Oligo(p-phenylene ethynylene)-BODIPY derivatives: Synthesis, energy transfer, and quantum-chemical calculations

Article abstract of DOI:10.1002/chem.201100454

The synthesis and energy-transfer properties of a series of oligo(p-phenylene ethynylene)-BODIPY (OPEB) cassettes are reported. A series of oligo(p-phenylene ethynylene)s (OPEs) with different conjugated chain lengths as energy donor subunit in the energy-transfer system were capped at both ends with BODIPY chromophores as energy-acceptor subunits. The effect of the conjugated chain of OPEs on energy transfer in the OPEB cassettes was investigated by UV/Vis and fluorescence spectroscopy and modeling. With increasing number n of phenyl acetylene units (n=1-7), the absorption and emission maxima of OPEn are bathochromically shifted. In the OPEBn analogues, the absorption maximum assigned to the BODIPY moieties is independent of the length of the OPE spacer. However, the relative absorption intensity of the BODIPY band decreases when the number of phenyl acetylene units is increased. The emission spectra of OPEBn are dominated by a band peaking at 613 nm, corresponding to emission of the BODIPY moieties, regardless of whether excitation is at 420 or 550 nm. Furthermore, a very small band is observed with a maximum between 450 and 500 nm, and its intensity relative to that of the BODIPY emission increases with increasing n, that is, the excited state of OPE subunits is efficiently quenched in OPEBn by energy transfer to the BODIPY moieties. Energy transfer (ET) from OPEn to BODIPY in OPEBn is very efficient (all φ_ET values are greater than 98 %) and only slightly decreases with increasing length of the OPE units. These results are supported by theoretical studies that show very high energy transfer efficiency (φ_ET>75 %) from the OPE spacer to the BODIPY end-groups for chains with up to 15-20 units.

Full text of DOI:10.1002/chem.201100454

FULL PAPER
DOI: 10.1002/chem.201100454
Oligo(p-phenylene ethynylene)–BODIPY Derivatives: Synthesis, Energy
Transfer, and Quantum-Chemical Calculations
Shouchun Yin,[a, b] Volker Leen,[a] Carine Jackers,[a, c] David Beljonne,*[d]
Bernard Van Averbeke,[d] Mark Van der Auweraer,[a, c] Noꢀl Boens,[a] and
Wim Dehaen*[a]
Abstract: The synthesis and energy-
alogues, the absorption maximum as-
signed to the BODIPY moieties is in-
dependent of the length of the OPE
spacer. However, the relative absorp-
tion intensity of the BODIPY band de-
creases when the number of phenyl
acetylene units is increased. The emis-
sion spectra of OPEBn are dominated
by a band peaking at 613 nm, corre-
sponding to emission of the BODIPY
moieties, regardless of whether excita-
tion is at 420 or 550 nm. Furthermore,
a very small band is observed with a
maximum between 450 and 500 nm,
and its intensity relative to that of the
BODIPY emission increases with in-
creasing n, that is, the excited state of
OPE subunits is efficiently quenched
in OPEBn by energy transfer to the
BODIPY moieties. Energy transfer
(ET) from OPEn to BODIPY in
OPEBn is very efficient (all FET values
are greater than 98%) and only slightly
decreases with increasing length of the
OPE units. These results are supported
by theoretical studies that show very
transfer properties of
a
series of
oligo(p-phenylene
ethynylene)–
BODIPY (OPEB) cassettes are report-
ed. A series of oligo(p-phenylene ethy-
nylene)s (OPEs) with different conju-
gated chain lengths as energy donor
subunit in the energy-transfer system
were capped at both ends with
BODIPY chromophores as energy-ac-
ceptor subunits. The effect of the con-
jugated chain of OPEs on energy trans-
fer in the OPEB cassettes was investi-
gated by UV/Vis and fluorescence
spectroscopy and modeling. With in-
creasing number n of phenyl acetylene
units (n=1–7), the absorption and
emission maxima of OPEn are batho-
chromically shifted. In the OPEBn an-
high energy transfer efficiency (FET
>
75%) from the OPE spacer to the
BODIPY end-groups for chains with
up to 15–20 units.
Keywords: BODIPY
· donor–ac-
ceptor systems · energy transfer ·
fluorescence
ethynylene)s
·
oligo(p-phenylene
Introduction
This is due to its important role in both natural and artificial
processes such as the oxidation of water to oxygen and the
fixation of carbon dioxide in photosynthetic organisms, pho-
tochemical conversion of solar energy, and information
processing.[1] Consequently, considerable effort has been de-
voted to the design of molecular arrays containing a well-de-
fined sequence of chromophores that might transfer elec-
tronic energy. Among the different chromophores, BODIPY
(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives are
of particular interest because of their valuable characteris-
tics, such as sharp absorption and fluorescence bands in the
visible wavelength range, relatively high fluorescence quan-
tum yields, large molar absorption coefficients, and robust-
ness against light and chemicals.[2] In recent years, several
BODIPY derivatives attached to energy donors such as
polycyclic aryl hydrocarbons,[3] oligothiophenes,[4] subphtha-
locyanines,[5] and to energy acceptors such as porphyrins,[6]
perylenediimides,[7] subphthalocyanine,[5,8] fullerenes[9] and
BODIPYs[10] have been reported. However, to the best of
our knowledge, there is no report about oligo(p-phenylene
ethynylene)s (OPEs) as donor or acceptor subunit in the
energy-transfer system. Conversely, OPEs with a short con-
jugated chain have been applied as spacers to transfer
energy from the donor to the acceptor moiety.[10]
For more than five decades electronic energy transfer has
been attracting the attention of the scientific community.
[a] Dr. S. Yin, Dr. V. Leen, C. Jackers, Prof. M. Van der Auweraer,
Prof. N. Boens, Prof. W. Dehaen
Department of Chemistry, Katholieke Universiteit Leuven
Celestijnenlaan 200f - bus 02404, 3001 Leuven (Belgium)
Fax : (+32)16-327990
E-mail: wim.dehaen@chem.kuleuven.be
[b] Dr. S. Yin
College of Material Chemistry and Chemical Engineering
Hangzhou Normal University, Hangzhou 310036 (P. R. China)
[c] C. Jackers, Prof. M. Van der Auweraer
Institute for Nanoscale Physics and Chemistry (INPAC)
Department of Chemistry, Katholieke Universiteit Leuven
Celestijnenlaan 200f - bus 02404, 3001 Leuven (Belgium)
[d] Prof. D. Beljonne, Dr. B. Van Averbeke
Laboratory for Chemistry of Novel Materials
Universitꢀ de Mons, Place du Parc 20, 7000 Mons (Belgium)
E-mail: david@averell.umh.ac.be
Supporting information for this article (1H NMR spectra of com-
pounds 2–5, 7, OPEn, and OPEBn and normalized absorption and
emission spectra of compounds 6, OPEn, and OPEBn in toluene) is
available on the WWW under http://dx.doi.org/10.1002/
chem.201100454.
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The OPEs have attracted much interest in the past
decade because of their intriguing luminescence properties,
high fluorescence quantum yields, and electronic proper-
ties.[11] OPEs can be model compounds to provide insight
into the structural and electronic properties of poly(p-phen-
ylene ethynylene) materials. They are also attractive func-
tional building blocks for the construction of new molecular
and supramolecular photoactive devices. Thus, OPEs have
been widely applied in organic electroluminescent light-
emitting devices,[12] molecular electronic switches,[13] and
nonlinear optical materials.[14]
Herein we report the preparation and energy-transfer
properties of oligo(p-phenylene ethynylene)–BODIPY
(OPEB) cassettes in which a series of OPEs with different
conjugated chain lengths are capped at both ends with
BODIPY chromophores. Attachment of BODIPY deriva-
tives at the 3-position of OPEs can enable electronic com-
munication across a linear OPE chain over a long distance
to the terminal BODIPY dyes due to the colinearity of the
OPE and BODIPY units.[15] A series of OPEs with different
chain lengths were synthesized in order to investigate the
effect of the conjugated chain of OPEs on energy transfer
in the OPEB cassettes.
Results and Discussion
Synthesis of OPE precursors: The synthesis of a series of
linearly conjugated p-phenylene ethynylene oligomers
(OPE) is outlined in Scheme 1 and Scheme S1 in the Sup-
porting Information. The essential building block 1,4-diiodo-
2,5-bis(dodecyloxy)benzene (1) for elongation of the OPE
chains was cross-coupled with 1.0 and 2.5 equiv of 2-methyl-
but-3-yn-2-ol under Sonogashira conditions to afford com-
pounds 2 and 3, respectively, in good yield. Our initial ap-
proach was to use trimethylsilyl as protecting group because
it can be easily removed.[16] However, the separation of the
product is very difficult and cumbersome, and it is not easy
to get the compound pure enough for NMR spectroscopic
characterization, especially for the synthesis of longer
OPEs. Thus, we choose 2-methylbut-3-yn-2-ol as a protect-
ing group in an attempt to facilitate separation of the de-
Scheme 1. Synthesis of OPEn (n=1, 3, 5,7). i) [PdACTHUNGRTNEUNG(PPh3)2Cl2], CuI, THF; ii) NaOH, toluene, reflux.
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Oligo(p-phenylene ethynylene)–BODIPY Derivatives
FULL PAPER
sired compound on the basis of the polarity imparted by the
hydroxyl group. Selective monodeprotection, by heating at
758C in toluene under basic conditions, afforded 4 in 51%
yield. Iteration of the cross-coupling reaction with an excess
of 1 converted 4 to dimeric phenyl acetylene 5.
Oligomer OPE1 was readily synthesized in excellent yield
by complete deprotection of 3 in refluxing toluene under
basic conditions. OPE3 was also obtained by a similar cross-
coupling reaction of 2 equiv of 2 and 1 equiv of OPE1 in the
presence of a catalytic amount of a palladium complex, fol-
lowed by complete deprotection. For the synthesis of phenyl
acetylene pentamer OPE5 and heptamer OPE7, our pre-
liminary efforts using a divergent elongation route were not
satisfactory. With increasing number of phenyl acetylene
units, the yields of the cross-coupling and deprotection reac-
tions decrease, and this makes it very difficult to obtain
Scheme 2. Synthesis of BODIPY derivative 7.
OPE7 from OPE5. Alternatively,
a convergent route
(Scheme 1) was used. OPE5 was obtained by reaction of
2 equiv of 5 with 1 equiv of OPE1 followed by the deprotec-
tion reaction, whereas OPE7 was synthesized under similar
experimental conditions from 5 and OPE3 followed by re-
moval of two propargylic groups. In this way, the decreased
yields for the cross-coupling reaction of higher oligomers
could be successfully bypassed. However, for the deprotec-
tion reaction, the decrease in yield is due to the difficulty of
removing the propargylic groups, which requires high tem-
peratures and a relatively long reaction time. Finally, OPE5
was obtained in modest yield, and OPE7 in acceptable
yield.
subsequent cross-coupling reactions with the alkynyl OPE
fragment by means of a catalytic reaction promoted by pal-
ladium (Scheme 2), except for the synthesis of OPEB1,
which can be obtained by reaction of the BODIPY deriva-
tive 6 containing an acetylene group with 1.[18] To this end,
the corresponding BODIPY derivative 6 with a terminal
acetylene group and a DPA group[19] and BODIPY deriva-
tive 7 bearing a terminal iodo group and a DPA group as
precursors must be prepared first. As outlined in Scheme 3,
precursor 7 bearing a terminal iodo group and a DPA group
was obtained in good yield (64%) by Sonogashira coupling
between 6 and an excess of 1.
With the OPE precursors in hand, we then attached
BODIPY derivative 7 at the termini of each OPE frame-
work. As shown in Scheme 3, we were able to couple OPE1,
Synthesis of OPEB: As reported earlier, 3,5-dichlorinated
BODIPY dyes can be functionalized through Pd-mediated
coupling and SNAr reactions.[17]
The resulting substituted prod-
ucts tend to fluorescence at
longer wavelengths. For reasons
of synthetic simplicity our ini-
tial approach is as follows. One
chlorine atom of 3,5-dichloro-
BODIPY was substituted by
di(2-picolyl)amine (DPA), and
the second chlorine atom of the
isolated compound was then
treated with OPEn in a palladi-
um-catalyzed reaction. Howev-
er, 3-chloro-5-(DPA)BODIPY
failed to participate in the So-
nogashira reaction with termi-
nal alkyne species (OPE). This
can be attributed to the lower
reactivity of the second chlorine
atom, because of the electron-
donating effect of the nitrogen
atom. A more successful syn-
thetic strategy starts from a pre-
fabricated BODIPY unit bear-
ing a reactive iodo group for Scheme 3. Synthesis of OPEBn (n=3, 5, 7).
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W. Dehaen, D. Beljonne et al.
OPE3, and OPE5 to BODIPY halide 7 in the presence of
[PdCl2A(PPh3)2]/CuI in THF/NEt3 to give OPEB3, OPEB5,
and OPEB7 in acceptable yields of 37, 28, and 18%, respec-
tively. OPEB1 was obtained in moderate yield (48%) by
treating 2 equiv of 1 with 1 equiv of 6 under Sonogashira
conditions.[18]
which are also observed for model compound 6, are attribut-
ed to the electron-donating effect of the nitrogen atom and
the extended conjugation of BODIPY at the 3-position.[20]
Comparing the absorption spectrum of OPEB3 with those
of reference compound 6 and OPE3 shows that the absorp-
tion peaks of the BODIPY moieties and the OPE units are
both redshifted, from 547 to 555 nm and from 396 to
415 nm, respectively, which is indicative of electronic com-
munication between the BODIPY moieties and the OPE
subunits. This further confirms that substitution at the 3,5-
positions of BODIPY can effectively modulate the electron-
ic conjugation properties of the BODIPY chromophore.
On increasing the number of phenyl acetylene units, with
n varying from 1 to 7, the maximum absorption peak of
OPEn is increasingly redshifted. With each addition of a re-
peating unit, the additional redshift becomes smaller, as ex-
pected for polyene-like chromophores: for n from 1 to 3,
Dl=61 nm; n from 3 to 5, Dl=20 nm; n from 5 to 7, Dl=
10 nm (Table 1, Figure 2). These results are in agreement
CHTUNGTRENNUNG
Figure 1. Normalized absorption spectra of 6, OPE3, and OPEB3 in
THF.
Optical properties: Figure 1 shows the normalized absorp-
tion spectra of OPEB3 together with those of reference
compounds 6 and OPE3 in THF. Spectroscopic data rele-
vant to the present discussion are collected in Table 1. In
Table 1. Absorption and fluorescence spectroscopic properties of 6,
OPEn, and OPEBn in THF.
Compound
Absorption
lmax [nm]
Luminescence
[a]
[b]
lmax [nm][a]
Ff1
Ff2
FET [%]
Figure 2. Normalized absorption spectra of OPEn in THF.
6
347, 547
335
391, 556
396
415, 555
416
422, 554
426
604[b]
0.10
with literature reports.[16] However, for OPEBn, the redshift
of the maximum absorption peak assigned to the OPE subu-
nit changes much less: for n from 1 to 3, Dl=24 nm; n from
3 to 5, Dl=7 nm; n from 5 to 7, Dl=2 nm (Table 1,
Figure 3). This is a result of the fact that electronic commu-
OPE1
OPEB1
OPE3
OPEB3
OPE5
OPEB5
OPE7
OPEB7
367[c]
0.63[c]
613
0.10
0.13
0.12
0.12
431, 453[c]
613
0.58[c]
0.14
0.58
0.12
0.50
0.10
99.9
99.4
98.6
461, 488
473, 614
468, 498
472, 613
424, 554
[a] The excitation wavelength was 420 nm. [b] The excitation wavelength
was 550 nm. [c] The excitation wavelength was 335 nm.
THF, the absorption spectrum of OPEB3 shows a strong
and broad S0!S1 (p–p*) transition with a maximum at
555 nm, assigned to the BODIPY chromophore.[20] The
second, more energetic transition with maximum at 415 nm
is attributed to the p–p* transition of the conjugated OPE
subunit. The weak and broad absorption band attributed to
the S0!S2 transition of BODIPY is not observed, as it is
hidden under the much stronger transition of the conjugated
OPE substituent. The significant bathochromic shift and the
increased width of the absorption peak assigned to the
BODIPY subunit compared to unsubstituted BODIPYs,[17b]
Figure 3. Normalized absorption spectra of OPEBn in THF. The spectra
were normalized at the maximum absorbance due to the OPE linker.
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Oligo(p-phenylene ethynylene)–BODIPY Derivatives
FULL PAPER
nication with the BODIPY moiety already leads to a signifi-
cant redshift of the OPE band for OPEB1. When n is in-
creased, this effect is reduced because of delocalization of
the excited state on the conjugated chain, and hence the
chain-length dependence is weaker. Although the position
of the maximum absorption peak assigned to the BODIPY
moieties is independent of the length of the OPE spacer,
the relative absorption intensity of the BODIPY band de-
creases when the number n of phenyl acetylene units is in-
creased (Table 1, Figure 3).
The normalized steady-state fluorescence spectra of 6,
OPE3, and OPEB3 in THF are shown in Figure 4. On exci-
Figure 5. Corrected normalized fluorescence emission spectra of OPEn in
THF (OPE1 and OPE3 excited at 335 nm; OPE5 and OPE7 excited at
420 nm).
sion (Table 1, Figure 5).[16] With increasing number of
phenyl acetylene moieties (n varying from 3 to 7), the emis-
sion maximum and the shoulder show a redshift which par-
allels that of the absorption spectra. These results are in line
with reported OPE systems.[16] On excitation at 355 nm
OPE1 shows a structureless band with a maximum at
367 nm. However, the emission spectra of OPEBn are domi-
nated by a band peaking at 613 nm, corresponding to emis-
sion of the BODIPY moieties (Table 1, Figure 6, Figure 7),
Figure 4. Corrected normalized fluorescence emission spectra of 6 (lex
550 nm), OPE3 (lex =335 nm), and OPEB3 (lex =420 nm) in THF.
=
tation at lex =335 nm, where light absorption occurs nearly
exclusively by the OPE units, OPE3 shows an emission
maximum at 431 nm, a less intense peak at 453 nm, and a
shoulder at 474 nm due to coupling of the stretching modes
of the phenylene ring to the electronic p–p* transition.[16]
On excitation at the absorption maximum (550 nm), 6 shows
an emission peak at 603 nm due to emission from the
BODIPY moiety. However, on excitation at 420 nm OPEB3
shows the emission characteristic of the BODIPY moiety at
613 nm as the main emission band, while almost no OPE
emission at about 454 nm is observed. These observations
clearly indicate the occurrence of efficient energy transfer
from the excited OPE units to the BODIPY core. The fluo-
rescence quantum yields Ff of OPEB3 were measured to be
0.14, and 0.13 for two different excitation wavelengths (420
and 550 nm), which were also close to that of 6. The very
weak OPE emission and the independence of Ff of
BODIPY emission from the excitation wavelength suggest
almost complete energy transfer from the donor (OPE
units) to the acceptor (BODIPY moieties).[3a] Furthermore,
these observations indicate that no electron transfer occurs
between the BODIPY moiety and OPE in THF, because
this would induce quenching of the BODIPY emission.
On excitation at 420 nm, all OPEn with the exception of
OPE1, which does not absorb at 420 nm, show a peak and
an accompanying shoulder shifted by between 900 and
1400 cmꢀ1 to longer wavelengths due to vibrational progres-
Figure 6. Corrected normalized fluorescence emission spectra of OPEBn
in THF (lex =420 nm).
regardless of whether excitation was at 420 or 550 nm. Fur-
thermore, a very small band is observed with a maximum
between 450 and 500 nm, the intensity of which relative to
that of the BODIPY emission increases with increasing n.
This band is attributed to residual emission of the OPE
chromophores. This indicates that the excited state of OPE
subunits is efficiently quenched in OPEBn by energy trans-
fer to the BODIPY moieties and that the quenching be-
comes less efficient with increasing n. The similar Ff values
of the BODIPY emission of OPEB3 to OPEB7 on excita-
tion at 420 and 550 nm suggest that no other quenching pro-
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W. Dehaen, D. Beljonne et al.
to toluene (Table 2, Figures S1 and S2 in the Supporting In-
formation). Since the Stokes shift between the absorption
and emission maxima is essentially independent of solvent
Table 2. Absorption and fluorescence spectroscopic properties of 6,
OPEn, and OPEBn in toluene.
Compound
Absorption
lmax [nm]
Luminescence
[a]
[b]
lmax [nm][a]
Ff1
Ff2
FET [%]
6
349, 557
337
390, 557
397
414, 565
415
423, 566
427
606[b]
0.11
OPE1
OPEB1
OPE3
OPEB3
OPE5
OPEB5
OPE7
OPEB7
370[c]
0.65[c]
614
0.12
0.22
0.14
0.12
432, 456[c]
611
0.60[c]
0.17
0.73
0.15
0.56
0.17
99.9
99.6
98.8
461, 490
473, 617
470, 503
471, 613
Figure 7. Corrected normalized fluorescence emission spectra of OPEBn
in THF (lex =550 nm).
426, 564
[a] The excitation wavelength was 420 nm. [b] The excitation wavelength
was 550 nm. [c] The excitation wavelength was 335 nm.
cesses occur. To roughly evaluate the efficiency of the
energy transfer processes, the equation FET =1ꢀFF(dyad)
/
FF(donor) is used,[21] where FET is the energy-transfer quantum
yield and FF(dyad) and FF(donor) are the fluorescence quantum
yields of the OPE moiety in the dyad (OPEB) and in the
OPE model compound, respectively. All FET values are
greater than 98% (Table 1), that is, energy transfer in
OPEBn is very efficient. Furthermore, the energy-transfer
efficiency decreases slightly with increasing length of OPE
units, from about 99.9% for OPEB1 and OPEB3, to 99.4%
for OPEB5, and to 98.6% for OPEB7. Efficient energy
transfer is also suggested by the similarity between the ab-
sorption and excitation spectra of the BODIPY emission
(Figure 8). If one assumes a fluorescent decay time of 662 ps
polarity, there is no significant change in dipole moment on
excitation. Interestingly, the absorption band of the
BODIPY moiety in OPEBn shows a redshift on replacing
THF by toluene. Such an effect was attributed to an in-
crease in solvent polarizability in other BODIPY deriva-
tives. However, the fluorescence emission maxima of
OPEBn, which are attributed to the BODIPY moiety, are
nearly independent of solvent polarity (Table 2, Figures S3,
S4, and S5 in the Supporting Information). This indicates
that the effects of solvent polarizability, which were shown
to be identical for absorption and emission in other BOPDI-
PY dyes, and solvent dipolarity nearly cancel.[20] This sug-
gests a small increase of the permanent dipole moment in
the excited state of BODIPY. Furthermore, the Ff values
measured were always higher in toluene than in THF. This
is in agreement with results obtained earlier for 3-amino-
substituted BODIPYs.[20]
Modeling: Figure 9 shows the evolution of the theoretical
absorption spectra of OPEBn versus n, as obtained on the
basis of INDO/SCI calculations and from the phenomeno-
logical model (see Experimental Section). In both cases, a
coplanar conformation was assumed.
From Figure 9, bathochromic and hyperchromic shifts of
the spectral band associated with the OPEn moiety (in the
range 3–3.5 eV) are observed, consistent with increasing p
conjugation of the main backbone when n is increased. In
contrast, the low-energy (ꢁ2.2 eV) transition involving the
BODIPY end groups shows a vanishingly small dependence
on size, indicative of rather localized electronic excitation.
INDO/SCI calculations suggest that the BODIPY-centered
excited state slightly extends over the first phenylene ethy-
nylene unit (see transition density map in Figure S6, Sup-
porting Information). Therefore, the relative intensities of
the BODIPY and OPEn optical features are highly sensitive
Figure 8. Corrected normalized fluorescence excitation spectra of 6 and
OPEBn in THF (lem =613 nm).
for the OPE moiety (as found for an OPE derivative similar
to OPE7; Fron et al., personal communication), this corre-
sponds to a value of the rate constant for energy transfer
ranging from 1.5ꢂ1012 sꢀ1 for OPEB1 and OPEB3 to 2.5ꢂ
1011 sꢀ1 and 1.1ꢂ1011 sꢀ1 for OPEB5 and OPEB7.
Oligomers OPEn show modest solvent dependence with a
few nanometers redshift when the solvent THF is changed
to the actual conjugation length, with the ratio I
ACHTUNGTRENN(UNG BODIPY)/
IACHTUNGTREN(NUNG OPEn) decreasing with increasing n, as clearly seen in
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Oligo(p-phenylene ethynylene)–BODIPY Derivatives
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room temperature (300 K). Thus, energy relaxation among
the electronic eigenstates of the end-capped polymer chains
proceeds by scattering to phonons (see Experimental Sec-
tion), and the energy-transfer efficiency is gauged by the
fraction of electronic excitations that reach the BODIPY
units within their lifetimes.
The corresponding experimental populations over donor
and acceptor can be extracted by integrating the steady-
state photoluminescence spectra over spectral ranges corre-
sponding to OPEn and BODIPY emission and renormaliz-
ing the data according to their relative absorption cross sec-
tions at 420 (OPE) and 560 nm (BODIPY). In Figure 10,
Figure 9. Theoretical absorption spectra of OPEBn versus n, as calculat-
ed at the INDO/SCI level (top) and the phenomenological model
(bottom).
Figure 10. Evolution of acceptor population pA as a function of oligomer
length n in end-capped OPEBn for different conformational potentials.
both the measured and INDO/SCI calculated spectra. The
salient features of the absorption spectrum, that is, the spec-
tral shifts with conjugation length and relative intensities of
the two main bands, are also captured by the phenomeno-
logical model (see Experimental Section).
To assess the efficiency of energy transfer from the OPE
core to the BODIPY end groups, we defined the normalized
steady-state populations in the eigenstates obtained by diag-
onalizing the phenomenological Hamiltonian [Eq. (1)].
the evolution with chain size of the measured population on
the acceptor is compared to the results of three theoretical
simulations that account for a growing amount of conforma-
tional disorder: “reference”, “gas phase”, and “free chain”.
The first case, “reference”, corresponds to OPEBn chains
without conformational defects. These chains are planar,
thereby ensuring full p delocalization. The second case, “gas
phase”, corresponds to the potential-energy surface ob-
tained from gas-phase B3LYP calculations[23], which takes
the form asin2 f with a=0.5 kcalmolꢀ1 and f the torsion
angle between two successive units. Finally, the “free-chain”
potential corresponds to a completely flat torsion potential.
Figure 10 shows that a reasonable agreement between
theory and experiment is obtained for the relatively small
oligomer lengths considered in this work (from 1 to 7 mono-
mer units in the OPEn chain), whatever the potential used
to generate the conformation of the chains. This suggests
that such small chains behave as single quantum entities
that act as efficient wires for energy migration to the end
caps. From Figure 10, we also see that increased physical
length and conformational disorder tend to reduce the effi-
ciency of energy transfer in longer chains. In the absence of
energetic disorder induced by conformational freedom
(planar conformation in the “reference” scenario), there is
excellent overlap, both energetic and spatial, between all
donor excitonic states. The excitations thus quickly relax in
1
Z
PiðtÞ
P
pi ¼
dt
ð1Þ
PiðtÞ
0
i
The rate constants of the different nonradiative processes
are incorporated in the Hamiltonian (see the Experimental
Section and the Supporting Information), and their values
are based on experimental ones obtained in previous pa-
pers.[17d,22] The energy-transfer efficiency is then monitored
through the time-integrated population on the acceptor pA,
that is, the population summed over the lowest two eigen-
states that are mostly confined on the two outer BODIPY
units. Note that: 1) at time t=0 (initial conditions), all ei-
genstates of the OPE donor are equally populated
ND
P
(
Pið0Þ ¼ 1), that is, we assume broadband excitation over
i
the donor band, and 2) all simulations are performed at
Chem. Eur. J. 2011, 17, 13247 – 13257
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13253

W. Dehaen, D. Beljonne et al.
model is based on the strong coupling regime, in which energy relaxation
among the eigenstates of the electronic Hamiltonian proceeds through
scattering by phonons (see ref. [25] for extensive details on the model).
We here consider an effective Hamiltonian that contains matrix elements
between a limited set of basis functions taken as localized and nearest-
neighbor charge-transfer configurations, as sketched in Figure 11.
the eigenstate manifold and reach low-lying excited states
that are highly delocalized. As a consequence, the electronic
excitations tend to to be “diluted” in space when n increas-
es, which leads to smaller electronic contacts with the
BODIPY end groups for through-bond energy transfer. This
explains the decrease in trans-
fer efficiency with increasing
chain size in the ideal disorder-
free case. In presence of confor-
mational disorder, the reduced
energetic and spatial overlap
results in a partitioning of the
chains into several conforma-
tional subunits, which are locat-
Figure 11. Schematic representation of the effective Hamiltonian for a OPEBn chain.
ed differently in space (the
system is no longer a single
The OPEBn chains are modeled as a successive alignment of phenylene
ethynylene monomer units end-capped by two BODIPY molecules. Each
unit has its own local excitation energy: ED for the units in the OPEn oli-
gomer, which acts as a “donor”, and EA for the BODIPY subunits, which
act as acceptors. In the investigations performed previously,[26] we found
that the electronic eigenstates of bichromophoric systems can be de-
scribed as combinations of localized (excitonic) and charge-transfer elec-
tronic configurations. We therefore included in our basis nearest-neigh-
bor charge-separated configurations with energies ECDT on the chain and
ECAT for donor moieties in contact with the end group. In reference [26],
the role of through-bond and through-space coupling was also unraveled.
These couplings are the parameters influencing the p delocalization in
the model. However, as shown in reference [26], the through-bond cou-
plings are sensitive to the conformational disorder. The presence of large
dihedral angles between the successive units should therefore reduce the
conjugation along the polymer chains. To account for this effect, the
matrix element mixing localized (covalent) and charge-transfer (ionic)
configurations is given the form of the following transfer integral
[Eq. (2)]
quantum object) and in energy (segments with different con-
jugation lengths have different excitation energies). This
slows down significantly the energy transfer to the end caps,
and the effect is larger in long chains because of the in-
creased number of conformational subunits.
Conclusion
We have synthesized a series of oligo(p-phenylene ethyny-
lene)–BODIPY (OPEB) cassettes in which a series of
OPEs with the different conjugated chain lengths have been
capped at both ends with BODIPY chromophores. Energy
transfer from OPEn to BODIPY in OPEBn is very efficient
and the energy transfer efficiency decreases somewhat with
increasing length of OPE units. Future work will focus on
the response of OPEBn to different metal ions and compar-
ing the sensitivity of OPEBn with model compound 6.
t ¼ VCT cos ꢀ
ð2Þ
where f is the dihedral angle between two successive units. Finally, the
localized excitations interact through space via dipole–dipole interactions,
which are limited to nearest neighbors and are insensitive to conforma-
tion. Note that matrix elements between ionic configurations are set to
zero.
Experimental Section
General: [PdCl2ACHTUNGTRENNUNG
(PPh3)2] and tetrabutylammonium fluoride (1 molLꢀ1 so-
Diagonalization of the model Hamiltonian yields a set of eigenstates jni
Thus, the “local” subunits (used as a basis) interact together to give rise
to the eigenstates involved in the energy relaxation process. For the sake
of illustration, we show in Figure S7 (Supporting Information) the transi-
tion densities (overlap between ground- and excited-state wave func-
tions) for two such eigenstates as obtained in the disorder-free case. One
excited state is mainly confined on the BODIPY end group but also
shows a small contribution on the closest PE unit, permitting electronic
communication with the polymer chain; the other (higher-lying) electron-
ic excitation is typical of unsubstituted OPE oligomers with a wave func-
tion peaking around the center of the polymer chain and negligible
weights on the edges.
lution in THF) were purchased from Aldrich and used without further
purification. 4-Diiodo-2,5-bis(dodecyloxy)benzene[24] and 1-ethynyl-4-(tri-
methylsilylethynyl)benzene[3e] were synthesized according to literature
procedures. The synthesis and characterization of 5-[N-(2-picolyl)amino]-
4,4-difluoro-3-[4-(ethynyl)phenylethynyl]-8-(4-tolyl)-4-bora-3a,4a-diaza-s-
indacene (6)[19] and 1,4-bis[(4-
ACHTNUTRGNE{NUG [5-N-(2-picolyl)amino-4,4-difluoro-8-(4-
tolyl)-4-bora-3a,4a-diaza-s-indacene-3-yl}ethynyl)phenylethynyl]-2,5-bis(-
dodecyloxy)benzene (OPEB1)[18] will be described elsewhere. Tetrahy-
drofuran and toluene were distilled from sodium prior to use. 1H and
13C NMR spectra were recorded at room temperature on a Bruker
1
Avance 300 operating at a frequency of 300 MHz for H and 75 MHz for
13C. UV/Vis absorption spectra were recorded on a PerkinElmer Lambda
40 UV/Vis spectrophotometer. Corrected steady-state excitation and
emission spectra were obtained by using a SPEX Fluorolog. Mass spectra
were recorded on a Hewlett-Packard 5989A mass spectrometer (ESI
mode).
The energy-diffusion process is then modeled by solving the following
Pauli master equations for the population of the eigenstates [Eq. (3)],
X
@
Pv ¼ ꢀkvPv þ
ðWvmPm ꢀ WmvPvÞ
ð3Þ
@t
m
Theoretical methodology: INDO/SCI calculations were performed on
AM1-optimized ground-state geometries to compute the vertical transi-
tion energies and transition dipole moments. In addition, we have devel-
oped a simple phenomenological model to account for the electronic
structure in the excited states and the energy diffusion dynamics. The
where kv is the radiative decay rate of the state jni, and W
avedA
scattering rate from state jmi
[jni] to state jni
ACHTUNGTRENNUNG
Equation (4),
13254
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13247 – 13257

Oligo(p-phenylene ethynylene)–BODIPY Derivatives
FULL PAPER
(
ꢀ
ꢁ
ꢃ
3.34 (s, 2H; CH), 1.84 (m, 12H; OCH2CH
(CH2)2CH2A(CH2)8CH3), 1.24 (m, 96H; O(CH2)
(m, 18H; O
(CH2)11CH3); 13C NMR (75 MHz, CDCl3): d=154.1, 153.5,
(CH2)9CH3), 1.48 (m, 12H;
ꢀ
1 þ n Ev ꢀ Em
Ev > Em
Em > Ev
Wmv ¼ DwJmv
ꢂ
ð4Þ
ꢀ
ꢁ
O
G
N
U
CHTUNGTRENNUNG
ꢀ
n Ev ꢀ Em
AHCTUNGTRENNUNG
153.3, 117.9, 117.2, 117.0, 115.0, 114.2, 112.5, 91.6, 91.3, 88.2, 82.3, 80.1,
69.7, 69.6, 32.0, 29.7, 29.5, 29.4, 29.3, 26.0, 22.7, 14.1 ppm.
ꢂ
ꢃ
w
w
where Dw ¼ W0 exp ꢀ
is the vibration spectral density of the bath
wc
wc
(W0: reorganization energy or exciton–phonon coupling, wc: cutoff fre-
preOPE5: The compound was prepared according to GP1, from
(673 mg, 0.6 mmol), OPE1 (148 mg, 0.3 mmol), THF (20 mL), Et3N
(2 mL), [PdCl2A(PPh3)2] (4.2 mg, 6 mmol) and CuI (1.2 mg, 6 mmol). Purifi-
cation was performed by chromatography on silica gel with CH2Cl2/
EtOAc (1/1, v/v) as eluent and afforded preOPE5 (604 mg, 81% yield)
as an orange solid. 1H NMR (300 MHz, CDCl3): d=6.98 (m, 10H), 3.98
5
N
ꢄ
ꢄ
ꢄ
ꢄ
P
2
2
quency), Jmv
¼
ꢀmn jꢀvn
j
the probability overlap that measures the
CTHUNGTRENNUNG
n¼1
spatial overlap between two eigenstates jni and jmi, n¯ the mean occupa-
tion number of a given vibrational mode, and Em [Ev] the energy of initial
[final] state, respectively. The Pauli master equations are solved for a set
of parameters describing the coupling of the electronic system to the
bath as well as the radiative and nonradiative contributions to the decay
of the eigenstates. These were adjusted against experiment or were given
literature values.[23,27]
(m, 20H; OCH
OCH2CH2A(CH2)9CH3), 1.64 (s, 12H; C
(CH2)2CH2A(CH2)8CH3), 1.25 (m, 160H; O
(m, 30H; O
(CH2)11CH3); 13C NMR (75 MHz, CDCl3): d=153.5, 153.4,
(CH2)10CH3), 2.04 (s, 2H; OH), 1.84 (m, 20H;
(CH3)2OH), 1.49 (m, 20H; O-
(CH2)3A(CH2)8CH3), 0.87 ppm
G
ACHTUNGTRENNUNG
R
G
N
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
Determination of fluorescence quantum yields: For the determination of
the relative fluorescence quantum yields Ff, only dilute solutions with an
absorbance of less than 0.1 at the excitation wavelength lex were used.
Quinine bisulfate in 0.05m H2SO4 (Ff =0.55, lex =335 nm), acridine
yellow in methanol (Ff =0.57, lex =420 nm) and cresyl violet in methanol
(Ff =0.55, lex =550 nm) were used as fluorescence standards. In all cases,
correction for the solvent refractive index was applied. All spectra were
recorded at 208C on undegassed samples.
117.2, 116.9, 114.3, 113.2, 99.2, 91.4, 78.6, 69.6, 69.3, 65.8, 32.0, 31.5, 29.7,
29.5, 26.0, 22.7, 14.1 ppm.
OPE5: The compound was prepared according to GP3, from preOPE5
(621 mg, 0.25 mmol), NaOH (2 g, 50 mmol), and toluene (40 mL). The
mixture was heated to reflux for 48 h. Purification was performed by
chromatography on silica gel with CH2Cl2 as eluent to give OPE5
1
(278 mg, 47% yield) as an orange solid. H NMR (300 MHz, CDCl3): d=
ꢃ
6.98 (m, 10H), 4.01 (m, 20H; OCH
(m, 20H; OCH2CH2A(CH2)9CH3), 1.48 (m, 20H; O
1.24 (m, 160H; O(CH2)3A(CH2)8CH3), 0.87 ppm (m, 30H; O
G
General procedure 1 (GP1) for the cross-coupling reaction: The iodo
and ethynyl derivatives were dissolved in argon-purged THF, and trie-
thylamine and finally [PdCl2ACHTNUTRGNE(UGN PPh3)2] and CuI were added. After the mix-
ture was heated at 608C for 12 h, the solvent was evaporated. The crude
product was extracted with CH2Cl2, dried over MgSO4, and the solvent
was evaporated under reduced pressure. The residue was purified by
column chromatography.
E
G
G
(CH2)11CH3);
13C NMR (75 MHz, CDCl3): d=153.5, 153.3, 151.5, 128.2, 125.5, 117.9,
117.2, 117.0, 115.0, 114.3, 114.1, 91.6, 82.3, 80.1, 69.7, 32.0, 30.3, 29.7, 29.5,
26.0, 22.7, 14.1 ppm.
preOPE7: The compound was prepared according to GP1, from
(673 mg, 0.6 mmol), OPE3 (429 mg, 0.3 mmol), THF (20 mL), Et3N
(2 mL), [PdCl2A(PPh3)2] (4.2 mg, 6 mmol) and CuI (1.2 mg, 6 mmol). Purifi-
5
General procedure 2 (GP2) for the deprotection reaction: An excess of
solid NaOH was added to a stirred solution of the protected ethynyl de-
rivative in toluene, and the mixture was heated at 758C. When the mono-
deprotected derivative was the major product (determined by TLC), the
reaction was quenched with water and a saturated solution of NH4Cl.
The product was extracted with dichloromethane, and the organic layers
were dried over MgSO4. The solvent was then evaporated and the com-
pound purified by chromatography.
CTHUNGTRENNUNG
cation was performed by chromatography on silica gel with CH2Cl2/
EtOAc (1/1, v/v) as eluent and afforded preOPE7 (708 mg, 69% yield)
as an orange solid. 1H NMR (300 MHz, CDCl3): d=6.98 (m, 14H), 4.00
(m, 28H; OCH
OCH2CH2A(CH2)9CH3), 1.64 (s, 12H; C
(CH2)2CH2A(CH2)8CH3), 1.25 (m, 224H; O
(m, 42H; O(CH2)11CH3).
(CH2)10CH3), 2.04 (s, 2H; OH), 1.84 (m, 28H;
(CH3)2OH), 1.50 (m, 28H; O-
(CH2)3A(CH2)8CH3), 0.88 ppm
G
ACHTUNGTRENNUNG
R
G
G
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
General procedure 3 (GP3) for the deprotection reaction: Similar to
GP2 but performed in refluxing toluene for 24 h.
OPE7: The compound was prepared according to GP3, from preOPE7
(684 mg, 0.2 mmol), NaOH (2 g, 50 mmol), and toluene (40 mL). The
mixture was refluxed for 48 h. Purification was performed by chromatog-
raphy on silica gel with CH2Cl2 as eluent to give OPE7 (185 mg, 28%
1,4-Diethynyl-2,5-didodecyloxybenzene OPE1: The compound was pre-
pared according to GP3, from 3 (1.22 g, 2 mmol), NaOH (3 g, 75 mmol),
and toluene (200 mL). Purification was performed by chromatography on
silica gel with CH2Cl2 as eluent to give OPE1 (810 mg, 82% yield) as a
yellow solid. 1H NMR (300 MHz, CDCl3): d=6.95 (s, 2H), 3.97 (t, J=
ꢃ
1
yield) as an orange solid. H NMR (300 MHz, CDCl3): d=6.98 (m, 14H),
ꢃ
4.02 (m, 28H; OCH
OCH2CH2A(CH2)9CH3), 1.43 (m, 28H; O
224H; O(CH2)3A(CH2)8CH3), 0.87 (m, 42H; O
G
E
G
G
(CH2)11CH3).
6.4 Hz, 4H; OCH2ACHTUNGTRENNUNG(CH2)10CH3), 3.32 (s, 2H; CH), 1.79 (m, 4H;
OCH2CH
G
ACHUTGTRENNGU(CH2)2CH2ACTHUNGTR(ENUNNG CH2)8CH3), 1.26 (m,
Compound 7: Compound 7 was prepared according to GP1, from 6
(60 mg, 0.1 mmol), 1 (1.40 g, 2 mmol), THF (30 mL), Et3N (0.5 mL),
32H; O(CH2)
N
E
(CH2)11CH3);
[PdCl
performed by chromatography on silica gel with CH2Cl2/ethyl acetate (1/
1, v/v) to give (75 mg, 64% yield) as
purple solid. 1H NMR
2ACHTUNGTRENN(NUG PPh3)2] (3.5 mg, 5 mmol) and CuI (1 mg, 5 mmol). Purification was
7
a
(300 MHz, CDCl3): d=8.59 (d, J=3.7 Hz, 2H), 7.67 (t, J=7.3 Hz, 2H),
7.36 (d, 6H), 7.24 (d, 2H), 7.19 (d, 2H), 7.13 (s, 1H), 7.10 (d, 2H), 6.91
(s, 1H), 6.84 (d, J=4.6 Hz, 1H), 6.59 (d, J=3.7 Hz, 1H), 6.36 (d, 1H),
preOPE3: The compound was prepared according to GP1, from
(1.31 g, 2 mmol), OPE1 (494 mg, 1 mmol), THF (40 mL), Et3N (3 mL),
[PdCl2A(PPh3)2] (14 mg, 0.02 mmol) and CuI (4 mg, 0.02 mmol). Purifica-
2
CHTUNGTRENNUNG
6.30 (d, 1H), 5.30 (s, 4H), 3.97 (m, 4H; OCH
CH3), 1.83 (m, 4H; OCH2CH2A(CH2)9CH3), 1.51 (m, 4H; O
(CH2)8CH3), 1.26 (m, 32H; O(CH2)3A(CH2)8CH3), 0.88 ppm (m, 6H; O-
(CH2)11CH3); 13C NMR (75 MHz, CDCl3): d=163.1, 155.4, 153.3, 150.8,
148.5, 138.1, 136.0, 135.3, 134.4, 132.8, 130.9, 130.8, 130.1, 129.4, 127.8,
124.4, 122.8, 122.6, 121.6, 120.8, 119.4, 118.3, 114.9, 114.3, 112.5, 94.3,
93.3, 86.7, 86.3, 85.0, 69.1, 68.9, 57.0, 30.9, 28.6, 28.3, 28.2, 25.0, 21.7, 20.3,
13.1 ppm; ESI-MS: m/z: 1196.7 [M+Na]+.
(CH2)10CH3), 2.42 (s, 3H;
tion was performed by chromatography on silica gel with CH2Cl2/EtOAc
(1/1, v/v) as eluent and afforded preOPE3 (1.35 g, 87% yield) as an
orange solid. 1H NMR (300 MHz, CDCl3): d=6.99 (s, 2H), 6.96 (s, 2H),
G
ACHTUNGTRENNUNG
R
G
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
6.90 (s, 2H), 3.98 (m, 12H; OCH
(m, 12H; OCH2CH2A(CH2)9CH3), 1.64 (s, 12H; C
12H; (CH2)2CH2A(CH2)8CH3), 1.24 (m, 96H;
0.88 ppm (m, 18H;
(CH2)11CH3); 13C NMR (75 MHz, CDCl3): d=
(CH2)10CH3), 2.05 (s, 2H; OH), 1.83
(CH3)2OH), 1.49 (m,
(CH2)3A(CH2)8CH3),
G
ACHTUNGTRENNUNG
O
R
G
O
N
CHTUNGTRENNUNG
OACHTUNGTRENNUNG
153.6, 153.5, 153.4, 151.8, 117.2, 116.9, 114.3, 114.2, 113.2, 91.4, 78.6, 69.7,
69.3, 65.8, 31.9, 31.5, 29.7, 29.5, 29.3, 26.1, 26.0, 22.7, 14.1 ppm.
OPEB3: The compound was prepared according to GP1, from 7 (47 mg,
0.04 mmol), OPE1 (10 mg, 0.02 mmol), THF (6 mL), Et3N (0.3 mL),
[PdCl2ACTHNUGTRNE(NUG PPh3)2] (1.4 mg, 2 mmol) and CuI (0.4 mg, 2 mmol). Purification
was performed by chromatography on silica gel with CH2Cl2/ethyl acetate
(1/1, v/v) followed by CH2Cl2/CH3OH (5/1, v/v) to give OPEB3 (19 mg,
37% yield) as a purple solid. 1H NMR (300 MHz, CDCl3): d=8.56 (d,
OPE3: The compound was prepared according to GP3, from preOPE3
(774 mg, 0.5 mmol), NaOH (3 g, 75 mmol), and toluene (50 mL). Purifi-
cation was performed by chromatography on silica gel with CH2Cl2 as
eluent to give OPE3 (429 mg, 60% yield) as an orange solid. 1H NMR
(300 MHz, CDCl3): d=6.98 (m, 6H), 3.99 (m, 12H; OCH2ACHTNUTRGNEUNG(CH2)10CH3),
Chem. Eur. J. 2011, 17, 13247 – 13257
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13255

W. Dehaen, D. Beljonne et al.
J=4.6 Hz, 4H), 7.68 (t, J=4.6 Hz, 4H), 7.45 (d, 12H), 7.34 (d, J=8.2 Hz,
4H), 7.21 (d, 8H), 7.01 (s, 6H), 6.83 (d, J=4.6 Hz, 2H), 6.60 (d, J=
3.7 Hz, 2H), 6.36 (d, 2H), 6.29 (d, 2H), 5.31 (s, 8H), 4.04 (t, J=6.4 Hz,
[6] a) F. R. Li, S. I. Yang, Y. Z. Ciringh, J. Seth, C. H. Martin, D. L.
Singh, D. Kim, R. R. Birge, D. F. Bocian, D. Holten, J. S. Lindsey, J.
Am. Chem. Soc. 1998, 120, 10001; b) R. K. Lammi, A. Ambroise, T.
Balasubramanian, R. W. Wagner, D. F. Bocian, D. Holten, J. S. Lind-
sey, J. Am. Chem. Soc. 2000, 122, 7579; c) D. Holten, D. F. Bocian,
J. S. Lindsey, Acc. Chem. Res. 2002, 35, 57; d) A. Ambroise, C. Kir-
maier, R. W. Wagner, R. S. Loewe, D. F. Bocian, D. Holten, J. S.
Lindsey, J. Org. Chem. 2002, 67, 3811; e) M. Koepf, A. Trabolsi, M.
Elhabiri, J. A. Wytko, D. Paul, A. M. A. Gary, J. Weiss, Org. Lett.
2005, 7, 1279.
12H; OCH
(CH2)9CH3), 1.52 (12H, m, O
(CH2)3A(CH2)8CH3), 0.86 (m, 18H; OACTHUNGTRENNNUG
(CH2)10CH3), 2.43 (s, 6H; CH3), 1.86 (m, 12H; OCH2CH2-
(CH2)2CH2A(CH2)8CH3), 1.25 (96H, m, O-
(CH2)11CH3).
G
R
CHTUNGTRENNUNG
R
U
OPEB5: The compound was prepared according to GP1, from 7 (24 mg,
0.02 mmol), OPE3 (15 mg, 0.01 mmol), THF (6 mL), Et3N (0.3 mL),
[PdCl2ACHTUNGTRENNUNG(PPh3)2] (0.7 mg, 1 mmol), and CuI (0.2 mg, 1 mmol). Purification
was performed by chromatography on silica gel with CH2Cl2/ethyl acetate
(1/1, v/v) followed by CH2Cl2/CH3OH (5/1, v/v) to give OPEB5 (10 mg,
28% yield) as a purple solid. H NMR (300 MHz, CDCl3): d=8.57 (4H),
[7] M. D. Yilmaz, O. A. Bozdemir, E. U. Akkaya, Org. Lett. 2006, 8,
2871.
1
7.68 (4H), 7.45 (12H), 7.35 (4H), 7.21 (8H), 7.01 (10H), 6.84 (2H), 6.60
[8] J. Y. Liu, E. A. Ermilov, B. Rçder, D. K. P. Ng, Chem. Commun.
2009, 1517.
[9] F. D’Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou, Y.
Araki, O. Ito, J. Am. Chem. Soc. 2004, 126, 7898.
(2H), 6.36 (2H), 6.30 (2H), 5.31 (8H, s), 4.03 (20H, OCH
2.43 (6H, CH3), 1.85 (20H, OCH2CH2A(CH2)9CH3), 1.56 (20H, O-
(CH2)2CH2A(CH2)8CH3), 1.26 (160H, (CH2)3A(CH2)8CH3), 0.87 ppm
(30H, O(CH2)11CH3).
2ACHTGNUTERN(NNUG CH2)10CH3),
CTHUNGTRENNUNG
A
N
O
G
CHTUNGTRENNUNG
ACHTUNGTRENNUNG
[10] a) A. Burghart, L. H. Thoresen, J. Chen, K. Burgess, F. Bergstrçm,
L. B. ꢃ. Johansson, Chem. Commun. 2000, 2203; b) V. A. Azov, A.
Schlegel, F. Diederich, Angew. Chem. 2005, 117, 4711; Angew.
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Chem. Soc. 2006, 128, 14474; d) X. L. Zhang, Y. Xiao, X. H. Qianl,
Org. Lett. 2008, 10, 29; e) S. Diring, F. Puntoriero, F. Nastasi, S.
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OPEB7: The compound was prepared according to GP1, from 7 (24 mg,
0.02 mmol), OPE5 (24 mg, 0.01 mmol), THF (6 mL), Et3N (0.3 mL),
[PdCl2ACHTUNGTRENNUNG(PPh3)2] (0.7 mg, 1 mmol), and CuI (0.2 mg, 1 mmol). Purification
was performed by chromatography on silica gel with CH2Cl2/ethyl acetate
(1/1, v/v) followed by CH2Cl2/CH3OH (5/1, v/v) to give OPEB7 (8 mg,
1
18% yield) as a purple solid. H NMR (300 MHz, CDCl3): d=8.57 (4H),
7.67 (4H), 7.45 (12H), 7.34 (4H), 7.21 (8H), 7.01 (14H), 6.84 (2H), 6.60
(2H), 6.36 (2H), 6.30 (2H), 5.30 (8H, s), 4.03 (28H, OCH
2.43 (6H, CH3), 1.85 (28H, OCH2CH2A(CH2)9CH3), 1.55 (28H, O-
(CH2)2CH2A(CH2)8CH3), 1.25 (224H, (CH2)3A(CH2)8CH3), 0.87 ppm
(42H, O(CH2)11CH3).
2ACHTGNUTERN(NNUG CH2)10CH3),
CTHUNGTRENNUNG
A
N
O
G
CHTUNGTRENNUNG
ACHTUNGTRENNUNG
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Technologie in Vlaanderen (IWT) is acknowledged for a fellowship to
V.L. We thank the Fonds voor Wetenschappelijk Onderzoek (FWO), the
Ministerie voor Wetenschapsbeleid, and the K.U.Leuven for continuing
financial support. The collaboration between Leuven and Mons is sup-
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(BELSPO - IAP project 6/27). Research in Mons is also supported by
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Received: February 10, 2011
Revised: July 23, 2011
Published online: October 11, 2011
Chem. Eur. J. 2011, 17, 13247 – 13257
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