Phenothiazine-Based Conjugated Polymers: Synthesis, Electrochemistry, and Light-Emitting Properties

Article abstract of DOI:10.1021/ma035087y

Two new phenothiazine-containing conjugated polymers, poly(10-hexylphenothiazine-3,7-diyl) (PHPT) and poly(10-hexylphenothiazine-3,7-diyl-alt-9,9-dihexyl-2,7-fluorene) (PPTF), were synthesized and characterized, and their photophysical, electrochemical, and electroluminescent properties were investigated. The optical band gaps of PHPT and PPTF were 2.69 and 2.76 eV, respectively. Both polymers showed greenish-blue photoluminescence (490 nm) in dilute solutions with a fluorescence quantum yield of 0.40. Identical solid-state and dilute solution absorption and emission spectra were observed, showing that excimers were not formed in PHPT or PPTF thin films. Ionization potentials (HOMO levels) estimated from cyclic voltammetry were 5.0-5.1 eV for the phenothiazine-based polymers, making them good candidates for hole transport materials in devices. Spectroelectrochemistry revealed that the observed multiple oxidation peaks in the cyclic voltammetry of PHPT have associated multiple absorption peaks due to the formation of radical cations (polarons) and dications (bipolarons). Greenish-blue electroluminescence with luminance of up to 320 cd/m² was observed for the PPTF organic light-emitting diodes. These results show that the phenothiazine ring is an excellent building block for lowering the ionization potential and for impeding π-stacking aggregation and excimer formation in conjugated polymers.

Full text of DOI:10.1021/ma035087y

8992
Macromolecules 2003, 36, 8992-8999
Phenothiazine-Based Conjugated Polymers: Synthesis,
Electrochemistry, and Light-Emitting Properties
Xia n gxin g Kon g, Abh ish ek P . Ku lk a r n i, a n d Sa m son A. J en ek h e*
Department of Chemical Engineering and Department of Chemistry, University of Washington,
Seattle, Washington 98195-1750
Received J uly 27, 2003; Revised Manuscript Received September 29, 2003
ABSTRACT: Two new phenothiazine-containing conjugated polymers, poly(10-hexylphenothiazine-3,7-
diyl) (PHPT) and poly(10-hexylphenothiazine-3,7-diyl-alt-9,9-dihexyl-2,7-fluorene) (PPTF), were synthe-
sized and characterized, and their photophysical, electrochemical, and electroluminescent properties were
investigated. The optical band gaps of PHPT and PPTF were 2.69 and 2.76 eV, respectively. Both polymers
showed greenish-blue photoluminescence (490 nm) in dilute solutions with a fluorescence quantum yield
of 0.40. Identical solid-state and dilute solution absorption and emission spectra were observed, showing
that excimers were not formed in PHPT or PPTF thin films. Ionization potentials (HOMO levels) estimated
from cyclic voltammetry were 5.0-5.1 eV for the phenothiazine-based polymers, making them good
candidates for hole transport materials in devices. Spectroelectrochemistry revealed that the observed
multiple oxidation peaks in the cyclic voltammetry of PHPT have associated multiple absorption peaks
due to the formation of radical cations (polarons) and dications (bipolarons). Greenish-blue electrolumi-
nescence with luminance of up to 320 cd/m2 was observed for the PPTF organic light-emitting diodes.
These results show that the phenothiazine ring is an excellent building block for lowering the ionization
potential and for impeding π-stacking aggregation and excimer formation in conjugated polymers.
Conjugated polymer semiconductors are finding grow-
of the highly nonplanar phenothiazine ring in the
homopolymer PHPT and alternating copolymer PPTF
impedes π-stacking aggregation and intermolecular
excimer formation, resulting in identical dilute solution
and solid-state photophysics.
ing applications in electronics and optoelectronics,1-7
including light-emitting diodes,1-3 photovoltaic cells,4,5
thin film transistors,6 and electrochromic cells.7 Syn-
thesis and investigation of new conjugated polymers are
essential to improving the electronic and optoelectronic
properties of these materials and in turn improvement
of the performance of the devices. One general challenge
Carbazole-based π-conjugated polymers were shown
to be good p-type (hole transport) conducting polymers
many years ago.10 Recent interest in the polycarbazoles
has focused on their potential as semiconductors for
light-emitting diodes (LEDs)10c,11a and photovoltaic
cells.11a Unlike carbazole, however, the related pheno-
thiazine ring has not been fully explored as a building
block for the synthesis of conjugated polymers even
though it is clearly a stronger electron donor by virtue
of the extra sulfur heteroatom.11 Efficient electrogen-
erated chemiluminescence (ECL) was recently observed
in co-oligomers of 10-methylphenothiazine,12a,b and
interesting redox properties were observed in other co-
oligophenothiazines.12c,d One particularly striking dif-
ference between the carbazole and phenothiazine rings
is that the former is planar whereas the latter is highly
nonplanar.12a,d The possible consequences of the non-
planarity of the phenothiazine ring for the photophysics,
light-emitting properties, molecular aggregation, and
charge transport of π-conjugated polymers containing
this ring are very intriguing to us and thus motivated
our studies.
in the field is achievement of high electron affinity (n-
2d-h,8
type) conjugated polymers
for improving electron
injection/transport and low ionization potential (p-type)
conjugated polymers9 for better hole injection/transport
in polymer electronic devices. Of particular interest are
polymers that combine high fluorescence quantum
yields with low ionization potential or high electron
affinity.
In this paper, we report the synthesis, photophysics,
electrochemistry, and electroluminescence of two new
soluble phenothiazine-based conjugated polymers: poly-
(10-hexylphenothiazine-3,7-diyl) (PHPT) and poly(10-
hexylphenothiazine-3,7-diyl-a lt-9,9-dihexyl-2,7-fluo-
rene) (PPTF). We show that the electron-rich phenothia-
zine ring is an excellent molecular building block for
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The general syn-
thetic routes to the monomers and polymers are outlined
in Scheme 1. The monomer 3,7-dibromo-10-hexylpheno-
thiazine was synthesized in two steps from the starting
phenothiazine. 9,9-Dihexylfluorene-2,7-bis(trimethylene
boronate) was synthesized from 9,9-dihexylfluorene-2,7-
diboronic acid. PHPT was synthesized in 77% yield
by Ni(0)-mediated coupling polymerization of dibromo-
phenothiazine in a toluene/DMF mixture solvent. The
alternating copolymer of fluorene and phenothiazine,
achieving low ionization potential conjugated polymer
semiconductors. We also demonstrate that the presence
* Corresponding author. E-mail: J enekhe@cheme.washington.
edu.
10.1021/ma035087y CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/07/2003

Macromolecules, Vol. 36, No. 24, 2003
Phenothiazine-Based Conjugated Polymers 8993
Sch em e 1a
a
Reaction conditions: (i) NaH, THF, 1-bromohexane; (ii)
Br2, NaAc/HAc, 5-10 °C; (iii) Ni(COD)2, COD, bpy, DMF, 60
°C; (iv) Pd(PPh3)4, toluene/2 M Na2CO3, Aliquat 336.
PPTF, was synthesized in 86% yield by Suzuki coupling
in a mixture of toluene and aqueous sodium carbonate
solution (2 M) containing 1 mol % Pd(PPh3)4 and a phase
transfer reagent (Aliquat 336) under vigorous stirring
at 100 °C for 3 days.
NMR spectra analyses clearly indicate that well-
defined PHPT and PPTF have indeed been obtained.
1
The H NMR and 13C NMR spectra of PHPT and PPTF
and their assignment shown in Figure 1 are consistent
with the proposed structures. In addition to the peaks
seen in PHPT, the 13C NMR spectra of PPTF showed
additional peaks corresponding to the 9,9-dihexyl-2,7-
fluorenyl units.
F igu r e 1. (a) 1H NMR and (b) 13C NMR spectra of PHPT and
PPTF in chloroform-d.
Ta ble 1. Molecu la r Weigh ts a n d Th er m a l P r op er ties of
P P TF a n d P HP T
Both polymers are readily soluble in common organic
solvents such as chloroform, THF, and toluene. The
weight-average molecular weights of PHPT and PPTF
were found to be 1.53 × 104 and 1.83 × 105, with
polydispersity indexes of 3.00 and 6.45 by gel perme-
ation chromatography (GPC) based on polystyrene
standards, respectively. The much larger polydispersity
in the molecular weight of PPTF may be a result of the
precipitation of polymer from the reaction solution
during polymerization. The polymers possess excellent
thermal stability with onset decomposition tempera-
tures (Td) of 320-324 °C (Table 1). PHPT showed a glass
transition at 166 °C and PPTF at 167 °C (Figure 2). The
similarity of the Tg of both polymers may seem surpris-
ing given the extra 9-hexyl side chain in PPTF compared
to PHPT. However, the 2,7-fluorene linkage in PPTF
makes the chain stiffer than the 3,6-phenothiazine
linkage of PHPT and thus balances the effect of the 9,9-
dihexyl side chains on the Tg. No melting transition was
observed in the DSC thermograms up to 300 °C,
indicating that both PPTF and PHPT are amorphous
polymers. The relatively high glass transition temper-
ature of these polymers is important and desirable for
many applications such as light-emitting diodes.
P h otop h ysica l P r op er ties. The optical absorption
and photoluminescence (PL) emission properties of
PHPT and PPTF in dilute THF solution (1 × 10-5 M)
and as thin films are shown in Figure 3. In dilute
solution, PHPT has a rather broad absorption with no
polymer yield (%) Mw (×104) Mw/Mn
Tg (°C) Td (°C)b
a
a
PHPT
PPTF
77
86
1.53
18.3
3.00
6.45
166
167
320
324
a
Determined by GPC in THF based on polystyrene standards.
Onset decomposition temperature measured by TGA under
b
nitrogen.
clear peak in the 320-400 nm region and an absorption
maximum (λmax) at 287 nm. The thin film absorption
spectrum of PHPT is identical to the dilute solution
spectrum. In the case of the phenothiazine-fluorene
alternating copolymer, PPTF, it has a strong absorption
in the 300-400 nm range with absorption maxima at
384 and 328 nm in solution and as a thin film. The
related polyfluorene homopolymer has an intense struc-
tureless absorption centered at 380 nm.13 The ground-
state electronic structure of the alternating copolymer
PPTF is thus completely different from those of the
related homopolymers.
The dilute solution PL emission spectra of PHPT and
PPTF shown in Figure 3 reveal that they are nearly
identical; the slight difference is that PHPT has a peak
at 490 nm whereas that of PPTF is at 485 nm. The PL
quantum yield in solution was 0.43 for PHPT and 0.39
for PPTF. Interestingly, the thin film PL spectra of both
polymers are identical to those in dilute solution (Figure
3). This exact correspondence of the PL spectra of PHPT
or PPTF in dilute solution and solid state clearly rules
out intermolecular aggregates or excimers14 as the

8994 Kong et al.
Macromolecules, Vol. 36, No. 24, 2003
F igu r e 2. Second heating DSC curves of PHPT and PPTF
with a heating rate of 10 °C/min in N2.
F igu r e 4. CV curves of PHPT film on Pt electrode in 0.1 M
Bu4NPF6 solution in acetonitrile: (a) CV curves in the 0.2-
1.3 V scaning range; (b) CV curve in the 0.3-1.8 V scanning
range with a scan rate of 40 mV/s.
ambient light conditions. The original greenish-blue
emission of PHPT in chloroform was dramatically
decreased in intensity in the blue-black aged solutions.
In other solvents such as THF, benzene, and toluene,
the color and emission properties of the PHPT solutions
remained unchanged even after being stored under
ambient room light for several weeks. The origin of this
phenomenon is likely due to the reaction between
photogenerated phenothiazine radical cation and the
halogenated solvent as known for phenothiazine com-
pounds in halogenated solvents.15 The photochemical
reaction between PHPT and chloroform is a good indica-
tion of the facile generation of radical cations (holes) in
PHPT. We note that the phenothiazine-fluorene co-
polymer PPTF does not exhibit such a photochemical
reaction in chloroform.
Electr och em ica l P r op er ties. Charge injection pro-
cesses and associated electronic states (HOMO/LUMO
levels) of conjugated polymer thin films, which are
important for understanding EL devices, can be inves-
tigated by cyclic voltammetry (CV).8b,16 No reduction
wave for either polymer was observed in the range from
0 to -2.5 V vs SCE, suggesting that both polymers are
intrinsic p-type semiconductors. We thus concentrate
the following discussion on the electrochemical oxidation
of the polymers.
F igu r e 3. Optical absorption and PL emission spectra of
PHPT and PPTF in THF solution (1 × 10-5 M) and as thin
films.
origin of emission in both polymers. The rather large
Stokes shift of 0.7 eV observed in the PL spectra of these
polymers must thus be explained by an alternative
mechanism. Toward this end we note that the pheno-
thiazine ring is highly nonplanar in the ground state,12a,d
precluding sufficiently close intermolecular interactions
essential to forming aggregates or excimers.14 We
propose that in dilute solution or thin film the pheno-
thiazine ring in excited PHPT or PPTF molecule is more
planar than in the ground state. Consequently, the
relaxed singlet excited state from which emission occurs
is lower lying than if photoinduced planarization were
absent. Additional studies such as time-resolved PL
spectroscopy will be necessary to confirm this picture
of the origin of the Stokes shift in the photophysics of
these polymers. The most interesting insight from these
photophysics results is that the phenothiazine ring is
an excellent building block for impeding π-stacking
aggregation and intermolecular excimer formation.
P h otoch em ica l Rea ction of P HP T in Ch lor ofor m
Solu tion s. An interesting photochemical phenomenon
was observed in chloroform solutions of PHPT. The
brownish color of freshly prepared PHPT solutions in
chloroform was noticed to change to dark blue, with
formation of some blue-black precipitate in the bottom
of the vial, upon storing the solutions several days in
Figure 4 shows the electrooxidation CVs of PHPT. The
anodic oxidation peak of PHPT in the first CV scan was
observed at 0.80 V (vs SCE) (not shown). However, all
subsequent scans shifted to a less positive potential and
stabilized at an anodic oxidation peak of 0.66 V, indicat-
ing that the PHPT film was swelled with electrolyte
during the first electrooxidation scan. The corresponding
cathodic peak at 0.46 V means that the oxidation of
PHPT is only quasi-reversible (Figure 4a). In addition
to the main peak at 0.66 V, a second anodic shoulder
peak at 0.9-1.0 V was observed. From the onset
onset
ox
oxidation potential (E
) 0.58 V) the ionization
potential (IP, HOMO level) of PHPT is estimated to be

Macromolecules, Vol. 36, No. 24, 2003
Phenothiazine-Based Conjugated Polymers 8995
Ta ble 2. P h otop h ysica l a n d Red ox P r op er ties of P P TF a n d P HP T
Abs
max
em
max
λ
(nm)a
λ
(nm)a
onset
ox
peak
ox
polymer
soln
log ꢀmax
film
Eogpt (eV)b
soln
film
Φf soln
E
(V)c
E
(V)
IP (eV)d
PHPT
PPTF
MPT
287
328
310
4.38
4.82
287
328
2.76
2.69
486
489
441
490
490
0.43
0.39
0.014
0.58
0.69
0.66
0.74
0.80
5.0
5.1
a
b
Measured in solution (THF, 10-5 M) and as a thin film on silica substrate. Optical band gap. c Onset oxidation potentials vs SCE.
onset
d
Ionization potential was obtained based on IP ) E
+ 4.4 eV.
ox
chemistry,16a it is clear that the HOMO level of the
phenothiazine-fluorene copolymer is dominated by
contribution from the phenothiazine moiety. Therefore,
one can expect the phenothiazine ring to be an excellent
building block for lowering the IP of conjugated copoly-
mers.
The observed electrochemical redox behavior of PHPT
and PPTF can be related to known redox properties of
10-methylphenothizine (MPT) (Table 2) and oligopheno-
thiazines.12c,d As expected, the conjugated homopolymer
PHPT has a lower oxidation potential (Eap ) 0.66 V)
than MPT (Eap ) 0.80 V vs SCE) due to the electron
delocalization in the polymer. However, the observed
0.14 V difference between the monomer and PHPT is
rather small compared to other monomer/polymer sys-
tems such as thiophene/polythiophene and pyrrole/
polypyrrole. The main reason is that electronic delocal-
ization is limited by the nonplanar geometry of the
phenothiazine ring. Interestingly, there is only a small
shift of the oxidation potential of PPTF (Eap ) 0.74 V),
containing alternating phenothiazine and fluorene,
compared to MPT. This means that there is even less
electronic coupling between two phenothiazine rings
separated by the 2,7-fluorene moiety.
The observed multiple oxidation peaks in the CV of
PHPT (Figure 4a) are analogous to similar observations
in oligomers of phenothiazine12c,d and carbazole.17 Three
reversible oxidations at 0.61, 0.715, and 0.837 V (vs Ag/
AgCl) were observed in the trimer of phenothiazine and
interpreted as due respectively to the formation of the
radical cation, dication, and trication.12d In 3,3′-dicar-
bazole, electrochemical oxidation revealed two peaks
that were assigned to the successive formation of the
radical cation and dication.17 We propose that the
oxidation of PHPT can be similarly described as shown
in Scheme 2. We further explored the nature of the
electrooxidation of PHPT by spectroelectrochemistry as
shown in Figure 6. The CV curve from the first scan
from 0.1 to 1.3 V is shown in the inset of Figure 6 for a
PHPT film on ITO glass. After the first complete CV
scan, the optical absorption was identical to the original
neutral polymer as expected. However, at a potential
of 0.63 V (vs SCE) a new broad absorption band at 560
nm and another in the infrared (>1000 nm) were
observed. The 560 nm peak increased to a maximum
when a potential of 0.83 V was applied. These absorp-
tion characteristics at 0.63-0.83 V potential can be
assigned to the radical cation (polaron) of PHPT.
Further increase of the potential to 0.93-1.03 V resulted
in the decrease of the 560 nm band and appearance of
another band at ∼500 nm while the infrared peak also
increased. We can also attribute these absorption spec-
tra changes at higher potentials to the dication of PHPT.
Electr olu m in escen ce. To evaluate the potential of
the two phenothiazine-based polymers as emissive and/
or hole transport materials for light-emitting diodes, a
preliminary investigation of simple device structures
was made. Figure 7 shows the device characteristics of
F igu r e 5. CV curves of PPTF film on Pt electrode in 0.1 M
Bu4NPF6 solution in acetonitrile at a scan rate of 40 mV/s:
(a) first scan and second scan; (b) three-cycle consecutive
scans.
onset
ox
5.0 eV based on IP ) E
+4.4 eV, where the SCE
energy level of -4.4 eV below the vacuum level is
used.8b,16
Shown in Figure 4b is a CV of PHPT film upon
scanning up to 1.8 V. A third oxidation with onset at
1.4 V and peak at 1.7 V is observed to follow that at
0.66 V. Both the first and second oxidations are com-
pletely irreversible when the scanning goes up to 1.4-
1.8 V. This is an indication that the trication of this
polymer is unstable.
Figure 5 shows the CV scans of PPTF films. The
anodic peak of the second scan at 0.76 V is shifted from
0.84 V observed in the first scan. All subsequent scans
were the same, showing an anodic peak at 0.74 V and
a cathodic peak at 0.66 V (Figure 5b). The one-electron
oxidation of PPTF is thus quite reversible. We note that
only one oxidation wave is observed in the CV of this
polymer. Scanning above 1.2 V leads to an irreversible
second oxidation due to the formation of an unstable
dication of PPTF. From the onset oxidation potential of
PPTF (0.69 V vs SCE) we similarly estimated the IP or
HOMO level to be 5.1 eV. Given that the HOMO level
of poly(9,9-dihexylfluorene) (PF6) or poly(9,9-dioctyl-
fluorene) (PFO) is 5.8 eV based on a similar (-4.4 eV
SCE level relative to vacuum) estimation from electro-

8996 Kong et al.
Macromolecules, Vol. 36, No. 24, 2003
Sch em e 2
F igu r e 7. (a) EL spectra of single-layer LED from PHPT. (b)
Current density-voltage characteristics of the corresponding
diodes with and without PEDOT.
∼490 nm is seen for all applied voltages (Figure 8a),
with the emission intensity progressively increasing
with increase in applied bias. The EL maximum matches
with the PL emission maximum of PPTF thin film,
suggesting that the same excited-state species is re-
sponsible for both the PL and EL emission. The rela-
tively higher brightness in PPTF than PHPT could be
due to the higher fluorescence quantum yield of PPTF
thin films containing fluorene units along the backbone.
Although the LED brightness and efficiencies using
these new polymers as emissive materials are modest,
we think they could be significantly improved by
optimizing the device architecture.
F igu r e 6. Spectroelectrochemistry of PHPT film on ITO glass
in 0.1 M Bu4NPF6 in acetonitrile at different potentials (vs
SCE). Inset is the CV curve of PHPT film on ITO glass with a
scan rate of 40 mV/s in 0.1 M Bu4NPF6/acetonitrile.
a single-layer LED fabricated from PHPT both with and
without a PEDOT layer, i.e., ITO/PHPT/Al and ITO/
PEDOT/PHPT/Al. Electroluminescence (EL) of very low
brightness levels was observed although the EL spectra
with a maximum at 480 nm (Figure 7a) could be
recorded. The EL spectra are nearly identical to the
previously discussed PL emission spectra. Figure 7b
shows the current-voltage characteristics of 40 nm
thick PHPT diodes with and without PEDOT. The turn-
on voltage for EL was quite low at 4 V in both cases,
and good rectifying diode-like behavior was observed,
indicating good hole injection and transport in PHPT
thin films. The identical turn-on voltage (4 V) of these
diodes with and without PEDOT suggests that holes can
be as efficiently injected into PHPT from ITO as from
PEDOT. The low brightness level of the PHPT single-
layer diodes is likely due to p-type doping near the ITO
electrode, the excessive holes in the diodes, and poor
electron injection and transport. The ITO/PEDOT/
PPTF(60 nm)/Al single-layer devices with the phenothi-
azine-fluorene copolymer showed brightness levels up
to 25 cd/m2, as shown in Figure 8. An EL maximum at
Bilayer devices were made with an electron trans-
port (n-type) polyquinoline, poly(2,2′-biphenyl-6,6′-bis-
(4-phenylquinoline)) (PBPQ),8a and PPTF as the hole
transport and emissive polymer. The EL spectra of
the ITO/PEDOT/PPTF/PBPQ/Al diodes are shown in
Figure 9a. At lower voltages (8.5 V or less), there is a
small contribution from PBPQ in the EL with emission
at ∼550-600 nm from PBPQ in addition to the main
peak at 490 nm from PPTF. As the voltage increases,
the emission originates solely from PPTF with a peak
at 490 nm at 12.5 V. This means that the recombination
zone is located in the PPTF layer at higher electric
fields. Depending on the film thickness of the electron
transport PBPQ layer, one could get emission exclu-
sively from PPTF. The current density-voltage-
luminance characteristics corresponding to the EL

Macromolecules, Vol. 36, No. 24, 2003
Phenothiazine-Based Conjugated Polymers 8997
F igu r e 8. (a) EL spectra of LED from PPTF. (b) Current
density-voltage-luminance characteristics of corresponding
diode. The inset shows the device schematic.
F igu r e 9. (a) EL spectra of bilayer LED from PPTF. (b)
Current density-voltage-luminance characteristics of corre-
sponding diode. The inset shows the device schematic.
spectra of Figure 9a are shown in Figure 9b. The turn-
on voltage of the diode is 5 V with a maximum bright-
ness of 320 cd/m2 and a maximum external quantum
efficiency of 0.10% at 12.5 V. This represents a factor
of 13 enhancement in performance compared to the
single-layer PPTF LED. The use of an electron transport
polymer to improve the performance of blue-green PPTF
electroluminescence confirms the fact that this polymer
is a poor electron acceptor (EA ∼ 2.4 eV, based on the
IP value of 5.1 eV and Eogpt of 2.76 eV) as revealed by
the previously discussed electrochemistry. These results
also suggest that both PHPT and PPTF are promising
as hole transport materials for LEDs and can be used
effectively in multilayer devices3g,h or as blends18 with
electron transport materials.
nonplanar geometry of the phenothiazine ring. The two
polymers have low ionization potentials at 5.0-5.1 eV,
suggesting good potential as p-type (hole transport)
semiconductors in organic devices. Spectroelectrochem-
istry of PHPT showed that this polymer undergoes
electrooxidation to radical cations at low potential (0.66
V vs SCE) and dications at much higher potentials
(>0.83 V). Initial light-emitting diodes fabricated from
PPTF showed blue-green electroluminescence that can
be significantly enhanced to 320 cd/m2 by using an
electron transport polyquinoline to improve electron
injection into the polymer.
Exp er im en ta l Section
Ch em ica ls. Phenothiazine, 10-methylphenothiazine, 1-bro-
mohexane, Aliquat 336, Ni(COD)2, 1,5-cyclooctadiene, tetrakis-
(triphenyl)phosphine palladium, and 2,2′-bipyridine were pur-
chased from Aldrich. Tetrahydrofuran (THF) (99.8%, anhydrous)
and N,N-dimethylformamide (DMF) (99.8%, anhydrous) were
obtained from Aldrich and used as received. 9,9-Dihexylfluo-
rene-2,7-bis(trimethylene boronate) was synthesized from 9,9-
dihexylfluorene-2,7-diborionic acid by the method in the
literature.19 Methylene chloride and methanol (HPLC grade)
were obtained from Fisher Chemicals.
Con clu sion s
New phenothiazine-containing conjugated polymers,
poly(10-hexylphenothiazine-3,7-diyl) (PHPT) and poly-
(10-hexylphenothiazine-3,7-diyl-alt-9,9-dihexyl-2,7-fluo-
rene) (PPTF), were synthesized by Ni(0)-catalyzed and
Suzuki coupling polymerizations, respectively. The mod-
erately high molecular weight polymers are amorphous
with a glass transition temperature of 166 °C. Both
polymers have identical solution and solid-state absorp-
tion and PL emission spectra, from which intermolecu-
lar aggregates and excimers can be excluded from their
photophysics. This result is a consequence of the highly
Ch a r a cter iza tion . UV-vis absorption spectra were ob-
tained on a Perkin-Elmer Lamda 900 spectrophotometer.
Steady-state photoluminescence (PL) studies were done by
using a PTI QM-2001-4 spectrofluorimeter (Photon Technology

8998 Kong et al.
Macromolecules, Vol. 36, No. 24, 2003
International (PTI) Inc.). The PL quantum yields of the
polymers were measured using 10-6 M solutions of the sample
in THF and determined relative to 9,10-diphenylanthracene
(DPA) as a standard (λex ) 380 nm; Φdpa ) 0.91 in benzene).20
Cyclic voltammetry (CV) was done on an EG&G Princeton
Applied Research potentiostat/galvanostat model 273A. The
redox properties of the polymer films were investigated by
doing CV in acetonitrile solution with 0.1 M Bu4NPF6 at room
temperature under nitrogen. A platinum wire electrode coated
with a polymer thin film was used as the working electrode.
Another platinum wire electrode was used as the counter
electrode, and a Ag/Ag+ (0.1 M AgNO3 in acetonitrile) electrode
was used as the reference electrode. The Ag/Ag+ (AgNO3)
reference electrode was calibrated at the beginning of the
experiments by running the CV of ferrocene as the internal
standard in an identical cell without any polymer on the
working electrode. The potential values obtained in reference
to Ag/Ag+ electrode were converted in reference to internal
standard of ferrocene/ferrocenium (E°′ ) 0.424 V vs NHE).12a
GPC analysis of both polymers was done on a Waters GPC
with Shodex gel columns and Waters 150 °C refractive index
detectors at 30 °C with a THF flow rate of 1.0 mL/min. The
molecular weight was calibrated by polystyrene standards.
Thermal analysis was carried out on TA Instruments model
Q50 TGA and Q100 DSC. The TGA and DSC thermograms
were obtained in nitrogen at a heating rate of 10 °C/min. Both
1H NMR and 13C NMR spectra were taken at 500 MHz on a
Bruker WM500 spectrometer.
The light-emitting diodes were fabricated by sequential spin-
casting of the polymer layers onto a cleaned ITO-coated glass
substrate (Delta Technologies Ltd., Stillwater, MN), and an
Al electrode was thermally evaporated through a shadow mask
onto the polymer films by using an AUTO 306 vacuum coater
(BOC Edwards, Wilmington, MA) at base pressures lower than
2 × 10-6 Torr. A 50 nm thick hole injection layer, poly-
(ethylenedioxythiophene) doped with poly(styrenesulfonate)
(PEDOT) was spin-coated on top of ITO from a 1.3 wt %
dispersion in water and dried at 200 °C for 1.5 h under
vacuum. Electroluminescence (EL) spectra were obtained using
a PTI QM-2001-4 spectrofluorimeter. Current-voltage char-
acteristics and luminance of the LEDs were simultaneously
measured using a HP4155A semiconductor parameter ana-
lyzer (Yokogawa Hewlett-Packard, Tokyo) and a model 370
optometer (UDT instruments, Baltimore, MD) equipped with
a calibrated luminance sensor head (model 211), respectively.
Further details of our polymer LED fabrication and charac-
terization can be found in previous reports.3f-h,13
10-Hexylp h en oth ia zin e. In a flame-dried flask attached
with a reflux condenser, 10 g (50 mmol) of phenothiazine was
dissolved in 200 mL of anhydrous THF under argon. 2.2 g of
sodium hydride (60% in mineral oil, 55 mmol) was added into
the clear solution. After stirring for 1 h, 10.52 mL of 1-bromo-
hexane (75 mmol) was added. The mixture was refluxed for
24 h and then poured into 200 mL of water. The product was
extracted with methylene chloride (100 mL × 2), and the
organic layer was dried over anhydrous sodium sulfate. After
purification by silica gel column chromatography with hexane
as eluent, 11.96 g of colorless oil was obtained with 84.5% yield.
1H NMR (CDCl3, TMS), δ (ppm): 7.14 (m, 4H, Ar-H), 6.89,
(m, 2H, Ar-H), 6.85 (d, 2H, Ar-H), 3.82 (t, 2H, CH2N), 1.79,
(m, 2H, CH2), 1.42 (m, 2H, CH2), 1.30 (m, 2H, 2 × CH2), 0.87
(t, 3H, CH3). 13C NMR (CDCl3, TMS), δ (ppm): 145.31, 127.38,
127.12, 124.86, 111.25, 115.32 (Ar-C), 47.39 (CH2N), 31.44,
26.87, 26.65, 22.57, 13.96 (CH3).
3,7-Dibr om o-10-h exylp h en oth ia zin e. 16 g of NaOH (0.4
mmol) was dissolved in 350 mL of acetic acid under argon and
cooled to 5-10 °C with ice-water bath. 14.17 g (50 mmol) of
10-hexylphenothiazine was added, followed with 50 mL of
chloroform under argon. After cooled back to 5-10 °C, 5.14
mL of bromine (100 mmol) in 50 mL of chloroform was added
dropwise. The mixture was stirred for 2 h at room tempera-
ture. All of the solvent was removed by rotary evaporator, and
then the residue solid was dissolved in 200 mL of chloroform
and washed with 5% sodium carbonate solution (200 mL) and
water (200 mL). The purple organic solution was dried over
anhydrous sodium sulfate and purified by silica gel column
flash chromatography with chloroform as eluent. The purple
solution was concentrated and distilled out by Kugel Rohr
distillation under vacuum. The pale yellow liquid was recrys-
tallized in ethanol. 13.2 g of colorless crystal was obtained;
yield 59.8%. 1H NMR (CDCl3, TMS), δ (ppm): 7.30 (m, 4H,
Ar-H), 6.73 (d, J ) 8.65, 2H, Ar-H), 3.78 (t, J ) 7.2, 2H,
CH2N), 1.78 (m, 2H, CH2CH2N), 1.57 (m, 2H, CH2), 1.32 (m,
4H, CH2), 0.91 (t, 3H, CH3). 13C NMR (CDCl3), δ (ppm): 143.83,
129.83, 129.47, 126.24, 116.44, 114.57 (aromatic C), 47.78
(CH2N), 31.57, 26.89, 26.74, 22.81, 14.24 (CH3). ESI-MS (M +
1): 439, 440, 441, 442; calcd M + 1: 439, 440, 441, 442.
P oly(10-h exylp h en oth ia zin e-3,7-d iyl) (P HP T). In a dry
flask, 515 mg of 2,2-bipyridine (3.3 mmol) and 825 mg of
Ni(COD)2 (3.0 mmol) were added in the glovebox. After taking
out the flask from the glovebox, 357 mg of 1,5-cyclooctadene
and 50 mL of anhydrous DMF were injected under argon. The
mixture was stirred at 60 °C for half an hour to obtain a dark
blue catalyst solution. In another dry flask, 1.103 g of 3,7-
dibromo-10-hexylphenothiazine (2.5 mmol) was dissolved in
a mixture of toluene (50 mL) and dry DMF (20 mL) under
argon. The catalyst solution was slowly transferred into the
monomer solution. After stirring for 24 h, the mixture was
poured into 200 mL of methanol. The polymer was purified
by precipitation from THF solution into methanol. After
filtration and drying in a vacuum, 0.540 g of yellow powder
was obtained; yield 77%. 1H NMR (CDCl3, TMS), δ (ppm): 7.30
(b, 4H, Ar-H), 6.86 (b, 2H, Ar-H ortho to MeN), 3.85 (b, 2H,
CH2N), 1.83 (b, 2H, CH2CH2N), 1.45 (b, 2H, CH2), 1.32 (b, 2H,
CH2), 0.88 (b, 3H, CH3). 13C NMR (CDCl3), δ (ppm): 143.96,
134.26, 125.21, 125.15, 124.72, 115.40, 47.59 (CH2N), 31.49,
26.88, 26.70, 22.62, 14.02 (CH3). GPC (THF, PSt standard)
results: Mw ) 1.53 × 104, Mw/Mn ) 3.00.
P oly(10-h exylp h en ot h ia zin e-3,7-d iyl-a lt-9,9-d ih exyl-
2,7-flu or en e) (P P TF ). In a flask, 3,7-dibromo-10-hexylpheno-
thiazine (1.103 g, 2.5 mmol), 9,9-dihexylfluorene-2,7-bis-
(trimethylene boronate) (1.2558 g, 2.5 mmol), sodium carbonate
(20 mmol, 2.12 g), and 0.15 g of Aliquat 336 were added under
argon. 15 mL of degassed toluene and 10 mL of water were
added in. The mixture was stirred until a solution was
obtained, and then tetrakis(triphenyl)phosphine palladium
[Pd(PPh3)4] was added. After the mixture was stirred at 100
°C for 6 h, another 30 mL of toluene was added. The mixture
was stirred for another 66 h and was cooled to room temper-
ature. It was poured into 200 mL of methanol and deionized
water (10:1 v/v). A fibrous solid was obtained by filtration. The
solid was washed with methanol, water, and then methanol.
1.32 g of polymer was obtained as a yellow fibrous solid; yield
1
86%. H NMR (CDCl3), δ (ppm): 7.75 (m, 2H), 7.55 (m, 8H),
6.99 (d, 2H), 3.94 (s, 2H), 2.02 (b, 4H, CH2CCH2), 1.95 (b, 2H,
CH2CH2N), 1.54 (b, 2H), 1.37 (b, 4H), 1.077 (b, 12H), 0.92 (b,
4H), 0.78 (b, 9H, 3 × CH3). 13C NMR (CDCl3), δ (ppm): 151.69,
144.19, 139.82, 138.78, 136.04, 126.02, 125.85, 125.34, 124.73,
120.82, 119.93, 115.46, 55.26, 47.66, 40.50, 31.53, 31.48, 29.73,
26.92, 26.75, 23.81, 22.65, 22.60, 14.01. GPC (THF, PSt
standard) results: Mw ) 1.83 × 105, Mw/Mn ) 6.45.
Ack n ow led gm en t . This research was supported
by a U.S. Army Research Office DURINT Program
(DAAD19-01-1-0499) and in part by the U.S. Army
Research Office TOPS MURI (DAAD19-01-1-0676).
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