Synthesis of symmetrical multichromophoric bodipy dyes and their facile transformation into energy transfer cassettes

Article abstract of DOI:10.1002/chem.200903449

Multichromophoric boron-dipyrromethene (Bodipy) dyes synthesized on phenylene-ethynylene platforms have been be converted to energy transfer cassettes in a one-step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time-re-solved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short-cut approach to similar energy transfer systems, could be useful as large pseudo-Stokes shift multichromophoric dyes with potential applications in diverse applications.

Full text of DOI:10.1002/chem.200903449

DOI: 10.1002/chem.200903449
Synthesis of Symmetrical Multichromophoric Bodipy Dyes and Their Facile
Transformation into Energy Transfer Cassettes**
O. Altan Bozdemir,[a] Yusuf Cakmak,[a] Fazli Sozmen,[b] Tugba Ozdemir,[a]
Aleksander Siemiarczuk,[c] and Engin U. Akkaya*[a, d]
Abstract: Multichromophoric boron-di-
pyrromethene (Bodipy) dyes synthe-
sized on phenylene-ethynylene plat-
forms have been be converted to
energy transfer cassettes in a one-step
chemical transformation. Excitation
energy transfer processes in these
highly symmetrical derivatives were
studied in detail, including time-re-
solved fluorescence spectroscopy tech-
niques. Excitation spectra and the
emission lifetimes suggest efficient
energy transfer between the donor and
acceptor chromophore. These novel
energy transfer cassettes, while high-
lighting a short-cut approach to similar
energy transfer systems, could be
useful as large pseudo-Stokes shift mul-
tichromophoric dyes with potential ap-
plications in diverse applications.
Keywords: dyes/pigments · energy
transfer · fluorescence spectroscopy ·
fluorophores · Sonogashira coupling
Introduction
A few years ago, we demonstrated that a dimeric Bodipy
structure can be easily transformed into an energy transfer
cassette by a selective reaction on one of the Bodipy
units.[7b] The Knoevenagel reaction of one of the methyl
groups on the Bodipy core results in the placement of a (E)-
phenylethenyl group that extends the conjugation and shifts
the absorbance and emission bands towards the red end of
the visible spectrum by 60–100 nm. These two different dyes
then constitute an energy transfer pair with close proximity
and significant spectral overlap. The energy transfer in this
kind of cassettes may have contributions from both through-
space and through-bond interactions, usually resulting in a
very efficient energy transfer.
Bodipy dyes, which are also known as boradiazaindacenes
or boron dipyrrins, have attracted great interest in recent
years.[1] This renewed interest is primarily due to advances
in the methodologies for the transformation[2–6] of the
parent structure and the increasing diversity of potential ap-
plications.[7–10] In addition to being a useful chromophores/
fluorophores, Bodipy dyes, with their unique arrangement of
substituent groups held at fixed angles in certain derivatives,
have great potential as a scaffold or building block in com-
plex supramolecular architectures.
In the work described herein, we want to demonstrate
that similar efficient energy transfer could take place in
other multi-chromophoric Bodipy dyes assembled on phen-
ylene-ethynylene cores. Even though 1,7-methyl groups on
the Bodipy structures enforce a near perpendicular arrange-
ment of the Bodipy “plane” and the meso-phenyl substi-
tuent,[7b,j] some conjugation is expected and through-bond
energy transfer cannot be discarded. The first set of targeted
molecules was the symmetrical oligo-Bodipy compounds 2–
4. In these compounds, Bodipy units are placed on an ethyn-
yl-substituted benzene at (1,4), (1,3,5), and (1,2,4,5) substitu-
tion patterns. The spectral characteristics of the Bodipy dyes
are not affected significantly, which is an indication of minor
(if any at all) interchromophoric interactions in these dyes.
In other words, they behave not much different than individ-
ual Bodipy units. Following spectral characterization, these
[a] Dr. O. A. Bozdemir, Y. Cakmak, T. Ozdemir, Prof. Dr. E. U. Akkaya
UNAM-Institute of Materials Science and Nanotechnology
Bilkent University, 06800 Ankara (Turkey)
Fax : (+90)312-266-4068
E-mail: eua@fen.bilkent.edu.tr
[b] F. Sozmen
Department of Chemistry, Faculty of Arts and Sciences
Akdeniz University, 07058 Antalya (Turkey)
[c] Dr. A. Siemiarczuk
PTI Fast Kinetics Laboratory
347 Consortium Road, N6E 2S8, London, ON (Canada)
[d] Prof. Dr. E. U. Akkaya
Department of Chemistry, Bilkent University, 06800 Ankara (Turkey)
[**] Bodipy=boron-dipyrromethene, 4,4-difluoro-4-bora-3a,4a-diaza-s-in-
dacene.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200903449.
6346
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Chem. Eur. J. 2010, 16, 6346 – 6351

FULL PAPER
Scheme 1. a) [PdACHTUNGTRENNUNG(PPh3)4], CuI, THF/toluene/triethylamine, 808C for 20 min then RT, 1 day. b) Acetic acid, piperidine/benzene, reflux.
compounds were converted into energy transfer cassettes in
one step by a Knoevenagel reaction with a small amount of
p-methoxybenzaldehyde. The use of excess aldehyde al-
lowed the production of other extended conjugation (styryl-
Bodipy) dyes at different positions, creating a complex reac-
tion mixture. These new energy transfer cassettes were then
analyzed by spectroscopic methods, showing very efficient
energy transfer, with an approximate pseudo-Stokes shift of
2400 cmÀ1. Bodipy dyes with their inherent desirable proper-
ties such as high quantum yields and large extinction coeffi-
cients would be even more valuable when endowed with
such relatively large Stokesꢁ shift values, compared to typical
400 cmÀ1 values for unmodified Bodipy fluorophores.
Results and Discussion
Synthesis of the multichromophoric dyes: 8-Iodophenyl-sub-
stituted Bodipy 1 is a known compound. Our strategy in-
volved the Sonogashira coupling of this Bodipy dye with dif-
ferent ethynylbenzenes with various substitution patterns.
Thus, in order to obtain the simplest dye of the series (2),
we carried out a Sonogashira coupling between the Bodipy
1 and p-diethynylbenzene. For the other dyes of higher sub-
stitution levels, we used 1,3,5-triethynylbenzene and 1,2,4,5-
Abstract in Turkish: Fenilenetilen platformu ꢀzerinde sentez-
lenen multikromoforik Bodipy boyarmaddeleri, tek basa-
maklı bir kimyasal transformasyonla enerji transferi kasetle-
rine dçnꢀs¸tꢀrꢀlmꢀs¸tꢀr. Zaman ayrımlı floresans spektrosko-
tetraethynylbenzene to generate
3 and 4, respectively
(Scheme 1). The reactions were initiated by heating the 8-io-
dophenyl-Bodipy and the ethynylbenzenes in THF/toluene
in the presence of tetrakis(triphenyl)palladium, cuprous
iodide, and triethylamine at 808C, for 20 min and then the
stirring was continued at room temperature for 24 h. Once
the products of the Sonogashira reaction were purified (2–
4), they were subjected to Knoevenagel conditions (aro-
matic aldehyde, piperidine, acetic acid, reflux under azeo-
tropic removal of water) using one equivalent of p-methoxy-
benzaldehyde (Scheme 1). The products 5–7 were purified
by silica-gel chromatography.
˘
pisi tekniklerinin de iÅinde bulundugu yçntemlerle, yꢀksek si-
˘
metri çgeleri bulunduran bu tꢀrevlerdeki eksitasyon enerjisi
transferi sꢀreÅleri ayrıntılı olarak Åalıs¸ılmıs¸tır. Eksitasyon
˘
spektrumları ve emisyon çmꢀrlerindeki degis¸im, donçr ve ak-
˘
septçr kromoforları arasında etkin bir enerji transferi oldugu-
nu dꢀs¸ꢀndꢀrmektedir. Bu yeni enerji transfer kasetleri,
benzer enerji transfer sistemlerine kolay bir geÅis¸ yolu gçster-
mekle birlikte, pek Åok farklı alanda potansiyel uygulamaları
˘
olabilecek, bꢀyꢀk pseudo-Stokes kayması degerlerine sahip
multikromoforik boyarmaddeler olarak da yararlı olabilirler.
Chem. Eur. J. 2010, 16, 6346 – 6351
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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E. U. Akkaya et al.
Absorption and steady state fluorescence characterization:
The absorption spectra of the dyes 2, 3, and 4 were acquired
in CHCl3 in dilute solutions (Table 1). The absorption lmax is
the number of Bodipy units increases. The concentrations
were adjusted so that the longer wavelength absorptions at
591 nm were equalized. Emis-
sion characteristics of the
energy transfer cassettes are
presented in comparison to two
reference compounds (1 and 8).
Emission spectra of 1, 5, and
8 are given in Figure 2. To facil-
itate comparison and provide
an easy handle on the extent of
energy transfer, concentrations
Table 1. Photophysical data of Bodipy derivatives in CHCl3 at 258C.
[a]
labs
emax
lems
t
F[a,b]
lems
t
F[a,c]
[nm]
G
]
[nm]
[ns]
[nm]
[ns]
1
2
3
4
5
528
528
528
529
529
591
529
592
529
592
540
540
545
545
545
–
545
–
545
–
4.3
4.5
4.3
4.2
<0.1
–
<0.1
–
<0.1
–
0.85
0.74
0.49
0.57
0.03
–
0.1
–
0.1
–
–
–
–
–
606
–
606
–
608
–
–
–
–
–
4.6
–
4.2
–
4.1
–
–
–
–
–
0.24
0.37
0.29
0.32
0.31
0.42
103000
296000
370000
82000
84000
218000
98000
were adjusted to equal absorb-
ance values at 528 nm (excita-
6
7
297000
93000
[a] Determined in CHCl3 solution. [b] Rhodamine 6G in water (Ff =
0.95) was used as reference.[c] Sulforhodamine 101 hydrate in ethanol
(Ff =0.90) was used as reference.
unchanged compared to the simpler Bodipy dye 1, at
528 nm (529 nm for 4). This suggests that ethynylphenyl
spacers place the chromophores at a distance, at which inter-
chromophoric interactions are minimal. Extinction coeffi-
cients show an increasing trend as the number of Bodipy
units increase, reaching
a
very large value of
370000 cmÀ1 mÀ1 for compound 4. Steady-state emission
spectroscopy of the novel chromophores shows a typical
Bodipy emission centered around 540 nm (2) and 545 nm
(compound 3 and 4), with no significant change in the peak
shape or width. High quantum yields were conserved in all
three compounds (0.74 for 2, 0.49 for 3, and 0.57 for 4). The
energy transfer cassettes obtained from these three com-
pounds had interesting properties: in the absorption spectra,
all three had two distinct peaks indicative of two different
classes of Bodipy dyes. The absorption spectra of these com-
pounds are presented in Figure 1, together with that of a ref-
erence compound styryl-bodipy 8;[2c] the spectra show the
progressive dominance of the shorter wavelength peak as
Figure 2. The emission spectra of 1, 5, and 8 at equal absorbances at
528 nm for 1 and 5 and at 591 nm for 5 and 8 in CHCl3.
tion wavelength for the shorter wavelength absorbing “an-
tenna” Bodipy) for 1 and 5, or at 591 nm for the styryl-
Bodipy (excitation wavelength). The data shows that the
emission from the shorter wavelength absorbing “antenna”
chromophore in compound 5 is reduced significantly com-
pared to that of the reference compound 1. On the other
hand, emission at the longer wavelength band (lmax 611 nm)
is increased considerably, demonstrating an antenna effect,
and efficient energy transfer. Figure 3 and 4 show a similar
comparative assessment of compounds 1, 6, 8 (Figure 3) and
Figure 1. Absorbance spectra of compounds 5, 6, 7, and 8 at equal absor-
bances at 591 nm in CHCl3 (concentrations are 5.96ꢂ10À7 m, 4.97ꢂ10À7 m,
5.25ꢂ10À7 m, 5.23ꢂ10À7 m, respectively).
Figure 3. The emission spectra of 1, 6, and 8 at equal absorbances at
528 nm for 1 and 6 and at 591 nm for 6 and 8 in CHCl3.
6348
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Symmetrical Multichromophoric Bodipy Dyes
FULL PAPER
Figure 6. The excitation spectra of 5, 6, and 7 at equal absorbances at
591 nm in CHCl3. The emission data were collected at 606 nm.
Figure 4. The emission spectra of 1, 7, and 8 at equal absorbances at
528 nm for 1 and 7 and at 591 nm for 7 and 8 in CHCl3.
1, 7, 8 (Figure 4). In both dyads 6 and 7, the emission from
the energy donor Bodipy is diminished, whereas the longer
wavelength emission is increased at equal absorbance con-
centrations of compounds 6 and 7 compared to 8. Figure 5
not result in qualitatively different spectra, eliminating any
complications due to multiphoton processes.
Time-resolved fluorescence spectroscopy: Emission lifetime
data provide solid evidence for the energy-transfer phenom-
ena. The emission lifetimes for compounds 2, 3, and 4 are
essentially identical to each other and the reference Bodipy
dye 1 (around 4.3 ns). In the energy-transfer cassettes 5, 6,
and 7, the emission from the donor dye is very short lived,
under the detection limit of the instrumental setup (<
0.1 ns) The emission lifetime from the acceptor styryl-
bodipy dyes have comparable lifetimes (in the range of 4.1–
4.6 ns) to the other styryl-Bodipy dyes.[2a,10f] Thus, the
energy transfer rate constants for the Fçrster model is calcu-
lated to be larger than 9.8ꢂ109 sÀ1 for compounds 5, 6, and
7. These values point to energy transfer efficiency values
over 97%.
Figure 5. The emission spectra of 5, 6, 7, and 8 at equal absorbances at
591 nm in CHCl3.
Potential of “post-assembly” modification in light-harvest-
ing systems and energy-transfer cassettes: As demonstrated
here, Bodipy dyes allow a one-step modification that trans-
forms oligomeric dye assemblies (covalent or non-covalent)
into efficient light harvesters or energy-transfer (ET) cas-
settes. This could be a significant synthetic advantage, essen-
tially resulting in a highly convergent synthesis. In most
other ET cassettes, the dyes have to be selected and appro-
priately modified before they are tethered together by a
linker. Considering the growing versatility of the Bodipy
dyes,[12] ET cassettes with large pseudo-Stokes shifts cover-
ing the entire spectrum between 560–800 nm seems to be
possible.
shows another view of the antenna effect; when compounds
5, 6, 7, and 8 were dissolved in CHCl3 to form dilute solu-
tions with equal absorbances at 591 (energy acceptor styryl-
Bodipy absorption peak) as the number of energy donor
Bodipy units increase, the antenna effect also increases
steadily, reaching tenfold in compound 8. Since the short
wavelength and long wavelength emission peaks are some-
what resolved in the emission spectrum, separate quantum
yields for both emissions can be defined and calculated
(Table 1). The data clearly show quenching of the donor
dyes as expected. Excitation spectra (Figure 6) also corrobo-
rate energy transfer between the donor and acceptor chro-
mophores: the emission data from the longer wavelength
emitting styryl-Bodipy dye are acquired and in the overlay
spectra shown in Figure 6, shorter wavelength excitation
peaks become more dominant in the spectra as the number
of donor units increase. Concentration-dependent emission
spectra, and spectra taken at different lamp intensities, do
Conclusion
Versatile Bodipy chemistry allows the straightforward con-
struction of multichromophoric systems. In this study, we
first demonstrated the feasibility of the synthesis of multiple
Bodipy-carrying phenylethynyl scaffolds. Our work shows
that despite their proximity, the Bodipy units, even in the
Chem. Eur. J. 2010, 16, 6346 – 6351
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6349

E. U. Akkaya et al.
moval of the solvents at reduced pressure, the residue was washed with
water (100 mL) and extracted into CHCl3. The organic layer was dried
on Na2SO4 and the solvent was removed under reduced pressure.
Column chromatographic separation of the residue on silica gel using
CHCl3 as the eluant yielded the desired product as an orange solid
(95 mg, 65%). 1H NMR (400 MHz, CDCl3): d=7.76 (s, 3H, ArH), 7.69
(d, 6H, J=8.2 Hz, ArH), 7.34 (d, 6H, J=8.1 Hz, ArH), 2.56 (s, 18H,
CH3), 2.34 (q, 12H, J=7.5 Hz, CH2), 1.36 (s, 18H, CH3), 1.01 ppm (t,
18H, J=7.5 Hz, CH3); 13C NMR (100 MHz, CDCl3): d=154.1, 139.0,
138.1, 136.4, 134.3, 133.0, 132.3, 130.5, 128.7, 123.9, 123.3, 90.2, 88.8, 17.1,
14.5, 12.5, 11.9 ppm; MS (TOF-ESI): m/z calcd for C81H81B3F6N6:
1284.6706 [M]+; found: 1284.6706 [M]+.
most densely functionalized derivative 7, behaved as individ-
ual entities, with unaltered absorption, emission, and life-
time characteristics. These compounds then are converted to
efficient energy-transfer cassettes in just one simple step by
simple high-yield condensation reactions. We have also
shown that the energy transfer between the unmodified
Bodipy dyes and the styryl-appended bodipy dyes takes
place an efficiency greater than 99.5%. The result is the
production of large extinction coefficient energy-transfer
cassettes with large antenna effects (signal ampilification
values). The resulting pseudo-Stokes shift is much larger
than that of a regular Bodipy dye, enhancing the chances of
their potential as bright fluorescent dyes, which could be
useful in many applications including DNA sequencing and
protein labeling. The Knoevenagel reaction leading to
styryl-Bodipys can also be carried out with carboxy-func-
tionalized benzaldehydes, which can be converted to amine-
reactive NHS esters following a simple procedure. Further
work in functionalization of these dyes, would facilitate such
applications. The reaction of additional methyl groups in the
Knoevenagel reactions, or the replacement of fluorine
atoms in any one of the Bodipy units with bioconjugatable
units are other likely paths for such functionalizations. In
any case, the future looks bright for styryl-Bodipy based
energy-transfer cassettes.
Synthesis of compound 4: In a 50 mL Schlenk tube were added 1
(0.442 mmol, 0.224 g), 1,2,4,5-tetraethynylbenzene (0.099 mmol, 17.3 mg),
[PdACHTNUGRTNEUNG(PPh3)4] (0.04 mmol, 46.2 mg), CuI (0.023 mmol, 4.34 mg), freshly dis-
tilled THF (5 mL), toluene (5 mL), and triethylamine (5 mL). The result-
ing suspension was deaerated by bubbling argon at 808C for 20 min. The
reaction mixture was stirred at room temperature for one day. After re-
moval of the solvents at reduced pressure, the residue was washed with
water (100 mL) and extracted into CHCl3. The organic layer was dried
on Na2SO4 and the solvent was removed under reduced pressure.
Column chromatographic separation of the residue on silica gel using
CHCl3 as the eluant yielded the desired product as an orange solid.
(100 mg, 60%). 1H NMR (400 MHz, CDCl3): d=7.90 (s, 2H, ArH), 7.74
(d, 8H, J=8.3 Hz, ArH), 7.34 (d, 8H, J=8.3 Hz, ArH), 2.55 (s, 24H,
CH3), 2.30 (q, 16H, J=7.5 Hz, CH2), 1.35 (s, 24H, CH3), 0.97 ppm (t,
24H, J=7.6 Hz, CH3); 13C NMR (100 MHz, CDCl3): d=154.3, 138.8,
138.0, 136.7, 133.2, 132.3, 130.5, 128.8, 125.4, 123.3, 95.3, 88.5, 17.1, 14.5,
12.5, 11.9 ppm; MS HRMS (TOF-ESI): m/z calcd for C106H106B4F8N8:
1686.8785 [M]+; found: 1686.8794 [M]+.
Synthesis of compound 5: In a 100 mL round-bottomed flask equipped
with a Dean–Stark trap and a reflux condenser were added benzene
(40 mL),
2 (0.17 mmol, 0.150 g), 4-methoxybenzaldehyde (0.17 mmol,
23.12 mg), acetic acid (0.5 mL), and piperidine (0.5 mL). The reaction
mixture was stirred at reflux temperature and concentrated nearly to dry-
ness. Progress of the reaction was monitored by TLC (3:1 hexanes:ethyl
acetate). When all the starting material had been consumed, water
(100 mL) was added and the mixture was extracted into CHCl3. The or-
ganic layer was dried on Na2SO4 and the solvent was removed under re-
duced pressure. Column chromatographic separation (silica gel, 3:1 hexa-
nes:ethyl acetate) and preparative TLC (silica gel, benzene) of the resi-
Experimental Section
General: 1H NMR and 13C NMR spectra were recorded on a Bruker
DPX-400 (operating at 400 MHz for 1H NMR and 100 MHz for
13C NMR) in CDCl3 and [D6]DMSO solvents with tetramethylsilane as
internal standard. All spectra were recorded at 258C and coupling con-
stants (J values) are given in Hz. Chemical shifts are given in parts per
million (ppm). Absorption spectra were performed by using a Varian
Cary-100 spectrophotometer. Fluorescence measurements were conduct-
ed on a Varian Eclipse spectrofluorometer. The Fluorescence decay
measurements were carried out with the TM-3 LaserStrobe Time-Re-
solved Fluorometer utilizing a pulsed nitrogen/dye laser excitation and
the stroboscopic detection system. The dye laser excitation was at 526
and 590 nm. The instrument response function was measured with an
aqueous Ludox solution. The decays were analyzed with a multiexponen-
tial fitting function by iterative reconvolution and chi-square minimiza-
tion. Mass spectra were recorded at the Ohio State University Mass
Spectrometry and Proteomics Facility, Ohio, USA. Reactions were moni-
tored by thin layer chromatography using Merck TLC Silica gel 60 F254
and Merck Aluminium Oxide 60 F254. Silica gel column chromatography
was performed over Merck Silica gel 60 (particle size: 0.040–0.063 mm,
230–400 mesh ASTM). 4,4-Difluoro-8-(4’-iodophenyl)-2,6-diethyl-1,3,5,7-
tetramethyl-4-bora-3a,4a-diaza-s-indacene (1),[7k] compound 2,[7c] 4,4-di-
fluoro-8-(4’-iodophenyl)-2,6-diethyl-1-(4’-methoxystyryl)-3,5,7-trimethyl-
4-bora-3a,4a-diaza-s-indacene (8),[2c] 1,3,5-triethynylbenzene,[11] and
1,2,4,5-tetraethynylbenzene[11] were synthesized according to literature
methods. Anhydrous tetrahydrofuran was obtained by refluxing over
sodium/benzophenone prior to use. All other reagents and solvents were
purchased from Aldrich and used without further purification.
1
due yielded the desired product as a violet solid. (35 mg, 20%). H NMR
(400 MHz, CDCl3): d=7.69 (d, 2H, J=8.3 ArH), 7.68 (d, 2H, J=8.2
ArH), 7.63 (d, 1H, J=17.0 Hz, CH), 7.59 (s, 4H, ArH), 7.56 (d, 2H, J=
8.7 Hz, ArH), 7.35 (d, 2H, J=7.9 ArH), 7.32 (d, 2H, J=8.0 Hz, ArH),
7.21 (d, 1H, J=16.5 Hz, CH), 6.93 (d, 2H, J=8.8 Hz, ArH), 3.85 (s, 3H,
OCH3), 2.62 (q, 2H, J=6.1 Hz, CH2), 2.60 (s, 3H, CH3), 2.55 (s, 6H,
CH3), 2.33 (q, 6H, J=6.1 Hz, CH2), 1.49 (s, 3H, CH3), 1.37 (s, 3H, CH3),
1.35 (s, 6H, CH3), 1.17 (t, 3H, J=7.5 Hz, CH3), 1.05–0.97 ppm (m, 9H,
CH3); 13C NMR (100 MHz, CDCl3): d=160.1, 136.3, 136.1, 135.1, 132.3,
131.7, 130.3, 128.9, 128.7, 123.6, 123.1, 114.2, 90.8, 90.3, 90.2, 55.4, 18.3,
17.1, 17.0, 14.6, 14.5, 14.1, 12.6, 11.9, 11.7 ppm; MS (TOF-ESI): m/z calcd
for C64H62B2F4O: 1000.5046 [M]+; found: 1000.5061 [M]+.
Synthesis of compound 6: In a 100 mL round-bottomed flask equipped
with a Dean–Stark trap and a reflux condenser were added benzene
(40 mL), 3 (0.047 mmol, 60 mg), 4-methoxybenzaldehyde (0.047 mmol,
6.36 mg), acetic acid (0.2 mL), and piperidine (0.2 mL). The reaction mix-
ture was stirred at reflux temperature and concentrated nearly to dryness.
Progress of the reaction was monitored by TLC (4:1 hexanes:ethyl ace-
tate). When all the starting material had been consumed, water (100 mL)
was added and the mixture was extracted into CHCl3. The organic layer
was dried on Na2SO4 and the solvent was removed under reduced pres-
sure. Column chromatographic separation (silica gel, 4:1 hexanes:ethyl
acetate) of the residue yielded the desired product as a violet solid.
(19.8 mg, 30%). 1H NMR (400 MHz, CDCl3): d=7.77 (s, 3H, ArH),
7.73–7.67 (m, 6H, ArH), 7.64 (d, 1H, J=16.7 Hz, CH), 7.57 (d, 2H, J=
8.8 Hz, ArH), 7.38–7.32 (m, 6H, ArH), 7.21 (d, 1H, J=17.5 Hz, CH),
6.93 (d, 2H, J=8.9 Hz, ArH), 3.85 (s, 3H, OCH3), 2.67–2.58 (m, 5H,
Synthesis of compound 3: In a 50 mL Schlenk tube were added 1
(0.415 mmol, 0.21 g), 1,3,5-triethynylbenzene (0.115 mmol, 17.3 mg), [Pd-
ACHTUNGTRENNUNG(PPh3)4] (0.035 mmol, 41 mg), CuI (0.02 mmol, 3.81 mg), freshly distilled
THF (5 mL), toluene (5 mL), and triethylamine (5 mL). The resulting
suspension was deaerated by bubbling argon at 808C for 20 min. The re-
action mixture was stirred at room temperature for one day. After re-
6350
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Symmetrical Multichromophoric Bodipy Dyes
FULL PAPER
CH2 and CH3), 2.55 (s, 12H, CH3), 2.33 (q, 10H, J=7.3 Hz, CH2), 1.40–
1.32 (m, 18H, CH3), 1.17 (t, 3H, J=7.5 Hz, CH3), 1.05–0.95 ppm (m,
15H, CH3); 13C NMR (100 MHz, CDCl3): d=165.0, 160.2, 154.2, 138.2,
136.4, 135.2, 134.4, 133.0, 132.3, 131.6, 130.5, 129.0, 128.7, 128.6, 124.0,
123.3, 123.2, 118.0, 117.8, 114.2, 90.2, 88.8, 55.4, 21.0, 18.6, 17.1, 14.6, 14.4,
14.2, 14.1, 12.5, 11.9 ppm; MS (TOF-ESI): m/z calcd for C89H87B3F6N6O:
1402.7125 [M]+ ; found: 1402.7073 [M]+.
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Synthesis of compound 7: In a 100 mL round-bottomed flask equipped
with a Dean–Stark trap and a reflux condenser were added benzene
(40 mL),
4 (0.13 mmol, 0.220 g), 4-methoxybenzaldehyde (0.13 mmol,
17.7 mg), acetic acid (0.5 mL), and piperidine (0.5 mL). The reaction mix-
ture was stirred at reflux temperature and concentrated nearly to dryness.
Progress of the reaction was monitored by TLC (3:1 hexanes:acetone).
When all the starting material had been consumed, water (100 mL) was
added and the mixture was extracted into CHCl3. The organic layer was
dried on Na2SO4 and the solvent was removed under reduced pressure.
Column chromatographic separation (silica gel, 4:1 hexanes:acetone) of
the residue yielded the desired product as a violet solid. (47 mg, 20%).
1H NMR (400 MHz, CDCl3): d=7.90 (s, 2H, ArH), 7.74 (d, 8H, J=
8.1 Hz, ArH), 7.62 (d, 1H, J=16.1 Hz, CH), 7.56 (d, 2H, J=8.8 Hz,
ArH), 7.38–7.32 (m, 8H, ArH), 7.19 (d, 1H, J=16.3 Hz, CH), 6.92 (d,
2H, J=8.6 Hz, ArH), 3.85 (s, 3H, OCH3), 2.63–2.56 (m, 5H, CH2 and
CH3), 2.54 (s, 18H, CH3), 2.30 (q, 14H, J=7.4 Hz, CH2), 1.38 (s, 3H,
CH3), 1.36–1.32 (m, 21H, CH3), 1.14 (t, 3H, J=7.4 Hz, CH3), 0.96 ppm
(t, 21H, J=7.6 Hz, CH3); 13C NMR (100 MHz, CDCl3): d=154.3, 138.8,
138.0, 137.9, 136.9, 136.7, 132.3, 129.1, 129.0, 128.8, 128.7, 125.5, 123.3,
114.2, 95.3, 93.3, 88.5, 55.4, 17.1, 17.0, 16.8, 16.7, 16.5, 14.6, 14.5, 14.4,
14.1, 14.0, 12.6, 12.5, 11.9 ppm; MS HRMS (TOF-ESI): m/z calcd for
C114H112B4F8N8O: 1804.9204 [M]+; found: 1804.9136 [M]+.
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Acknowledgements
The authors gratefully acknowledge support from the Turkish Academy
of Sciences (TUBA).
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Received: December 16, 2009
Published online: April 16, 2010
Chem. Eur. J. 2010, 16, 6346 – 6351
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