Investigation of the photophysical and electrochemical properties of alkoxy-substituted arylene-ethynylene/arylene-vinylene hybrid polymers

Article abstract of DOI:10.1021/ma0301395

High-molecular-weight, soluble and thermostable alkoxy-substituted arylene-ethynylene/arylene-vinylene conjugated polymers, 18 and 14, have been successfully synthesized through the Horner-Wadsworth-Emmons olefination of luminophoric dialdehydes 7 and 9 and bisphosphonate 12 in very good yields. They were characterized through ¹H NMR, ¹³C NMR, IR, and elemental analysis. The investigation of their photophysical and electrochemical properties has been carried out. Although almost identical absorption and emission spectra were obtained in dilute chloroform solution for all polymers 13, the full width at half-maximum (fwhm) value of the emission curves depends on the length of the attached side chains. The presence of anthracenylene units in 14 leads to a red shift of its absorption and emission spectra relative to 13. Strong self-reabsorption after excitation in solution was observed for this polymer. The solid-state photophysical properties of 13 and 14 (photoconductivity, absorption and emission spectra, fluorescence quantum yield, Stokes shift, and fwhm) greatly depend on the nature (linear or branched), length, and location of the grafted alkoxy side groups. Photoconductivity is easily detected in polymers having octadecyloxy chains (13aa, 13ab, 14). Long linear (octadecyl, i.e., 13aa) or short branched (2-ethylhexyl, i.e., 13cc) side chains at position R₂ (phenylene-vinylene segment) are necessary to obtain sharp and well-resolved emission spectra accompanied by high fluorescence quantum yields. The quasi-donor (phenylene-vinylene segment)-acceptor (arylene-ethynylene segment) nature of these polymers could explain the great discrepancy between the electrochemical band gap energy, E_g^ec ≈ 1.60 eV, as obtained from the onset values of the redox potentials in cyclic voltammetry and in differential pulse polarography measurements, and the optical band gap energy, E_g^opt ≈ 2.30 eV, from the absorption spectra.

Full text of DOI:10.1021/ma0301395

Macromolecules 2003, 36, 5459-5469
5459
Investigation of the Photophysical and Electrochemical Properties of
Alkoxy-Substituted Arylene-Ethynylene/Arylene-Vinylene Hybrid
Polymers
Da n iel Ayu k Mbi Egbe,* Ba d er Cor n elia , J u1 r gen Now otn y, Wolfga n g Gu1 n th er , a n d
Elisa beth Klem m *
Institut fu¨r Organische Chemie und Makromolekulare Chemie der Friedrich-Schiller-Universita¨t J ena,
Lessingstrasse 8, D-07743 J ena, Germany
Received February 24, 2003; Revised Manuscript Received April 22, 2003
ABSTRACT: High-molecular-weight, soluble and thermostable alkoxy-substituted arylene-ethynylene/
arylene-vinylene conjugated polymers, 13 and 14, have been successfully synthesized through the
Horner-Wadsworth-Emmons olefination of luminophoric dialdehydes 7 and 9 and bisphosphonate 12
in very good yields. They were characterized through 1H NMR, 13C NMR, IR, and elemental analysis.
The investigation of their photophysical and electrochemical properties has been carried out. Although
almost identical absorption and emission spectra were obtained in dilute chloroform solution for all
polymers 13, the full width at half-maximum (fwhm) value of the emission curves depends on the length
of the attached side chains. The presence of anthracenylene units in 14 leads to a red shift of its absorption
and emission spectra relative to 13. Strong self-reabsorption after excitation in solution was observed for
this polymer. The solid-state photophysical properties of 13 and 14 (photoconductivity, absorption and
emission spectra, fluorescence quantum yield, Stokes shift, and fwhm) greatly depend on the nature (linear
or branched), length, and location of the grafted alkoxy side groups. Photoconductivity is easily detected
in polymers having octadecyloxy chains (13a a , 13a b, 14). Long linear (octadecyl, i.e., 13a a ) or short
branched (2-ethylhexyl, i.e., 13cc) side chains at position R2 (phenylene-vinylene segment) are necessary
to obtain sharp and well-resolved emission spectra accompanied by high fluorescence quantum yields.
The quasi-donor (phenylene-vinylene segment)-acceptor (arylene-ethynylene segment) nature of these
ec
polymers could explain the great discrepancy between the electrochemical band gap energy, Eg ≈ 1.60
eV, as obtained from the onset values of the redox potentials in cyclic voltammetry and in differential
opt
pulse polarography measurements, and the optical band gap energy, Eg ≈ 2.30 eV, from the absorption
spectra.
In tr od u ction
Polymers 13a a (R1 ) R2 ) octadecyl) and 13a b (R1 )
octadecyl, R2 ) octyl) were reported in one of our
previous articles,14c in which we described the effects
of alkoxy side chains in the photophysical properties of
these polymers. In this report we extend the study of
Since the past three decades, much attention has been
focused on the investigation of the properties of π-
conjugated polymers, culminating with the award of the
Nobel Prize in chemistry in the year 2000 to Alan J .
Heeger, Alan G. MacDiarmid, and Hideki Shirakawa
for the discovery and development of conductive poly-
mers.1-5 Among semiconducting polymers, poly(phenyl-
enevinylene)s (PPV) have been most widely studied
since the discovery of electroluminescence in PPV by the
group of Cambridge in 1990.6 PPV’s are good hole
transporting materials but poor electron transporters.
The need for materials with approximately balanced
hole- and electron-transporting properties, which is a
precondition for obtaining light-emitting-diode (LED)
devices with high electroluminescence efficiencies,
prompted many research groups to design and synthe-
size PPV derivatives with increased electron affinity,
such as cyano-substituted PPVs,7-10 trifluoromethyl-
substituted PPVs,11 oxadiazole-substituted PPVs,12 and
pyridine-containing PPVs.13 A recent approach to in-
crease the electron uptake of PPVs, which has been
reported by our group14 and others,15 is to insert the
electron-withdrawing acetylene (-CtC-) into the PPV
backbone, leading to hybrid poly(phenylene-vinylene)/
poly(phenylene-ethynylene) (PPV/PPE) polymers.
the side chains effects to polymers 13bb (R1 ) R2
)
octyl) and 13cc (R1 ) R2 ) 2-ethyhexyl) in order to make
a clear and conclusive assertion about their influence
on the properties on this class of compounds. Our
synthetic strategy enables us to also obtain low band
gap and defect-free polymer 14 by incorporating anthra-
cenylene units into the polymer backbone. Polymers
with low optical band gap energy and high absorption
coefficient are of great interest for the design of organic
photovoltaic cells.16a We attached long octadecyloxy side
chains in 14 in order to confirm the fact that long side
chains are needed for the easy detection of photo-
conductivity in this class of compounds.14c The good
photoconductive behavior, the high fluorescence quan-
tum yields in thin films, and the high absorption
coefficients, ꢀmax, around 100 000 M-1 cm-1 of these
polymers make them potential candidate for design of
organic light-emitting diodes and organic photovoltaic
devices.
To fit the energetic scheme of a photovoltaic device,
it is necessary to determine through electrochemistry
the energy levels of the valence band (HOMO) and the
conduction band (LUMO) and the width of the gap
between the bands of each component.16 The energy gap
between the bands can moreover be easily determined
* Corresponding authors: e-mail c5ayda@uni-jena.de or c9klel@
rz.uni-jena.de.
10.1021/ma0301395 CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/28/2003

5460 Egbe et al.
Macromolecules, Vol. 36, No. 15, 2003
32.14, 32.16 (CH3(CH2)6-), 69.85 and 70.22 (-CH2O-), 111.01
with the absorption spectroscopy. In this work the
electrochemical behavior of polymers 13 and 14 and
their corresponding monomers 7 and 9 has been inves-
tigated through cyclic voltammetry and differential
pulse polarography. Their HOMO and LUMO energy
levels have been estimated. A comparison between their
electrochemical energy band gap, Egec, and their optical
energy band gap, Egopt, has been carried out.
and 118.84 (-Caryl-H), 121.34 (-Caryl-Br), 124.65 (-Caryl
-
CHO), 150.24 and 156.15 (Caryl-OR), 189.33 (-CHO). Anal.
Calcd for C23H37BrO3 (441.46): C, 62.57; H, 8.44; Br, 18.09.
Found: C, 62.68; H, 8.55; Br, 18.40.
2,5-Dioctyloxy-4-trimethylsilylethynylbenzaldehyde (3). 4-
Bromo-2,5-dioctyloxybenzaldehyde (2) (3 g, 6.8 mmol), Pd-
(PPh3)2Cl2 (105 mg, 0.15 mmol), and CuI (31.8 mg, 0.16 mmol)
were added to a degassed solution of diisopropylamine (75 mL).
Trimethylsilylacetylene (670 mg, 6.8 mmol) was added slowly
and dropwise to the vigorously stirred suspension. The reaction
mixture was then stirred at reflux for 8 h. After cooling, the
white ammonium bromide precipitate was filtered off. The
solvent was removed under reduced pressure, and the residue
was chromatographed over a silica gel column with toluene
as eluent. 2.6 g (84%, Rf ) 0.83) of a dark yellow oil was
obtained, which crystallizes when kept under 4 °C for weeks.
1H NMR (250 MHz, CDCl3): δ/ppm ) 0.08 (-Si(CH3)3), 0.67
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 or cooling at a rate of 10 °C/min. Mass spectroscopy
was performed by chemical ionization with H2O vapor as gas
on a Finnigan Mat SSQ 710. 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 an LS 50 luminescence spectrometer
(Perkin-Elmer). Photoluminescence quantum yields were cal-
culated according to Demas and Crosby17 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. The films were cast from chlorobenzene.
The quantum yield in the solid state was determined
f 1.63 (-(CH2)6CH3), 3.80 (-CH2O-), 6.69 and 7.03 (-Caryl
-
H), 10.28 (-CHO). 13C NMR (62 MHz, CDCl3): δ/ppm ) 0.11
(-Si(CH3)3), 14.23, 22.80, 22.82, 26.19, 29.30, 29.36, 29.39,
29.45, 29.53, 31.94, 32.00 (CH3(CH2)6-), 69.42 (-CH2O-),
100.64 and 103.13 (-CtC-), 110.10 and 118.00 (Caryl-H),
120.30 (Caryl-Ct), 125.24 (Caryl-CHO), 154.39 and 155.53
(Caryl-OR), 189.37 (-CHO).
4-Ethynyl-2,5-dioctyloxybenzaldehyde (4). Methanol (28 mL)
and aqueous KOH (4 mL, 10%) were added at room temper-
ature to a stirred solution of 3 (2.5 g, 5.4 mmol) in 55 mL of
THF. The reaction mixture was then stirred 3 h at room
temperature. The solvent was removed on a rotatory evapora-
tor, and the residue was chromatographed on a silica gel
column with toluene as eluent. Thus, 1.3 g (65%, Rf ) 0.77)
of a yellow substance was obtained. Mp: 116-117 °C. 1H
NMR (250 MHz, CDCl3): δ/ppm ) 0.88 f 1.86 (30H, m,
CH3(CH2)6-), 3.47 (1H, s, -CtC-H), 4.04 (4H, t, 3J ) 6.5 Hz,
-CH2O-), 7.09 (1H, s, Caryl-H), 7.31 (1H, s, Caryl-H), 10.45
(1H, s, -CHO). 13C NMR (62.9 MHz, CDCl3): δ/ppm )
14.44, 23.02, 26.27, 26.40, 29.40, 29.50, 29.58, 29.65, 32.16
(CH3(CH2)6-), 69.67 and 69.82 (-CH2O-), 79.84, 84.93
(-CtC-), 110.45 and 118.79 (Caryl-H), 119.40 (Caryl-Ct),
125.76 (Caryl-CHO), 154.61 and 155.64 (Caryl-OR), 189.49
(-CHO). IR (KBr): 3346 (w, -CtC-H), 2924 and 2853 (vs,
-CH2- and -CH3), 2760 (w, -CHO), 1683 (vs, -CHO), 1600
(s, phenyl ring), 1218 (Caryl-OR) cm-1. UV-vis (CHCl3, 4.4 ×
10-5 M): λmax/nm (ꢀ/(L mol-1 cm-1)), 268 (9800), 300 (13 700),
315 (13 000), 340 (11 250), 411 (17 000). Anal. Calcd for
against
a
CF3P-PPV (poly{1,4-phenylene-[1-(4-trifluoro-
methylphenyl)ethenylene]-2,5-dimethoxy-1,4-phenylene-[2-(4-
trifluoromethylphenyl)ethenylene]}) copolymer reference that
has been measured by integrating sphere as 0.43.18 Electro-
chemical measurements (cyclic voltammetry and differential
pulse polarography) were carried with a Princeton Research
PAR 273 A [Pt disk electrode, dichloromethane, tetrabutyl-
ammonium hexafluorophosphate (Bu4NPF6), concentration
10-3 M, sweep rate 0.02 V/s (differential pulse polarography),
0.167 V/s (cyclic voltammetry)].
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 sparkling with argon or nitrogen 1 h prior
to use. 1,4-Dibromo-2,5-dioctyloxybenzene (1),19 1,4-diethynyl-
2,5-dioctyloxybenzene (5),19 2,5-dialkoxy-p-xylylenebis(di-
ethylphosphonate)s (12),14 4-diiodo-2,5-di(2-ethyl)hexyloxy-
benzene (6),14c,20 and 9,10-dibromoanthracene21 were prepared
according to known literature procedures.
1-Bromo-4-formyl-2,5-dioctyloxybenzene (2). To a solution of
1,4-dibromo-2,5-dioctyloxybenzene (1)19 (4.9 g, 10 mmol) in
diethyl ether (150 mL), cooled at 10 °C and kept under argon,
was added a solution of butyllithium (2.7 M in heptane, 3.75
mL, 10 mmol). After 15 min, DMF (0.96 mL, 12.5 mmol) was
added to the mixture, while the temperature was allowed to
rise to 15 °C. The clear solution was kept between 10 and 15
°C and was stirred for 1.5 h. A 10% aqueous HCl solution (50
mL) was subsequently added to the mixture, and the phases
C
25H38O3 (386.57): C, 77.67; H, 9.90. Found: C, 77.39; H, 9.77.
1,4-Bis(4-formyl-2,5-dioctyloxyphenylethynyl)-2,5-dioctyloxy-
benzene (7b). 1,4-Diethynyl-2,5-dioctyloxybenzene (5)19 (2.0 g,
5.58 mmol), 1-bromo-4-formyl-2,5-dioctyloxybenzene (2) (5.30
g, 12 mmol), Pd(PPh3)4 (242 mg, 0.209 mmol, 4 mol %), and
CuI (43.3 mg, 0.209 mmol, 4 mol %) were added to a degassed
solution of 35 mL of diisopropylamine and 80 mL of toluene.
The reaction was heated at 70 to 80 °C for 24 h. After being
cooled to room temperature, the ammonium bromide salt was
filtered off; the filtrate was evaporated to around 30 mL and
was added dropwise into 500 mL of vigorously stirred metha-
nol. The precipitate was collected and chromatographed on
silica gel column with toluene as eluent. Yield: 4.2 g (69%).
Mp: 85-86 °C. MS (70 eV, ESI in H2O): m/z ) 1104 (M+ + 1,
100%), 992 (20%), 880 (10%). 1H NMR (250 MHz, CDCl3):
δ/ppm ) 0.79 f 1.83 (90H, m, CH3(CH2)6-), 3.93 f 4.01(12H,
m, -CH2O-), 6.95 (2H, s, Cphenyl-H), 7.03 (2H, s, Cphenyl-H),
7.25 (2H, s, Cphenyl-H), 10.37 (2H, s, -CHO).13
C NMR
(62.9 MHz, CDCl3): δ/ppm ) 14.47 (CH3-), 23.05, 26.34,
26.41, 26.48, 29.58, 29.61, 29.70, 29.76, 29.81, 32.18, 32.23
(-(CH2)6-), 69.62, 69.91, 70.09 (-CH2O-), 91.58, 94.19
(-CtC-), 110.48, 114.73, 117.73, 117.93, 121.07, 125.29,
153.97, 154.07, 155.90 (Cphenyl’s), 189.55 (-CHO). IR (KBr):
2926 and 2855 (vs, -CH2- and CH3-), 2755(w, -CHO), 2203
(w, disubst -CtC-), 1681 (s, -CHO), 1601 (s, -CdCphenyl-),
1287 and 1207 (s, Cphenyl-OR) cm-1. UV-vis (CHCl3, 1.8 × 10-5
M): λmax/nm (ꢀ/(L mol-1 cm-1)) 288.0 (22 930), 328.8 (28 600),
423.2 (57 060). Anal. Calcd for C72H110O8 (1103.66): C, 78.36;
H, 10.05. Found: C, 78.72; H, 9.55.
were separated. The organic phase was washed with
a
NaHCO3 solution and dried over CaCl2. Diethyl ether was then
distilled off, and the residue was chromatographed on a silica
gel with a mixture of toluene/hexane (2/1) as eluent. 2 was
obtained at Rf ) 0.70 (3.3 g, 74.6%) as light yellow crystals.
Mp: 58.2-58.9 °C. 1H NMR (250 MHz, CDCl3): δ/ppm ) 0.83
f 1.86 (CH3(CH2)6-), 3.82 f 4.03 (-CH2O-), 6.76 f 7.29
(Caryl-H), 10.39 (CHO). 13C NMR (62 MHz, CDCl3): δ/ppm )
14. 45, 14.46, 23.02, 26.31, 26.37, 29.39, 29.44, 29.58, 29.62,

Macromolecules, Vol. 36, No. 15, 2003
Arylene-Ethynylene/Arylene-Vinylene Polymers 5461
1,4-Bis(4-formyl-2,5-dioctyloxyphenylethynyl)-2,5-di(2-ethyl)-
hexyloxybenzene (7c). 1-Ethynyl-4-formyl-2,5-dioctyloxyben-
zene (4) (1.6 g, 4.14 mmol), 1,4-diiodo-2,5-bis(2-ethylhexyloxy)-
benzene (6)14c,20 (1.155 g, 1.97 mmol), Pd(PPh3)4 (91 mg, 0.079
mmol, 4 mol %), and CuI (15 mg, 0.079 mmol, 4 mol %) were
given to a degassed solution of 15 mL of diisopropylamine and
45 mL of tetrahydrofuran. The reaction mixture was heated
at 65-70 °C for 22 h. The ammonium iodide precipitate was
filtered off after cooling to room temperature; the solvent was
removed under reduced pressure. The residue was collected
and chromatographed on a silica gel column with toluene as
eluent. The desired product 7c was obtained at Rf ) 0.36 (1.2
g, 55%) alongside 1,4-bis[(4-formyl-2,5-dioctyloxy)phenyl)]but-
1,3-diyne (15) at Rf ) 0.52 (100 mg, 6.8%).
CHO), 1600 (s, -CdCaryl-), 1219 (vs, Cphenyl-OR) cm-1. UV-
vis (CHCl3, 1.3 × 10-5 M): λmax/nm (ꢀ/(L mol-1 cm-1)): 261
(46 230), 283.4 (48 420), 329.6 (26 190), 381.6 (14 570), 480.8
(57 400), 512.0 (71 140). Anal. Calcd for C64H80O6 (945.33): C,
81.32; H, 8.53. Found: C, 81.31; H, 8.99.
Benzyldiethylphosphonate (11). A mixture of benzyl bromide
(10) (10 g, 0.058 mol) and an excess of triethyl phosphite (19
g, 0.114 mol) was heated slowly to 150 °C, and the evolving
ethyl bromide was distilled off simultaneously. After heating
4 h at 150 °C, vacuum was applied for 1 h to remove the excess
of triethyl phosphite. Benzyldiethylphosphonate was obtained
at 1.5 mbar and 120 °C as a colorless liquid. Yield: 11.5 g
1
3
(87%). H NMR (250 MHz, CDCl3): δ/ppm ) 1.19 (6H, t, J )
7.05 Hz, CH3-), 3.10 (2H, d, 3J ) 21.56 Hz, CH2P-), 3.99 (4H,
q, 3J ) 6.45 Hz, -CH2O-), 7.17 f 7.30 (Cphenyl-H’s). 13C NMR
(62 MHz, CDCl3): δ/ppm ) 15.92, 16.23, 16.33 (CH3-), 32.63,
34.83 (-CH2P-), 61.95, 62.06 (-CH2O-), 126.74, 126.80,
128.41, 128.46, 129.65, 129.76, 131.51, 131.65 (Cphenyl’s).
7c: Mp: 69-72 °C. MS (70 eV, ESI with H2O): m/z ) 1104
1
(M+, 100%), 992 (50%). H NMR (250 MHz, CDCl3): δ/ppm )
0.79-1.81 (90H, m, alkyl side groups), 3.84 (4H, d, 3J ) 5 Hz,
-CH2O- ethylhexyl), 3.97 (8H, m, -CH2O- octyl), 6.94 (2H,
s, Cphenyl-H), 7.03 (2H, s, Cphenyl-H), 7.26, (2H, s, Cphenyl-H),
10.38 (2H, s, -CHO). 13C NMR (62.90 MHz, CDCl3): δ/ppm )
11.91 (Cb), 14.71 (Cc), 23.29, 23.72, 24.68, 26.59, 26.70, 29.77,
29.83, 29.86, 29.93, 29.98, 31.27, 32.44, 32.46 (-CH2-), 40.21
(Ca), 69.86, 70.07, 72.54, (-CH2O-), 91.75, 94.53 (-CtC-),
110.81 (C3), 114.89 (C12), 117.51 (C6), 118.15 (C13), 121.47 (C5),
125.53 (C2), 154.20, 154.55, 156.16 (Cphenyl-OR), 189.78 (-CHO).
IR (FTIR): 2922 and 2854 (vs, -CH2- and CH3-), 2753 (vw,
-CHO), 2213 (vw, disubst -CtC-), 1679 (vs, -CHO), 1600
(s, -CdCphenyl-), 1207 (vs, Caryl-OR) cm-1. UV-vis (CHCl3,
1.1 × 10-5 M): λmax/nm (ꢀ/(L mol-1 cm-1)) 329 (28 200), 428
(51 300). Anal. Calcd for C48H74O6 (1103.66): C, 78.36; H,
10.04. Found: C, 77.92; H, 9.84.
Poly{1,4-(2,5-dioctyloxyphenylene)ethynylene-1,4-[2,5-di(2-
ethylhexyloxy)phenylene]-1,4-(2,5-dioctyloxyphenylene)-ethene-
1,2-diyl-1,4-[2,5-di(2-ethylhexyloxy)phenylene]ethene-1,2-
diyl} (13cc). Dialdehyde 7c (1 g, 0.906 mmol) and bisphos-
phonate 12c (575.15 mg, 0.906 mmol) were dissolved in dried
toluene (40 mL) while stirring vigorously under argon and
heating under reflux. Potassium tert-butoxide (600 mg, 5.36
mmol) was added to this solution. After 2 h heating at reflux,
three drops of benzyldiethylphosphonate (11) were added; 30
min later three drops of benzaldehyde were also added with
an additional 100 mg of potassium tert-butoxide. After a total
reaction time of 3 h, more toluene was added, and 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 and evaporated under vacuum
to the minimum, and the polymer was precipitated in metha-
nol. The polymer was extracted for 8 h with methanol,
dissolved once more in toluene, reprecipitated in methanol,
and dried under vacuum. Thus, 1.0 g (77.2%) of orange-red
15: Mp: 96-102 °C. MS (70 eV, ESI with H2O): m/z ) 771
(M+, 60%), 363 (100%), 93 (100%). 1H NMR (250 MHz,
CDCl3): δ/ppm ) 0.78 f 1.81 (60H, m, CH3(CH2)6-), 3.92 f
3.98 (8H, m, -CH2O-), 6.92 (2H, s, Cphenyl-H), 7.23 (2H, s,
Cphenyl-H), 10.37 (-CHO). 13C NMR (62 MHz, CDCl3): δ/ppm
) 13.06, 21.64, 24.88, 25.01, 27.96, 28.09, 28.18, 28.22, 28.26,
30.77 (CH3(CH2)6-), 68.30, 68.55 (-CH2O-), 78.77 and 79.90
(-CtC-CtC-), 109.11, 117.39, 117.59 (Cphenyl-H), 124.71,
127.20, 128.01 (Cphenyl-C) 154.02, 154.18(Cphenyl-OR), 188.03
(-CHO). IR (KBr): 2926 and 2855 (vs, -CH2- and CH3-),
2759 (w, -CHO), 2209 and 2100 (vw, -CtC-CtC-), 1683
polymer was obtained. GPC (THF): Mh n ) 18 000 g/mol, Mh w
)
90 000 g/mol, Mh z ) 280 000 g/mol, Mp ) 49 000 g/mol; PDI )
1
5.0. H NMR (400 MHz, CDCl3): δ/ppm ) 0.85 f 1.85 [120H,
(vs, -CHO), 1600 (s, -CdCphenyl-), 1286 and 1218 (Cphenyl
-
-(CH2)6CH3 and -CH(CH2CH3)(CH2)3CH3], 3.49 f 4.09 (16H,
-CH2O-), 6.81 f 7.16 (8H, phenylene H’s), 7.43 f 7.50 (4H,
vinylene H’s). 13C NMR (100 MHz, CDCl3): δ/ppm ) 11.64
(CH3- ethyl), 14.40 (CH3- hexyl and octyl), 23.03, 23.46,
24.47, 24.70, 26.47, 29.69, 31.06, 31.30, 32.23 (-(CH2)3- hexyl
and -(CH2)6- octyl), 40.10, 40.23 (-CH-), 69.19, 69.90, 70.30,
72.30, 72.55 (-CH2O-), 91.33, 92.27 (-CtC-), 110.67, 111.13,
113.64, 114.87, 117.51, 117.82, 119.02 (Cphenyl-H), 123.26,
124.65 (vinylene C’s), 127.38, 127.93, 129.26 (Cphenyl-C),
150.93, 151.74, 154.20, 154.55 (Cphenyl-OR). IR (FTIR): 3055
(vw, Caryl-H), 2956, 2923, and 2856 (s, -CH3 and -CH2-),
2201 (vw, disubst -CtC-), 1599 (w, -CdCphenyl-), 1251 and
1199 (vs, Caryl-OR), 970 cm-1 (trans -CHdCH-). UV-vis
(CHCl3, 8.8 × 10-6 M): λmax/nm (ꢀ/(L mol-1 cm-1)) 318 (29 600),
470 (105 200). Anal. Calcd for (C96H148O8)n (1430.22)n: C, 80.62;
H, 10.43. Found: C, 80.24; H, 10.37.
OR) UV-vis (CHCl3, 2.0 × 10-5 M): λmax/nm (ꢀ/(L mol-1 cm-1))
300 (24 280), 314 (23 000), 340 (20 200), 411.2 (31 000). Anal.
Calcd for C50H74O6 (771.13): C, 77.88; H, 9.67. Found: C, 77.03;
H, 9.56.
9,10-Bis[(4-formyl-2,5-dioctyloxy)phenylethynyl]a nthra -
cene (9). 9,10-Dibromoanthracene (8) (470 mg, 1.39 mmol),
4-ethynyl-2,5-dioctyloxybenzaldehyde (4) (1.108 g, 2.866 mmol),
Pd(PPh3)4 (65 mg, 5.59 × 10-2 mmol, 4 mol %), and CuI (11
mg, 5.59 × 10-2 mmol, 4 mol %) were given to a degassed
solution of 20 mL of diisopropylamine and 50 mL of toluene.
The reaction mixture was heated at 70-80 °C for 24 h in an
argon atmosphere. After cooling to room temperature, the
precipitated diisopropylammonium bromide was filtered off
and the solvent was distilled off under vacuum. The residue
was chromatographed on a silica gel column with toluene as
eluent. 800 mg (Rf ) 0.64, 60.53%) of a red substance was
obtained. Mp ) 138-142 °C. MS (70 eV ESI with H2O): m/z
) 947 (M+ + 1, 100%), 835 (10%), 535 (5%), 158 (30%). 1H
NMR (400 MHz, CDCl3): δ/ppm ) 0.79 f 1.87 (30H, m,
Poly[1,4-(2,5-dioctyloxyphenylene)ethynylene-1,4-(2,5-di-
octyloxyphenylene)-1,4-(2,5-dioctyloxyphenylene)ethene-1,2-diyl-
1,4-(2,5-dioctyloxyphenylene)ethene-1,2-diyl] (13bb). Dialde-
hyde 7b (1.655 g, 1.5 mmol) and bisphosphonate 12b (953 mg,
1.5 mmol) were dissolved in dried toluene (40 mL) while
stirring vigorously under argon and heating under reflux.
Potassium tert-butoxide (994 mg, 8.87 mmol) was added to this
solution. After 1 h heating at reflux, 0.6 g of benzyldiethyl-
phosphonate (11) was added; 30 min later 0.6 g of benzalde-
hyde was also added with additional 100 mg of potassium tert-
butoxide. After a total reaction time of 3.5 h, more toluene was
added, and 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 and evaporated
3
CH3(CH2)6-), 4.13 (8H, t, J ) 6.46 Hz, -CH2O-), 7.26 (2H,
s, Cphenyl-H), 7.38 (2H, s, Cphenyl-H), 7.62 (4H, d, 3J ) 9.88
Hz, Canthracenyl-H), 8.78 (4H, d, 3J ) 9.88 Hz, Canthracenyl-H),
10.48 (2H, s, CHO). 13C NMR (100 MHz, CDCl3): δ/ppm )
14.07 (CH3-), 22.59, 22.64, 26.04, 26.10, 29.22, 29.33, 29.42,
29.52, 31.76, 31,79 (-(CH2)6-), 69.35 and 69.47 (-CH2O-),
94.61 and 99.04 (-CtC-), 109.36 and 117.04 (Cphenyl-H),
118.88 (Cphenyl-CtC-), 120.21 (Canthracenyl-CtC-), 125.15
(Cphenyl-CHO), 126.92 and 132.25 (Canthracenyl-H), 127.44
(Canthracenyl-Cd), 154.01 and 155.60 (Cphenyl-OR), 189.11
(-CHO). IR (KBr): 3056 (w, Cphenyl-H) 2929 and 2856 (vs, CH2
and CH3), 2756 (w, CHO), 2188 (w, disubst -CtC-), 1682 (s,

5462 Egbe et al.
Macromolecules, Vol. 36, No. 15, 2003
Sch em e 1
under vacuum to the minimum (60 mL), and the polymer was
precipitated in methanol (400 mL). The polymer was extracted
for 8 h with methanol and dried under vacuum. Thus, 1.9 g
the reaction mixture was heated at reflux for 3 h. After this
time more toluene was added, and 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 under vacuum to the minimum, and
precipitated in methanol. The polymer was extracted with
methanol/water for 10 h, dissolved once more in toluene,
reprecipitated in methanol, and dried under vacuum. 715 mg
(86.8%) of purple-red polymer was obtained.
(88%) of orange-red polymer was obtained. GPC (THF): Mh n
16 300 g/mol, Mh w ) 37 100 g/mol, Mh z ) 67 300 g/mol, Mp
)
)
35 700 g/mol; PDI ) 2.27. 1H NMR (400 MHz, CDCl3): δ/ppm
) 0.85-0.87 (24H, CH3-), 1.27-1.86 (96H, -(CH2)6-), 3.62-
3.66 and 3.90-4.10 (16H, -CH2O-), 6.72-7.14 (Cphenyl-H),
7.43-7.48 (-CHdCH-). 13C NMR (100 MHz, CDCl3): δ/ppm
) 14.45 (CH3-), 23.06, 26.46, 26.50, 26.65, 29.74, 29.85, 32.28
(-(CH2)-), 69.15, 69.83, 69.95, 70.23, 70.42 (-CH2O-), 91.24,
92.41 (-CtC-), 111.20, 111.53, 114.94, 117.24, 117.69, 117.88
(Cphenyl-H), 123.73, 124.92 (-CHdCH-), 113.50, 119.06,
126.38, 127.94, 129.22 (Cphenyl-C), 151.00, 151.62, 153.96,
154.52 (Cphenyl-OR). IR (KBr): 3059 (vw, Cphenyl-H), 2924 and
2853 (vs, -CH2- and CH3-), 2203 (vw, disubst -CtC-), 1747
(vw, -CHO), 1600 (-CdCphenyl-), 1206 (Cphenyl-OR), 968 cm-1
GPC (THF): Mh w ) 51 190 g/mol, Mh n ) 25 570 g/mol, Mh z
)
144 400 g/mol, Mp ) 44 700 g/mol, PDI ) 2.0. 1H NMR (400
MHz, CDCl3): δ/ppm ) 0.84-2.05 (130H, m,CH3(CH2)16- and
CH3(CH2)6-), 3.62 f 4.20 (12H, m, -CH2O-), 6.84-6.91; 7.19;
7.51-7.60 and 8.84 (18H, -arylene and vinylene H’s). 13C
NMR (100 MHz, CDCl3): δ/ppm ) 14.07, 22.66, 26.22, 29.29,
29.34, 29.47, 29.53, 29.70, 31.87, 31.89 (CH3(CH2)16- and
CH3(CH2)6-), 69.35, 69.55, 69.71 (-CH2O-), 116.95, 126.47,
127.59, 132. 07, 150. 54, 154.56 (arylene and vinylene C’s). IR
(KBr): 3057 (w, Cphenyl-H), 2923 and 2852 (vs, CH3 and
-CH2-), 2184 (vw, -CtC-), 1597 (w, -CdCaryl-), 1203 (s,
Cphenyl-OR), 971 cm-1 (m, trans -CHdCH-). UV-vis (CHCl3,
9.1 × 10-6 M): λmax/nm (ꢀ/(L mol-1 cm-1)): 284 (42 500), 328
(19 000), 408.8 (18 500), 547.2 (82 200), 587.2 (32 500). Anal.
Calcd for (C108H160O6)n (1554.45)n: C, 83.44; H, 10.37. Found:
C, 80.29; H, 10.53.
(m, trans-CHdCH-). UV-vis (CHCl3, 6.57 × 10-6 M): λmax
/
nm (ꢀ/(L mol-1 cm-1)): 320.8 (24 000), 469 (69 300). Anal. Calcd
for (C96H148O8)n (1430.22)n: C, 80.62; H, 10.43. Found: C,
79.82; H, 10.28.
Poly[1,4-(2,5-dioctyloxyphenylene)ethynylene-8,9-a nthra -
cenyleneethynylene-1,4-(2,5-dioctyloxyphenylene)ethene-1,2-diyl-
1,4-(2,5-dioctyloxyphenylene)ethene-1,2-diyl] (14). Dialdehyde
9 (501 mg, 0.53 mmol) and bisphosphonate 12a (485 mg, 0.53
mmol) were dissolved in dried toluene (50 mL) while stirring
vigorously under argon and heating under reflux. Potassium
tert-butoxide (238 mg, 2.12 mmol) was added to this solution;

Macromolecules, Vol. 36, No. 15, 2003
Arylene-Ethynylene/Arylene-Vinylene Polymers 5463
Sch em e 2
Ta ble 1. Da ta fr om GP C (TF H) w ith P olystyr en e a s
Sta n d a r d a n d Th er m a l Sta bilitiesa
Resu lts a n d Discu ssion
The syntheses of the various 2,5-dialkoxy-p-xylylene-
bis(diethylphosphonate)s (12a -c) and of the fluoro-
phoric dialdehyde 7a [1,4-bis(formyl-2,5-dioctyloxy-
phenylethynyl)-2,5-dioctadecyloxybenzene] have been
reported elsewhere.14 Scheme 1 depicts the various syn-
thetic steps leading to dialdehydes 7b, 7c, and 9. The
Bouveault formylation22 of 1,4-dibromo-2,5-dioctyloxy-
benzene (1) and subsequent chromatographic purifica-
tion provided 1-formyl-4-bromo-2,5-dioctyloxybenzene
(2) in 74.6% yield alongside negligible among of 2,5-
dioctyloxyterephthalaldehyde. The Pd-catalyzed eth-
ynylation of 2 with trimethysilylacetylene afforded 2,5-
dioctyloxy-4-trimethylsilylbenzaldehyde (3) in 84% yield,
whose hydrolysis with KOH/MeOH led to 4-ethynyl-2,5-
dioctyloxybenzaldehyde in 65% yield. The Pd-catalyzed
cross-coupling reactions4,23 of 1,4-diethynyl-2,5-dioctyl-
benzene19 (5) with 2 equiv of 2 and of 1,4-diiodo-2,5-
bis(2-ethylhexyloxy)benzene14c,20 with 2 equiv of 4 led
to dialdehyde 7b [1,4-bis(formyl-2,5-dioctyloxyphenyl-
ethynyl)-2,5-dioctyloxybenzene] in 69% yield and 7c
[1,4-bis(formyl-2,5-dioctyloxyphenylethynyl)-2,5-di(2-
ethyl)hexyloxybenzene] in 55% yield, respectively. A
small amount (6.8%) of 1,4-bis[(4-formyl-2,5-dioctyloxy)-
phenyl)]but-1,3-diyne (15) was obtained alongside 7c.
The dialdehyde 9 (9,10-bis[(4-formyl-2,5-dioctyloxy)-
phenylethynyl]anthracene) was synthesized through the
cross-coupling reaction of 9,10-dibromoanthracence21
with 2 equiv of 4; it was obtained as a purple-red
substance in a yield of 60.5% after purification through
column chromatography. All the peaks from the 13C
NMR spectra of 7c and 9 in deuterated chloroform can
be readily assigned to their corresponding carbons.
code
Mh n
Mh w
Mp
PDI Dh P
T5%/°C T10%/°C
13a b 29 400 82 500 66 500 2.8
13a a 27 500 62 400 53 300 2.2
13bb 16 300 37 100 35 500 2.2
13cc 15 400 77 200 51 000 5.0
17
14
12
11
16
386
361
356
352
350
424
400
381
379
371
14
25 600 51 200 44 700 2.0
a
Values are given for 5%, T5%, and 10%, T10%, weight loss.
the Michealis-Arbuzov reaction of benzyl bromide (10)
and triethyl phosphite in 87% as shown in Scheme 1)
in the reaction medium after a reaction time of 2 h. The
polymers were obtained in yields above 70% as orange-
red materials in the case of 13 and as a dark purple-
red substance in the case of 14. All the polymers were
readily dissolved in common organic solvents such as
THF, chloroform, toluene, chlorobenzene, and dichloro-
methane. The chemical structures of the polymers were
confirmed by IR (KBr), 1H NMR, 13C NMR, and elemen-
tal analysis. The 13C NMR (100 MHz, CDCl3) of polymer
13cc is similar to that of 13a b,14c apart from the
additional signals at 11 and 40 ppm typical of 2-ethyl-
hexyloxy side groups. From the 1H NMR (400 MHz,
CDCl3) of 14, the protons of the alkyl side chains appear
upfield in the region between 0.84 and 2.05 ppm. The
signals of the protons of the -CH2- group adjacent to
oxygen were detected between 3.62 and 4.20 ppm. The
vinylene and arylene protons peaks were found down-
field between 6.84 and 8.84 ppm. The average molecular
weights were measured by gel permeation chromatog-
raphy (GPC) with polystryrene as standards. THF
served as the eluting solvent. The number-average-
molecular weights, Mh n, were between 15 000 and 30 000
g/mol, leading to degrees of polymerization (DP) between
11 and 17. The polydispersity indexes (PDI) were found
between 2 and 3 except for 13cc, whose PDI was 5. Data
from GPC are given in Table 1.
Polymers 13 and 14 were obtained through the
Horner-Wadsworth-Emmons olefination reaction24 of
dialdehydes 7 or 9 with bisphosphonates 12 as depicted
in Scheme 2. End-capping was carried out in the case
of 13bb and 13cc by adding freshly distilled benzalde-
hyde and benzyldiethylphosphonate (11) (obtained from
According to thermogravimetric analysis (TGA), the
polymers are thermostable compounds. The start of the

5464 Egbe et al.
Macromolecules, Vol. 36, No. 15, 2003
Ta ble 2. Da ta fr om th e UV-Vis Absor p tion Sp ectr oscop y in Dilu te Ch lor ofor m Solu tion a n d in th e 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
opt
code
concn/M
λ
max,abs/nm
ꢀmax/M-1 cm-1
λ
10%max/nm
λT/nm
Eg (10%)/eVa
Eg (T)/eVb
7a
7b
7c
9
0.93 × 10-5
1.85 × 10-5
1.10 × 10-5
1.30 × 10-5
8.6 × 10-6 c
7.6 × 10-3 c
6.2 × 10-6 c
5.0 × 10-3 c
7.0 × 10-6 c
1.4 × 10-2 c
8.8 × 10-6 c
1.4 × 10-2 c
9.1 × 10-6 c
1.3 × 10-2 c
421
423
423
512
472
491
468
496
469
484
470
485
547 (sh: 587)
548, 581
60 750
57 060
51 300
71 140
101 160c
478
474
472
534
520
551
521
558
524
554
521
551
614
651
465
468
468
534
522
554
520
560
523
557
523
554
622
633
2.59
2.61
2.62
2.32
2.38
2.25
2.38
2.22
2.36
2.24
2.38
2.25
2.01
1.90
2.66
2.64
2.64
2.32
2.37
2.24
2.38
2.21
2.37
2.23
2.37
2.24
1.99
1.95
13a b
13a bd
13a a
13a a d
13bb
13bbd
13cc
13ccd
14
86 300c
69 310c
105 200c
82 240c
14d
a
opt
b
opt
d
Eg
) hc/λ10%max
.
Eg
) hc/λT. c Per mole of the constitutional unit. Solid state.
(10%)
(T)
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
code
7a
7b
7c
λ
exc/nm
λ
max,em/nm
shift/nm fwhm/nm φfl/%
423
424
424
512
472
491
472
496
464
484
472
485
515
581
466
468
468
43
45
45
12
47
62
47
56
51
109
51
57
30
41
53
53
58
26
36
114
37
67
67
119
59
73
65
67
80
70
29
77
54
60
23
65
45
56
24
9
524 (sh: 563)
519 (sh: 560)
553, 591
519 (sh: 560)
552, 592
520 (sh: 560)
559, 593
521(sh: 560)
542, 582
13a b
13a ba
13a a
13a a a
13bb
13bba
13cc
13cca
14
F igu r e 1. Absorption and emission spectra in dilute CHCl3
solution of monomers 7c and 9.
67
45
78
577 (sh: 615)
622 (sh: 665)
14a
Figure 1 illustrates the absorption and emission
spectra of monomer 7c (representative of all the mono-
mers of type 7) and of the anthracene-containing
monomer 9. Monomers 7 are characterized with absorp-
tion maxima at 421-423 nm and emission maxima
around 468 nm. An optical band gap energy of 2.60 eV,
extinction coefficients around 60 000 M-1 cm-1, and
quantum yields between 60 and 70% were obtained for
these compounds. The presence of anthracenylene unit
in 9 leads to a 90 nm bathochromic shift of its λmax, abs
thermal degradation under air lies between 350 and 386
°C, where 5% weight loss was recorded (Table 1). No
glass transition temperature, Tg, was obtained for all
polymers by DSC measurements while heating to
295 °C.
The photophysical characteristics of polymers 13 and
14 and the monomers 7 and 9 were studied by UV-vis
absorption and photoluminescence in dilute chloroform
solution (concentration ≈ 10-6 M) as well as in the solid
state. The absorption maxima, λmax,abs, the solution
concentrations, the extinction coefficients at the maxi-
mum wavelength, ꢀmax, and the optical band gap ener-
gies, Egopt, are given in Table 2. Two ways to determine
opt
located at 512 nm (Eg ) 2.3 eV, ꢀ ) 71 140 M-1 cm-1),
relative to 7. Its well-resolved fluorescence curve has
its maximum at 524 nm and a low-energy peak at 563
nm. The very sharp emission of 9 is characterized with
a fwhm value of 26 nm and a Stokes shift of 12 nm,
which are less than half of the corresponding values of
7, resulting in a higher fluorescence quantum yield of
80% after exciting at 512 nm or φfl > 95%, when the
excitation was done at 480 nm.
Identical absorption spectra were obtained for all
polymers 13 in dilute chloroform solution, which are
characterized with a maximum peak around 470 nm
(Figure 2). As expected is the anthracene-containing
polymer 14 red-shifted relative to 13; its absorption
spectrum consists of a maximum at 547 nm and a
shoulder at 587 nm. Optical band gap energies of 2.36-
2.38 and 2.0 eV are obtained for 13 and 14, respectively;
their extinction coefficients are between 70 000 and
100 000 M-1 cm-1. The dilute solution emission spectra
of polymers 13 are well-resolved and are made up of a
maximum at 520 nm and a low-energy shoulder at 560
nm. However, both the intensity of the shoulder relative
to the main peak and the fwhm value increase from the
long linear (octadecyloxy) side chains polymers (fwhm
opt
the Eg of each substance have been presented in Table
2, namely from values of 10% of the absorption maxi-
mum (taken from the lower energy side), λ10%max, and
of the intersection of the tangential through the turning
point of the lower energy side of the spectrum and the
lengthened baseline for each substance, λT.25 Both
determination methods lead to identical results only
when the slope of lower energy side is steep enough,
which is also a prerequisite for the determination of the
opt
Eg
from the cross-point between absorption and
emission spectra.15d This condition is fulfilled by all our
compounds except 14, whose solution absorption spec-
trum has a lower energy shoulder at 587 nm. The
excitation wavelengths, λexc, the emission maxima,
λ
max,em, the Stokes shift, the full width at half-maximum
(fwhm) of the emission curves, and the fluorescence
quantum yields, φfl, are presented in Table 3. All the
emission data given here were obtained after exciting
at the main absorption peak.

Macromolecules, Vol. 36, No. 15, 2003
Arylene-Ethynylene/Arylene-Vinylene Polymers 5465
F igu r e 2. Absorption and emission spectra in dilute CHCl3 solution of polymers 13 and 14.
F igu r e 3. Solid-state absorption and emission spectra of polymers 13 and 14 (thin films spin-casted from 10-2 to 10-3
M
chlorobenzene solution).
) 36 nm for both 13a a and 13a b ) over the short
branched (2-ethylhexyloxy) side chains polymer (fwhm
) 51 nm for 13cc) to the short linear side chains
polymer (fwhm ) 67 nm for 13bb). From these observa-
tions, one can ascribe the emission from the long side
chains polymers as coming basically from isolated main
chain fluorophores; the emission from short side chains
polymers is a contribution of isolated main chain fluo-
rophores and a certain degree of aggregation. This can
be attributed to the lyotropic behavior of this class of
compounds as observed on polarized optical micros-
copy.14b,c The φfl values between 60% and 80% were
obtained for these compounds. The shape of the emis-
sion curve of 14 is similar to that of 13; it is however
red-shifted and consists of a maximum at 577 nm and
a shoulder at 615 nm. Its fwhm value of 45 nm is closer
to those of 13a a and 13a b, due to the presence of
octadecyl side chains. The existence of a strong overlap
of the absorption and emission spectra, greatly inducing
self-reabsorption might explain the relatively (to 13)
lower photoluminescence quantum yield of 56% for 14,
despite its lower Stokes shift of 30 nm.
Transparent thin films of our polymers were spin-casted
on a quartz substrate from a chlorobenzene solution
(concentration ≈ 10-3-10-2 M), leading to thicknesses
between 100 and 150 nm. Chlorobenzene as solvent is
known to interact preferentially with aromatic rings,
causing the polymer chains to lie open and flat and
thereby enhancing π-stacking between neighboring
chains and aggregate formation.26 This contributes to
lower the photoluminescence efficiency of the polymers
in thin films compared to the solution. The enhanced
planarization of the conjugated backbone gives rise to
the bathochromic shift of the absorption and emission
spectra of the polymers 13 and 14 in the solid state,
shown in Figure 3, as compared to their solution
samples.
Contrary to the solutions where the dependence of the
photophysical properties of polymers 13 on the side
groups is minimal, the solid-state properties are greatly
dependent on the nature (linear or branched), size, and
location of the grafted alkoxy side groups. The absorp-
tion maximum of polymers 13a a , 13a b, 13bb, and 13cc
appears at 496, 491, 484, and 485 nm, respectively,
clearly indicating that longer side groups (R1 and/or R2
) octadecyl) enable a bathochromic shift of the maxi-
mum peak. An optical band gap energy, Egopt, of 2.21-
The properties of conjugated polymers thin films are
quite sensitive to chain packing morphology, which can
vary dramatically depending on preparation conditions.1d

5466 Egbe et al.
Macromolecules, Vol. 36, No. 15, 2003
2.24 eV was obtained for these compounds. The an-
thracene-containing compound 14 has a red-shifted
absorption curve, which consists of two maxima at 548
and 581 nm (corresponding respectively to the solution
main peak at 547 nm and the shoulder peak at 587 nm)
opt
and an Eg of 1.90 eV.
The grafting of longer linear side chains (octadecyl
in 13a a ) or short branched side chains (2-ethylhexyl in
13cc) at position R2 provides very sharp and well-
resolved emission spectra. An identical fwhm value of
67 nm was obtained for both polymers; however, the
positions of their maxima are different. While the
emission peaks in 13a a are found at 552 and 592 nm,
those in 13cc are 10 nm blue-shifted and are located at
542 and 582 nm, which may be due to a greater
nonplanarity of the conjugated backbone resulting from
the presence of the bulky branched 2-ethylhexyl side
chains. The curve of 13cc moreover shows a tailed
emission in the region of 600-670 nm. The intensity of
the peak at 552 nm for 13a a or at 542 nm for 13cc is
greatly higher than that at 592 nm for 13a a or at 582
nm for 13cc. The shape of their emission curves and
their high fluorescence quantum yields of 54% (13a a )
and 45% (13cc) are evidence of minimal contribution
of aggregation species (excimers) during the photo-
luminescence process.
F igu r e 4. Photoconductivity spectra of thin films of polymers
13 and 14 [surface type cell, slit width 0.2 mm, light intensity
20 µW, threshold voltage of 20 V (A) and of 10 V (B)].
Excimer contributions are clearly evident in the case
of polymers 13a b and 13bb having short linear side
chains (R2 ) octyl) at the phenylene-vinylene segments,
which are reflected by the shape of their curves, their
relatively (to 13a a and 13cc) higher fwhm values of 114
nm (for 13a b) and 119 nm (for 13bb), and lower
fluorescence quantum yields of 29% (for 13a b) and 23%
(for 13bb). Although the grafting of longer side chains
(octadecyl) at R1 in 13a b does not lead to the same effect
as when grafted at R2, it however contributes, to a
smaller extent, in the limitation of the excimer emission.
This explains the differences in emission data (fwhm
values, Stokes shift and φfl) obtained for 13a b and 13bb,
which has both R1 and R2 equal to octyl. While in 13a b
the emission peak at 553 nm is more intense than that
at 591 nm, in 13bb the maximum at 553 nm is slightly
lower than that at 592 nm.
maximum photocurrents ranging from 2.0 × 10-11 A at
19 400 cm-1 to 2.0 × 10-10 A at 19 000 cm-1, probably
as a result of different conformational structures caused
by the bulky 2-ethylhexyl side chains.
When materials are used as an emissive layer for
organic light-emitting diodes (OLEDs) or as a donor (or
acceptor) component in organic photovoltaic devices
(OPVDs), matches of their valence band (HOMO) and
their conduction band (LUMO) energy levels with work
functions of the electrodes and/or with the HOMO and
LUMO energy levels of other components of the OPVDs
as well as their optical, electrical, and chemical stability
are of paramount importance. The ionization potential
(IP, i.e., the highest occupied molecular orbitals (HOMO)
of an organic molecule) is determined through ultra-
violet photoelectron spectroscopy.27 The electron affinity
(EA, i.e., the lowest unoccupied molecular orbitals
(LUMO) of the organic molecule) is deduced from the
IP value and the band gap obtained from the absorption
spectrum, which is not a direct means of determination.
Cyclic voltammetry (CV) and/or differential pulse po-
larography (DPP) are easy and effective methods to
measure redox potentials and to simultaneously evalu-
ate both the HOMO and LUMO energy levels and the
band gap energy, Egec, of a polymer. The electrochemical
processes are similar to the charge injection and trans-
port in LED and photovoltaic devices.
The emission spectrum of the film of 14 is of almost
similar shape as the solution sample, although red-
shifted. It consists of a maximum at 621 nm and a
shoulder at 665 nm. A fwhm value of 78 nm and a
photoluminescence quantum yield of 24% were obtained
for this compound.
Both types of polymers 13 and 14 are photoconductive
even without any sensitizer (Figure 4). Three thin film
samples of each polymer, obtained from chlorobenzene
solution, and of thickness between 100 and 150 nm,
were measured for the purpose of reproducibility.
Photoconductivity is detected already at 10 V from
polymers 13a a , 13a b, and 14, which have in common
octadecyloxy side groups, confirming the assumption
that photoconductivity is more an intramolecular proc-
ess than an intermolecular one.14c The maximum photo-
current, Iph, was 1.1 × 10-9 A at 20 000 cm-1 for 13a a ,
3.9 × 10-11 A at 18 900 cm-1 for 13a b, and 3.8 × 10-11
A at 16 800 cm-1 for 14. A voltage of 20 V is needed to
detect photoconductivity from polymers with shorter
side groups, 13bb and 13cc. Iph of 13bb was 2.0 × 10-10
A at 20 000 cm-1. The photoconductivity spectra of all
polymers were approximately reproducible except 13cc,
whose three measured samples provided spectra having
The CV was carried out in dichloromethane at a
potential scan rate of 167 mV/s and the DPP at 20 mV/
s. Ag/AgCl served as the reference electrode; it was
1/2
ferrocene
calibrated with ferrocene (E
) 450 mV vs Ag/
AgCl). The working and the counter electrodes were a
platinum disk. The supporting electrolyte was tetra-
butylammonium hexafluorophosphate (n-Bu4NPF6) in
anhydrous dichloromethane (10-3 M). The onset poten-
tials are the values obtained from the intersection of
the two tangents drawn at the rising current and the
baseline charging current of the CV and the DPP curves.

Macromolecules, Vol. 36, No. 15, 2003
Arylene-Ethynylene/Arylene-Vinylene Polymers 5467
F igu r e 5. Cyclic voltammetry for oxidation (A) and reduction (B) of monomer 7a and polymer 13a a and differential pulse
polarography for oxidation (C) and reduction (D) of monomers 7a and 9 and polymers 13a a , 13a b, and 14.
Ta ble 4. Red ox P oten tia ls (vs Ag/AgCl), Electr och em ica l En er gy Ga p s, HOMO a n d LUMO En er gies As Obta in ed fr om
Cyclic Volta m m etr y a n d Differ en tia l P u lse P ola r ogr a p h yc
code
Ered/onset/V
Ered/peak/V
Eox/onset/V
Eox/peak/V
Egec/onset/eV
Egec/peak/eV
EHOMO/eV
ELUMO/eV
7a a
-0.73
-0.76
-0.85
-0.80
-0.80
-0.70
-0.88
-0.65
-0.75
-0.60
-0.76
-0.76
-0.84
-0.67
-1.09
-1.08
-1.18
-1.22
-1.10
-1.07
-1.19
-1.10
-1.09
-0.97
-1.21
-1.12
-1.24
-1.10
1.32
1.28
1.16
1.10
0.80
0.77
0.88
0.87
0.80
0.77
0.88
0.80
0.71
0.75
1.43
1.39
1.28
1.21
0.85
1.41
0.93
1.21
0.88
1.43
0.93
2.05
2.04
2.01
1.90
1.60
1.47
1.76
1.52
1.55
1.37
1.64
1.56
1.54
1.42
2.52
2.46
2.46
2.43
1.95
2.48
2.12
2.31
1.97
2.40
2.14
-5.67
-5.63
-5.51
-5.45
-5.15
-5.12
-5.23
-5.22
-5.15
-5.12
-5.23
-5.15
-5.06
-5.10
-3.62
-3.59
-3.50
-3.55
-3.55
-3.65
-3.47
-3.70
-3.60
-3.75
-3.59
-3.59
-3.51
- 3.68
7a b
9a
9b
13a ba
13a bb
13a a a
13a a b
13bba
13bbb
13cca
13ccb
14a
0.90
1.26
2.14
2.38
14b
a
b
Obtained from cyclic voltammetry. Obtained from differential pulse polarography. c EHOMO/ELUMO ) [-(Eonset - 0.45) - 4.8] eV where
the value 0.45 V for ferrocene vs Ag/Ag+ and 4.8 eV the energy level of ferrocene below the vacuum.
Several ways to evaluate HOMO and LUMO energy
0.90 V with estimated onset values around 0.80 V
obtained for all polymers. 13a a , moreover, shows a very
shallow second oxidation peak around 1.37 V. The
oxidation CV traces of the monomers 7 and 9 show
peaks respectively at 1.44 V (onset at 1.32 V) and 1.28
V (onset at 1.16 V). The CV reduction process was
reversible for all compounds. Reduction peaks around
-1.10 to -1.20 V (onset values between -0.70 and
-0.88 V) were obtained. These values were confirmed
by the DPP reduction processes (Ered/peak ) -0.97 to
-1.22 V and Ered/onset ) -0.65 to -0.80 V). In compari-
son with the reduction, the DPP oxidation processes
provided broader signals for the polymers than for the
monomers. The curve of the electron-rich anthracene-
containing polymer 14 has the smallest onset value of
0.75 V and a very broad almost plateaulike maximum,
levels from the onset potentials, Eox/onset and Ered/onset
,
have been proposed in the literature.25,28-31 They were
estimated here on the basis of the reference energy level
of ferrocene (4.8 eV below the vacuum level)29 according
to the following equation: EHOMO/ELUMO ) [-(Eonset
-
0.45) - 4.8] eV. Figure 5 shows representatively the CV
traces for oxidation and reduction of 7a and 13a a the
DPP traces for oxidation and reduction of 7a , 9, 13a a ,
13a b, and 14. The onset and the peak potentials, the
electrochemical band gap energy, and the estimated
position of the upper edge of the valence band (HOMO)
and of the lower edge of conduction band (LUMO) are
listed in Table 4.
The CV for oxidation did not provide clear and sharp
peaks. Peaks of very low intensity were obtained around

5468 Egbe et al.
Macromolecules, Vol. 36, No. 15, 2003
whose lowest point was located at 1.26 V. Its corre-
sponding monomer 9 has its peak centered at 1.21 V
with a relatively higher onset value of 1.10 V. 1.21 V is
also the maximum of the oxidation peak of 13a a , whose
onset value at 0.87 V is smaller than that of its
corresponding monomer 7a , found at 1.28 V. The DPP
peak of 7a is found at 1.39 V. It is similar to that from
its CV trace and is of almost the same range as those
from the DPP oxidation curves of 13b b (1.43 V) and
13a b (1.41 V). Polymer 13a b is moreover characterized
with a shoulder peak at 0.86 V, which corresponds to
the CV oxidation peak around 0.90 V of these polymers.
the grafted alkoxy side groups. Photoconductivity is
easily detected in polymers having octadecyloxy chains
(13a a , 13a b, and 14). Long linear (octadecyl) or short
branched (2-ethylhexyl) side chains at position R2 (in
the phenylene-vinylene segment) are required to obtain
sharp and well-resolved emission spectra accompanied
by high fluorescence quantum yields. The quasi-donor
(phenylene-vinylene segment) and -acceptor (arylene-
ethynylene segment) nature of these polymers could
explain the great discrepancy between the electrochemi-
cal band gap and optical band gap energies. These
polymers are presently used in the design of OLEDS
and organic photovoltaic devices.
We assume from these observations that the broad
DPP oxidation peak of the polymers is actually a
superimposition of two oxidation steps. The first oxida-
tion step occurs around the phenylene-vinylene seg-
ment of the polymer which can be linked to the shoulder
peak at 0.86 V in the case of 13a b or the very weak CV
oxidation peaks around 0.90 V for all the polymers.
These values are closer to 0.70 V of the oxidation peak
potential of MEH-PPV measured under the same
conditions.32 The second oxidation step, which can be
ascribed to the peaks around 1.40 V, involves the
arylene-ethynylene part of the polymer.33 The reduc-
tion peak potential at around -1.10 V proves that the
reduction processes are limited basically on the arylene
ethynylene section of the compounds due to the high
electron affinity of the triple bonds.23d Despite the
extended π-conjugation of the backbone of 13 and 14,
one can consider, to a certain extent, these compounds
to be donor-acceptor copolymers. The phenylene-
vinylene segment would act as the donor and the
arylene-ethynylene segment as the acceptor. This
would explain the great discrepancy between the band
Ack n ow led gm en t. We gratefully thank Dr. Eck-
hard Birckner for carrying out the photoluminescence
measurements in solution.
Su p p or tin g In for m a tion Ava ila ble: 13C NMR spectrum
(62 MHz, CDCl3) of monomer 7c, 13C NMR spectrum (62 MHz,
CDCl3) of monomer 9, 13C NMR spectrum (100 MHz, CDCl3)
of polymer 13cc, 1H NMR spectrum (400 MHz, CDCl3) of
polymer 14, and the TGA curves of polymers 13 and 14. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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