Influence of the conjugation pattern on the photophysical properties of alkoxy-substituted PE/PV hybrid polymers

Article abstract of DOI:10.1021/ma030339g

Alkoxy-substituted phenylene-ethynylene (PE)/phenylene-vinylene (PV) hybrid polymers of general constitutional structure (-Ar-C≡C-Ar-CH=CH-)_n (2), (-Ar-C≡C-Ar-CH=CH-Ar-C≡C-)_n (3), and (-Ar-C≡C-Ar-C≡C-Ar-CH=CH-Ar-CH=CH-)_n (4) have been synthesized and characterized. Comparisons of their photophysical properties in solution as well as in solid state (photoconductivity, absorption, emission, and electroluminescence) with those of their corresponding alkoxy-substituted poly(phenylene-ethynylene) (1) and poly(phenylene-vinylene) (5) have been carried out. Large octadecyloxy groups were selected as side chains in order to reduce the effect of π-π stacking interaction on the properties of the polymers in the solid state. This resulted in easy detection of photoconductivity and higher fluorescence quantum yields in solid state. The hybrid conjugation pattern in 4 is more favorable for photoconductivity than that in 2. A red shift of the absorption and emission spectra in solution is observed from 1 over 2b, 3, and 4 to 5. LED devices of ITO/PEDOT/polymer/Ca configuration have been fabricated with all compounds, except 2a. The phenylvinylene side groups in 3 not only give rise to a red shift of the solid-state photoluminescence spectrum and electroluminescence spectrum (relative to 2b) but also bring about a decrease of the turn-on voltage and improve the electroluminescence efficiency for more than 100 times.

Full text of DOI:10.1021/ma030339g

Macromolecules 2003, 36, 9303-9312
9303
Influence of the Conjugation Pattern on the Photophysical Properties of
Alkoxy-Substituted PE/PV Hybrid Polymers
Da n iel Ayu k Mbi Egbe,*,† Cor n elia Ba d er ,† Elisa beth Klem m ,† Lim in g Din g,‡
F r a n k E. Ka r a sz,‡ Ulr ich -Wa lter Gr u m m t,§ a n d Eck h a r d Bir ck n er §
Institut fu¨r Organische Chemie und Makromolekulare Chemie der Friedrich-Schiller-Universita¨t J ena,
Lessingstr. 8, 07743 J ena, Germany; Department of Polymer Science and Engineering, University of
Massachusetts, Amherst, Massachusetts 01003; and Institut fu¨r Physikalische Chemie der
Friedrich-Schiller Universita¨t J ena, Lessingstr. 10, D-07743 J ena, Germany
Received J une 17, 2003; Revised Manuscript Received September 18, 2003
ABSTRACT: Alkoxy-substituted phenylene-ethynylene (PE)/phenylene-vinylene (PV) hybrid polymers
of general constitutional structure (-Ar-CtC-Ar-CHdCH-)n (2), (-Ar-CtC-Ar-CHdCH-Ar-
CtC-)n (3), and (-Ar-CtC-Ar-CtC-Ar-CHdCH-Ar-CHdCH-)n (4) have been synthesized and
characterized. Comparisons of their photophysical properties in solution as well as in solid state
(photoconductivity, absorption, emission, and electroluminescence) with those of their corresponding
alkoxy-substituted poly(phenylene-ethynylene) (1) and poly(phenylene-vinylene) (5) have been carried
out. Large octadecyloxy groups were selected as side chains in order to reduce the effect of π-π stacking
interaction on the properties of the polymers in the solid state. This resulted in easy detection of
photoconductivity and higher fluorescence quantum yields in solid state. The hybrid conjugation pattern
in 4 is more favorable for photoconductivity than that in 2. A red shift of the absorption and emission
spectra in solution is observed from 1 over 2b, 3, and 4 to 5. LED devices of ITO/PEDOT/polymer/Ca
configuration have been fabricated with all compounds, except 2a . The phenylvinylene side groups in 3
not only give rise to a red shift of the solid-state photoluminescence spectrum and electroluminescence
spectrum (relative to 2b) but also bring about a decrease of the turn-on voltage and improve the
electroluminescence efficiency for more than 100 times.
In tr od u ction
ing alkoxy-substituted poly(phenylene-ethynylene) (PPE,
1) and poly(phenylene-vinylene) (PPV, 5) have also
been synthesized and characterized. The above-men-
tioned comparison takes into account the hybrid poly-
mer 4, whose synthesis has been described elsewhere
(Chart 1).20
The discovery of electroluminescence in poly(phen-
ylene-vinylene)s (PPV) by Burroughes et al.1 paved the
way to intensified studies of the properties of the
derivatives of PPV, making them the most thoroughly
investigated type of semiconducting polymers.2-5 PPVs
have mostly been used as active layer in the design of
light-emitting diodes. Their poor electron-accepting
nature resulted in low electroluminescence efficiencies
in the early monolayered LED devices.1,4 To circumvent
this problem, many approaches to enhance the electron
affinity of PPVs have been proposed in the literature,6-14
the most recent one of which has been the incorporation
of triple bonds (-CtC-) into the polymer backbone,
leading to phenylene-vinylene/phenylene-ethynylene
hybrid polymers.15-21
Alkyl-substituted hybrid polymers of the general
chemical structure (-Ar-CtC-Ar-CHdCH-)n were
synthesized through Mo(CO)6-catalyzed acyclic diyne
metathesis by Bunz et al.15 The absorption bands of
alkyl-substituted conjugated polymers are blue-shifted
compared to their corresponding alkoxy-substituted
congeners due to less electron-donating nature of alkyl
groups and strong steric hindrance.22 In this article we
report the synthesis and characterization of alkoxy-
substituted hybrid polymers 2 (having the same general
structure as those of Bunz) and 3 (bearing styryl side
groups). For the purpose of comparison, the correspond-
Exp er im en ta l Section
In str u m en ta tion . 1H NMR and 13C NMR spectra were
obtained in deuterated chloroform using a Bruker DRX 400
and a Bruker AC 250. Chemical shifts (δ values) are given in
parts per million with tetramethylsilane as an internal
standard. Elemental analysis was measured on a CHNS-932
Automat Leco. Infrared spectroscopy was recorded on a Nicolet
Impact 400. A homemade apparatus served for the thermo-
gravimetric measurements. Differential scanning calorimetry
(DSC) was obtained with a Perkin-Elmer DSC 2C while
heating at a rate of 10 °C/min. Gel permeation chromatography
(GPC) was performed on a set of Knauer using THF as eluent
and polystyrene as a standard. The absorption spectra were
recorded in dilute chloroform solution (10-5-10-6 M) on a
Perkin-Elmer UV/vis-NIR spectrometer Lambda 19. Quantum-
corrected emission spectra were measured in dilute chloroform
solution (10-6 M) with a LS 50 luminescence spectrometer
(Perkin-Elmer). Photoluminescence quantum yields were cal-
culated according to Demas and Crosby23 against quinine
sulfate in 0.1 N sulfuric acid as a standard (φfl ) 55%). The
solid-state absorption and emission were measured with a
Hitachi F-4500 spectrometer. The films were spin-casted from
chlorobenzene solutions (concentration 10-2-10-3 M). The
quantum yield in the solid state was determined against a
CF3P-PPV (poly{1,4-phenylene-[1-(4-trifluoromethylphenyl)-
ethenylene]-2,5-dimethoxy-1,4-phenylene-[2-(4-trifluorometh-
ylphenyl)ethenylene]}) copolymer reference that has been
measured by integrating sphere as 0.43.24
† Institut fu¨r Organische Chemie und Makromolekulare Chemie
der Friedrich-Schiller-Universita¨t J ena.
‡ University of Massachusetts.
§ Institut fu¨r Physikalische Chemie der Friedrich-Schiller Uni-
versita¨t J ena.
LED F a br ica tion a n d Mea su r em en t. PEDOT/PSS (Bay-
er Co.) was spin-cast onto ITO glass (OFC Co.) to be used as
an anode. The polymer solutions (20 mg/mL in chloroform)
* Corresponding author: e-mail c5ayda@uni-jena.de.
10.1021/ma030339g CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/14/2003

9304 Egbe et al.
Macromolecules, Vol. 36, No. 25, 2003
Ch a r t 1
96 mmol), and NaBr (3.7 g, 36 mmol) in glacial acetic acid
(160 mL) was heated at 100-110 °C. A mixture of concentrated
sulfuric acid (10 g) and glacial acetic acid (10 g) was added
dropwise, and the reaction mixture was stirred for 2 days at
100-110 °C. After the reaction mixture was cooled at 0 °C,
the precipitate was filtered off, washed with water, and
recrystallized from hexane (100 mL). 7.9 g (70%) of white solid
was obtained. Mp: 82-84 °C. 1H NMR (250 MHz, CDCl3):
δ/ppm ) 0.88f1.86 (70H, m, -(CH2)16CH3)), 3.88f 4.03 (4H,
m, -CH2O-), 4.52 and 4.55 (2H, 2s, -CH2P-), 6.80f7.13
(2H, m, Caryl-H). 13C NMR (62 MHz, CDCl3): δ/ppm ) 14.49,
23.07, 26.39, 29.68, 29.75, 29.96, 29.98, 30.05, 30.09, 32.32
(CH3(CH2)16-), 29.11 (-CH2Br), 69.43, 69.60, 70.64 (-CH2O-
), 113.62, 115.06, 116.46, 117.81, 126.48, 127.93, 149.89,
151.07, 151.61, 152.35 (Caryl’s). Anal. Calcd for C43H78O2Br2
(786.92): C, 65.65; H, 9.99; Br, 20.30. Found: C, 65.29; H, 9.58;
Br, 20.30.
4-Bromo-2,5-dioctadecyloxybenzyldiethylphosphonate (10). A
mixture of 9 (2.6 g, 3.3 mmol) and an excess of triethyl
phosphite (1 g, 6 mmol) was heated slowly to 160 °C, and the
evolving ethyl bromide was distilled off simultaneously. After
heating 3 h at 160 °C, vacuum was applied for 1 h at 180 °C.
The resulting oil solidified after cooling at room temperature.
It was recrystallized from hexane (10 mL). 1.8 g (75%) of white
solid was obtained. Mp: 61-62 °C. 1H NMR (250 MHz,
CDCl3): δ/ppm ) 0.87f1.84 (76H, m, -(CH2)16CH3 and
CH3-ethyl), 3.20 (2H, d, 3J ) 21.71 Hz, -CH2P-), 3.89f 4.11
(8H, m, -CH2O-), 6.98 and 7.05 (2H, s, Caryl-H). 13C NMR
(62 MHz, CDCl3): δ/ppm ) 14.50 (CH3-octadecyl), 16.72 and
16.81 (CH3-ethyl), 23.08, 25.63, 26.38, 26.47, 27.85, 29.75,
29.99, 30.09, 32.31 (-(CH2)16-), 62.29 and 62.39 (-CH2O-
ethyl), 69.68 and 70.50 (-CH2O- octadecyl), 111.06, 111.13,
117.09, 117.17, 117.31, 117.36, 120.72, 120.86, 149.71,
149.77, 151.43, 151.55 (Caryl’s). Anal. Calcd for C47H88BrO5P
(844.0905): C, 66.88; H, 10.51; Br, 9.47. Found: C, 67.80; H,
10.17; Br, 9.62.
1-(4-Bromophenyl)-2-(4-bromo-2,5-dioctadecyloxyphenyl)eth-
ylene (12a ). A solution of 4-bromobenzaldehyde (11a ) (1.0 g,
5.40 mmol) and 10 (4.5 g, 5.4 mmol) in toluene (100 mL) was
heated at reflux under argon. Potassium tert-butoxide (1.21
g, 10.8 mmol) was added portionwise to it, and the mixture
was heated for 3 h under reflux. The reaction was quenched
with 5% aqueous HCl (20 mL). It was then extracted with
water until neutrality. After drying the toluene solution, the
solvent was removed under vacuum, and the resulting solid
was chromatographed on a silica gel column using toluene as
eluent. The obtained yellow substance was washed with little
amount of methanol and dried. Yield: 3.6 g (76%). 1H NMR
(250 MHz, CDCl3): δ/ppm ) 0.78f 2.28 (70H, m, CH3(CH2)16-),
3.31 (t, 3J ) 6.66 Hz, -CH2O-), 3.51 (t, 3J ) 6.62 Hz,
-CH2O-), 3.81f 3.99 (4H, -CH2O-), 6.55f7.41 (phenyl and
vinylene H’s). 13C NMR (62 MHz, CDCl3): δ/ppm ) 14.10,
22.69, 26.02, 26.19, 26.30, 29.29, 29.36, 29.61, 29.70, 31.93
(CH3(CH2)16-), 69.61, 70.36 (-CH2O-), 111.81, 112.28, 117.89,
121.27, 123.87, 124.24, 125.59, 126.16, 126.78, 127.97, 128.09,
130.47, 131.34, 131.77, 136.68, 136.91, 149.86, 151.17 (phenyl
and vinylene C’s). UV-vis (THF): λmax/nm (ꢀ/(L mol-1 cm-1)):
297.6 (24 700), 346.4 (22 900). Anal. Calcd for C50H82Br2O2
(875.01): C, 68.63; H, 9.45. Found: C, 70.04; H, 9.72.
were filtered through 0.2 µm Millex-FGS Filters (Millipore Co.)
and were spin-cast onto dried PEDOT/ITO substrates under
a nitrogen atmosphere. The polymer films were typically 75
nm thick. Calcium electrodes of 400 nm thickness were
evaporated onto the polymer films at about 10-7 Torr, followed
by a protective coating of aluminum. The devices were
characterized using a homemade system, which has been
described elsewhere.25
Ma ter ia ls. All starting materials were purchased from
commercial suppliers (Fluka, Merck, and Aldrich). Toluene,
tetrahydrofuran, and diethyl ether were dried and distilled
over sodium and benzophenone. Diisopropylamine was dried
over KOH and distilled. If not otherwise specified, the solvents
were degassed by bubbling with argon or nitrogen 1 h prior to
use.
Bromohydroquinone (7). A solution of bromine (47 mL, 0.45
mol) in 200 mL of acetic acid was added slowly and dropwise
within 2-3 h in a cooled (ice bath) suspension of hydroquinone
(6) (100 g, 0.9 mol) in 1 L of acetic acid. The mixture was
further stirred for 2 h while keeping the temperature between
2 and 8 °C. Acetic acid was removed under reduced pressure,
and the residue was recrystallized twice from a 20 to 1 mixture
of chloroform and ethanol. 100 g (58%) of white solid was
obtained. 1H NMR (250 MHz, CDCl3): δ/ppm ) 6.75 (m), 6.94
(d, 3J ) 8.76 Hz), 7.01 (d, 4J ) 2.87 Hz), 7.28 (s). 13C NMR
(62.89 MHz, CDCl3): δ/ppm ) 110.18, 110.29, 116.59, 116.72,
116.76, 118.90, 119.96, 146.97, 147.06, 149.88 (Caryl’s). Anal.
Calcd for C6H5O2Br (189.00): C, 38.13; H, 2.67. Found: C,
38.44; H, 2.66.
1-Bromo-2,5-dioctadecyloxybenzene (8). A suspension of
KOH powder (56.1 g, 1 mol) in dried DMSO (300 mL) was
stirred and degassed in a 500 mL three-neck flask for 1 h.
2-Bromohydroquinone (7) (14.8 g, 0.078 mol) and octadecyl
bromide (104.0 g, 0.312 mol) were then added, whereby the
temperature rose to 30 °C. The reaction mixture was stirred
for 8 h at room temperature and finally poured into ice water.
The precipitated product was filtered and washed with water
and ethanol. The recrystallization from 500 mL of toluene/
ethanol (4/1) gave 50 g (92%) of colorless crystals. Mp: 68-70
°C. 1H NMR (250 MHz, CDCl3): δ/ppm ) 0.88f1.91 (70H, m,
-(CH2)16CH3)), 3.88f 4.00 (4H, m, -CH2O-), 6.77f6.87 (2H,
m, Caryl-H), 7.13 (1H, d, 4J ) 2.40 Hz, Caryl-H). 13C NMR
(62 MHz, CDCl3): δ/ppm ) 12.30, 20.89, 24.20, 24.42, 26.39,
26.98, 27.49, 27.56, 27.77, 27.79, 27.90, 30.13, 31.06, 32.18
(CH3(CH2)16-), 67.07, 68.49, 69.17 (-CH2O-), 111.05, 112.26,
112.62, 112.99, 113.63, 117.74, 148.01, 151.83 (Caryl’s). Anal.
Calcd for C42H77O2Br (693.976): C, 72.69; H, 11.18; Br, 11.51.
Found: C, 73.02; H, 10.90; Br, 11.87.
1-(4-Trimethylsilylethynylenephenyl)-2-(4-trimethylsilylethy-
nylene-2,5-dioctadecyloxyphenyl)ethylene (13a ). A solution of
12a (3.6 g, 4.1 mmol) in diisopropylamine (60 mL) was
degassed for 1 h. Pd(PPh3)4 (140 mg, 0.2 mmol) and CuI (0.2
mg, 0.2 mmol) were given to it. Trimethylsilylacetylene (0.88
g, 9 mmol) was added dropwise to it. The reaction mixture
was then stirred for 4 h at 80 °C. After cooling, the ammonium
bromide precipitate was filtered off. The solvent was removed
on a rotary evaporator; the remaining solid was dissolved in
toluene and purified through silica gel column chromatography
with toluene as eluent. 3.3 g (80%) of a brown-yellowish
substance were thus obtained. 1H NMR (250 MHz, CDCl3):
δ/ppm ) 0.00f0.07 ((CH3)3Si-), 0.66f 1.98 (CH3(CH2)16-),
3.20f3.85 (-CH2O-), 6.45f7.32 (phenylene and vinylene
H’s). 13C NMR (62 MHz, CDCl3): δ/ppm ) -0.12, 0.38, 0.42
((CH3)3Si-), 14.51, 23.08, 26.47, 26.60, 29.75, 29.89, 30.09,
1-Bromo-4-bromomethyl-2,5-dioctadecyloxybenzene (9). A
suspension of 8 (10 g, 14.4 mmol), paraformaldehyde (2.8 g,

Macromolecules, Vol. 36, No. 25, 2003
Alkoxy-Substituted PE/PV Hybrid Polymers 9305
32.32 (CH3(CH2)16-), 69.76, 70.13 (-CH2O-), 95.46, 99.73
(-C≡C-), 105.64, 111.20, 113.31, 117.71, 122.43, 124.62,
126.72, 128.22, 129.45, 132.67, 138.26, 150.89, 155.04 (phen-
solid was filtered, dissolved in toluene, and purified over a
silica gel column with toluene as eluent. 3 g (79%) of brown-
orange solid were obtained. 1H NMR (250 MHz, CDCl3): δ/ppm
) 0.88f 1.88 (CH3(CH2)16- and CH3(CH2)6-), 3.34 (-C≡C-
H), 3.64f4.10 (-CH2O-), 6.71f7.47 (phenylene and vinylene
H’s). 13C NMR (62 MHz, CDCl3): δ/ppm ) 14.50, 23.08, 26.00,
26.56, 29.71, 29.75, 30.10, 32.24, 32.32 (CH3(CH2)16- and
CH3(CH2)6-), 69.76, 70.16 (-CH2O-), 80.85, 81.95 (-C≡C-),
111.18, 111.89, 118.18, 124.87, 129.27, 150.78, 155.04 (phen-
ylene and vinylene C’s). Anal. Calcd for C70H116O4 (1021.69):
C, 82.29; H, 11.44. Found: C, 81.39; H, 11.20.
ylene and vinylene C’s). Anal. Calcd for
C60H100O2Si2
(909.62): C, 79.23; H, 11.08. Found: C, 78.66; H, 10.90.
1-(4-Ethynylphenyl)-2-(4-ethynyl-2,5-dioctadecyloxyphenyl)-
ethylene (14a ). A solution of 2.3 mL of aqueous KOH (20%) in
26 mL of methanol was added dropwise to a stirred solution
of the trimethylsilyl derivative 13a (3.3 g, 3.62 mmol) in 50
mL of THF. The reaction was stirred for 1 day at room
temperature. A black greaselike precipitate was obtained,
which was subsequently extracted twice with ethanol to
provide 1.2 g (43%) of a yellow substance. 1H NMR (250 MHz,
CDCl3): δ/ppm ) 0.78f 1.78 (70H, m, CH3(CH2)16-), 3.06 (1H,
s, ≡C-H), 3.19 (1H, s, ≡C-H), 3.31 (t, 3J ) 6.68 Hz, -CH2O-
Poly[1,4-(2,5-dioctadecyloxyphenylene)ethynylene-1,4-(2,5-
dioctyloxyphenylene)ethene-1,2-diyl] (2b). Dibromo derivative
12b (2.00 g, 1.76 mmol), diethynyl derivative 14b (1.806 g,
1.76 mmol), Pd(PPh3)4 (82 mg, 7.07 × 10-2 mmol, 4 mol %),
and CuI (13.4 mg, 7.07 × 10-2 mmol, 4 mol %) were added to
a degassed solution of diisopropylamine (15 mL) and toluene
(40 mL). After degassing for a further 30 min, the reaction
was then stirred for 3 days at 80 °C. The precipitated
diisopropylammonium bromide was filtered off. Aqueous HCl
was given to the filtrate, and the organic phase was extracted
with water until neutrality (pH ) 6-7). The organic phase
was dried in a Dean-Stark apparatus, filtered and evaporated
to 50 mL, and precipitated in 300 mL of methanol. The
polymer was extracted for 1 day with methanol and dried
under vacuum at 50 °C. 2.9 g (85%) of a magenta substance
were obtained. GPC (THF): Mh n ) 8600 g/mol, Mh w ) 34 000
g/mol, Mh z ) 91 000 g/mol, Mp ) 18 000 g/mol; polydispersity
index ) 3.94. 1H NMR (400 MHz, CDCl3): δ/ppm ) 0.85f 1.84
(100H, CH3(CH2)16- and CH3(CH2)6-), 3.62f4.09 (8H, -CH2O-
), 6.6f7.13 (4H, arylene H’s), 7.40f7.47 (2H, vinylene H’s).
13C NMR (100 MHz, CDCl3): δ/ppm ) 14.47, 23.07, 26.52,
26.64, 29.76, 29.91, 30.12, 32.32 (CH3(CH2)16- and CH3(CH2)6-
), 69.79, 70.42, 71.37 (-CH2O-), 91.76 (-C≡C-), 111.68,
117.58, 118.34 (Cphenyl-H), 124.60 (vinylene C’s), 113.98, 128.80
(Cphenyl-C), 151.10, 154.44 (Cphenyl-OR). UV-vis (CHCl3, 1.28
3
3
), 3.89 (2H, t, J ) 6.50 Hz, -CH2O-), 3.98 (2H, t, J ) 6.60
Hz, -CH2O-), 6.84f7.45 (8H, phenylene and vinylene H’s).
13C NMR (62 MHz, CDCl3): δ/ppm ) 14.52, 23.09, 26.36, 26.60,
29.71, 29.76, 30.01, 30.10, 32.32 (CH3(CH2)16-), 69.78, 70.23,
71.37 (-CH2O-), 80.74, 82.11, 84.15 (-CtC-), 111.14, 112.20,
118.16, 121.45, 124.78, 126.83, 128.45, 129.52, 132.84, 138.54
(phenylene and vinylene C’s), 150.86, 155.00 (Cphenyl-OR).
Anal. Calcd for C54H84O2 (765.26): C, 84.75; H, 11.06. Found:
C, 66.09; H, 9.35.
1-(4-Bromo-2,5-dioctyloxyphenyl)-2-(4-bromo-2,5-diocta -
decyloxyphenyl)ethylene (12b). A solution of 4-bromo-2,5-
dioctyloxybenzaldehyde (11b) (1.0 g, 2.26 mmol) and 10 (1.90
g, 2.26 mmol) in toluene (50 mL) was heated at reflux under
argon. Potassium tert-butoxide (1.21 g, 10.8 mmol) was added
in two portions to it, and the mixture was heated for 3 h under
reflux. The reaction was quenched with 5% aqueous HCl (20
mL). It was then extracted with water until neutrality. After
drying the toluene solution, the solvent was removed under
vacuum, and the resulting solid was chromatographed on a
silica gel column using toluene as eluent. The obtained yellow
substance was washed with a little amount of methanol and
dried. Yield: 1.92 g (75%). 1H NMR (250 MHz, CDCl3): δ/ppm
) 0.79f2.28 (100H, m, CH3(CH2)16- and CH3(CH2)6-), 3.30
f 3.97 (8H, m, -CH2O-), 6.61f 7.33 (phenyl and vinylene
H’s). 13C NMR (62 MHz, CDCl3): δ/ppm ) 14.48, 23.07,
26.39, 26.45, 26.53, 29.44, 29.65, 29.75, 30.09, 32.23, 32.32
(CH3(CH2)16- and CH3(CH2)6-), 69.26, 69.99, 70.68 (-CH2O-
), 112.26, 115.21, 118.28, 124.18, 125.77, 127.42, 150.26, 151.49
× 10-5 M):
λ
max/nm (ꢀ/(L mol-1 cm-1)): 323 (19 420), 454
(29 600). Anal. Calcd for (C68H114O4)n (995.65)n: C, 82.03; H,
11.54. Found: C, 80.27; H, 11.05; Br, 2.47.
Poly[1,4-phenyleneethynylene-1,4-(2,5-dioctadecyloxyphen-
ylene)ethene-1,2-diyl] (2a ). Dibromo derivative 12a (800 mg,
0.914 mmol), diethynyl derivative 14a (1.806 g, 1.76 mmol),
Pd(PPh3)4 (42.2 mg, 3.62 × 10-2 mmol, 4 mol %) and CuI (7
mg, 3.62 × 10-2 mmol, 4 mol %) were added to a degassed
solution of diisopropylamine (7.5 mL) and toluene (20 mL).
After degassing for further 30 min, the reaction was then
stirred 50 h at 80 °C. The precipitated diisopropylammonium
bromide was filtered off. Aqueous HCl was given to the filtrate,
and the organic phase was extracted with water until neutral-
ity (pH ) 6-7). The organic phase was dried in a Dean-Stark
apparatus, filtered, and precipitated in 200 mL of methanol.
The polymer was extracted for 1 day with methanol and dried
under vacuum at 50 °C. 1 g (74%) of an orange-brown
(phenyl and vinylene C’s). UV-vis (THF):
λmax/nm
(ꢀ/(L mol-1 cm-1)): 292.8 (19 420), 362.4 (25 270). Anal. Calcd
for C66H114Br2O4 (1131.45): C, 70.06; H, 10.15; Br, 14.12.
Found: C, 70.55; H, 10.10; Br, 13.69.
1-(4-Trimethylsilylethynylene-2,5-dioctyloxyphenyl)-2-(4-tri-
methylsilylethynylene-2,5-dioctadecyloxyphenyl)ethylene (13b).
A solution of 12b (5.7 g, 5 mmol) in diisopropylamine (70
mL) was degassed for 1 h. Pd(PPh3)4 (175 mg, 0.25 mmol) and
CuI (47.6 mg, 0.25 mmol) were added to it. Trimethylsilyl-
acetylene (1.08 g, 11 mmol) was added dropwise to it. The
reaction mixture was then stirred at reflux for 4 h. After
cooling, the ammonium bromide precipitate was filtered off.
The solvent was removed on a rotary evaporator; the remain-
ing solid was dissolved in toluene and purified through silica
gel column chromatography with toluene as eluent. 4.6 g
substance was obtained. GPC (THF): Mh n ) 6000 g/mol, Mh w
)
26 500 g/mol, Mh z ) 70 090 g/ mol, Mp ) 12 900 g/mol;
polydispersity index ) 4.46. 1H NMR (250 MHz, CDCl3):
δ/ppm ) 0.80f 1.79 (70H, CH3(CH2)16-), 3.32 and 3.95 (4H,
-CH2O-), 6.96f7.45 (8H, phenylene and vinylene H’s). 13C
NMR (62 MHz, CDCl3): δ/ppm ) 14.13, 22.71, 26.13, 29.73,
31.94 (CH3(CH2)16-), 69.37 (-CH2O-), 126.49, 128.01, 131.86
1
(80%) of a yellow substance was thus obtained. H NMR (250
MHz, CDCl3): δ/ppm ) 0.05f0.09 ((CH3)3Si-), 0.68f 1.98
(CH3(CH2)16-and CH3(CH2)6-),3.20f3.85(-CH2O-),6.45f7.27
(phenylene and vinylene H’s). 13C NMR (62 MHz, CDCl3):
δ/ppm ) -0.55, 0.00 ((CH3)3Si-), 14.04, 14.06, 22.64, 26.08,
26.14, 29.32, 29.44, 29.50, 29.67, 31.84, 31.89 (CH3(CH2)16-
and CH3(CH2)6-), 69.32, 69.60 (-CH2O-), 99.10, 101.69
(-C≡C-), 110.77, 112.55, 117.31, 124.31, 125.81, 128.62,
150.27, 150.39, 154.65 (phenylene and vinylene C’s). Anal.
Calcd for C76H132O4Si2 (1166.05): C, 78.28; H, 11.41. Found:
C, 77.25; H, 10.87.
1-(4-Ethynyl-2,5-dioctyloxyphenyl)-2-(4-ethynyl-2,5-dioctade-
cyloxyphenyl)ethylene (14b). A solution of 2.3 mL of aqueous
KOH (20%) in 26 mL of methanol was added dropwise to a
stirred solution of 7b in 52 mL of THF. The reaction was
stirred 3 h at room temperature. The diethynyl compound
precipitated after standing for long time. The brown-yellow
(phenylene and vinylene C-H). IR (KBr): 3066 (w, Cphenyl
-
H), 2920 and 2850 (vs, -CH2-, CH3-), 1600 (w, -CdCphenyl),
1207 (s, Cphenyl-OR), 968 cm-1 (m, trans -CHdCH-). UV-
vis (CHCl3, 1.8 × 10-5 M): λmax/nm (ꢀ/(L mol-1 cm-1)): 432.4
(29 370). Anal. Calcd for (C52H82O2)n (739.22)n: C, 84.49; H,
11.18. Found: C, 81. 49; H, 10.68; Br, 2.58.
Poly[1,4-(2,5-bis(tra ns-styryl)phenylene)ethynylene-1,4-
(2,5-dioctadecyloxyphenylene)ethynylene-1,4-(2,5-dioctyloxy-
phenylene)ethene-1,2-diyl] (3). trans,trans-2,5-Distyryl-1,4-di-
bromobenzene (15) (438 mg, 1 mmol), 14b (1021 mg, 1 mmol),
Pd(PPh3)4 (46 mg, 4 × 10-2 mmol, 4 mol %), and CuI (7 mg, 4
× 10-2 mmol, 4 mol %) were added to a degassed solution of
diisopropylamine (20 mL), toluene (80 mL), and THF (20 mL).
After stirring for 24 h at 65-70 °C, 2 mL of phenylacetylene
and 2 mL of bromobenzene were added to the reacting mixture,

9306 Egbe et al.
Macromolecules, Vol. 36, No. 25, 2003
Sch em e 1a
a
(i) Br2, CH3COOH, 5 °C. (ii) C18H37Br, KOH, DMSO, Ar. (iii) (CH2O)n, NaBr/H2SO4, CH3COOH. (iv) P(OCH2CH3)3, 180 °C. (v)
t-BuOK, toluene, 3-4 h, 110 °C. (vi) (CH3)3SiC2H, diisopropylamine, (PPh3)2Cl2/CuI, 3-4 h, Ar. (vii) KOH/MeOH, THF, 3 h. (viii)
Pd(PPh3)4/CuI, diisopropylamine, toluene, 3 days, 80 °C.
and the reaction was allowed to continue for further 24 h. After
cooling to room temperature, the mixture was poured on a 2
cm plug of silica gel 60 to remove the diisopropylammonium
bromide salt and the catalysts. The plug was washed with
toluene. The combined filtrate was reduced to 100 mL under
vacuum and was added dropwise into 500 mL of stirred
methanol. The precipitate was extracted 9 h with methanol,
dissolved in 80 mL of toluene, and reprecipitated in a methanol/
ethanol (9/1) mixture. 1058 mg (81.4%) of an brown-red
substance was obtained after drying in a vacuum. GPC
(THF): Mh n ) 18 000 g/mol, Mh w ) 85 000 g/mol, Mh z ) 315 000
g/mol, Mp ) 36 800 g/mol; polydispersity index ) 4.7. VPO
(CHCl3): Mn ) 35 000 g/mol. 1H NMR (400 MHz, CDCl3):
δ/ppm ) 0.79f 1.85 (100H, CH3(CH2)16- and CH3(CH2)6-),
4.03f4.11 (8H, -CH2O-), 6.99f7.99 (22H, vinylene and
phenylene H’s). 13C NMR (100 MHz, CDCl3): δ/ppm ) 14.5f
32.33 (CH3(CH2)16- and CH3(CH2)6-), 69.81, 70.40 (-CH2O-
), 111.42, 117.36, 127.35, 128.27, 129.05, 137.74 (phenylene
and vinylene C’s). IR (FTIR): 3030 (w, Cphenyl-H), 2921 and
2852 (vs, -CH2-, CH3-), 2202 (w, disubst -CtC-), 1598 (w,
-CdCphenyl), 1205 (s, Cphenyl-OR), 960 cm-1 (m, trans -CHd
(s,trans-CHdCH-). UV-vis (CHCl3): λ
max/nm (ꢀ/(L mol-1
cm-1)) 328 (15 962), 488.4 (43 211). Anal. Calcd for (C68H116O4)n
(997.67)n: C, 81.87; H, 11.72. Found: C, 81.38; H, 11.51.
Poly(2,5-diocta decyloxyphenyleneethynylene-2,5-dioctyl-
oxyphenyleneethynylene) (1). 1,4-Diiodo-2,5-dioctyloxybenzene
(16) (1 g, 1.7 mmol), 1,4-diethynyl-2,5-dioctadecyloxybenzene
(17) (1.127 g, 1.7 mmol), Pd(PPh3)4 (70 mg, 0.0605 mmol), and
CuI (13 mg, 0.0605 mmol) were added to a degassed solution
of diisopropylamine (20 mL) and toluene (40 mL). The mix-
ture was heated at 85-90 °C. After a reaction time of 12 h,
0.5 mL of phenylacetylene was added; 14 h later 0.5 mL of
bromobenzene was also added. The reaction mixture was
heated at 85-90 °C for further 8 h and was allowed to cool to
room temperature. The ammonium iodide salt was filtered off
and washed with toluene; the combined filtrate was evaporated
to ca. 70 mL and precipitated in 300 mL of methanol. The
resulting substance was extracted in hot methanol, dissolved
in toluene, and reprecipitated in acetone. After drying in a
vacuum at 50 °C, 1.5 g (90%) of dark yellow polymer was
obtained. GPC (THF): Mh n ) 28 000 g/mol, Mh w ) 71 000 g/mol,
Mh z ) 158 000 g/mol, Mp ) 41 000 g/mol; polydispersity index
) 2.53. 1H NMR (400 MHz, CDCl3): δ/ppm ) 0.80 f1.84
(CH3(CH2)16- and CH3(CH2)6-), 3.62 and 4.01 (-CH2O-),
6.99, 7.31, and 7.51 (phenylene H’s). 13C NMR (100 MHz,
CDCl3): δ/ppm ) 14.40, 21.89, 23.03, 26.43, 27.83, 29.70, 29.81,
30.08, 32.29 (CH3(CH2)16- and CH3(CH2)6-), 70.29 (-CH2O-
), 92.00 (-CtC-), 114.99 (Cphenyl-C≡), 118.04 (Cphenyl-H),
154.066 (Cphenyl-OR). IR (FTIR): 2920 and 2852 (vs, -CH2-,
CH3-), 2205 (w, disubst -CtC-), 1598 (w, -CdCphenyl), 1211
CH-). UV-vis (CHCl3, 9 × 10-6 M):
λ
max/nm (ꢀ/(L mol-1
cm-1)): 336.8 (43 700), 368 (44 800), 460.8 (56 200). Anal. Calcd
for (C92H130O4)n (1300.04)n: C, 85.00; H, 10.08. Found: C, 83.61;
H, 10.39; Br, 0.15.
Poly[2,5-diocta decyloxyphenyleneethene-1,2-diyl-2,5-di-
octyloxyphenyleneethene-1,2-diyl] (5). 2,5-Dioctyloxyterephthal-
adehyde (18) (1.00 g, 2.56 mmol) and 2,5-dioctadecyloxy-p-
xylylenebis(diethylphosphonate) (19) (2.343 g, 2.56 mmol) were
dissolved in dried toluene (50 mL) while stirring vigorously
under argon and heating under reflux. Potassium tert-butoxide
(1.14 g, 10.24 mmol) was added to this solution. After 2 h
heating at reflux, the reaction was quenched with aqueous
HCl. The organic phase was separated and extracted several
times with distilled water until the water phase became
neutral (pH ) 6-7). The organic layer was dried in a Dean-
Stark apparatus. The resulting toluene solution was filtered,
evaporated to the minimum (50 mL), and precipitated in
methanol (300 mL). The resulting precipitate was extracted
for 8 h with methanol and dried under vacuum. 1.7 g (68%) of
bright red polymer was obtained. GPC (THF): Mh n ) 6600
g/mol, Mh w ) 10 300 g/mol, Mh z ) 15 300 g/mol, Mp ) 7400 g/mol;
polydispersity index ) 1.55. 1H NMR (250 MHz, CDCl3): δ/ppm
) 0.77 f1.78 (CH3(CH2)16- and CH3(CH2)6-), 3.53 and 3.97
(-CH2O-), 6.66f7.41 (phenylene and vinylene H’s). 13C NMR
(62 MHz, CDCl3): δ/ppm ) 14.12, 22.70, 26.33, 29.40, 29.75,
31.93 (CH3(CH2)16- and CH3(CH2)6-), 69.51 (-CH2O-), 110.54,
123.34, 127.47, 151.10 (phenylene and vinylene C’s). IR
(FTIR): 3058 (w, Cphenyl-H), 2920 and 2850 (vs, -CH2- and
CH3-), 1600 (w, -CdCphenyl), 1204 (vs, Cphenyl-OR), 966 cm-1
cm-1 (s, Cphenyl-OR). UV-vis (CHCl3):
λ
max/nm (ꢀ/(L mol-1
cm-1)) 313 (13 130), 435.2 (23 230). Anal. Calcd for (C68H112O4)n
(993.64)n: C, 82.20; H, 11.36. Found: C, 81.53; H, 11.05; I,
1.14.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . Polymers 2 were
obtained in an eight step synthetic route starting from
hydroquinone (6), as illustrated in Scheme 1. The mono-
bromination of 6 in cooled acetic gave 2-bromohydro-
quinone (7) in 58% yield. 2-Bromo-1,4-dioctadecyloxy-
benzene (8) was obtained in 92% yield after reacting 7
with octadecyl bromide in the presence of KOH in
anhydrous dimethyl sulfoxide. The subsequent bro-
momethylation of 8 using paraformaldehyde and NaBr/
H2SO4 in acetic acid led to 1-bromo-4-bromomethyl-2,5-
dioctadecylbenzene (9) in 70% yield. The latter was
converted to the corresponding phosphonate ester 10 by
the Michealis -Arbusov reaction26 in 75% yield. The

Macromolecules, Vol. 36, No. 25, 2003
Alkoxy-Substituted PE/PV Hybrid Polymers 9307
for 2a and 6500 g/mol for 2b are obtained.33 These
values approximately correlate with those obtained from
GPC. This assumption, however, cannot be made for 1
and 3, where end-capping was carried out. Residual
iodine of 1.14% for 1 and bromine of 0.15% for 3 were
measured. Mh n values of 2.2 × 105 g/mol for 1 and 1.06
× 106 g/mol for 3 would be estimated from the halogen
contents, which are very far from the reality. The
extremely high solubility of compound 3 enabled us to
furthermore determine its Mn value through vapor
pressure osmometry (VPO). A value of 35 000 g/mol was
obtained, which is approximately the same as the GPC
peak value, Mp ) 37 000 g/mol. All the polymers are
thermostable up to 300-320 °C under ambient condi-
tions, where around 5% weight loss was recorded by
thermogravimetric analysis. The DSC analysis shows
side chains dependent transition phases in the region
between 40 and 80 °C for all polymers except 3 (Figure
3),34,35 but no glass transition temperature, Tg, was
observed after heating to 200 °C.
Sch em e 2
Horner-Wadsworth-Emmons (HWE) olefination reac-
tion of 10 with commercially available 4-bromobenzal-
dehyde (11a ) and with 4-bromo-2,5-dioctylbenzene20
provided both dibromo derivatives 12a and 12b in 76
and 75% yield, respectively. The ethynylation of 12
using trimethylsilylacetylene according to Sonogashira
reaction conditions27 provided 13a ,b (80%), whose hy-
drolysis resulted in the diethynyl derivatives 14a (43%)
and 14b (79%). The Sonogashira reactions of 12a with
14a and of 12b with 14b led to polymers 2a (74%) and
2b (85%), respectively, after work-up.
P h otocon du ctivity Stu dies. Photoconductivity mea-
surements were carried out on thin film samples (thick-
ness ≈ 100 nm) casted from a chlorobenzene solution
on thin glass substrates. Three samples of each com-
pound were measured for the purpose of reproducibility.
No sensitizer was required for the detection of photo-
conductivity in all cases. Data from the photoconductiv-
ity measurements are presented in Table 1. Figure 4
illustrates the photoconductivity spectra of polymers 1,
2b, 3, 4, and 5. It can be ascertained from the results
obtained that three parameters have an influence on
the photoconductive behavior of the polymers: (1) size
and (2) numbers of the grafted alkoxy side chains and
(3) the backbone conjugation pattern. The comparison
of compounds 2a and 2b , having the same backbone
conjugation pattern (-Ar-CtC-Ar-CHdCH-)n, but
different numbers of side chains per repeating units,
clearly shows that photoconductivity is easily detected
with 2b (20 V) possessing a higher number of side
groups than with 2a (400 V) with less side chains. The
maximal photocurrents, IPh, of 2a and 2b are 3.2 × 10-11
A (at 20 600 cm-1) and 6.4 × 10-11 A (at 19 600 cm-1),
respectively. The higher number of side chains in 1, 2b,
3, 4, and 5 and the presence of octadecyloxy groups, in
particular, help to reduce the influence of π-π inter-
molecular interaction on the photoconductivity. This
explains the low threshold voltages of 20 and 10 V
needed for these compounds.20 However, to understand
the differences in the photoconductive behavior of
polymers 1, 2b, 3, 4, and 5, having different conjugation
patterns, one should recall the fact that π-electrons in
the surroundings of triple bonds (-CtC-) find them-
selves in a deeper potential well than, for example,
π-electrons of double bonds (-CHdCH-), so that their
migration along the molecule requires the overcoming
of a higher energy threshold.36 The phenylene ethy-
nylene “homopolymer” 1 has the lowest IPh of 3.8 × 10-12
A (at 20 000 cm-1), which is at least 1 order of magni-
tude less than that of its hybrid counterpart 2b. The
hybrid conjugation pattern in 4 (-Ph-CtC-Ph-Ct
C-Ph-CHdCH-Ph-CHdCH-)n, which can be con-
sidered as a quasi-phenylene-ethynylene/phenylene-
vinylene “block copolymer”, is more favorable for
photoconductivity than that in 2b and 3. This is evident
through the lower threshold voltage of 10 V for the
detection of its photoconductivity. The fact that its
maximal photocurrent, IPh ) 1.1 × 10-9 A (at 20 000
The diethynyl derivative 14b was further used as a
starting material for the synthesis of polymer 3 (Scheme
2). The styryl-substituted hybrid polymer 3 was ob-
tained as a red material in 81% yield after reacting 14b
with trans,trans-2,5-distyryl-1,4-dibromobenzene (15).28
Polymers 2 and 3 are nonregioregular as a result of
different side chains (octadecyloxy and octyloxy) at-
tached to the backbone. Scheme 2 also depicts the
synthesis of PPE 1 and PPV 5 having the same alkoxy
side groups as 2b and 3. PPE 1 was obtained as an
orange material in a yield of 90% after allowing 1,4-
diodo-2,5-dioctyloxybenzene (16)29 and 1,4-diethynyl-2,5-
dioctadecylbenzene (17)30 to react under the same
conditions as for the synthesis of 2 and 3. End-capping
with phenylacetylene and bromobenzene was done in
the cases of 1 and 3. The HWE polycondensation
reaction of 2,5-dioctyloxyterephthaladehyde (18)31 and
2,5-dioctadecyloxy-p-xylylenebis(diethylphosphonate)
(19)19 provided PPE 5 as a bright red material in 68%
yield. The chemical structures of the monomers and of
the polymers were confirmed by 1H NMR, 13C NMR,
elemental analysis, and infrared spectroscopy. Figures
1 and 2 depict the 13C NMR (100 MHz) spectra of 2b
and 3, respectively, in CDCl3. The peaks could be readily
assigned to the side chains (14-72 ppm) and the
backbone carbons (91-155 ppm). The NMR spectra of
PPE 1 and PPV 5 are similar to those obtained from
the literature.31,32 The average molecular weights were
obtained by GPC with polystyrene as standards. THF
was used as the eluting solvent. Number-average mo-
lecular weights, Mh n, of 28 000 g/mol (PDI ) 2.5), 6000
g/mol (PDI ) 4.4), 8600 g/mol (PDI ) 3.9) 18 000 g/mol
(PDI ) 4.7), and 6600 g mol (PDI ) 1.5) were measured
for 1, 2a , 2b, 3, and 5, respectively. End groups bromine
content of 2.58% for 2a and 2.47% for 2b were obtained
from the elemental analysis. Assuming bromine at both
ends of the polymers, estimated Mh n values of 6200 g/mol

9308 Egbe et al.
Macromolecules, Vol. 36, No. 25, 2003
F igu r e 1. 13C NMR (100 MHz, CDCl3) spectrum of polymer 2b.
F igu r e 2. 13C NMR (100 MHz, CDCl3) spectrum of polymer 3.
Ta ble 1. Da ta fr om P h otocon d u ctivity Stu d ies (Su r fa ce
Cell, Slit Wid th , 0.2 m m ; Ir r a d ia tion , 20 µW/cm 2)
b
code
voltage [V]
IPh [A]a
νmax [cm-1
]
1
20
400
20
20
10
3.8 × 10-12
3.2 × 10-11
6.4 × 10-11
1.2× 10-11
1.1 × 10-9
3.0 × 10-10
20 000
20 600
19 600
19 200
20 000
20 000
2a
2b
3
4
5
10
a
b
Maximal photocurrent. Wavenumber of irradiating light at
IPh
.
optical energy gaps, Egopt, are presented in Table 2. The
Eg values are calculated from λT, the intersection of
opt
F igu r e 3. DSC heating curves of polymers 1, 2a , 2b, and 5.
the tangent through the turning point of the lower
energy band edge of the spectrum and the lengthened
baseline.37 Data from the photoluminescence studies are
summarized in Table 3, namely the emission maxima,
λe, the Stokes shifts, the fwhme, and the fluorescence
quantum yields, φfl. The maxima of the excitation
spectra are mostly identical with those of the absorption
maxima. In solution the absorption spectra are charac-
terized by an unstructured broad (fwhma: 4000-6000
cm-1) long wavelength absorption band indicating dif-
ferent geometries of the absorbing chromophore units.
The absorption maxima are determined by the conjuga-
cm-1), is 4 times higher than that of the phenylene-
vinylene “homopolymer” 5, IPh ) 3.0 × 10-10 A (at 20 000
cm-1), obtained at the same voltage, shows the influence
of additional effects.
Absor p tion a n d P h otolu m in escen ce Stu d ies. The
absorption and photoluminescence characteristics of the
polymers have been investigated in dilute chloroform
solution as well as in thin films. The positions of the
absorption maxima, λa, the extinction coefficients at the
maximum wavelength, ꢀmax, the full width at half-
maximum of the absorption spectra, fwhma, and the

Macromolecules, Vol. 36, No. 25, 2003
Alkoxy-Substituted PE/PV Hybrid Polymers 9309
F igu r e 5. Normalized absorption and fluorescence spectra of
the polymers in dilute chloroform solution. Normalization: 1
to 100, 2a to 90, 2b to 80, 3 to 70, 4 to 60, and 5 to 50.
The fluorescence spectra are moderately red-shifted
with a Stokes shift of 2000-2500 cm-1. The better
resolvable vibrational structure and the smaller band-
widths (fwhme: 2000-3000 cm-1) in comparison with
the absorption spectra are caused by the reduced
flexibility of the emitting chromophore due to stronger
conjugation in the excited S1 state.
There is a bathochromic shift of the absorption and
emission spectra from the solution to the solid state, as
shown in Figure 6, which can be attributed to an
enhanced planarization of the conjugated backbone
forced by the formation of aggregates in the solid film.
A vibrational structure of the absorption spectra is
indicated with 1 and 3 in the solid film. An asymmetric
broadening in the low-energy band edge with the other
compounds (except 4) can be interpreted as vestiges of
a vibrational structure.
The fwhm values of the absorption spectra are nearly
the same in the solution and the solid state. This is also
valid for the fluorescence spectra. An increase of the
Stokes shifts between 1000 and 2000 cm-1 from solution
to the solid state is observed. The fluorescent band
shapes vary in a less uniform manner. Compounds 4
and 5 show the closest similarity between film and
solution. The vibrational structure is better resolvable
in the solid film. Particularly with 3 and 2b in the film,
an additional unstructured largely Stokes-shifted emis-
sion occurs, which can be interpreted as an excimer-
like fluorescence.38 Compounds 2a and 1 represent
intermediate cases. The interpretation of the long-
wavelength emission as an excimer luminescence is
based on the systematic dependence of its intensity on
the size and number of the chain substituents. Thus,
for instance, the formation of excimers is reduced to
some extent through the grafting of long octadecyloxy
side groups, which may also explain the relatively high
fluorescence quantum yields in the films. The higher
number of alkoxy side chains in 2b give rise to a red
shift of its absorption [∆λa ) 22 nm (solution) and 24
nm (film)] and emission maxima [∆λe ) 27 nm (solution)
and 31 nm (film)] relative to those of 2a . The differences
of their other absorption and emission characteristics
are minimal, however. Two-dimensional and extended
π-conjugation is obtained in 3 comparatively to 2b
through the attachment of styryl units as side groups.
The observed absorption maxima in solution (λa ) 461
nm) and in the film (λa ) 487 and 510 nm), as we
assume, are emanating from a largely nonplanar con-
F igu r e 4. Photoconductivity spectra of 1, 2b, 3, 4, and 5
(surface type cell, slit width 0.2 mm, irradiation 20 µW/cm2,
threshold voltage 20 V (A) and 10 V (B)).
Ta ble 2. UV-Vis Da ta in Dilu te CHCl3 Solu tion a n d in
Solid Sta te (Th in F ilm s of 100-150 n m Th ick n ess
Sp in -Ca sted fr om Ch lor oben zen e Solu tion )
opt
ꢀmax
[M-1 cm-1
fwhma
Eg
b
code
λa [nm]
435
]
[cm-1
]
λT [nm] [eV]c
1
23 230
29 370
29 600
56 200
86 300
43 200
5680
4530
5490
5460
5330
5740
486
514
487
510
516
550
516
565
520
560
554
590
2.55
2.41
2.54
2.43
2.40
2.25
2.40
2.19
2.38
2.21
2.23
2.10
1a
2a
2a a
2b
2ba
3
462 (sh: 500)
432
448
454
472
461
487, 510
472
496
488
3a
4
4770
4280
4730
5760
4a
5
5a
487
a
b
opt
Solid state. Per mole of the constitutional unit. c Eg ) hc/
λT.
Ta ble 3. P h otolu m in escen ce Da ta in Dilu te Ch lor ofor m
Solu tion (∼10-8 M) a n d in Solid Sta tea
Stokes shift
fwhme
code
λe [nm]
474, 506
552
486
547
513
578
507
[cm-1
]
[cm-1
]
φfl [%]
1
1890
3530
2570
4040
2530
3890
1970
3760
1920
2050
2340
3350
2070
2910
2600
3080
2700
3000
2820
2830
2180
2080
2230
1250
(52) 43
21
54
19
47
16
76
14
77
1a
2a
2a a
2b
2ba
3
3a
4
596
519 (sh: 560)
552, 592
551(sh: 591)
582, 628
4a
5
54
42
27
5a
a
Solid state.
tion length which increases as well with the number of
double bonds as with the number of alkoxy side groups
per repeating unit from the pure PPE (1) to the pure
PPV (5) as depicted in Figure 5.

9310 Egbe et al.
Macromolecules, Vol. 36, No. 25, 2003
F igu r e 6. Normalized absorption and photoluminescence spectra in dilute chloroform solution and in film and normalized
electroluminescence spectra.
jugated system in the ground state. The large Stokes
shift of 109 nm (3750 cm-1) in the film leading to an
emission maximum, λe ) 596 nm, gives evidence of large
contribution of an excimer emission. This is furthermore
confirmed by the large fwhme value of 106 nm (2820
cm-1) and the relatively low fluorescence quantum yield
of 14%. Similar explanations can be applied to 2b and
to a lesser extent to 2a . Taking the conjugation pattern
into consideration, there is a gradual bathochromic shift
of the absorption from phenylene-ethynylene polymer
Electr olu m in escen ce Stu d ies. Polymer LEDs were
made by using 1, 2b, 3, 4, and 5 as an emissive layer
and PEDOT as a hole transporting layer. The devices
emit green, green-yellow, yellow-orange, green-yellow,
and yellow-orange light with EL peak wavelengths at
516, 554, 602, 543, and 574 nm, respectively (Figure 6).
The maxima of the electroluminescence spectra are
located between the emission maxima in solution and
those in solid film, except in the case of 3, where a clear
overlap of the electroluminescence and the solid-state
fluorescence is observed. This might be ascribed to the
different preparation methods for the solid film (e.g.,
for PL, from chlorobenzene solution; for EL, from
chloroform solution), which might lead to different film
morphologies, as demonstrated, for instance, by Heeger
et al.39 Data from the electroluminescence investigations
are summarized in Table 4. Comparing polymer 1 with
polymer 5, one observes a ∼60 nm red shift, when triple
bonds are substituted by double bonds. When one of the
two triple bonds in the green-emitting polymer 1 was
replaced with one double bond, the band gap decreased;
a green-yellow polymer 2b was obtained with the
opt
1 [Eg ) 2.55 eV (solution) and 2.41 eV (film)] through
opt
the hybrid compounds 2b [Eg ) 2.40 eV (solution) and
opt
2.25 eV (film)] and 4 [Eg ) 2.38 eV (solution) and 2.21
opt
eV (film)] to the phenylene-vinylene polymer 5 [Eg
) 2.23 eV (solution) and 2.10 eV (film)]. This is also valid
with the emission in solution but not in the solid state,
where other factors play an important role. Compound
4 exhibits a higher ꢀmax and a higher fluorescence
quantum yield in solution as well as in the film than
2b, which are related to its sharp and well-structured
emission curves in solution as well as in the solid state.
This situation is similar to that of polymer 5.

Macromolecules, Vol. 36, No. 25, 2003
Alkoxy-Substituted PE/PV Hybrid Polymers 9311
Ta ble 4. Da ta fr om Electr olu m in escen ce In vestiga tion
(F ilm Ca sted fr om CHCl3 Solu tion )a
we may tentatively conclude that most of the triple bond
units and double bond units act as independent chro-
mophores in the LED and contribute simultaneously to
the total emission. The use of styryl side groups in 3
leads to a yellow-orange emission. The phenylvinylene
units in polymer 3 could facilitate the intramolecular
energy transfer significantly and also intermolecular
energy transfer. From polymer 2b to 3, there is 48 nm
red shift in EL, demonstrating a successful chemical
color-tuning method for LED. The turn-on voltages of
the five devices were 7, 10, 7, 6, and 9 V (Figure 7).
These data are related to the band gap of the polymers,
the work function of electrode, and the thickness of
device. The external quantum efficiency, η, of the
devices reaches 4.6 × 10-2%, 1.4 × 10-3%, 0.15%, 1.7 ×
10-2%, and 4.9 × 10-3%. Comparing polymer 3 with 2b,
the styryl units do not only red shift the EL spectrum
and decrease the device turn-on voltage but also im-
fwhmel
luminance
[cd/m2]
code
λel [nm]
516
[cm-1
]
η [%]
1
4060
3023
2928
2069
1803
4.6 × 10-2
1.4 × 10-3
0.15
55.7
1.0
144.7
27.9
7.6
2b
3
4
554
602
543, 581 (sh)
574, 619 (sh)
1.7 × 10-2
5
4.9 × 10-3
aThe following setup was used: ITO/PEDOT/polymer/Ca.
emission energy between that of 1 and 5. When using
the repetition units (ru) of polymer 1 and polymer 5 to
form a conjugated -ru1-ru5-ru1-ru5- alternating copoly-
mer, we get polymer 4, which has an almost average
emission energy. The emission peak of 4 stands in the
middle of 1 and 5, suggesting that if there is intramo-
lecular energy transfer from the triple bond units to
double bond units, the transfer would be incomplete. Or
F igu r e 7. Current density (b)-voltage-luminance (O) relationship for devices ITO/PEDOT/polymer/Ca.

9312 Egbe et al.
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Con clu sion s
Hybrid phenylene-vinylene/phenylene-ethynylene
polymers 2a , 2b, 3, and 4 have been synthesized and
characterized. A comparison of their photophysical
properties taking into account the phenylene-ethy-
nylene “homopolymer” 1 and the phenylene-vinylene
“homopolymer” 5 has been carried out. It can be
ascertained from the obtained results that three pa-
rameters have an influence on the photophysical prop-
erties of the polymers: (1) size and (2) numbers of the
grafted alkoxy side chains and (3) the backbone conju-
gation pattern. The conjugation pattern in 4 is more
favorable to photoconductivity than that in 2b. The long
octadecyloxy side groups not only contribute to the red
shift of the absorption and emission spectra of the
above-mentioned compounds with respect to their alkyl-
substituted congeners, but they do also limit to a greater
extent the intermolecular π-π stacking, thus enabling
an easy detection of photoconductivity and higher
fluorescence quantum yields in solid films. The maxima
of the electroluminescence spectra lie between those of
the emission spectra in solution and the emission
spectra in solid state, except in the case of polymer 3
where a clear overlap of the solid film photolumines-
cence and electroluminescence can be observed. The
styryl side groups in 3 not only contribute to the red
shift of the electroluminescence but also bring about a
decrease of the turn-on voltage (relative to 2b) and an
enhancement of the EL efficiency to more than 100
times.
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