The synthesis and spectroscopic characterization of poly(p-phenylene ethynylene) with 3-connected BODIPY end groups

Article abstract of DOI:10.1016/j.dyepig.2010.08.006

A novel 3-connected BODIPY end-capped poly(p-phenylene ethynylene) and a matching model compound were synthesized by palladium-catalyzed cross-coupling reaction. The structures were confirmed using ¹H NMR, UV-vis spectrophotometry and fluoresce

Full text of DOI:10.1016/j.dyepig.2010.08.006

Dyes and Pigments 88 (2011) 372e377
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and spectroscopic characterization of poly(p-phenylene ethynylene)
with 3-connected BODIPY end groups
,
Shouchun Yin a b, Volker Leen a, Carine Jackers a, Mark Van der Auweraer a, Mario Smet a, Noël Boens a,
,
Wim Dehaen a
*
a Department of Chemistry, Katholieke Universiteit Leuven and Institute for Nanoscience in Physics and Chemistry (INPAC), Celestijnenlaan 200f e bus 02404, 3001 Heverlee (Leuven),
Belgium
b College of Material Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
novel 3-connected BODIPY end-capped poly(p-phenylene ethynylene) and a matching model
Received 27 May 2010
Received in revised form
6 August 2010
Accepted 13 August 2010
Available online 21 August 2010
compound were synthesized by palladium-catalyzed cross-coupling reaction. The structures were
confirmed using 1H NMR, UVevis spectrophotometry and fluorescence spectroscopy. Both the polymer
and the model compound showed absorption and emission bands characteristic for the BODIPY chro-
mophore and the p-phenylene ethynylene linker. However, while upon excitation of the p-phenylene
ethynylene linker energy transfer occurs for nearly 100% in the model compound, it is only a minor decay
channel of the singlet excited state of the p-phenylene ethynylene linker in the polymer.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
BODIPY
Fluorescent dye
Poly(p-phenylene ethynylene)
Conjugated polymer
Spectroscopic properties
Energy transfer
1. Introduction
Covalent incorporation of BODIPY into PPE can efficiently tune the
photophysical properties of conjugated polymer systems [21e25].
In the past decades, there has been a vast increase in the research
andapplication ofconjugated polymers. Particularly, poly(phenylene
ethynylene)s (PPEs) have attracted considerable interest due to their
easy synthesis via the Sonogashira cross-coupling methodology, and
interesting properties resultingfromtheirlinear structure andstrong
fluorescence [1e3]. As promising materials, PPEs have been applied
widely in chemo- and biosensors [2,3] and electronic devices such as
Organic Light Emitting Diodes (OLEDs) [4,5], Organic Field Effect
Transistors (OFETs) [6] and solar cells [7,8].
Chujo et al. have reported the preparation of highly fluorescent PPE
polymers containing BODIPY, which can self-assemble into parti-
cles, fibers, and network structures by intermolecular
pep staking
of BODIPY [21]. Also, a series of color-tunable PPE polymers with
narrow emission band have been synthesized by attaching them
directly to the BODIPY cores to extend the p-conjugation of the PPE
polymers [23e25]. Furthermore, Li et al. have reported that the
BODIPY component in polymers can enhance the nonlinear optical
properties of the PPE polymer [22].
BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) deriva-
tives are interesting dyes because of their advantageous charac-
teristics, such as sharp absorption and fluorescence bands in the
visible wavelength range, reasonably high fluorescence quantum
yields, relatively large molar absorption coefficients, and robust-
ness against light and chemicals [9,10]. All of these features
stimulate their applications as fluorescent chemosensors [11e15],
light-harvesting systems [16e18], fluorescent labels [19], and in
some cases potential sensitizers in photodynamic therapy [20].
As an addition to these intriguing systems, here we report the
design and synthesis of BODIPY end-capped PPE and its optical prop-
erties. Such a BODIPY end-capped PPE polymer can offer a model to
study the energy transfer along the rigid chain and help one to design
novel PPE polymers useful for optical and electronic applications.
2. Experimental
2.1. Materials
1,4-Diethynyl-2,5-bis(dodecyloxy)benzene (1) and 1,4-diiodo-
2,5-bis(dodecyloxy)benzene (2) were synthesized according to
* Corresponding author. Tel.: þ32 16 327439; fax: þ32 16 327990.
E-mail address: Wim.Dehaen@chem.kuleuven.be (W. Dehaen).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.08.006

S. Yin et al. / Dyes and Pigments 88 (2011) 372e377
373
OC12H25
OC12H25
Pd(PPh3)2Cl2, CuI
OC12H25
OC12H25
OC12H25
I
(
+
I
I
I
)
n
NEt3, THF
C12H25
O
C12H25
O
C12H25
O
C12H25
O
C12H25O
1
2
poly1
Scheme 1. Synthetic route to poly1.
literature procedures [26]. Bis(triphenylphosphine)palladium(II)
chloride [Pd(PPh3)2Cl2] and CuI were purchased from Aldrich and
used without further purification. Tetrahydrofuran (THF) and
toluene were distilled from sodium prior to use.
filtered off. The soluble filtrate was concentrated to 3 mL, and added
dropwise into 60 mL of methanol and acetone (4:1, v/v) under
stirring to precipitate the polymer. Then the product was redis-
solved in 3 mL of THF, and added dropwise through a cotton filter
into 60 mL of methanol and acetone (4:1, v/v). The dissolution-
precipitation process was repeated three times, and the final, iso-
lated precipitate was dried under vacuum at 40 ꢀC to a constant
weight (575 mg, 62% yield). Mw 16 100; Mw/Mn 2.0 (GPC, poly-
2.2. Instrumentation
1H NMR spectra were recorded at room temperature on a Bruker
Avance 300 instrument operating at a frequency of 300 MHz. GPC
measurements with linear PS standard calibration were performed
on a Shimadzu apparatus using PLgel mixed-D columns (Polymer
Laboratories) at 1 mL/min at 30 ꢀC. All the polymer solutions were
styrene calibration). 1H NMR (300 MHz, CDCl3),
d (ppm): 7.30,
7.02e6.89 (br, 2H, AreH), 4.01 [br, 4H, OCH2(CH2)10CH3], 1.83 [br,
4H, OCH2CH2(CH2)9CH3], 1.51 [br, 4H, O(CH2)2CH2(CH2)8CH3], 1.26
[br, 32H, O(CH2)3(CH2)8CH3], 0.87 [br, 6H, O(CH2)11CH3].
prepared in THF (ca. 2 mg/mL) and filtered through 0.45-mm PTFE
2.3.2. Poly(p-phenylene ethynylene) with phenyl terminal groups
(poly2, Scheme 2)
syringe-type filters before being injected into the GPC system.
UVevis absorption spectra were recorded on a Perkin Elmer
Lambda 40 UVevis spectrophotometer. Corrected steady-state exci-
tation and emission spectra were obtained using an SPEX Fluorolog.
50 mg poly1 and 11
dissolved in 10 mL of THF and 0.3 mL of Et3N under argon. To this
solution 1 mg (1.4 mol) PdCl2(PPh3)2 and 0.2 mg (1 mol) CuI were
mL (0.1 mmol) phenylacetylene (3) were
m
m
For thedetermination of the relative fluorescence quantumyields (Ff
)
added. The reaction mixture was heated at 60 ꢀC for 48 h. After the
reaction mixture was cooled to room temperature, the solution was
concentrated. The residue was washed three times with acetone,
and dried under vacuum at 40 ꢀC to a constant weight (44 mg, 88%
yield). Mw 15 700; Mw/Mn 2.1 (GPC, polystyrene calibration). 1H
in solution (THF and toluene), only dilute solutions with an absor-
bance below 0.1 at the excitation wavelength lex were used. Acridine
yellow in methanol (Ff ¼ 0.57, lex ¼ 420 nm) and cresyl violet in
methanol (Ff ¼ 0.55, lex ¼ 550 nm) were used as fluorescence stan-
dards. In all cases, correction for the solvent refractive index was
applied. All spectrawere recorded at 20 ꢀC using undegassed samples.
NMR (300 MHz, CDCl3),
d (ppm): 7.53, 7.33, 7.02e6.89 (br, 2.8H,
AreH), 4.02 [br, 4H, OCH2(CH2)10CH3], 1.83 [br, 4H,
OCH2CH2(CH2)9CH3], 1.52 [br, 4H, O(CH2)2CH2(CH2)8CH3], 1.25 [br,
32H, O(CH2)3(CH2)8CH3], 0.87 [br, 6H, O(CH2)11CH3].
2.3. Synthesis
2.3.1. Poly(p-phenylene ethynylene) with iodide terminal groups
(poly1, Scheme 1)
490 mg (1 mmol) 1,4-diethynyl-2,5-bis(dodecyloxy)benzene (1)
and 694 mg (1 mmol) 1,4-diiodo-2,5-bis(dodecyloxy)benzene (2)
were dissolved in 15 mL of THF and 1 mL of Et3N under argon. To
2.3.3. Poly(p-phenylene ethynylene) with BODIPY terminal groups
(poly3, Scheme 3)
The synthesis and characterization of 5-N-(2-picolyl)amine-4,4-
difluoro-3- (4-(ethynyl)phenylethynyl)-8-(4-tolyl)-4-bora-3a,4a-
diaza-s-indacene (4), which is used in the synthesis of poly3
(Scheme 3) and model compound 5 (Scheme 4) will described
this solution 14 mg (0.02 mmol) PdCl2(PPh3)2 and
4 mg
(0.02 mmol) CuI were added. The reaction mixture was heated at
60 ꢀC for 24 h. Then, 69 mg (0.1 mmol) of 2 was added and reacted
for another 3 h to ensure that at the end of polymerization the
polymer chain was terminated by iodine atoms. After the reaction
mixture was cooled to room temperature, insoluble solids were
elsewhere [27]. 50 mg poly1 and 4 mg (6.6
solved in 10 mL of THF and 0.3 mL of Et3N under argon. To this
solution 1 mg (1.4 mol) PdCl2(PPh3)2 and 0.2 mg (1 mol) CuI were
added. The reaction mixture was heated at 60 ꢀC for 48 h. After
mmol) of 4 were dis-
m
m
OC12H25
OC12H25
OC12H25
I
Pd(PPh3)2Cl2, CuI
NEt3, THF
(
+
)
I
n
C12H25O
C12H25O
C12H25O
poly1
OC12H25
3
)
(
n
C12H25O
poly2
Scheme 2. Synthetic route to poly2.

374
S. Yin et al. / Dyes and Pigments 88 (2011) 372e377
OC12H25
(
OC12H25
OC12H25
I
Pd(PPh3)2Cl2, CuI
NEt3, THF
)
I
+
N
N
n
B
F2
C12H25
O
C12H25
O
C12H25O
N
poly1
N
N
4
N
N
N
N
F2B
OC12H25
N
)
(
n
N
BF2
C12H25
O
N
N
poly3
N
N
Scheme 3. Synthetic route to poly3.
evaporating the solvent, the crude product was extracted with
CH2Cl2 (3 ꢁ 40 mL), dried over MgSO4, and CH2Cl2 was evaporated
under reduced pressure. The residue was washed three times with
acetone until the solution was colorless. The obtained solid was
further purified by column chromatography on silica gel, first
eluting with a mixture of CH2Cl2 and ethyl acetate (1:1, v/v) and
followed by a mixture of CH2Cl2 and methanol (5:1, v/v) to give poly
(p-phenylene ethynylene) capped with BODIPY end groups (17 mg,
35% yield). Mw 13 300; Mw/Mn 1.3 (GPC, polystyrene calibration). 1H
solution 3.5 mg (5
m
mol) PdCl2(PPh3)2 and 1 mg (5 mmol) CuI were
added. The reaction mixture was heated at 60 ꢀC for 20 h. After
evaporating the solvent, the crude product was extracted with
CH2Cl2 (3 ꢁ 40 mL), dried over MgSO4, and CH2Cl2 was evaporated
under reduced pressure. Purification was preformed by chroma-
tography on silica gel with a mixture of CH2Cl2 and ethyl acetate
(1:1, v/v), followed by a mixture of CH2Cl2 and methanol (1:10, v/v)
to give 5 (40 mg, 48% yield). 1H NMR (300 MHz, CDCl3)
d (ppm):
8.56 (d, 4H, J ¼ 4.6 Hz, pyridine-6), 7.68 (t, 4H, J ¼ 7.3 Hz, pyridine-
4), 7.45 (m, 12H), 7.34 (d, 4H, J ¼ 7.3 Hz), 7.21 (m, 8H), 7.01 (s, 2H),
6.84 (d, 2H, J ¼ 4.9 Hz), 6.60 (d, 2H, J ¼ 3.7 Hz), 6.36 (d, 2H,
J ¼ 4.9 Hz), 6.29 (d, 2H, J ¼ 3.7 Hz), 5.30 (s, 8H), 4.04 [t, 4H,
J ¼ 6.4 Hz, OCH2(CH2)10CH3], 2.42 (s, 6H, CH3), 1.86 [m, 4H,
OCH2CH2(CH2)9CH3], 1.54 [m, 4H, O(CH2)2CH2(CH2)8CH3], 1.25 [m,
32H, O(CH2)3(CH2)8CH3], 0.87 [m, 6H, O(CH2)11CH3]. 13C NMR (75
NMR (300 MHz, CDCl3),
d (ppm): 8.56, 7.79e7.28, 7.08e6.81 (br,
2.7H, AreH), 5.30 [br, 0.24H, N(CH2)2], 4.01 [br, 4H,
OCH2(CH2)10CH3], 2.43 (br, 1.8H, ArCH3), 1.84 [br, 4H,
OCH2CH2(CH2)9CH3], 1.51 [br, 4H, O(CH2)2CH2(CH2)8CH3], 1.25 [br,
32H, O(CH2)3(CH2)8CH3], 0.87 [br, 6H, O(CH2)11CH3].
2.3.4. Model compound 1,4-bis((4-((5-N-(2-picolyl)amine-4,4-
difluoro)-8-(4-tolyl)-4-bora-3a,4a- diaza-s-indacene-3-yl)ethynyl)
phenylethynyl)-2,5-bis(dodecyloxy)benzene (5, Scheme 4)
60 mg (0.1 mmol) of 4 and 35 mg (0.05 mmol) of 2 were dis-
solved in 16 mL of THF and 0.3 mL of Et3N under argon. To this
Mz, CDCl3), d (ppm): 164.2, 156.4, 153.6, 149.5, 139.2, 137.0, 136.3,
135.4, 133.8, 131.9, 131.8, 131.3, 130.4, 128.9, 125.5, 123.6, 122.7,
121.9, 121.3, 120.5, 119.3, 116.9, 115.3, 114.0, 95.4, 95.1, 87.8, 86.0,
69.6, 58.1, 31.9, 29.7, 29.4, 26.0, 22.7, 21.4, 14.2. ESI-MS: m/z 1672.7
[M þ Na]þ.
N
N
Pd(PPh3)2Cl2, CuI
N
2
4
+
NEt3, THF
N
F2B
OC12H25
N
N
C12H25
O
BF2
N
5
N
N
N
Scheme 4. Synthetic route to 5.

S. Yin et al. / Dyes and Pigments 88 (2011) 372e377
375
3. Results and discussion
3.1. Synthesis
The synthesis of poly3 is highlighted in Scheme 3. The initially
formed poly1 (Mw of 16 100 and polydispersity index (PDI) of 2.0)
was end-capped by reacting it with an excess of the ethynyl
substituted BODIPY 4. After washing several times with acetone,
poly3 was further purified by column chromatography to ensure
that poly3 was terminated by fluorophore 4. The Mw of poly3 is
13 300 and PDI is 1.3. As a result of the chromatography higher
molecular weight fractions were removed, yielding a narrower PDI
and a lower Mw Poly1 was also reacted with excess phenyl-
acetylene 3 to afford poly2 (Scheme 2) with Mw of 15 700 and PDI of
2.1. A low molecular mass model compound (5) was prepared
starting from diiodoarene 2 and BODIPY 4.
poly1
poly3
3.2. Structure characterization
The 1H NMR spectra of poly1 and poly3 in d-chloroform are
displayed in Fig. 1. At first glance, the spectra of poly1 and poly3
look very similar. However, there are some new small signals at
2.4 ppm (methyl of p-tolyl), 5.3 ppm (benzylic H of 4), 6.1 ppm
(pyrrole H of 4) and above 7.3 ppm (pyridine H), which indicate that
BODIPY 4 has been connected to poly1.
8
6
4
ppm
2
0
The 1H NMR spectrum was also used to determine the BODIPY
content in poly3. GPC analysis shows that Mw and Mn of poly3 are
13.3 and 10.3 kDa, respectively, indicating the degree of polymer-
ization is about 19 (not including the end groups). Thus, each poly3
is estimated to be end-capped with 1.2 BODIPY groups by the
integration of the PPE CH2O group (
d 4.01 ppm) and the picolyl CH2
5.30 ppm) signals in 1H NMR [28,29].
poly1
(d
3.3. UVevis absorption spectra of poly2, poly3, 4 and 5
The normalized UVevis absorption spectra of poly2, poly3 and
the model compounds 4 and 5 in toluene are displayed in Fig. 2. In
this solvent, the absorption spectrum of 5 shows a strong and broad
poly3
S1)S0 (pe
p*) transition with maximum at 567 nm, assigned to the
BODIPY chromophore [30]. The shoulder at 535 nm is assigned to
vibrational progression of the same electronic transition. A second
more energetic transition with maximum at 390 nm is attributed to
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
ppm
poly1
1.2
4
5
1.0
poly2
poly3
0.8
0.6
0.4
0.2
0.0
poly3
2.50
2.45
2.40
2.35
300
350
400
450
500
550
600
650
700
ppm
Wavelength / nm
Fig 1. 1H NMR spectra of poly1 and poly3 in CDCl3.
Fig 2. Normalized UVevis absorption spectra of 4, 5, poly2 and poly3 in toluene. The
spectra of 5, poly2 and poly3 are normalized at the maximum of absorption band of
the p-phenylene ethynylene linker. The spectrum of 4 is normalized at the maximum
of the UV absorption band.

376
S. Yin et al. / Dyes and Pigments 88 (2011) 372e377
5 (420nm)
1
0.8
0.6
0.4
0.2
0
Poly2 (420nm)
Poly3 (420nm)
5 (550nm)
Poly3 (550nm)
4 (550nm)
400
450
500
550
600
650
700
750
800
Wavelength / nm
Fig 3. Normalized fluorescence emission spectra in toluene solution of poly2, poly3 and 5 upon excitation at 420 nm and of poly3, 4 and 5 with lex ¼ 550 nm. The lex values used
are given in parentheses. All the spectra are normalized at the maximum of the emission band.
the
p
e
p* transition of the p-phenylene ethynylene linker [31]. The
Upon excitation (of the BODIPY chromophore) at 550 nm, poly3
and 4 show emission spectra in toluene with maxima at 612 nm and
607 nm, respectively. The long wavelength part of the fluorescence
emission spectrum of 5 is independent of the excitation wavelength
weak and broad absorption band attributed to the Sn)S0 transition
of BODIPY is not observed because it is hidden under the much
stronger transition of the p-phenylene ethynylene substituent [30].
The long wavelength part of the absorption spectrum of 5 corre-
sponds, except for a red shift, to that of model compound 4. Poly2
shows a very strong absorption peak at 429 nm, assigned to the
(lex ¼ 420 nm and 550 nm: grey and black curves in Fig. 3). Upon
excitation at 550 nm, the measured Ff values of poly3, 4 and 5 in
toluene amount to 0.18, 0.11 and 0.14, respectively. These values are
comparable to those of other 3-amino substituted BODIPYs [30].
The emission spectra of poly2, poly3, 4 and 5 in THF are very
similar to those obtained in toluene under the same conditions.
Upon 420 nm excitation, the fluorescence quantum yields of poly2
and poly3 in THF equal 0.63 and 0.52, respectively. For poly3, 4 and
5 in THF, the Ff values obtained upon 550 nm excitation are 0.14,
0.10 and 0.10, respectively.
pe
p* transition of poly(p-phenylene ethynylene) [32] and has no
absorption after 510 nm. The UVevis absorption spectrum of
a dilute toluene solution of poly3 displays an intense absorption
centered at 424 nm as well as a much weaker absorption with
a maximum around 555 nm assigned to the BODIPY-based terminal
groups, which further confirms that BOPIPY has been successfully
connected to poly1.
Similar absorption spectra of poly2, poly3, 4 and 5 were
measured in THF. In this solvent, the maxima of poly2 and poly3
were found at 427 and 423 nm, respectively, while the maximum of
5 corresponding to the S1)S0 transition was observed at 556 nm
with a shoulder at 526 nm and the maximum of the Sn)S0 tran-
sition at 390 nm. The spectral maxima of 4 were blue-shifted
compared to those of 5: S1)S0 transition at 547 nm and Sn)S0
transition at 347 nm.
The long wavelength band found in the excitation spectrum of 4
is characteristic for the BODIPY chromophore. The excitation
spectrum of 5 consists besides a long wavelength band character-
istic for absorption by the BODIPY chromophore of a second band of
similar intensity which coincides with the absorption band attrib-
uted to the linker. The relative intensities of both bands are quite
similar to those in the absorption spectrum which suggests energy
1.0
4
3.4. Fluorescence emission properties of poly2, poly3, 4 and 5
5
poly2
The steady-state fluorescence emission spectra of poly2, poly3,
4 and 5 in toluene are displayed in Fig. 3. Upon excitation at
lex ¼ 420 nm, poly2 shows an emission peak at 470 nm and
a shoulder at 503 nm due to a coupling of the phenylene ring
stretching modes of the main chain to the electronic transitions
0.8
poly3
0.6
0.4
0.2
0.0
between
p and p* states [32]. Excitation of poly3 at the same
wavelength (420 nm) gives a main emission peak at 474 nm,
a shoulder at 498 nm, and a weak emission peak at 613 nm, which
can be assigned to the BODIPY moiety. Comparing the emission
spectra of poly2 and poly3 suggests that at 613 nm about 50% of the
emission is due to the BODIPY chromophore. Because at 420 nm the
absorption of the BODIPY chromophore will be negligible (see
excitation spectrum of 4 in Fig. 4) compared to that of the linker,
this indicates that excitation transfer occurs.
300
350
400
450
Wavelength / nm
500
550
600
The fluorescence quantum yield Ff upon excitation at 420 nm of
poly3 in toluene equals 0.53, which is similar to that of poly2
Fig 4. Normalized fluorescence excitation spectra of 4, 5, poly2 and poly3 in toluene at
room temperature observed at 615 nm. All the spectra are normalized at the maximum
of the main excitation band (<450 nm).
(Ff ¼ 0.54) under the same conditions.

S. Yin et al. / Dyes and Pigments 88 (2011) 372e377
377
transfer with nearly 100% efficiency. The excitation spectrum of
poly3 consists of a long wavelength band corresponding to that
found in 4 and 5 and an extra band with a maximum around
430 nm. The latter band which is also observed in the excitation
spectrum of poly2 corresponds to the absorption bands of the poly
(p-phenylene ethynylene) linker in poly2 and poly3. From the
emission spectrum it is clear that the emission of poly3 at 613 nm is
only for 50% due to the linker. Furthermore, the maximum of the
band at 474 nm is about ten times more intense than that due to the
BODIPY chromophore. This means that in the excitation spectrum
of the emission of the BODIPY chromophore the band due to the
linker is five times more intense than that of the BODIPY chro-
mophore while in the absorption spectrum it is about twenty times
more intense. The limited excitation transfer in poly3 comes as no
surprise because the edge to edge distance of chromophores in the
center of the PPE linker to the BODIPY is more than 10 nm in poly3,
a value clearly exceeding generally accepted values for the Förster
distance (4e6 nm) for completely allowed transitions [33]. This
suggests that changing the conditions of the polymerization in
order to reduce the length of the OPE linker by a factor of two
would be necessary to obtain efficient energy transfer.
thank the K.U.Leuven Research Fund through GOA 2004/2 and
BELSPO through IAP VI/27.
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BODIPY chromophores have been successfully introduced at the
ends of PPE by a palladium-catalyzed cross-coupling reaction. The
absorption and emission spectra show that linking BODIPY to the
PPE linker does not perturb the spectroscopic properties of both the
linker and BODIPY. The similar fluorescence quantum yields
obtained upon direct excitation of the BODIPY chromophore in
model compound 5 and in polymer poly3 suggests that linking the
chromophores does not induce significant quenching, e.g. by elec-
tron transfer. Although the PPE linker was shown to act as antenna
in both the model compound 5 and the polymer poly3, excitation
transfer only occurs with limited yield in poly3.
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Acknowledgements
The ‘Instituut voor de aanmoediging van innovatie door
Wetenschap en Technologie in Vlaanderen’ (IWT) is acknowledged
for a fellowship to VL. We thank the ‘Fonds voor Wetenschappelijk
Onderzoek’ (FWO), the ‘Ministerie voor Wetenschapsbeleid’ and
the K.U.Leuven for continuing financial support. The authors also