MHz, CDCl
3
C, 59.87; H, 6.95; P, 10.68.
1
Poly(2,7-dibromo-9,9-bis(6′-diethoxylphosphoryl-
hexyl)fluorene) (P2). A solution of Ni(COD) (0.85 g, 3.0
2
dibromo-9-cyclobutylfluorene (1.2 g, 21%) was separated as the
1
main byproduct; mp 215-216 °C. H NMR (CDCl
3
) δ (ppm):
.89 (s, 2H), 7.50 (m, 4H), 2.65 (t, 4H, J ) 7.4 Hz), 2.43 (m,
H, J ) 11.1 Hz). 13C NMR (75 MHz, CDCl
) δ (ppm): 148.16,
31.57, 124.55, 120.46, 115.93, 115.15, 46.24, 27.24, 11.09.
,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene. A mixture
of 2,7-dibromofluorene (5.0 g, 15 mmol), 1,6-dibromohexane
30 mL), tetrabutylammonium bromide (0.1 g), and sodium
hydroxide (30 mL, 50% w/w) aqueous solution was stirred at
0 °C for 4 h under nitrogen. After diluting the reaction
mmol), 2,2′-dipyridine (0.25 g, 2.2 mmol), cyclooctadiene (0.35
g, 2.2 mmol), and DMF (5 mL) was heated to 80 °C for half an
hour. Then a solution of 2 (0.38 g, 0.50 mmol) in 5 mL of
toluene was added, and the reaction mixture was stirred at
7
2
1
3
2
8
0 °C for 4 days. After cooling to room temperature, the
reaction mixture was poured into chloroform and washed with
dilute HCl, water, and brine. The separated organic layer was
dried over magnesium sulfate, and the solvent was evaporated.
(
6
The product was obtained as a yellowish fiber (190 mg, 63%)
mixture with dichloromethane, the organic layer was washed
with water and brine. The separated organic layer was dried
over magnesium sulfate, and dichloromethane was evaporated.
The nonreacted 1,6-dibromohexane was distilled in a vacuum,
and 2,7-dibromo-9,9-bis(6′-bromohexyl)fluorene (8.3 g, 81%)
was obtained as a white crystal by chromatography with
1
after precipitation from hexane. H NMR (300 MHz, CDCl
3
) δ
(
1
ppm): 7.84 (b, 2H), 7.69 (b, 4H), 4.04 (b, 8H), 2.19 (b, 4H),
2
.63 (b, 4H), 1.48 (b, 4H), 1.27 (b, 20H), 0.85 (b, 4H). IR (CaF ),
-1
cm : 2981 (sh), 2930 (s), 2857 (m), 1731 (m), 1607 (w), 1458
(
m), 1401 (w), 1248 (s), 1030 (s), 957 (s), 815 (m). Anal. Calcd
for C33 ‚H O: C, 63.65; H, 8.42; P, 9.94. Found: C,
3.96; H, 7.89; P, 9.83.
H
50
6
O P
2
2
1
petroleum ether as the eluent; mp 71-72 °C. H NMR (300
6
MHz, CDCl
3
) δ (ppm): 7.54 (d, 2H, J ) 8.0 Hz), 7.47 (d, 2H, J
9
,9-Bis(3′-diethoxylphosphorylpropyl)-2,7-bis(9,9-di-n-
)
)
8.0 Hz), 7.43 (s, 2H), 3.29 (t, 4H, J ) 6.8 Hz), 1.93 (t, 4H, J
8.3 Hz), 1.67 (m, 4H, J ) 7.1 Hz), 1.20-1.05 (m, 8H), 0.58
) δ (ppm):
46.42, 133.32, 124.59, 120.35, 115.82, 115.47, 49.81, 34.27,
8.05, 26.86, 23.19, 21.99, 17.71.
,7-Dibromo-9,9-bis(3′-diethoxylphosphorylpropyl)-
octylfluorene-2-yl)fluorene (3). To a solution of 1 (0.68 g,
1
3
1 mmol) and 2-(9,9-dioctylfluoren-2-yl)-4,4,5,5-tetramethyl-
(
m, 4H, J ) 8.0 Hz). C NMR (75 MHz, CDCl
3
[
1,3,2]dioxaborolane (1.55 g, 3 mmol) in toluene (25 mL) was
1
2
added Pd(PPh
3
)
4
(10 mg) and 2 M aqueous Na
2 3
CO solution
(
2
15 mL). The mixture was degassed and stirred at 80 °C for
2
4 h and then was poured into a saturated solution of
fluorene (1). A solution of 2,7-dibromo-9,9-bis(3′-bromo-
propyl)fluorene (3.0 g, 5 mmol) in triethyl phosphite was
heated to 140 °C for 16 h. Then the excess triethyl phosphite
was distilled in a vacuum, and monomer 1 (3.3 g, 91%) was
obtained as a white crystal after purification with chromatog-
ammonium chloride and extracted with ethyl acetate; the
combined organic layer was washed with brine and dried over
Na
2 4
SO . After removing the solvent, the residue was purified
by column chromatography using ethyl acetate as eluent to
1
1
give 0.90 g (69%) of yellowish oil. H NMR (300 MHz, CDCl
δ (ppm): 7.80 (m, 6 H, Ar-H), 7.65 (m, 8 H Ar-H), 7.35 (m,
H, Ar-H), 3.92 (m, 8 H), 2.05 (m, 12 H), 1.56-1.08 (m, 56
3
)
raphy (ethyl acetate as the eluent); mp 101-103 °C. H NMR
(
3
300 MHz, CDCl ) δ (ppm): 7.54 (d, 2H, J ) 8.6 Hz), 7.51 (d,
6
2
8
H, J ) 6.4 Hz), 7.45 (s, 2H), 3.93 (m, 8H), 2.08 (m, 4H, J )
.2 Hz), 1.50 (m, 4H), 1.20 (t, 12H, J ) 7.0 Hz), 0.90 (m, 4H).
1
3
H), 0.96-0.87 (m, 24 H). C NMR (75 MHz, CDCl
151.92, 151.34, 150.55, 141.35, 141.17, 140.84, 140.66, 140.39,
3
) δ (ppm):
1
3
C NMR (75 MHz, CDCl
26.52, 122.16, 121.85 (C-fluorene ring), 61.74 (-OCH
5.76 (C -fluorene ring), 41.04 (-CH -), 26.86 (-CH -), 25.00
-), 16.77 (-CH ). Anal. Calcd for C27 : C,
7.67; H, 5.63; Br, 23.49; P, 9.11. Found: C, 47.33; H, 5.79;
3
) δ (ppm): 151.37, 139.47, 131,10,
1
1
4
1
32.58, 132.45, 129.00, 128.84, 127.42, 127.19, 126.51, 123.35,
21.76, 121.66, 120.68, 120.28, 120.12, 61.75, 55.61, 53.79,
1.25, 40.81, 32.17, 30.47, 29.64, 27.04, 25.19, 24.25, 22.98,
1
5
2
-),
9
2
2
(
-CH
2
3
2 6 2
H38Br O P
+
7.53, 16.72, 14.44. MS m/z: 1298.4 (M ).
4
+
Br, 23.84; P, 8.61. MS m/z: 680.7 (M ).
9,9-Bis(6′-diethoxylphosphorylhexyl)-2,7-bis(9,9-di-n-
2
,7-Dibromo-9,9-bis(6′-diethoxylphosphorylhexyl)-
octylfluorene-2-yl)fluorene (4). To a solution of 2 (0.76 g,
1 mmol) and 2-(9,9-dioctylfluoren-2-yl)-4,4,5,5-tetramethyl-
[1,3,2]dioxaborolane (1.55 g, 3 mmol) in toluene (25 mL) was
fluorene (2). A solution of 2,7-dibromo-9,9-bis(6′-bromo-
hexyl)fluorene (4.0 g, 6 mmol) in triethyl phosphite was heated
to 140 °C for 16 h. Then the excess triethyl phosphite was
distilled in a vacuum, and monomer 2 (3.9 g, 83%) was
3 4 2 3
added Pd(PPh ) (10 mg) and 2 M aqueous Na CO solution
(15 mL). The mixture was degassed and stirred at 80 °C for
24 h and then was poured into a saturated solution of
ammonium chloride and extracted with ethyl acetate; the
combined organic layer was washed with brine and dried over
obtained as colorless oil after purification with chromatography
1
(
ethyl acetate as the eluent). H NMR (300 MHz, CDCl
3
) δ
(
ppm): 7.56 (d, 2H, J ) 8.0 Hz), 7.49 (d, 2H, J ) 8.2 Hz), 7.44
s, 2H), 4.08 (m, 8H, J ) 7.8 Hz), 1.93 (t, 4H, J ) 8.2 Hz), 1.63
m, 4H), 1.45 (m, 4H), 1.32 (t, 12H, J ) 8.5 Hz), 1.13 (m, 8H),
(
(
0
1
(
(
2
Na
2 4
SO . After removing the solvent, the residue was purified
by column chromatography using ethyl acetate as eluent to
1
3
1
.61 (m, 4H). C NMR (75 MHz, CDCl
39.44, 130.67, 126.47, 121.91, 121.58 (C-fluorene ring), 61.66
-), 55.95 (C -fluorene ring), 40.53 (-CH -), 30.49
-), 29.72 (-CH -), 26.86 (-CH -), 25.00 (-CH -),
3.90 (-CH -), 13.87 (-CH ). Anal. Calcd for C33
3
) δ (ppm): 152.63,
3
give 0.93 g (67%) of yellowish oil. H NMR (300 MHz, CDCl )
δ (ppm): 7.80 (m, 6H, Ar-H), 7.65 (m, 8H Ar-H), 7.35 (m,
6H, Ar-H), 4.05 (m, 8H), 1.95 (12H, m), 1.66-1.08 (m, 68H),
-OCH
-CH
2
9
2
1
3
2
2
2
2
3
0.96-0.70 (m, 24H). C NMR (75 MHz, CDCl ) δ (ppm):
2
3
H
50Br
2
O
6
P
2
:
151.92, 151.87, 151.37, 141.15, 140.95, 140.82, 140.71, 140.38,
132.57, 132.44, 129.00, 127.42, 127.20, 126.93, 126.42, 123.35,
121.69, 120.66, 120.40, 120.31, 120.12, 61.91, 55.83, 40.99,
40.75, 32.17, 30.91, 30.69, 30.51, 30.41, 30.06, 29.58, 26.89,
C, 51.84; H, 6.59; Br, 20.90; P, 8.10. Found: C, 51.12; H, 6.88;
+
Br, 21.18; P, 7.39. MS m/z: 764.7 (M ).
Poly(9,9-bis(3′-diethoxylphosphorylpropyl)fluorene)
+
(
P1). A mixture of Ni(COD)
2
(0.85 g, 3.0 mmol), 2,2′-dipyridine
25.03, 24.21, 24.11, 22.97, 16.84, 14.44. MS m/z: 1382.5 (M ).

5424 Zhou et al.
Macromolecules, Vol. 38, No. 13, 2005
Acknowledgment. This work was supported by
(23) Liu, B.; Yu, W.; Lai, Y.; Huang, W. Macromolecules 2002,
35, 4957.
National Natural Science Foundation of China
(
(
(
(
(
24) Pinto, M. R.; Kristal, B. M.; Schanze, K. S. Langmuir 2003,
9, 6523.
25) Balanda, P.; Ramey, M.; Reynolds, J. Macromolecules 1999,
2, 3970.
26) Fan, C.; Plaxco, K. W.; Heeger, A. J. J. Am. Chem. Soc. 2002,
Project No. 29992530 and 20174042) and 973 Project
2002CB613402).
1
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