Donor-acceptor polymers: A conjugated oligo(p-phenylene vinylene) main chain with dangling perylene bisimides

Article abstract of DOI:10.1002/chem.200400097

Two new donor-acceptor copolymers that consist of an enantiomerically pure oligo(p-phenylene vinylene) main chain with dangling perylene bisimides have been synthesized by using a Suzuki cross-coupling polymerization. Absorption and circular dichroism spe

Full text of DOI:10.1002/chem.200400097

FULL PAPER
Donor Acceptor Polymers: A Conjugated Oligo(p-Phenylene Vinylene)
Main Chain with Dangling Perylene Bisimides
Edda E. Neuteboom, Paul A. van Hal, and Renÿ A. J. Janssen*[a]
Abstract: Two new donor acceptor co-
polymers that consist of an enantiomer-
ically pure oligo(p-phenylene vinylene)
main chain with dangling perylene bisi-
mides have been synthesized by using a
Suzuki cross-coupling polymerization.
Absorption and circular dichroism
spectroscopy revealed that the transi-
tion dipole moments of the donor in
the main chain and the dangling ac-
ceptor moieties of the copolymers are
coupled and in a helical orientation in
solution, even at elevated tempera-
tures. A strong fluorescence quenching
of both chromophores indicates an effi-
cient photoinduced charge transfer
after photoexcitation of either donor
or acceptor. The formation and recom-
bination kinetics of the charge-separat-
ed state were investigated in detail
with femtosecond and near-steady-state
photoinduced absorption spectroscopy.
The charge-separated state forms
within 1 ps after excitation, and recom-
bination occurs with a time constant of
45 60 ps, both in solution and in the
solid state. These optical characteristics
indicate a short distance and apprecia-
ble interaction between the electron-
rich donor chain and the dangling elec-
tron-poor acceptor chromophores.
Keywords: donor acceptor
tems ¥ electron transfer ¥ photo-
chemistry polymers time-
resolved spectroscopy
sys-
¥
¥
Introduction
ing and large-scale phase separation of the donor and ac-
ceptor phases, which may occur when the two individual
moieties are mixed. By virtue of the covalently linked struc-
ture, a bicontinuous network on a molecular scale is formed.
In photovoltaic devices based on double-cable polymers,
holes are expected to move away from the electron accept-
ors by intrachain and interchain migration, while the elec-
trons can hop between the acceptor units. The majority of
double cable polymers reported in the literature have fuller-
ene C60 as the dangling acceptor unit. These materials have
been synthesized by either electrochemical polymeriza-
An increasing number of polymers is being reported that
contain donor and acceptor moieties incorporated in the
main chain, as endgroups, pendant groups, or as block co-
polymers.[1 These donor acceptor polymers are designed
7]
to enable energy and electron transfer in the electronically
excited state of the polymer, and thereby create novel opto-
electronic properties for application in light-emitting diodes
and photovoltaic cells.
Especially in solar cells, mesoscopic ordering of donor
and acceptor moieties is crucial for the creation of a photo-
active layer that is able to convert absorbed photons effi-
ciently into electrons and holes as well as for the subsequent
transportation of these charges to the electrodes. One at-
tractive strategy is the preparation of ™double-cable∫ poly-
mers.[8] These polymers consist of a conjugated donor main
chain (donor ™cable∫) bearing a number of closely spaced
acceptor moieties (acceptor ™cable∫). Double-cable poly-
mers are designed to ensure an intimate contact between
donor and acceptor segments by avoiding extensive cluster-
12]
tion,[9 chemical polymerization,[13,14] or by grafting a func-
tionalized conjugated polymer with fullerene C60 moiet-
ies.[10,15,16] In addition to fullerene-based double-cable poly-
mers, polythiophenes with pendant tetracyanoanthraquino-
dimethane moieties have been reported.[17,18] Although some
of these double-cable polymers were incorporated in work-
ing photovoltaic devices,[13,14] their photophysical properties
have not been studied on short timescales. Hence, the de-
tailed kinetics of charge separation and recombination in
double-cable polymers is unknown.
Recently, there has been an increasing interest in the in-
corporation of perylene bisimides as energy- or electron-ac-
5,19 25]
ceptors with conjugated oligomers or polymers.[1
We
[a] Dr. E. E. Neuteboom, Dr. P. A. van Hal, Prof. R. A. J. Janssen
Molecular Materials and Nanosystems
Eindhoven University of Technology
have reported on the properties of two alternating copoly-
mers of oligo(p-phenylene vinylene) (OPV) and perylene
bisimide that exhibit an efficient charge separation in solu-
tion and in the solid state.[26] The photophysical properties
P.O. Box 513 5600 MB Eindhoven (The Netherlands)
Fax : (+31)40-2451036
E-mail: R.A.J.Janssen@tue.nl
Chem. Eur. J. 2004, 10, 3907 3918
DOI: 10.1002/chem.200400097
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPER
in the solid state indicated that these polymers form stacks
of alternating OPV and perylene bisimide units in the solid
state as a result of favorable interactions of the electron-rich
donor moieties with the electron-poor acceptor units, similar
to the Aedamers (aromatic electron donor acceptor-mers)
pioneered by Lokey and Iverson.[27] Another attempt to
mesoscopically organize OPV and perylene bisimide chro-
mophores has been reported for a triad consisting of two tri-
dodecyloxy-OPV units attached to a central perylene bis-
imide core that possesses a liquid-crystalline mesophase
and, hence, provides a handle to achieve ordered morpholo-
gies upon annealing.[28] Indeed, charge recombination was
reduced in more ordered phases as a consequence of im-
proved charge transport. Changing the polymer architecture
from a linear array of alternating donors and acceptors to a
conjugated donor main chain with pendant acceptors, could
induce differences in the photophysical properties. With this
in mind, new polymers involving OPV and perylene bisimide
were designed.
Herein we present the synthesis and photophysical prop-
erties of two new copolymers (P1 and P2, Scheme 1) that
consist of enantiomerically pure OPV donor segments in the
main chain alternating with phenylenes carrying a pendant
perylene bisimide acceptor. These polymers differ with re-
spect to the substitution pattern of the phenylene ring con-
necting two OPV units. For P1, the OPV units are placed in
the para positions with respect to each other, while in P2
they are in a meta configuration.
emic 2-ethylhexyl bromide, yielding alcohol 2. Subsequently,
alcohol 2 was coupled under Mitsunobu conditions with
enantiomerically pure tert-butyl ((S)-1-hydroxymethyl-3-
methylbutyl)carbamate (3)[26] to the butoxycarbonyl (BOC)-
protected diether 4, which was deprotected with trifluoro-
acetic acid (TFA) and NaHCO3 to afford the free amine 5.
N,N’-Bis(1-ethylpropyl)perylene-3,4:9,10-tertacarboxylic-bis-
imide (6)[30] was partially hydrolyzed with potassium hydrox-
ide in tert-butyl alcohol to the anhydride imide 7.[31,32] The
final reaction of amine 5 with monoanhydride 7 resulted in
perylene bisimide 8, which was obtained as a mixture of two
diastereomers.
The perylene bisimide co-monomer for P2 (Scheme 3)
was synthesized starting with a Mitsunobu reaction of 2,4-di-
bromophenol (9) with alcohol 3 that lead to the formation
of ether 10. After deprotection of 10 with TFA and
NaHCO3, amine 11 was treated with the anhydride 7 to
afford the perylene bisimide 12. Monomer 13, which is used
as a reference compound for monomer 12, was obtained by
a Williamson etherification of phenol 9 with racemic 2-eth-
ylhexyl bromide.
In all polymerization reactions, bisboralane (E,E)-1,4-
bis{4-{4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl-}-2,5-
bis[(S)-2-methylbutoxy]styryl}-2,5-bis[(S)-2-methylbutoxy]-
benzene (14)[26] was allowed to react with the chosen dibro-
moaryl co-monomer in a palladium-catalyzed Suzuki reac-
tion (Scheme 4). Reaction of co-monomer 14 with perylene
bisimide co-monomers 8 and 12 resulted in the formation of
perylene bisimide-substituted polymers P1 and P2, respec-
tively. Likewise, polymerization of 14 with 1,4-dibromo-2,5-
di(2-ethylhexyloxy)benzene (15)[33,34] and 13 provided the
corresponding reference polymers RP1 and RP2 that have
the same main chains as P1 and P2; however, they lack the
dangling perylene bisimide chromophores. The polymers
Results and Discussion
Synthesis: To synthesize polymers P1 and P2, two different
perylene bisimide co-monomers were prepared that were
subsequently allowed to react with an OPV monomer in a
Suzuki polymerization.
The first step in the synthesis of the chiral perylene bis-
imide co-monomer for P1 (Scheme 2) was the Williamson
etherification of 2,5-dibromobenzene-1,4-diol (1)[29] with rac-
1
were characterized by H and 13C NMR spectroscopy, and
size-exclusion chromatography (SEC). The molecular
weights and polydispersities (PDI), determined by SEC in
chloroform versus polystyrene standards, are Mn
=
8.2 kgmolꢀ1 for P1 and Mn = 8.0 kgmolꢀ1 for P2 and a
Scheme 1. Structures of donor acceptor copolymers P1 and P2.
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Donor Acceptor Polymers
3907 3918
Scheme 2. Synthesis of the perylene bisimide monomer 8: a) K2CO3, 2-ethylhexyl bromide, ethanol, reflux, 28%; b) PPh3, DEAD, toluene, 36%;
c) i) TFA, CH2Cl2; ii) NaHCO3, 91%; d) KOH, tBuOH, 20%; e) DMF, 1558C, 39%.
Scheme 3. Synthesis of the perylene bisimide monomer 12 and the reference monomer 13: a) PPh3, DEAD, toluene, 28%; b) i) TFA, CH2Cl2; ii) NaH-
CO3, 83%; c) DMF, 1608C, 69%. d) K2CO3, ethanol, reflux, 24%.
PDI of 3.3 and 2.8, respectively. Hence these polymers have
a rather low degree of polymerization (n = 5 6 units). The
mers and the reference polymers is not known; however,
the solubility of the polymers might play a role because the
products precipitate in the reaction mixture. The integrals of
reference polymers have higher molecular weights of Mn
=
24.6 kgmolꢀ1 (RP1, PDI
=
4.5, n
=
22) and Mn
=
the H NMR spectra show that the perylene bisimide mono-
1
13.8 kgmolꢀ1 (RP2, PDI = 3.5, n = 14), with a correspond-
ingly higher degree of polymerization. The reason for the
difference with respect to Mn of the donor acceptor poly-
mers (or their respective reference monomers) and the
OPV monomer are incorporated in an equimolar fashion in
all four polymers.
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R. A. J. Janssen et al.
FULL PAPER
Scheme 4. Overview of the synthesis of the perylene bisimide-substituted polymers P1 and P2, their reference polymers RP1 and RP2, and the structure
of model compound 16. a) [Pd(PPh3)4], K2CO3, water, THF, 908C, 72%; b) [Pd(PPh3)4], K2CO3, water, THF, 908C, 75%; c) [Pd(PPh3)4], K2CO3, water,
THF, 908C, 51%; d) [Pd(PPh3)4], K2CO3, water, THF, 908C, 55%.
Absorption spectra in solution: The polymers and model
compound 6 were also characterized with UV/Visible ab-
sorption spectroscopy in toluene solution (Figure 1). The
perylene bisimide segment (PERY) absorbs at l = 458 nm,
489 nm and 526 nm, as demonstrated by 6. The maximum of
the absorption of RP1 at l = 431 nm is slightly red-shifted
compared to that of RP2 at 426 nm, as a result of the differ-
ent topology at the phenylene rings connecting the OPV
segments. In RP1, the para-phenylene ring causes a slightly
more effective conjugation of the adjacent OPV segments
than in RP2, in which the OPV segments are linked by
meta-phenylene. The absorption spectra of P1 and P2 clear-
ly show that both the OPV backbone and the perylene bis-
imide are incorporated. It seems, however, that in both
cases the absorption intensity in the 400 470 nm region is
too high compared to the perylene absorption at 528 nm. It
is unlikely that this is caused by to a significant deviation
from the equimolar incorporation of the OPV and perylene
A possible explanation is an electronic interaction between
the two chromophores, which was also observed for a mac-
rocycle containing exactly one OPV and one perylene bis-
imide that shows the same deviation.[26] When the two chro-
mophores are in close proximity and the angle between
their transition dipole moments is less than the magic angle
of 54.78, exciton coupling will increase the probability of the
high-energy transition of the OPV segments compared to
that of the low-energy transition of the perylene bisimide,
resulting in increased absorption at lower wavelengths. Be-
cause of the flexible linker between the backbone and the
perylene bisimides, such electronic coupling is also possible
in polymers P1 and P2. Absorption spectra in toluene were
recorded as a function of the temperature in the range from
20 to 908C, with heating steps of 108C (Figure 2a,c). The
UV/Vis spectra show a small blue shift with increasing tem-
perature, which is commonly observed for dialkoxy-substi-
tuted PPVs.[35] In addition, the intensity of the band at lꢁ
430 nm decreases slightly relative to the band at ꢁ530 nm.
This might indicate a decreasing electronic interaction. The
1
bisimide monomers in the polymer chain because H NMR
spectroscopy confirmed that their ratio is 1:1 in P1 and P2.
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Figure 1. Absorption spectra in toluene of a) P1, 6, RP1, and b) P2, 6,
RP2 together with the 1:1 summation of the spectra of the reference poly-
mers and 6. The spectra are normalized at ~527 nm. The spectra of RP1
and RP2 are normalized with respect to the normalized spectra of the
summation spectra.
spectral changes observed on changing the temperature are
fully reversible because the original spectra at 208C were re-
covered after cooling the sample from 908C.
Circular dichroism spectra in solution: The stereochemistry
of P1 and P2 can be used to address the electronic interac-
tion between the perylene bisimide and the enantiomerically
pure OPV segments by circular dichroism (CD) spectrosco-
py in more detail. In these polymers, an exciton coupling be-
tween main-chain OPV segments and the pendant chromo-
phores will result in a CD signal when the transition dipole
moments are in a preferential helical orientation with re-
spect to each other. In this case, the preferential helicity can
originate from the interaction between the perylene bis-
imide, having an enantiomerically pure (S)-leucinoxy linker
to the backbone, and the OPV with its enantiomerically
pure (S)-2-methylbutoxy sidechains. The CD spectra of the
polymers P1 and P2 were recorded in toluene as a function
of the temperature in heating steps of 108C, starting at 208C
and ending at 908C (Figure 2b,d). Both polymers exhibit a
negative CD signal at the absorption of the OPV segments
and a positive CD signal at the perylene bisimide absorp-
tion. This indicates exciton coupling between the donor and
the acceptor chromophores with a positive helicity, namely,
a right-handed rotation will superimpose the two transition
dipole moments (which are essentially parallel to the long
axis in both chromophores). This effect has also been ob-
served for an OPV-perylene bisimide macrocycle, which ex-
hibited a similar spectrum.[26] As the temperature increases,
the CD spectra maintain their shape but become gradually
less intense. As in the absorption experiments, the tempera-
ture-dependent CD measurements were also reversible. The
combined data from the UV/Vis and CD spectra indicate
Figure 2. Temperature dependence of the UV/Vis absorption (a and c)
and circular dichroism spectra (b and d) of solutions of P1 (a,b) and P2
(c,d) in toluene, recorded upon heating from 208C to 908C in steps of
108C.
that the two chromophores are in relatively close proximity,
probably as a consequence of the stacking propensity of the
donor chain and the dangling acceptors, with their transition
dipole moments in a right-handed helical orientation with
an angle of less than 54.78.
In fact, polymers P1 and P2 exhibit somewhat different
CD effects for the perylene bisimide manifold. P1 shows a
small bisignated signal at lꢁ530 nm that points to an addi-
tional perylene perylene coupling. A different interaction
between the chromophores in the meta- versus para-con-
nected systems may be considered as a tentative explanation
for this difference. A more detailed understanding can prob-
ably be obtained by investigating the diastereomers of P1
Chem. Eur. J. 2004, 10, 3907 3918
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R. A. J. Janssen et al.
FULL PAPER
Table 1. Free energy of intramolecular and intermolecular charge-sepa-
rated states calculated from Equation (1) (see text for parameters used)
in toluene relative to the ground state and the singlet-excited state of
OPV and PERY.
and P2. In this respect, it is important to mention that al-
though P1 and P2 contain enantiomerically pure (S)-2-
methylbutoxy side chains on the OPV unit and a (S)-leuci-
nol linker at the perylene bisimide, there are some subtle
stereochemical differences. P1 was synthesized from co-
monomers 12 and 14 that resulted in a stereochemical irreg-
ularity along the polymer chain because racemic 2-ethylhex-
yl side chains are used in 14. This stereochemical aspect
does not apply to the polymer P2 because its co-monomer
12 contains only one stereocenter.
DGCS = GCSꢀE00
Rcc [ä]
GCS [eV]
S1 OPV[eV]
S1 PERY[eV]
4
16
150
¥
0.85
1.98
2.32
2.36
ꢀ1.71
ꢀ0.57
ꢀ0.24
ꢀ0.20
ꢀ1.47
ꢀ0.34
0
0.04
Energetics of charge separation: Before addressing the pho-
toinduced charge separation in polymers P1 and P2 experi-
mentally, it is instructive to consider the thermodynamics of
such a process. In general, the Gibbs free energy of an intra-
molecular charge-separated state (GCS) in a covalently
bonded donor acceptor system can be estimated from the
Weller equation.[36]
GCS ¼ e½EoxðDÞꢀEredðAފ
ꢀ
ꢁꢀ
ꢁ
e2
e2
1
1
rꢀ
1
eref
1
es
ð1Þ
ꢀ
ꢀ
þ
þ
4pe0esRcc 8pe0 rþ
To obtain GCS, the first reduction potential Ered(A) of
compound 6 (ꢀ0.65 V versus SCE) in dichloromethane (eref
= 8.93) and the first oxidation potential Eox(D) of OPV
model compound 16 (+0.80 V versus SCE) were used.[26]
Although the backbones of P1 and P2 are more extended,
a comparison with 16 is justified because the absorption
spectra are very similar (lmax = 425 nm for 16), which indi-
cates that the conjugation length in the polymers P1 and P2
is comparable to that of 16. The radius of the PERY anion
(rꢀ
= 4.7 ä) was estimated from the density (1 =
Figure 3. Fluorescence emission spectra in toluene of a) polymers P1 and
RP1 upon excitation at l = 433 nm and compound 6 upon excitation at
l = 529 nm, and of b) polymers P2 and RP2 upon excitation at l =
427 nm and 6 upon excitation at l = 529 nm. The spectra are corrected
for the optical density at the excitation wavelength.
1.59 gcmꢀ3) of N,N’-dimethylperylene-3,4:9,10-tetracarboxyl-
ic-bisimide and from the X-ray crystallographic data with
rꢀ = [3M/(4p1NA)]1/3.[37] The radius of the positive ion of
the OPV segment was estimated in a similar way to be r+
=
5.1 ä.[38] The distance between the centers of the donor and
acceptor segments Rcc was estimated by means of molecular
modeling to be within the range of 4 to 16 ä for both P1
and P2. This wide range of distances is a consequence of
the flexible spacer connecting the phenylene ring of the
backbone and the perylene bisimide. Substitution of these
parameters in Equation (1) shows that the intramolecular
ortho-dichlorobenzene (ODCB). In these experiments, P1
and P2 were excited at either l = 433 nm or 427 nm, and at
529 nm, to ensure (almost) selective excitation of the OPV
segments and the perylene bisimide chromophores, respec-
tively. The fluorescence intensity was compared to the fluo-
rescence of the reference compounds RP1, RP2, and 6
(lmax = 482 485 nm, 485 486 nm, and 534 nm respectively),
which were excited at the same wavelengths as P1 and P2.
The quenching factors Q were determined by comparing the
fluorescence intensities of the OPV and perylene bisimide
chromophores of P1 and P2 with those of RP1, RP2, and 6
at the wavelengths of maximum emission. In toluene, the
fluorescence quenching factors for P1 are QOPV = 390
(compared to RP1) and QPERY = 540 (compared to 6),
while P2 exhibited quenching factors of QOPV = 200 (com-
pared to RP2) and QPERY = 440 (compared to 6). In
ODCB, the quenching is similar with QOPV = 280 and
QPERY = 600 for P1, and QOPV = 200 and QPERY = 400 for
P2.
charge-separated state in the polymers in toluene (es
=
2.38) is lower than the energy of the OPV and PERY singlet
excited states determined from the 0 0 transition of the
fluorescence (S1 OPV = 2.56 eV, S1 PERY = 2.32 eV,
Table 1). In fact, DGCS would still be negative up to a
donor acceptor distance of 150 ä, which is much larger
than the actual distance that can occur in these two poly-
mers. The estimates show that electron transfer in P1 and
P2 is an exergonic reaction, irrespective of whether it origi-
nates from the OPV or perylene bisimide S1 states.
Fluorescence spectra and fluorescence quenching in solu-
tion: The occurrence of an intramolecular photoinduced
electron transfer in P1 and P2 was studied experimentally
by fluorescence spectroscopy in toluene (Figure 3) and
The almost complete quenching of the fluorescence of
both chromophores demonstrates that an efficient charge
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Donor Acceptor Polymers
3907 3918
separation takes place in P1 and P2 after excitation of the
OPV segments in the backbone or the pendant perylene bis-
imides. It is important to note that the small residual fluo-
rescence of P1 and P2 may originate from minute amounts
(<0.5%) of highly fluorescent impurities, such as mono-
mers, and therefore the quenching factors for P1 and P2
should not be taken as absolute values, but should be con-
sidered to be a lower limit of the actual numbers.
fluorescence quenching after selective excitation of the pery-
lene bisimide (QPERY) and the fluorescence lifetime tPERY
=
4 ns of compound 6[26] by means of Equation (3). This gives
kiCS = 1.3î1011 sꢀ1 for P1 and kCi S = 1.1î1011 sꢀ1 for P2,
both in toluene.
QPERYꢀ1
kiCS
¼
ð3Þ
tPERY
As shown in Figure 4, excitation of the OPV segment to
its S1 state may result in the direct formation (kdCS) of a
charge-separated state (CSS) or in an indirect formation of
Because the quenching factors are lower limits, these
rates must also be considered as lower estimates.
Photoinduced absorption in solution: The charge-separated
state can also be monitored by transient photoinduced ab-
sorption (PIA) spectroscopy. In order to investigate the
charge separation and recombination processes, toluene so-
lutions of P1 and P2 were studied by time-resolved femto-
second pump-probe spectroscopy. The polymers were excit-
ed with a ~150 fs pulse at 450 nm or 525 nm to distinguish
between processes occurring from either donor or acceptor
excitation.
Figure 5 shows the normalized transient change in trans-
mission DT/T at 1450 nm (0.86 eV) as a function of the time
delay between the pump and probe pulses arriving at the
Figure 4. Jablonski diagram representing the different photophysical
events that can take place in the donor acceptor (D A) polymers P1
and P2 upon excitation of the OPV backbone (open arrow). The singlet
energy transfer (kET), the direct (kdCS) and indirect (kCi S) electron transfer,
the radiative emission (kR) and non-radiative emission (kNR) are indicat-
ed.
CSS via singlet-energy transfer (kET) to an intermediate per-
ylene bisimide S1 state, followed by charge transfer (kiCS). Of
course, direct excitation of perylene bisimide also gives CSS,
with a rate constant kiCS. It is possible to estimate the rate
constants for charge separation by the direct and indirect
pathways (kdCS and kCi S) and the rate of energy transfer (kET
)
from fluorescence quenching Q (Table 2). The sum of kET
and kdCS can be estimated with Equation (2) from the OPV
fluorescence quenching (QOPV) and the fluorescence lifetime
of the OPV segments tOPV ( = (kDR + kNDR)ꢀ1) (Figure 4),
which equals 0.9 ns for RP1 and 1.1 ns for RP2 in toluene
(determined by time-correlated single-photon counting).
Figure 5. Normalized differential transmission dynamics of toluene solu-
tions of P1 and P2 at room temperature, recorded at l = 1450 nm (low-
energy absorption of OPV radical cations) after excitation at l = 450 nm
and 525 nm.
sample. The probe wavelength of 1450 nm corresponds to
the D0!D1 absorption of the doublet state OPV+C radical
cation and, hence, monitors the formation and decay of the
charge-separated state. The negative value of DT/T is consis-
tent with an absorption attributed to OPV+C radical cations,
which are formed within 0.5 ps (kCS ꢂ2î1012 sꢀ1) after arriv-
al of the pump pulse. For both
QOPVꢀ1
kET þ kdCS
¼
ð2Þ
tOPV
Thus kET + kdCS = 4.3î1011 sꢀ1 for P1 and kET + kdCS
=
1.8î1011 sꢀ1 for P2. Similarly, kCi S can be estimated from the
polymers, the recombination
time constant is ~45 ps for time
delays of 0 250 ps after excita-
tion at 450 nm. When the pery-
lene bisimide chromophores of
P1 and P2 are selectively excit-
ed at 525 nm, charge separation
is equally fast, whereas recom-
bination appears to be slightly
slower, resulting in a lifetime of
~60 ps.
Table 2. Rate constants for energy transfer, direct and indirect charge separation, and charge recombination
as obtained from photoluminescence quenching and pump-probe PIA spectroscopy for P1 and P2 in toluene
solutions and the solid state.
PL quenching[a]
PIA OPV
PIA PERY
QOPV
QPERY
kET + kdCS
kiCS
kiCS or kET + kdCS
kCR
kiCS
[nsꢀ1
kCR
[nsꢀ1
]
[nsꢀ1
]
[nsꢀ1
]
[nsꢀ1
]
]
[nsꢀ1
]
P1
P2
toluene
film
toluene
film
390
200
540
440
430
130
ꢂ2000
ꢂ2000
ꢂ2000
ꢂ2000
22
18
22
16
ꢂ2000
ꢂ2000
ꢂ2000
ꢂ2000
18
16
16
18
180
110
[a] Rate constants determined from PL quenching are lower limits to the actual values as explained in the
text.
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R. A. J. Janssen et al.
FULL PAPER
In a control experiment, pump-probe spectroscopy was
performed on RP1, RP2, and compound 6 in toluene.
Again, the solutions were excited at 450 nm (RP1 and
RP2) and 525 nm (6), and probed at 1450 nm. The intensi-
ties obtained for all three solutions are lower by a factor of
5 10 compared to those of P1 and P2, and the signals have
much longer decay constants. Therefore, the transient sig-
nals of RP1, RP2, and 6 probably correspond to an excited-
state S1!Sn absorption, whose lifetime corresponds to
either tOPV or tPERY. The very different intensities and life-
times of the photoinduced absorptions at 1450 nm of P1
and P2, compared to the control experiments, support our
assignment that they originate from an intramolecular
charge-separated state.
Pump-probe measurements can give reliable rate con-
stants for charge separation and recombination, although
they are limited by the width of the excitation pulse. A com-
parison of the rates of charge separation measured by
pump-probe spectroscopy kCS ꢂ2î1012 sꢀ1 with the values of
kET + kdCS and kCi S (1 4î1011 sꢀ1), obtained from fluores-
cence quenching, reveals that they are in satisfactory agree-
ment, particularly if account is taken of the fact that the
fluorescence quenching experiments are sensitive to impuri-
ties and therefore provide lower estimates.
clearly visible in the spectra.[39] The absorptions at 0.70 eV
and in the region of 1.5 2.1 eV are attributed to OPV+C radi-
cal cations, based on previous results for OPV3+C and
OPV4+C.[40] The 1.5 2.1 eV absorption of OPV+C overlaps
with the absorptions of the PERYꢀC radical anions.
The PIA signals at 0.70 and 1.54 eV of both P1 and P2 in
Figure 6 show a sublinear dependence with increasing inten-
sity of the excitation. When the data are fitted to a power-
law expression for DT as function of the pump intensity, ex-
ponents between 0.38 and 0.47 are obtained. This indicates
that the charged species associated with these signals proba-
bly decay via a bimolecular recombination mechanism, for
which an exponent of 0.5 would be expected. Exponents of
less than 0.5 can be explained when the steady-state concen-
tration of charges is trap-limited.[41] The signal intensities at
0.70 eV and 1.54 eV for P1 and P2 were found to decrease
with increasing modulation frequency in an identical fash-
ion, closely following a power-law decay with the modula-
tion frequency. This indicates that the signals in the spec-
trum have the same origin and that a distribution of life-
times exists in the solid state, extending into the millisecond
time domain. The distribution of lifetimes is consistent with
a trap-filling model for the long-lived charges observed in
this experiment.
The rate constants for charge separation were indepen-
dent of the excitation wavelength (450 or 525 nm). This sug-
gests that an ultrafast singlet energy transfer from the sin-
glet excited state of OPV to the perylene bisimide moiety
precedes the electron transfer, which originates from pery-
lene bisimide singlet excited state S1. However, it is not pos-
sible to make an unambiguous conclusion on the prevailing
mechanism because the measured rates for charge separa-
tion are limited by the resolution of the pump-probe set-up.
The actual charge formation and recombination processes
in films of P1 and P2 were studied with respect to time at
room temperature by femtosecond pump-probe spectrosco-
py (Figure 7). The pump wavelengths were 450 or 525 nm
Photoinduced absorption in the solid state: In the solid state
it was possible to study the process of photoinduced charge
transfer on long (microsecond to millisecond) and short
(sub-picosecond to nanosecond) timescales by the use of dif-
ferent PIA set-ups. Near-steady-state PIA spectra of thin
films of P1 and P2 on quartz were recorded at 80 K with
excitation at 458 nm (Figure 6). The distinct absorptions of
the PERYꢀC radical anions at 1.28, 1.54, and 1.72 eV are
Figure 7. Normalized differential transmission dynamics of films of P1
and P2 at room temperature, recorded at l = 1450 nm (low-energy ab-
sorption of OPV radical cations) after excitation at l = 450 nm and
525 nm.
and the signals were probed at 1450 nm (0.86 eV). The
charge formation and recombination kinetics of P1 and P2
are similar and independent of the excitation wavelengths.
As in solution (Figure 5), the grow-in of the photoinduced
absorption signals occurs extremely fast and is complete
within 1 ps. The recombination of the positive and negative
charges between 0 and 250 ps after charge formation occurs
with a time constant of ꢁ60 ps. This lifetime corresponds to
the value obtained for the solutions excited at 525 nm. The
much longer lifetimes observed in the near-steady-state ex-
periments are attributed to charges that escape from this
fast geminate recombination by diffusion to different sites
Figure 6. Near-steady-state photoinduced absorption spectra of P1 (c)
and P2 (b) as thin films on quartz recorded at 80 K. The excitation
wavelength is 458 nm, modulation frequency 275 Hz.
3914
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3907 3918

Donor Acceptor Polymers
3907 3918
PS spectrometer, consisting of a 400 nm picosecond laser (PicoQuant
PDL800B), operated at 2.5 MHz, and a Peltier-cooled Hamamatsu mi-
crochannel plate photomultiplier (R3809U-50). The Edinburgh Instru-
ments software package was used to determine the lifetimes from the
data.
on the same polymer chain or different chains, and stabiliza-
tion owing to the low temperature (80 K).
Conclusion
Photoinduced absorption spectroscopy: Near-steady-state photoinduced
absorption (PIA) spectra were recorded between 0.25 and 3 eV by exci-
tation of a thin drop-cast film on quartz in an Oxford Optistat continuous
flow cryostat with a mechanically modulated (typically 275 Hz) cw Ar-
ion laser (Spectra Physics 2025) pump beam tuned to 458 nm (25 mW,
beam diameter of 2 mm) and monitoring the resulting change in trans-
mission (DT) of a tungsten-halogen white-light probe beam after disper-
sion by a triple grating monochromator, with Si, InGaAs, and (cooled)
InSb detectors.
Two new copolymers consisting of a main chain of enantio-
merically pure OPV segments alternating with phenylenes
with pendant perylene bisimides have been synthesized and
studied. Photoluminescence quenching shows that an effi-
cient photoinduced charge transfer takes place between the
donor backbone and its pendant acceptors in toluene and
ODCB solutions. In accordance with estimated values for
the Gibbs free energy or charge separation, charge separa-
tion occurs irrespective of which of the two chromophores is
initially excited. Femtosecond pump-probe spectroscopy on
these polymer solutions allowed the rate of formation of the
OPV+C radical cations to be monitored. Charge separation
occurs within 1 ps and the charge-separated state decays
with a time constant of 45 60 ps. The time constants for
charge separation and recombination in the solid state are
similar to those in solution. This suggests that the relative
orientation of the OPV and perylene bisimide chromophores
in solution is similar to that in the solid state. UV/Vis and
CD spectra reveal that the transition dipole moments of the
OPV and perylene bisimide are coupled. This implies that
these chromophores are in close proximity and have a pref-
erential helical orientation. The combination of these results
suggests that, both in solution and in films, the OPV and
perylene bisimide are in close proximity owing to stacking
of the electron-rich and electron-poor segments. This config-
uration enables fast and efficient charge separation, and
eventually fast charge recombination. Such a fast recombi-
nation is probably not advantageous for the preparation of
photovoltaic cells, where long lifetimes enhance the chances
for charge collection. On the other hand, the rapid response
and relaxation may open possibilities for the materials to be
used in optical data processing.
The femtosecond laser system used for pump-probe experiments consists
of an amplified Ti-sapphire laser (Spectra Physics Hurricane) that pro-
vides 150 fs pulses at 800 nm with an energy of 750 mJ at 1 kHz. Pump
(450 nm or 525 nm, fluence 0.5 mJmmꢀ2) and probe (1450 nm) pulses
were created by optical parametric amplification and twofold frequency
doubling with two OPAs (Spectra Physics OPA-C). The pump beam was
linearly polarized at the magic angle (54.78) with respect to the probe
beam. The temporal evolution was recorded with an InGaAs detector
and standard lock-in detection at 500 Hz.
2,5-Dibromo-4-(2-ethylhexyloxy)phenol (2): 2,5-Dibromo-benzene-1,4-
diol (1, 1.34 g, 5.0 mmol) was dissolved in ethanol (50 mL) in an argon at-
mosphere. After the mixture had been stirred with K2CO3 (0.69 g,
5.0 mmol), 2-ethylhexyl bromide (0.9 mL, 5.0 mmol) was added. The re-
action mixture was heated to reflux and stirred for 22 h. The reaction
mixture was cooled to room temperature and evaporated in vacuo. The
residue was dissolved in CH2Cl2, and the solution was washed twice with
distilled water and once with brine. After drying over MgSO4, the solu-
tion was filtered, and the solvent was evaporated in vacuo. After purifica-
tion by column chromatography (silica gel, CH2Cl2/n-pentane 3:1), 2 was
obtained as
a
brown oil. Yield: 0.54 g (28%); 1H NMR (CDCl3,
400 MHz): d = 7.26 (s, 1H), 6.97 (s, 1H), 5.13 (s, 1H), 3.82 (d, J =
5.5 Hz, 2H), 1.75 (m, 1H), 1.60 1.40 (m, 4H), 1.40 1.25 (m, 4H), 0.94 (t,
J = 7.5 Hz, 3H), 0.98 ppm (t, J = 7.0, 3H); 13C NMR (CDCl3, 75 MHz):
d = 150.27, 146.62, 120.25, 116.24, 112.42, 108.30, 72.54, 39.41, 30.45,
29.03, 23.87, 23.00, 14.06, 11.15 ppm; elemental analysis calcd (%) for
C14H20Br2O2 (380.1): C 44.24, H 5.30; found: C 44.27, H 5.21.
tert-Butyl
methylbutyl}carbamate (4): To
{(1S)-[2,5-Dibromo-4-(2-ethylhexyloxy)phenoxymethyl]-3-
solution of ((S)-1-hydroxymethyl-3-
a
methylbutyl)carbamic acid tert-butyl ester (3, 0.39 g, 1.79 mmol), com-
pound 2 (0.69 g, 1.82 mmol), and triphenylphosphine (0.71 g, 2.71 mmol)
in toluene (15 mL) under an argon atmosphere, a solution of diethyl azo-
dicarboxylate (DEAD) (0.43 mL, 2.73 mmol) in toluene (5 mL) was
added slowly so that the temperature of the reaction mixture did not
exceed 358C. After stirring overnight at room temperature, the reaction
mixture was filtered and washed with 1m KHSO4, distilled water and
brine, and was subsequently dried over Na2SO4. After filtration and evap-
oration of the solvent in vacuo, the residue was purified by column chro-
matography (silica gel, ethyl acetate/n-heptane 1:4, Rf = 0.5). The prod-
uct 4 was obtained as a clear sticky oil. Yield: 0.39 g (36%); 1H NMR
(CDCl3, 400 MHz): d = 7.07 (s, 1H), 7.00 (s, 1H), 4.79 (brd, 1H), 4.05
3.85 (m, 3H), 3.83 (d, J = 5.5 Hz, 2H), 1.80 1.60 (m, 2H), 1.60 1.20 (m,
10H), 1.45 (s, 9H), 1.00 0.85 ppm (m, 12H); 13C NMR (CDCl3, 75 MHz):
d = 155.38, 150.74, 149.56, 118.89, 117.95, 111.28, 111.17, 79.38, 72.49,
48.33, 40.96, 39.40, 30.49, 29.02, 28.40, 24.86, 23.85, 23.00, 22.90, 22.39,
14.06, 11.14 ppm; MALDI-TOF MS: m/z: 602.10 [M+Na]+.
Experimental Section
General methods: THF was freshly distilled over potassium/sodium. 1H
NMR and 13C NMR spectra were recorded at room temperature on a
Varian Gemini 300 or a Varian Mercury 400 MHz spectrometer. Chemi-
cal shifts are given relative to tetramethylsilane. Matrix-assisted laser de-
sorption ionization time-of-flight (MALDI-TOF) mass spectrometry was
conducted on a Perseptive Biosystems Voyager DE-Pro MALDI-TOF
mass spectrometer. A Shimadzu LC-Chemstation3D (HP1100 Series)
with a Polymer Laboratories MIXED-D column (particle size 5 mm;
length/i.d. (mm): 300î7.5) and UV detection was employed for size-ex-
clusion chromatography (SEC), with CHCl3 as the eluent (1 mLminꢀ1).
Elemental analyses were carried out on a Perkin-Elmer 2400 series II
CHN analyzer.
(1S)-[2,5-Dibromo-4-(2-ethylhexyloxy)phenoxymethyl]-3-methylbutyl-
amine (5): To a solution of compound 4 (0.253 g, 0.44 mmol) in CH2Cl2
(4 mL), was added TFA (2.5 mL, 32 mmol). The mixture was stirred for
16 h under an argon atmosphere at room temperature. Subsequently,
NaHCO3 was added to the reaction mixture until the mixture became
basic. After addition of CH2Cl2 (20 mL), the mixture was washed three
times with distilled water and once with brine. After drying over Na2SO4,
the solution was filtered, and the solvent was removed in vacuo to give a
brown oil. Yield: 0.19 g (91%). The product was used without further pu-
rification. 1H NMR (CDCl3, 300 MHz): d = 7.10 (s, 1H), 7.08 (s, 1H),
3.94 (dd, J = 8.5, 3.6 Hz, 1H), 3.83 (d, J = 5.5 Hz, 2H), 3.68 (t, J =
UV/Vis absorption spectra were recorded on
a Perkin Elmer
Lambda 900 and a Lambda 40 spectrophotometer. Fluorescence spectra
were recorded on an Edinburgh InstrumentsFS920 double-monochroma-
tor spectrometer and a Peltier-cooled red-sensitive photomultiplier. Cir-
cular dichroism spectra were recorded on a Jasco J-600 spectropolarime-
ter.
Fluorescence lifetimes: Time-correlated single-photon counting fluores-
cence studies were performed with an Edinburgh Instruments LifeSpec-
Chem. Eur. J. 2004, 10, 3907 3918
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3915

R. A. J. Janssen et al.
FULL PAPER
1
8.2 Hz, 1H), 3.30 (m, 1H), 1.85 1.60 (m, 4H), 1.60 1.40 (m, 4H), 1.40
1.25 (m, 6H), 1.00 0.85 ppm (m, 12H); 13C NMR (CDCl3, 75 MHz): d =
150.65, 149.61, 118.84, 117.98, 111.23, 111.14, 75.77, 72.49, 48.70, 42.81,
39.41, 30.44, 29.03, 24.70, 23.86, 23.27, 23.00, 22.18, 14.06, 11.15 ppm;
MALDI-TOF MS: m/z: 480.04 [M+H]+.
out any further purification. H NMR (CDCl3, 300 MHz): d = 7.66 (d, J
= 2.5 Hz, 1H), 7.35 (dd, J = 8.8, 2.5 Hz, 1H), 6.75 (d, J = 8.8 Hz, 1H),
3.96 (dd, J = 8.8, 3.6 Hz, 1H), 3.70 (dd, J = 8.7, 7.6 Hz, 1H), 3.30 (m,
1H), 1.79 (m, 1H), 1.34 (t, J = 7.0 Hz, 2H), 0.96 ppm (t, J = 6.7 Hz,
6H); 13C NMR (CDCl3, 100 MHz): d = 154.56, 135.42, 131.21, 114.40,
113.18, 113.06, 75.10, 48.48, 43.06, 24.70, 23.36, 22.11 ppm; MALDI-TOF
MS: m/z: 351.85 [M+H]+.
N-(1-Ethylpropyl)perylene-3,4:9,10-tetracarboxylic-3,4-anhydride-9,10-
imide (7): A mixture of N,N’-di(1-ethylpropyl)perylene-3,4:9,10-tertacar-
boxylic-bisimide (6, 2.87 g, 5.4 mmol) and potassium hydroxide (0.91 g,
0.016 mol) in tert-butyl alcohol (100 mL) was heated at 1008C for 30 min.
The reaction mixture was then poured into 10% HCl (400 mL), and the
precipitate was filtered. The residue was stirred into a warm solution of
potassium hydroxide (20 g, 0.36 mol) and potassium chloride (16 g,
0.21 mol) in water (200 mL). The solid was filtered and subsequently
washed with the aqueous solution until the solution no longer had a
yellow/green color. The solid was then stirred in water and subsequently
filtered. The dark red filtrate was precipitated by addition of hydrochlo-
ric acid to a final total percentage of 10% HCl concentration. The pre-
cipitate was filtered, washed with water, and dried at 908C under vacuum
N-(1-Ethylpropyl)-N’-[(1S)-(2,4-dibromophenoxymethyl)-3-methylbutyl]-
perylene-3,4:9,10-tetracarboxylic bisimide (12): Compound 11 (0.34 g,
0.97 mmol) and N-(1-ethylpropyl)perylene-3,4:9,10-tetracarboxylic-3,4-
anhydride-9,10-imide (7, 0.45 g, 0.98 mmol) were stirred in DMF (25 mL)
at 1408C under an argon atmosphere. After 2.5 h, the temperature was
elevated to 1608C. After subsequent 17 h of stirring, the reaction mixture
was cooled to room temperature, and the solvent was evaporated in
vacuo. After purification by column chromatography (silica gel, CH2Cl2),
12 was obtained as a red solid. Yield: 0.53 g (69%); 1H NMR (CDCl3,
300 MHz): d = 8.80 8.60 (m, 8H), 7.51 (d, J = 2.5 Hz, 1H), 7.34 (dd, J
= 8.7, 2.3 Hz, 1H), 6.80 (d, J = 8.8 Hz, 1H), 5.83 (m, 1H), 5.07 (m, 1H),
4.73 (t, J = 8.9 Hz, 1H), 4.39 (dd, J = 9.1, 5.8 Hz, 1H), 2.28 (m, 3H),
1.95 (m, 2H), 1.78 (m, 1H), 1.67 (m, 1H), 1.02 (dd, J = 13.6, 6.5 Hz,
6H), 0.93 ppm (t, J = 7.4 Hz, 6H); 13C NMR (CDCl3, 75 MHz): d =
164.00, 154.24, 135.29, 134.73, 134.44, 131.65, 131.16, 129.61, 126.45,
123.50, 123.14, 114.59, 113.17, 69.44, 57.72, 50.97, 38.17, 25.58, 25.01,
23.15, 22.41, 11.34 ppm; MALDI-TOF MS: m/z: 793.88 [MC]ꢀ; elemental
analysis calcd (%) for C41H34Br2N2O5 (794.6): C 61.98, H 4.31; found: C
61.76, H 4.23.
1
to afford a black solid. Yield: 0.50 g (20%); H NMR (CDCl3) d = 8.80
8.60 (m, 8H), 5.07 (m, 1H), 2.35 2.20 (m, 2H), 2.00 1.90 (m, 2H),
0.93 ppm (t, J = 7.5 Hz); 13C NMR (CDCl3) d = 160.15, 136.61, 133.86,
133.76, 131.81, 124.10, 123.35, 123.24, 119.23, 58.03, 57.86, 25.16,
11.50 ppm; MS (EI): m/z: 461 [M]+.
N-(1-Ethylpropyl)-N’-[(1S)-(2,5-dibromo-4-(2-ethylhexyloxy)phenoxy-
methyl)-3-methylbutyl] perylene-3,4:9,10-tetracarboxylic bisimide (8):
Compound 5 (0.16 g, 0.33 mmol) and N-(1-ethylpropyl)perylene-3,4:9,10-
tetracarboxylic-3,4-anhydride-9,10-imide (7, 0.15 g, 0.33 mmol) were stir-
red at 1558C in DMF (20 mL) under an argon atmosphere for 24 h. The
solvent was removed in vacuo, and the product was purified by column
chromatography (silica gel, CH2Cl2) to afford a red solid. Yield: 0.12 g
(39%); 1H NMR (CDCl3, 300 MHz): d = 8.64 (d, J = 8.0 Hz, 4H), 8.56
(d, J = 8.0 Hz, 4H), 7.14 (s, 1H), 6.90 (s, 1H), 5.80 (m, 1H), 5.07 (m,
1H), 4.71 (t, J = 8.9 Hz, 1H), 4.34 (dd, J = 8.9, 5.6 Hz, 1H), 3.80 3.60
(m, 2H), 2.20 2.05 (m, 3H), 1.96 (m, 2H), 1.85 1.55 (m, 3H), 1.55 1.15
2,4-Dibromo-1-(2-ethylhexyloxy)benzene (13): To a stirred solution of
2,4-dibromophenol (9, 1.03 g, 4.09 mmol) in ethanol (25 mL), was added
K2CO3 (0.57 g, 4.12 mmol) and subsequently 2-ethylhexyl bromide
(0.73 mL, 4.10 mmol) under an argon atmosphere. After refluxing for 2 h,
the reaction mixture was cooled to room temperature, and the solvent
was evaporated in vacuo. The residue was dissolved in CH2Cl2 and
washed with 1m NaOH, distilled water, and brine and dried over
Na2SO4. Purification by column chromatography (silica gel, CH2Cl2), fol-
lowed by evaporation of the solvent, gave a residue that was heated at
808C in vacuo. The resulting product was obtained as a clear liquid.
Yield: 0.36 g (24%); 1H NMR (CDCl3, 300 MHz): d = 7.65 (d, J =
2.5 Hz, 1H), 7.34 (dd, J = 8,7, 2.3 Hz, 1H), 6.75 (d, J = 8.8 Hz, 1H),
3.87 (d, J = 5.8 Hz, 2H), 1.77 (m, 1H), 1.60 1.40 (m, 4H), 1.40 1.20 (m,
4H), 1.00 0.85 ppm (m, 6H); 13C NMR (CDCl3, 75 MHz): d = 155.02,
135.37, 131.06, 114.08, 113.17, 112.47, 71.75, 39.31, 30.45, 29.03, 23.87,
22.99, 14.05, 11.14 ppm; elemental analysis calcd (%) for C14H20Br2O
(364.1): C 46.18, H 5.54; found: C 45.64, H 5.36.
(m, 8H), 1.15 0.80 ppm (m, 18H); 13C NMR (CDCl3, 75 MHz): d
=
164.14, 150.57, 149.34, 134.57, 134.40, 131.98, 131.48, 129.55, 126.37,
124.83, 123.67, 123.05, 118.88, 117.78, 111.09, 72.39, 70.32, 57.73, 51.27,
39.33, 38.25, 30.36, 28.97, 25.61, 25.02, 23.79, 23.15, 22.96, 22.46, 14.02,
11.37, 11.10 ppm; MALDI-TOF MS: m/z: 921.90 [MC]ꢀ; elemental analy-
sis calcd (%) for C49H50Br2N2O6 (922.8): C 63.78, H 5.46; found: C 63.14,
H 5.41.
tert-Butyl [(1S)-(2,4-Dibromophenoxymethyl)3-methylbutyl]carbamate
(10): ((S)-1-Hydroxymethyl-3-methylbutyl)carbamic acid tert-butyl ester
(3, 1.017 g, 4.73 mmol), 2,4-dibromophenol (9, 1.19 g, 4.72 mmol), and tri-
phenylphosphine (1.86 g, 7.09 mmol) were dissolved in toluene (15 mL),
P1: A mixture of monomer 8 (0.040 g, 0.043 mmol), monomer (E,E)-1,4-
bis{4-{4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl-}-2,5-bis[(S)-2-methyl-
and stirred under an argon flux.
A
solution of DEAD (1.1 mL,
butoxy]styryl}-2,5-bis[(S)-2-methylbutoxy]benzene
(14,
0.0456 g,
6.99 mmol) in toluene (10 mL) was added dropwise to the reaction mix-
ture so that the temperature did not exceed 358C. After the mixture had
been stirred overnight at room temperature, a white precipitate was fil-
tered off from the reaction mixture. The remaining solution was washed
with 1m KHSO4 (2î), with distilled water (3î), and with brine (1î).
The organic phase was dried over Na2SO4, filtered, and the solvent was
evaporated in vacuo. Cyclohexane and diethyl ether were added to the
residue to yield a precipitate, which was filtered off. The solvents in the
remaining solution were evaporated in vacuo. After purification by
column chromatography (silica gel, ethyl acetate/n-heptane 1:4, Rf = 0.4)
the product was crystallized from n-hexane. The product 10 was obtained
as white crystals. Yield: 0.84 g (39%); 1H NMR (CDCl3, 300 MHz): d =
7.66 (d, J = 2.2 Hz, 1H), 7.36 (dd, J = 8.9, 2.1 Hz, 1H), 6.76 (d, J =
8.8 Hz, 1H), 4.75 (brd, 1H), 4.05 3.90 (m, 3H), 1.70 1.60 (m, 1H), 1.60
1.40 (m, 2H), 1.44 (s, 9H), 0.96 ppm (dd, J = 6.4, 2.1 Hz, 6H); 13C NMR
(CDCl3, 100 MHz): d = 155.40, 154.47, 135.42, 131.27, 114.45, 113.23,
79.49, 71.50, 48.13, 40.93, 28.38, 24.85, 22.93, 22.31 ppm; MALDI-TOF
MS: m/z: 474.08 [M+Na]+.
0.043 mmol), and [Pd(PPh3)4] (0.0025 g, 0.002 mmol) in distilled THF
(10 mL) was purged with argon for 15 min. A solution of K2CO3 (0.024 g,
0.17 mmol) in water (1.2 mL), which had also been purged with argon for
15 min, was added to this mixture with a syringe. The whole mixture was
purged with argon for 15 min before stirring in the dark at 908C under a
flow of argon. After 22 h, the reaction mixture was cooled to room tem-
perature, and dried in vacuo. The residue was dissolved in toluene
(3 mL). Methanol (300 mL) was added and the precipitated solid was fil-
tered. Yield: 0.048 g (72%) of a red solid; 1H NMR (CDCl3, 300 MHz):
d = 8.80 8.10 (m, 8H), 7.70 6.40 (m, 12H), 5.90 5.60 (br signal, 1H),
5.10 4.90 (m, 1H), 4.80 4.50 (br signal, 1H), 4.50 4.10 (br signal, 1H),
4.00 3.20 (m, 14H), 2.40 1.20 (m, 34H), 1.20 1.10 (m, 6H), 1.10
0.70 ppm (m, 48H); 13C NMR (CDCl3, 75 MHz): d = 163.98, 163.53,
150.96, 150.61, 150.39, 149.61, 149.43, 134.56, 134.22, 131.42, 130.42,
129.62, 129.42, 129.26, 128.43, 127.62, 127.14, 126.78, 126.32, 125.28,
123.62, 123.02, 122.40, 117.10, 116.69, 115.80, 110.90, 110.39, 110.06,
108.67, 74.43, 73.81, 71.81, 57.54, 51.07, 39.53, 38.14, 35.12, 34.89, 30.47,
29.02, 26.40, 26.19, 26.02, 25.57, 25.01, 23.83, 23.15, 23.00, 22.57, 16.83,
16.70, 14.03, 11.48, 11.39, 11.32, 10.97 ppm; SEC (CHCl3, versus polystyr-
(1S)-(2,4-Dibromophenoxymethyl)-3-methylbutylamine (11): A solution
of compound 10 (0.76 g, 1.68 mmol) in CH2Cl2 (5 mL) and was stirred
with TFA (5 mL, 65 mmol) under argon. After 15 h, NaHCO3 was added
to the reaction mixture until it was basic. The mixture was subsequently
washed with distilled water (4î) and with brine (1î). The solution was
dried over Na2SO4, and after filtration and evaporation in vacuo, 11 was
obtained as a pink oil. Yield: 0.49 g (83%). The product was used with-
ene): Mw = 27.2 kgmolꢀ1, Mn = 8.2 kgmolꢀ1
.
P2: Monomer 12 (0.151 g, 0.19 mmol), monomer 14 (0.200 g, 0.19 mmol),
and [Pd(PPh3)4] (0.009 g, 0.008 mmol) in distilled THF (30 mL) were
purged with argon for 20 min. A solution of K2CO3 (0.10 g, 0.72 mmol) in
water (5 mL) was purged for 30 min, and this solution was added to the
THF solution with a syringe. The whole solution was again purged with
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Chem. Eur. J. 2004, 10, 3907 3918

Donor Acceptor Polymers
3907 3918
argon for 30 min. The reaction mixture was heated to 908C, and was stir-
red under an argon atmosphere in the dark for 18 h. After the mixture
was cooled to room temperature, the solvents were evaporated in vacuo.
The residue was dissolved in CHCl3 (7 mL), and methanol (500 mL) was
added. The resulting precipitate was filtered off, and the filtrate was
dried in vacuo. The precipitation procedure was repeated from toluene
(4 mL) in methanol (250 mL). The polymer was obtained as a red solid.
Yield: 0.202 g (75%); 1H NMR (CDCl3, 400 MHz): d = 8.80 8.05 (m,
8H), 7.70 6.70 (m, 13H), 5.95 5.65 (br signal, 1H), 5.20 4.90 (br signal,
1H), 4.80 4.60 (m, 1H), 4.60 4.30 (br signal, 1H), 4.10 3.00 (m, 12H),
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Ego, A. Grimsdale, K. M¸llen, Chem. Phys. Lett. 2002, 362, 534.
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Becker, D. Marsitsky, K. M¸llen, Phys. Rev. B 2001, 64, 195203.
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Friend, G. D. Scholes, S. Setayesh, K. M¸llen, J. L. Brÿdas, Proc.
Natl. Acad. Sci. USA 2002, 99, 10982.
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kov, G. Hadziioannou, Polymer 2001, 42, 9097.
2.30 0.60 ppm (m, 73H); 13C NMR (CDCl3, 100 MHz): d
= 163.96,
150.94, 134.60, 132.00, 130.39, 129.40, 127.78, 126.32, 123.66, 123.12,
122.38, 115.57, 110.31, 109.99, 108.72, 74.51, 74.22, 57.50, 50.73, 38.08,
35.10, 34.95, 34.80, 30.92, 26.34, 26.17, 25.94, 25.54, 25.02, 23.10, 22.53,
[7] U. Stalmach, B. de Boer, C. Videlot, P. F. van Hutten, G. Hadziioan-
nou, J. Am. Chem. Soc. 2000, 122, 5464.
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1996, 35, 648.
16.78, 16.32, 11.43 ppm; SEC (CHCl3, versus polystyrene): Mw
22.2 kgmolꢀ1, Mn = 8.0 kgmolꢀ1
RP1: solution of 1,4-dibromo-2,5-di-(2-ethylhexyloxy)benzene (15,
=
.
A
0.018 g, 0.037 mmol), 14 (0.038 g, 0.036 mmol), and [Pd(PPh3)4] (0.002 g,
0.001 mmol) in distilled THF (7 mL) was purged with argon for 15 min.
A solution of K2CO3 (0.020 g, 0.14 mmol) in water (1 mL), which had
also been purged with argon for 15 min, was added to this mixture with a
syringe. This whole solution was purged with argon for 15 min. The tem-
perature was elevated to 908C, and the reaction mixture was stirred for
23 h in the dark. After the mixture was cooled to room temperature, the
solvents were evaporated in vacuo. The residue was dissolved in toluene
(4 mL) and poured into methanol (300 mL). The precipitate was filtered
off and was washed with water and methanol to afford a yellow solid.
Yield: 0.021 g (51%); 1H NMR (CDCl3, 400 MHz): d = 7.57 (brs, 4H),
7.40 7.20 (brs, 4H), 7.01 (s, 2H), 6.98 (s, 2H), 4.00 3.60 (m, 16H), 2.05
1.85 (brs, 4H), 1.85 1.05 (m, 36H), 1.05 0.75 ppm (m, 48H); 13C NMR
(CDCl3, 100 MHz): d = 151.08, 150.95, 150.36, 150.13, 127.55, 123.11,
122.50, 117.10, 110.47, 110.07, 74.38, 74.30, 71.88, 39.57, 35.09, 34.90,
30.54, 29.70, 29.04, 26.39, 26.12, 23.85, 23.02, 16.82, 16.72, 14.07, 11.47,
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Andersson, H. Neugebauer, N. S. Sariciftci, Chem. Commun. 2000,
2487.
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Menna, M. Svensson, M. R. Andersson, C. J. Brabec, N. S. Sariciftci,
J. Phys. Chem. B 2002, 106, 70.
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len, R. A. J. Janssen, J. Am. Chem. Soc. 2001, 123, 6714.
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Menna, O. Ingan‰s, Adv. Mater. 2001, 13, 1871.
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2002, 43, 2049.
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Rapid Commun. 2001, 22, 1313.
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J. L. Segura, N. MartÌn, M. Svensson, M. R. Andersson, J. Phys.
Chem. A 2001, 105, 4172.
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Lupsac, Org. Lett. 2003, 5, 1669.
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Hofkens, F. C. De Schryver, K. M¸llen, Chem. Eur. J. 2001, 7, 4844.
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Hampel, K. M¸llen, J. W. Verhoeven, M. Van der Auweraer, F. C.
De Schryver, J. Am. Chem. Soc. 2002, 124, 9918.
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M. Cotlet, T. Weil, K. M¸llen, J. W. Verhoeven, M. Van der Auwera-
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11.28, 11.00 ppm; SEC (CHCl3, versus polystyrene): Mw
=
110.8 kgmolꢀ1, Mn = 24.6 kgmolꢀ1
.
RP2: Monomer 13 (0.0279 g, 0.077 mmol), monomer 14 (0.0805 g,
0.077 mmol), and [Pd(PPh3)4] (0.0035 mg, 0.003 mmol) were dissolved in
distilled THF (13 mL) and the solution was purged with argon for
20 min. A solution of K2CO3 (0.04 g, 0.029 mmol) in water (2 mL) was
purged with argon for 15 minutes and was subsequently added to the or-
ganic solution. The reaction mixture was purged with argon for 30 mi-
nutes before heating to 908C. After stirring in the dark for 18 h, the reac-
tion mixture was dried by evaporation in vacuo. The solid residue was
washed with water (2î) and then dissolved in toluene (4 mL). The solu-
tion was poured in methanol (100 mL), and the precipitate was filtered
off to give a yellow solid. Yield: 0.042 g (55%); 1H NMR (CD2Cl2,
300 MHz): d = 7.60 7.40 (m, 6H), 7.30 7.05 (m, 4H), 7.00 6.80 (m, 3H),
4.00 3.80 (m, 14H), 1.95 (m, 4H), 1.80 (m, 2H), 1.75 1.20 (m, 21H),
1.20 0.70 ppm(m, 42H); 13C NMR (CD2Cl2, 100 MHz): d
= 156.29,
151.45, 151.36, 150.79, 134.40, 132.71, 131.03, 130.19, 129.19, 127.82,
126.77, 126.51, 123.25, 122.69, 117.02, 115.76, 112.60, 111.61, 110.27,
110.11, 74.81, 74.71, 74.27, 71.23, 39.77, 35.40, 35.25, 35.17, 30.83, 29.35,
26.67, 26.47, 26.38, 24.16, 23.33, 16.87, 16.60, 14.14, 11.55, 11.30,
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Lazzaroni, J.-L. Brÿdas, D. Beljonne, J. Am. Chem. Soc. 2003, 125,
8625.
11.14 ppm; SEC (CHCl3, versus polystyrene): Mw = 48.8 kgmolꢀ1, Mn
=
13.8 kgmolꢀ1
.
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The authors would like to thank E. H. A. Beckers, Dr. S. C. J. Meskers,
and Dr. M. M. Wienk for measurements and helpful discussions. This
work was financially supported by the Council for Chemical Sciences of
the Netherlands Organization for Scientific Research (CW-NWO) and
the Eindhoven University of Technology in the PIONIER program
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Chem. Eur. J. 2004, 10, 3907 3918
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: January 31, 2004
Published online: June 24, 2004
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Chem. Eur. J. 2004, 10, 3907 3918