1,7-disubstituted boron dipyrromethene (BODIPY) dyes: Synthesis and spectroscopic properties

Article abstract of DOI:10.1021/jo201082z

1,7-Dihalogenated boron dipyrromethene dyes were successfully synthesized and substituted, thus providing an entry to the final, elusive reactivity pattern. The spectroscopic properties of 1,7-disubstituted BODIPY dyes were studied and are discussed as a

Full text of DOI:10.1021/jo201082z

ARTICLE
pubs.acs.org/joc
1,7-Disubstituted Boron Dipyrromethene (BODIPY) Dyes: Synthesis
and Spectroscopic Properties
||
Volker Leen,† Dominique Miscoria,† Shouchun Yin,†,‡ Aleksander Filarowski,†,§ Joseph Molisho Ngongo,†,
Mark Van der Auweraer,† No€el Boens,† and Wim Dehaen*,†
†Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200f - bus 02404, 3001 Leuven, Belgium
‡College of Material Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036,
People's Republic of China
§Faculty of Chemistry, University of Wroczaw, F. Joliot-Curie 14, 50-383 Wroczaw, Poland
Faculty of Science, Universitꢀe de Kinshasa, B.P. 190 Kinshasa XI, Democratic Republic of the Congo
S Supporting Information
b
ABSTRACT: 1,7-Dihalogenated boron dipyrromethene dyes
were successfully synthesized and substituted, thus providing an
entry to the final, elusive reactivity pattern. The spectroscopic
properties of 1,7-disubstituted BODIPY dyes were studied and
are discussed as a function of their structure.
’ INTRODUCTION
One of the major reasons for the vast increase in the use of
boron dipyrromethene (BODIPY) dyes is undoubtedly their
potential for derivatization.1 With limited synthetic effort, a large
number of functional groups can be introduced through well-
documented synthetic approaches to the BODIPY core. More-
over, in recent years, several reactive BODIPY scaffolds have been
reported, which allow a nearly unlimited structural variation.
Upon analysis of the literature data on such reactive BODIPY
Figure 1. Overview of the methods of direct derivatization of the
dyes, it is clear that substitution at almost all positions has been
BODIPY core.
investigated (Figure 1). The most straightforward method, electro-
philic substitution at the 2,6-positions, has found widespread use
due to its easy accessibility from 2,4-dimethylpyrrole.1 Halogenated
are rather electron poor and are expected to show reactivity similar
to that for the 3,5- and 8-positions. Additionally, the structural
arrangement of new substituents on these 1,7-positions allows
integration of cooperative effects in the design of new sensors.8
Therefore, we set out to prepare and evaluate the spectroscopic
characteristics of such 1,7-disubstituted BODIPY dyes.
systems arising from such protocols have also been subjected to
transition-metal-catalyzed cross-coupling reactions.2 Furthermore,
the 2,6-positions are susceptible to direct hydrogen substitution with
both alkenyl and aryl groups.3 Similar nucleophilic substitution
reactions and palladium-catalyzed functionalization reactions have
been reported for 8-thiomethylated BODIPY dyes, with the
thioether acting as a pseudohalogen.4 Recently, the use of 3,5-
halogenated systems has been attracting a great deal of attention,
because these dyes show excellent reactivity in both nucleophilic
aromatic substitution and Pd-catalyzed cross-coupling reactions.5 As
an alternative to halogenated systems, it was shown that the 3,5-
hydrogens can be substituted directly by nucleophiles, either by an
oxidative mechanism or via vicarious elimination.6 Such substitu-
tions at the 3,5-positions tend to have profound effects on the
spectral properties. Finally, substitution of the 4-fluorine atoms by
carbon and oxygen nucleophiles has been shown to be a versatile
method for the introduction of functionality.7
’ RESULTS AND DISCUSSION
Synthesis. Since direct halogenation of the BODIPY core
would preferably halogenate other positions, the use of this
approach can only be effective through blockage of all the other
positions.
Such 2,3,5,6,8-pentasubstituted dyes can be conveniently pre-
pared through standard BODIPY preparations with substituted
pyrroles. For example, condensation of 2,3-dimethylpyrrole (1)
with acetyl chloride in dichloromethane, followed by in situ
As such, 1,7-disubstitution and the effect thereof on the
spectral properties remain largely unexplored. These positions
Received: May 30, 2011
Published: September 12, 2011
r
2011 American Chemical Society
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complex formation, afforded the BODIPY dye 2 in a typical yield
(Scheme 1). Bromination of this dye was fast with molecular
bromine in dichloromethane, and the desired 1,7-dibrominated
dye 3 was isolated in excellent yield and on a large scale. Although
direct iodination is also possible, the resulting compounds are
exceedingly difficult to purify and, hence, were not further
examined. In theory, BODIPY compounds such as 3, where
the 1,7-positions are halogenated, are accessible starting from
4-halogenated pyrroles where the 5-position is unsubstituted and
at least the 2-position is blocked (e.g., 4-bromo-2-methyl-1H-
pyrrole). Unfortunately, such starting pyrroles are unstable and,
furthermore, have limited synthetic accessibility.
However, attempts to subject dyes such as 3 to Pd-catalyzed
cross-coupling reactions showed that reactions were always
accompanied by reductive dehalogenation, and the resulting
reaction products could not be purified by common column
chromatography. These side reactions occurred under the Suzuki,
Stille, Heck, and Sonogashira protocols. As steric crowding of
the intermediate palladium complex was reasoned to be a
plausible origin of this side reaction, we switched to meso-
unsubstituted systems.
In this case, halogenation of the meso position could interfere;
therefore, halogenation at the pyrrole stage was desirable. More-
over, placing a hydrogen substituent at the 8-position would
require working with aldehydes. From these premises, a strategy
was designed that would use the decarbonylative condensation of
two pyrrole carbaldehydes to dipyrromethenes, and the corre-
sponding BODIPY dyes, as discovered by Burgess et al.9
Thus, 2,3-dimethylpyrrole (1)10 was formylated in moderate
yield under VilsmeierÀHaack conditions, setting the stage for
halogenation studies (Scheme 2). From a screening of pyrrole
halogenation protocols, the chlorinated and brominated deri-
vatives 5a,b were isolated as highly crystalline solids. The yield
of chlorination was significantly lower than that of bromination,
without a clear reason and despite numerous attempts at
improvement. Subjecting the aldehydes 5 to phosphorus oxy-
chloride in dichloromethane efficiently gave the corresponding
dipyrromethenes. After a standard complexation with boron
trifluoride etherate, the 1,7-dihalogenated BODIPY dyes 6 were
isolated as the sole product from the reaction, in good yield.
Using aldehyde 4 directly leads to 1,7,8-unsubstituted BODIPY
6c, which will be used as a reference for the spectroscopic
properties.
Substitution. Gratifyingly, the compounds 6a,b showed excel-
lent reactivity in Pd-catalyzed reactions, because dehalogenation
was no longer a problem.
The double Suzuki cross-coupling reaction of the 1,7-dibro-
minated dye 6b with benzene boronic acid proceeded in
excellent yield, under standard conditions (i.e., refluxing toluene
and aqueous Na2CO3 with Pd(PPh3)4 as catalyst). Conducting
the same reaction with 2-thienyl boronic acid also furnished the
substituted product 7b in good yield (Table 1).
Similar observations could be made for the Stille reaction,
where a cross-coupling reaction with the corresponding tin
reagents cleanly led to the doubly substituted products in near-
quantitative yield. As noted in previous cross-coupling reactions
with halogenated BODIPY dyes, the use of the mildly electron
donating ligand trifurylphosphine leads to more efficient trans-
metalation and acceptable reaction times.5
The Sonogashira reaction with phenylethyne in DMF was
exceptionally fast, even with low catalyst loadings, and the 1,7-
disubstituted product 7c was isolated in high yield after just 30 min.
Similarly, cross coupling of 6b with styrene in a Heck reaction
resulted in the 1,7-disubstituted product 7d.
In these Pd-catalyzed reactions, selective monocoupling was not
achieved, indicating that the first cross-coupling reaction does not
reduce the reactivity of the remaining bromine significantly. For the
Table 1. Palladium-Catalyzed Derivatization of 1,7-dibro-
moBODIPY 6b
reacn type
Suzukib
R
reacn time/h
yield/%a
product
Ph
16
16
2
81
65
96
90
76
62
7a
7b
7a
7b
7c
7d
2-thienyl
Ph
Stillec
2-thienyl
PhCtC
PhCHdCH
7
Sonogashirad
Hecke
0.5
Scheme 1. Synthesis of a 1,7-Dihalogenated Meso-Substi-
tuted BODIPY Dye
2
a Isolated yields for the reaction on a 0.2 mmol scale. b Conditions:
toluene/Na2CO3(aq) (1 M), Pd(PPh3)4, boronic acid (2.2 equiv), 100 °C.
c Conditions: 1,4-dioxane, Pd2(dba)3 (5%), trifurylphosphine (5%),
RSnBu3 (2.2 equiv), Na2CO3 (3 equiv), 100 °C. d Conditions: DMF/
Et3N (8/2 v/v), Pd2(dba)3 (5%), trifurylphosphine (10%), CuI (10%),
PhCtCH (2.6 equiv), 60 °C. e Conditions: DMF, Et3N (6 equiv),
styrene (2.6 equiv), Pd(PPh3)4, 65 °C.
Scheme 2. HalogenationÀCondensation Approach of Pyrrole Carbaldehydes to 1,7-Dihalogenated BODIPY Fluorophores
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Scheme 3. Synthesis of Asymmetrically Substituted Product through Sequential Palladium-Catalyzed Substitution
Scheme 4. Nucleophilic Substitution of 1,7-Dichlorinated
Dye 6a with Thiophenol
Scheme 5. Derivatization of Rotationally Restricted 1,7-Di-
halogenated BODIPY
synthesis of asymmetric 1,7-disubstituted BODIPYs, the desired
monohalogenated intermediate has to be separated from a mixture
of remaining starting material 6b and the 1,7-disubstituted product.
As an example of such synthesis, the product 8 of a single
Suzuki reaction with 1 equiv of aryl boronic acid was prepared in
48% yield (Scheme 3). This product (8) was subsequently
transformed into the asymmetric dye 9 by means of the
Sonogashira protocol. Attesting to the exceptional reactivity
toward the Sonogashira alkynation, the reaction was complete
after 15 min in excellent yield.
As for the 3,5-dihalogenated dyes, the 1,7-positions are rather
electron poor, and this may render them susceptible to nucleo-
philic aromatic substitution. Nonetheless, only strongly nucleo-
philic thiolate anions were able to participate in the reaction with
the 1,7-dichloro derivative 6a, yielding the double thioether 10
(Scheme 4). All attempts to introduce nitrogen, oxygen, and
carbon nucleophiles failed, with the starting material as the only
recovered product. This lowering of the reactivity of the 1,7-
compared to the 3,5-positions is likely to be due to their smaller
HOMO coefficients.
Evidently, the synthetic strategy outlined in Scheme 2 can also be
applied to other 2,3-substituted pyrroles different from 2,3-dimethyl-
pyrrole, which would allow the introduction of different functional-
ities or the extension of conjugation. Thus, passing through a
reaction sequence similar to that in in Scheme 2 with 4,5-dihydro-
benzo[g]indole as starting material resulted in the 1,7-dihaloge-
nated, conformationally restricted BODIPY 11 (X = Cl, Br).
The reactivity of 11 is comparable to that of 6a,b (Scheme 5).
The double Stille reaction affords 12, isolated in moderate yield.
The lowered yield in the case of SNAr with thiophenol to 13 is
associated with inefficient separation from trace impurities.
UVÀVis Spectroscopic Properties. Generally, the introduc-
tion of new substituents directly on the BODIPY scaffold has a
profound effect on the spectroscopic characteristics of the dye.
When we isolated the reaction products, we immediately noticed
that the bathochromic shift induced by the extended conjugation
was not as strong as previously observed for analogous 3,5-
disubstituted BODIPY compounds. For all the 1,7-disubstituted
dyes, the Stokes shift Δν̅ is rather small, being in the normal
range for classic BODIPY dyes (Table 2). The visible absorption
(λabs(max)) and fluorescence emission maxima (λem(max)) of
7a are blue-shifted in comparison to these values for 3,5-diphenyl
BODIPY analogues by about 10 and 35 nm, respectively,
resulting in much reduced Stokes shifts Δν
̅
(360À370 cmÀ1
for 7a vs 1000À1100 cmÀ1 for 3,5-diphenyl derivatives).11
Compound 7b with 2-thienyl substituents at the 1,7-positions
has λabs(max) and λem(max) values which are blue-shifted by
about 70 nm compared to those for a 3,5-di(2-thienyl) BODIPY
analogue.12 λabs(max) and λem(max) values of the 1,7-distyryl
dye 7d are also hypsochromically shifted in comparison to
around 630À640 and 640À650 nm, respectively, for 3,5-distyryl
BODIPYs.11,13 Similar blue shifts are found for the 1,7-diethy-
nylphenyl derivative (7c) in comparison to the 3,5-substituted
counterparts with λabs(max) 605À615 nm and λem(max)
620À630 nm.11 Our preliminary quantum chemical calculations
indicate that the smaller effect of 1,7- compared to that for 3,5-
substituents may be due to the fact that the HOMO has smaller
coefficients in the 1,7-positions compared to the 3,5-positions.
The absorption and emission spectra of 7 all shift to longer
wavelengths upon increasing polarizability of the solvent, while
Δν̅ does not depend much upon the solvent. This suggests that
there is no difference in the permanent dipole moments of the
ground state (S0) and excited state (S1) for 7. The larger Stokes
shifts of 7b,d compared to those for 7a,c must therefore be due to
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Table 2. Selected Spectroscopic/Photophysical Data
(Absorption Maximum λabs(max), Fluorescence Emission
Maximum λem(max), Stokes Shift Δν̅ , and Fluorescence
Quantum Yield Φ) of 1,7-Substituted BODIPY Dyes in
Several Solvents
BODIPY solventa λabs(max)/nm λem(max)/nm Δν
̅
b/cmÀ1
Φ
6c
7a
7b
7c
7d
8
MeOH
MeCN
THF
532
532
534
539
538
538
541
545
548
548
551
555
570
570
573
577
572
572
577
582
534
534
536
540
554
554
556
560
550
551
553
556
634
636
640
646
643
640
644
649
542
542
544
548
549
549
552
556
572
571
572
578
580
579
583
588
588
589
595
603
543
545
546
550
563
565
567
571
568
567
568
572
648
650
651
664
663
661
663
668
347
347
344
305
372
372
368
363
766
735
666
717
302
273
299
324
476
505
524
598
322
372
342
348
289
341
344
344
576
512
478
503
341
339
264
420
469
496
445
438
0.88
0.70
0.93
0.91
0.94
0.93
0.99
0.97
0.44
0.52
0.57
0.57
1.00
1.00
1.00
1.00
0.72
0.55
0.41
0.44
0.06
0.06
0.07
0.10
0.21
0.19
0.22
0.26
0.07
0.11
0.15
0.30
0.56
0.84
0.86
0.87
0.59
0.41
0.88
0.79
toluene
MeOH
MeCN
THF
toluene
MeOH
MeCN
THF
Figure 2. Normalized absorption (dashed) and emission (full) profiles
of 1,7-diaryl-substituted BODIPY dyes in toluene, either connected
directly (7a, phenyl; 7b, 2-thienyl) or connected through a double bond
(7d, ethenylphenyl), or a triple bond (7c, ethynylphenyl), in comparison
to the unsubstituted standard dye 6c.
toluene
MeOH
MeCN
THF
methyl groups in 2,6-positions will lead to a rotation out of the
plane of the phenyl (in 7a) and 2-thienyl (in 7b) moieties and
decrease further the electron delocalization over those groups. The
1,7-diethynylphenyl dye 7c has the highest fluorescence quantum
yield, Φ (1.00), in accordance with observations made for a 3,5-
diethynylphenyl BODIPY analogue.11 Styryl substituents (in 7d)
produce the largest bathochromic shifts in both the absorption and
emission spectra, followed by ethynylphenyl substituents (in 7c),
while phenyl groups (in 7a) generate the smallest bathochromic
shifts compared to the reference 2,3,5,6-tetramethylBODIPY (6c)
with no substituents at the 1,7-positions. The same red-shift trend
(styryl > ethynylphenyl > phenyl) has been observed already for
BODIPYs with these functionalities at the 3,5-positions, and
quantum chemical calculations have provided a rationale for these
spectral shifts.11 The smaller fluorescence quantum yields Φ of 7b,
d in comparison to those for 7a,c can be associated with an
increased change in equilibrium geometry upon excitation, which
toluene
MeOH
MeCN
THF
toluene
MeOH
MeCN
THF
toluene
MeOH
MeCN
THF
9
toluene
MeOH
MeCN
THF
10
12
13
is also suggested by the larger Stokes shift Δν̅ and the broader
absorption and emission spectra of 7b,d (Figure 2). This displace-
ment of the potential energy surface of the S1 state versus that of
the S0 state—referred to as exciton phonon coupling—will lead to
increased FranckÀCondon factors between the low vibrational
levels of the S1 state and isoenergetic higher vibrational levels of
the S0 state.14 The type of vibration involved in this process is less
clear, but it certainly is no high-frequency stretching mode of the
conjugated system. In this case, one would observe a prolonged
vibrational progression rather than band broadening and an
increased Stokes shift. Moreover, an increased coplanarity of the
styryl (7d) or thienyl moieties (7b) with the BODIPY moiety in
the excited state can be excluded. Indeed, as observed for
oligoarylenes or oligoarylene vinylenes, such increased coplanarity
in the excited state would lead to a broadening of the absorption
bands rather than of the emission spectra, in contrast to the
observations made for 7b,d.15
toluene
MeOH
MeCN
THF
toluene
MeOH
MeCN
THF
toluene
a The solvents are listed according to increasing refractive index at 20 °C
(methanol (1.3288), acetonitrile (1.34423), tetrahydrofuran (THF,
1.4050), toluene (1.4961)). b Stokes shift (=1/λabs(max) À 1/λem(max)).
a larger change in excited-state geometry. This is also reflected in
the increased width of the fluorescence emission spectra of 7b,d
compared to those of 7a,b (see Figure 2). The more extensive red
shift for 7c,d in comparison to 7a,b is not surprising because triple
and double bonds are more available for delocalization than
aromatic moieties, since for the latter delocalization leads to a
partial loss of aromaticity. Furthermore, steric strain with the
Heavy-atom quenching by Br in compound 8 may account for
the much lower Φ value in comparison to that for the standard
dye 6c. It is unlikely that this reduced fluorescence quantum yield
Φ is due to exciton phonon coupling with torsions of the phenyl
group, because this should also be observed for 7a. Furthermore,
the small Stokes shift Δν̅ and features of the spectra do not
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Table 3. Molar Absorption Coefficients εmax (( Standard
combined with the restricted rotational mobility (and increased
coplanarity) of the aromatic substituents. The absorption and
fluorescence emission maxima of conformationally constrained
12 are bathochromically shifted by ∼90 and ∼80 nm, respec-
tively, in comparison to those for 7b with four methyl groups at
the 2,3,5,6-positions. Similarly, λabs(max) and λem(max) of
ring-fused 13 are red-shifted by ∼90 and ∼95 nm, respectively,
in relation to those for 10. In analogy to what was observed
for dyes 7, the solvent dependence of λabs(max), λem(max), and
Error) and Brightness at the Given Absorption Maxima
λ
abs(max) for a Selection of BODIPY Dyes in the Solvents
of Table 2
λabs-
max brightness Φ Â
BODIPY solvent (max)/nm εmax/103 MÀ1 cmÀ1 εmax/104 MÀ1 cmÀ1
6c
7a
10
MeOH
MeCN
THF
532
532
534
539
538
538
541
545
550
551
553
556
42 ( 3
53 ( 2
3.74
3.71
6.41
4.13
6.63
8.18
9.05
8.22
0.51
0.76
1.41
2.57
Δν̅ of 12 and 13 suggests that there is no change in dipole
68.9 ( 0.5
45 ( 7
moment between the S0 and S1 states. The quantum yields Φ of
conformationally restricted 12 and 13 are substantially higher
than those of the respective analogues 7b and 10 with a 2,3,5,6-
tetramethyl substitution pattern, while the Stokes shifts are
smaller. Comparable effects have been found for other ring-
fused BODIPY dyes.18 This suggests that the change in the
equilibrium geometry in the excited state of 12 (respectively 13)
is smaller than in 7b (respectively 10), which will lead to
less extensive exciton phonon coupling. The Φ value of 13 is
significantly larger than that of 10 and approaches the Φ value of
12. This supports our earlier assumption that the small Φ
value of 10 is not related to a heavy-atom effect, as the latter
should also be observed for 13. In analogy to 10 and 12 and in
contrast with the other molecules discussed here, the Φ value of
13 clearly decreases with increasing solvent polarity. This could
suggest internal conversion induced by interaction with a state
with charge transfer character situated a short distance above
the S1 state.
toluene
MeOH
MeCN
THF
70 ( 8
88.0 ( 0.2
91 ( 2
toluene
MeOH
MeCN
THF
84.8 ( 0.5
73 ( 2
69 ( 1
94 ( 2
toluene
86 ( 3
suggest such increased exciton phonon coupling. The blue shift
of λabs(max) and λem(max) upon increasing solvent polarity and
the independence of Δν̅ of the solvent polarity indicate that no
significant change of the permanent dipole occurs in the excited
state S1 of 8. After the Sonogashira reaction of the remaining Br
in derivative 8, both λabs(max) and λem(max) of 9 shift bath-
ochromically about 20 nm in comparison to 8, indicative of the
extension of conjugation by the ethynylphenyl group. Φ of 9
increases 3-fold in relation to that of 8 but remains substantially
lower than that of 6c. It is unlikely that this low Φ value can be
attributed to exciton phonon coupling with rotational modes of
the p-tert-butylphenyl group because 7a,c with similar substitu-
ents have Φ values close to 1.0. Also, the small Stokes shift and
the features of absorption and emission spectra exclude such
exciton phonon coupling.
An important photophysical property of a fluorescent dye is its
brightness,19 defined as the product of the fluorescence quantum
yield Φ and the molar absorption coefficient ε(λ) at wavelength
λ. The maximum brightness values, corresponding to the εmax
values at λabs(max), of a selection of BODIPY dyes (1,7-
unsubstituted 6c, 1,7-diphenyl 7a, and 1,7-dithiophenyl 10) in
the solvents used in Table 2 are compiled in Table 3. The εmax
values are in line with those of reported BODIPY dyes. The
maximum brightness is the smallest for 10, due to the consis-
tently low Φ value. In contrast, 1,7-diphenyl BODIPY 7a has the
highest brightness, as a result of the favorable combination of
large εmax and high Φ. Intermediate brightness values are found
for 6c, owing to the small εmax in combination with high Φ.
The λabs(max) and λem(max) values of 10 are shifted to
wavelengths slightly longer than those of 7a due to conjugation
with the sulfur that can act as electron donor or electron acceptor
(involving respectively 3p and 3d orbitals). However, there is no
charge-transfer character of the excited state, because the emis-
sion spectra shift to shorter wavelength upon increasing the
solvent polarity (which for the solvents used is accompanied by a
decrease in the polarizability of the solvent). Moreover, the
’ CONCLUSION
1,7-DihaloBODIPY dyes are readily synthesized in a sequence
of high-yielding steps, thus providing an entry to the final missing
arrangement of substituents on the boron dipyrromethene
scaffold. Even though the changes in spectral properties are
somewhat attenuated in comparison to other substitution pat-
terns, they nevertheless combine high fluorescence quantum
yields with red-shifted absorption and fluorescence emission
spectra. Because of the beneficial alignment of the introduced
group, these systems may prove especially useful in the prepara-
tion of new sensors with improved properties.20
Stokes shift Δν̅ is (within experimental error) independent of
the solvent polarity, indicative of equality of the dipole moments
of S0 and S1. The small fluorescence quantum yield Φ of 10 is
surprising. The small Stokes shift (intermediate between those of
7a and 7b) excludes that this is due to extensive exciton phonon
coupling. Considering the inefficient intersystem crossing in
other sulfur-substituted BODIPYs,16 it is also not evident to
attribute the small Φ to enhanced intersystem crossing. In
contrast to the case for the other 1,7-disubstituted BODIPYs,
the Φ value of 10 decreases markedly upon increasing solvent
polarity. Similar results were obtained earlier for other BODIPY
analogues with weakly electron releasing substituents at the 8-, 3-,
and 3,5-positions.17 Also for those compounds, Φ sometimes
decreased with increasing solvent polarity, even in the absence of
a red shift of λem(max).
’ EXPERIMENTAL SECTION
All reactions were carried out in flame-dried glassware, but no special
precautions were taken for the exclusion of moisture. Solvents were not
dried prior to use.
1H NMR spectra (300 MHz) in CDCl3 were recorded at room
temperature and referenced to tetramethylsilane (0.00 ppm) as an
The ring-fused compounds 12 and 13 absorb and fluoresce in
the red spectral range due to the extended conjugation
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internal standard. 13C NMR spectra (75 MHz) in CDCl3 were refer-
enced to the CDCl3 (77.16 ppm) signal.
and CH2Cl2 (1/3 (v/v); 40 mL), and the mixture was cooled to 0 °C. N-
Chlorosuccinimide (1.6 g, 12 mmol, 1.15 equiv) was added, and the
mixture was stirred at 0 °C for 30 min. Subsequently, the darkened mixture
was partitioned between diethyl ether (300 mL) and water (300 mL). The
organic layer was separated, extracted with water, dried over MgSO4,
filtered, and concentrated in vacuo. After column chromatography (silica;
CH2Cl2/ethyl acetate, 9/1 (v/v)) the pure solid was obtained as off-white
crystals (525 mg, 3.30 mmol, 33%): mp106À107 °C; 1H NMRδ 11.13 (s,
1H), 9.42 (s, 1H), 2.29 (s, 3H), 1.97 (s, 3H) ppm; 13C NMR δ 175.8,
136.8, 126.3, 125.7, 117.4, 11.9, 8.2 ppm; MS (EI, 70 eV; m/z) 156, 158;
HRMS (m/z) calcd for C7H8ClNO 157.029 44, found 157.029 16.
3-Bromo-4,5-dimethyl-1H-pyrrole-2-carbaldehyde (5b).
Pyrrole carbaldehyde 4 (246.3 mg, 2 mmol) was dissolved in a mixture
of DMF and CH2Cl2 (1/3 (v/v); 8 mL), and the mixture was cooled to
0 °C. N-Bromosuccinimide (462.7 mg, 2.3 mmol, 1.15 equiv) was
added, and the mixture was stirred at 0 °C for 30 min. The darkened
mixture was partitioned between diethyl ether and water. The organic
layer was separated, extracted with water, dried over MgSO4, filtered,
and concentrated in vacuo. After column chromatography (silica;
CH2Cl2/ethyl acetate, 9/1 (v/v)) the pure solid was obtained as off-
white crystals (355 mg, 1.76 mmol, 88%): mp 144À148 °C; 1H NMR δ
10.94 (s, 1H), 9.30 (s, 1H), 2.24 (s, 3H), 1.91 (s, 3H) ppm; 13C NMR δ
177.1, 136.9, 127.0, 119.4, 113.7, 12.1, 9.6 ppm; MS (EI, 70 eV; m/z)
201, 203; HRMS (m/z) calcd for C7H8BrNO 200.978 93, found
200.977 708.
3-Chloro-4,5-dihydro-1H-benzo[g]indole-2-carbaldehyde
(S1). To a stirred solution of dihydrobenzindole aldehyde9 (197 mg,
1 mmol) and NaHCO3 (102 mg, 1.2 mmol, 1.2 equiv) in CH2Cl2
(10 mL) was added sulfuryl chloride (1 mL of a 1 M solution in CH2Cl2)
while the temperature was kept at 0 °C. The resulting mixture was stirred
for 16 h, followed by pouring it into aqueous NaHCO3. Dichloro-
methane (50 mL) was added, and the solution was extracted with water
and subsequently with brine. The organic layer was collected, dried over
MgSO4, filtered, and evaporated to dryness. The crude mixture was
purified by column chromatography (silica; CH2Cl2/ethyl acetate, 9/1
(v/v)) to yield a white, crystalline solid (78 mg, 34%): mp 199À206 °C;
1H NMR δ 10.60 (s, br, 1H, NH), 9.64 (s, 1H), 7.68 (d, 1H, J = 7.35 Hz),
7.30 (m, 3H), 2.98 (t, 2H, J = 7.35 Hz), 2.75 (t, 2H, J = 7.74 Hz) ppm;
13C NMR δ 176.6, 137.4, 135.8, 128.9, 128.8, 127.7, 127.3, 126.7, 123.6,
121.8, 120.7 ppm; LRMS (EI, 70 eV; m/z): 231; HRMS (m/z) calcd for
C13H10ClNO 231.045 09, found 231.043 46.
Freshly prepared samples in 1 cm quartz cells were utilized to
perform all UVÀvis absorption and fluorescence measurements. For
the determination of the relative fluorescence quantum yields (Φ) in
solution, only dilute solutions with an absorbance below 0.1 at the
excitation wavelength were used. Rhodamine 6G in ethanol (for UV
spectroscopy, ACS reagent, Φ = 0.88) and cresyl violet in methanol
(g99.9%, ACS spectrophotometric grade, Φ = 0.55) were used as
references to determine Φ values. In all cases, correction for the
refractive index was applied. Molar absorption coefficients ε(λ) were
obtained from the linear regression analysis of the absorbance A(λ)
versus dye concentration C data. Between 4 and 10 such {A(λ), C} data
points were used in each regression analysis. All spectroscopic mea-
surements were done at 20 °C.
2,3-Dimethylpyrrole (1) and 4,5-dihydro-1H-benzo[g]indole were
prepared in a Trofimov reaction according to a literature procedure.10
2,3,5,6,8-Pentamethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-
indacene (2). 2,3-Dimethylpyrrole (1; 0.70 g, 7.5 mmol) was dissolved
in CH2Cl2 (10 mL), followed by the addition of acetyl chloride (0.291 g,
264 μL, 3.7mmol). The mixture wasrefluxedfor 2 h andcooledto0 °C by
means of an ice bath, followed by the addition of triethylamine (5 mL).
After 10 min at 0 °C, boron trifluoride etherate (5 mL) was added and the
reaction mixture was stirred at room temperature for 16 h. The solution
was poured into diethyl ether (200 mL) and thoroughly washed with
water. The organic layer was dried over MgSO4, filtered, and concentrated
in vacuo. Chromatographic purification (silica; CH2Cl2-petroleum ether,
1/1 (v/v)) yielded the compound as an orange solid (175 mg, 18%): mp
161À165 °C; 1H NMR δ 6.82 (s, 2H), 2.49 (s, 6H), 2.35 (s, 3H), 2.02 (s,
6H) ppm; 13C NMR δ 154.7, 137.5, 133.3, 127.1, 125.2, 15.0, 12.6, 11.2
ppm; LRMS (EI, 70 eV; m/z) 262; HRMS (m/z) calcd for C14H17BF2N2
262.145 29, found 262.144 99.
1,7-Dibromo-2,3,5,6,8-pentamethyl-4,4-difluoro-4-bora-
3a,4a-diaza-s-indacene (3). A solution of 2,3,5,6,8-pentamethyl-
BODIPY (0.178 g, 0.679 mmol) and NaHCO3 (130 mg, 1.5 mmol, 2.2
equiv) was stirred at 0 °C, followed by the slow addition of bromine (217
mg, 1.36 mmol, 2 equiv). The resulting reaction mixture was stirred at
room temperature for 2 h, followed by quenching of the reaction with an
aqueous Na2S2O3 solution. The organic layer was extracted with water,
dried over MgSO4, filtered, and evaporated to dryness. The crude
product was purified by column chromatography (silica; CH2Cl2/
petroleum ether, 1/1 (v/v)): red solid (234 mg, 82%); mp >300 °C;
1H NMR δ 3.08 (s, 3H), 2.52 (s, 6H), 2.05 (s, 6H) ppm; 13C NMR δ
152.8, 141.7, 129.1, 118.9, 16.6, 13.2, 10.9 ppm (one aromatic carbon
not observed); LRMS (EI, 70 eV; m/z) 420; HRMS (m/z) calcd for
C14H15BBr2F2N2 419.964 27, found 419.963 28.
4,5-Dimethyl-1H-pyrrole-2-carbaldehyde (4). To N,N-di-
methylformamide (DMF, 18.7 mmol, 1.44 mL) at 0 °C was added
phosphorus oxychloride (37.4 mmol, 5.74 mL, 3 equiv) dropwise, and
the resulting suspension was stirred at room temperature for 1 h. The
mixture was cooledto0 °C, and 2,3-dimethylpyrrole (12.5 mmol, 1.187 g)
in dichloromethane (50 mL) was added, followed by stirring at room
temperature for 16 h. The reaction was quenched by the rapid addition of
excessNa2CO3 (50mmolin50 mLofH2O), followedbyheatingtoreflux
for 1 h. The mixture was cooled and extracted with dichloromethane (2 Â
100 mL). The organic layer was dried over MgSO4, filtered, and
evaporated to dryness. The crude solid was purified by flash chromatog-
raphy (silica; CH2Cl2/ethyl acetate, 9/1 (v/v)) to yield the aldehyde as an
off-white solid (1.170 g, 9.54 mmol, 51%): mp 118À123 °C; 1H NMR δ
10.25 (s, br, 1H, NH), 9.27 (s, 1H), 6.74(d, 1H, J = 2.07 Hz), 2.28 (s, 3H),
2.03 (s, 3H) ppm; 13C NMR δ 177.6, 136.8, 130.4, 123.8, 119.2, 11.61,
10.9 ppm; MS (EI, 70 eV; m/z) 123.
3-Bromo-4,5-dihydro-1H-benzo[g]indole-2-carbaldehyde
(S2). To a stirred solution of dihydrobenzindole aldehyde9 (394 mg,
2 mmol) and NaHCO3 (168 mg, 2 mmol, 2 equiv) in CH2Cl2 (10 mL)
was added bromine (320 mg, 2 mmol, 1 equiv), while the temperature
was kept at 0 °C. The resulting mixture was stirred at room temperature
for 2 h, followed by pouring it into aqueous Na2S2O3. Dichloromethane
(50 mL) was added, and the solution was extracted with water and
subsequently with brine. The organic layer was collected, dried over
MgSO4, filtered, and evaporated to dryness. The crude mixture was
purified by column chromatography (silica; CH2Cl2/ethyl acetate, 9/1
(v/v)) to yield a white, crystalline solid (385 mg, 70%): mp
1
208À210 °C; H NMR δ 10.14 (s, br, 1H, NH), 9.57 (s, 1H), 7.54
(d, 1H, J = 6.6 Hz), 7.26 (m, 3H), 2.99 (t, 2H, J = 7.53 Hz), 2.73 (t, 2H,
J = 7.53 Hz) ppm; 13C NMR δ 177.7, 137.4, 128.9, 128.8, 128.7, 127.3,
126.3, 115.9, 121.3, 110.0, 29.0, 19.9 ppm; LRMS (EI, 70 eV; m/z) 275;
HRMS (m/z) calcd for C13H10BrNO 276.992 54, found 276.993 85.
1,7-Dichloro-2,3,5,6-tetramethyl-4,4-difluoro-4-bora-
3a,4a-diaza-s-indacene (6a). The compound was obtained accord-
ing to General Procedure for the Decarbonylative Condensation as a
purple solid (151 mg, 48%): mp >300 °C; 1H NMR δ 7.19 (s), 2.51 (s,
6H), 2.01 (s, 6H) ppm; 13C NMR δ 155.8, 131.4, 130.3, 125.3, 118.7,
13.4, 8.9 ppm; MS (EI, 70 eV; m/z) 316; HRMS (m/z) calcd for
C13H13BF2N2Cl2 316.051 69, found 316.051 54.
3-Chloro-4,5-dimethyl-1H-pyrrole-2-carbaldehyde (5a). Pyr-
role carbaldehyde 4 (1.254 g, 10 mmol) was dissolved in a mixture of DMF
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The Journal of Organic Chemistry
ARTICLE
1,7-Dibromo-2,3,5,6-tetramethyl-4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (6b). General Procedure for the Decarbonylative
Condensation. To a solution of brominated pyrrole carbaldehyde 5b (400
mg, 2 mmol) in dichloromethane (10 mL) at 0 °C was added phosphorus
oxychloride (920 mg, 550 μL, 6 mmol), and the resulting mixture was
stirred at room temperature for 16 h. Triethylamine (2.023 g, 2.78 mL,
20 mmol, 10 equiv) was added dropwise at 0 °C, followed 10 min later by
boron trifluoride etherate (2.78 mL, 22 mmol, 11 equiv). The mixture was
stirred at room temperature for 2 h and subsequently poured into diethyl
ether (200 mL). The ether solution was extracted with water (3 Â
200 mL), dried over MgSO4, filtered, and evaporated to dryness. The
crude product was purified by column chromatography (silica; petroleum
ether/ethyl acetate, 9/1 (v/v)) to yield a dark red solid (284 mg, 70%): mp
and the mixture was stirred at 60 °C for 30 min. The reaction mixture was
poured into diethyl ether (200 mL) and repeatedly washed with water.
The organic layer was dried over MgSO4, filtered, and evaporated to
dryness. After purification via column chromatography (silica, petroleum
ether/CH2Cl2, 2/1 (v/v)), the compound was obtained as a purple solid
(34 mg, 76%): mp >300 °C; 1H NMR δ 7.58À7.56 (m, H), 7.37 (t, 6H,
J = 3.03 Hz), 7.34 (s, 1H), 2.52 (s, 6H), 2.14 (s, 6H) ppm; 13C NMR
δ 155.9, 135.3, 131.9, 130.3, 128.9, 128.8, 128.6, 123.1, 119.8, 100.4, 82.2,
12.9, 10.3 ppm; MS (EI, 70 eV; m/z) 448; HRMS (m/z) calcd for
C29H23BF2N2 448.192 24, found 448.195 25.
1,7-Bis(phenylethenyl)-2,3,5,6-tetramethyl-4,4-difluoro-
4-bora-3a,4a-diaza-s-indacene (7d). 1,7-DibromoBODIPY (6b;
0.1 mmol, 40.6 mg) was dissolved in DMF (1 mL), followed by the
addition of triethylamine (0.4 mmol, 56 μL, 4 equiv), styrene (0.30
mmol, 30 μL, 2.6 equiv), and Pd(OAc)2 (10 μmol, 2 mg, 10%). The
mixture was flushed with nitrogen and stirred under a nitrogen atmo-
sphere at 65 °C until the reaction was complete. The reaction mixture
was poured into diethyl ether (200 mL) and repeatedly washed with
water. The organic layer was dried over MgSO4, filtered, and evaporated
to dryness. After purification via column chromatography (silica;
petroleum ether/CH2Cl2, 2/1 (v/v)), the compound was obtained as
a purple solid (28 mg, 62%): mp 275À278 °C; 1H NMR δ 7.53 (d, 4H,
J = 7.35 Hz), 7.41À7.30 (m, 7H), 7.20, 7.14 (d, 2H, J = 16.38 Hz), 7.02,
6.96 (d, 2H, J = 16.38 Hz), 2.55 (s, 6H), 2.18 (s, 6H) ppm; 13C NMR δ
158.3, 153.0, 138.6, 137.0, 135.0 133.5, 131.9, 131.2, 128.8, 128.5, 127.8,
126.7, 126.4, 125.1, 120.8, 119.7, 118.9, 118.4, 13.3, 13.1, 12.9, 10.6,
10.26, 10.21 ppm; MS (EI, 70 eV; m/z) 452; HRMS (m/z) calcd for
C29H27BF2N2 452.223 54, found 452.223 64.
>300 °C; 1H NMR δ 7.12 (s, 1H), 2.52 (s, 6H), 2.02 (s, 6H) ppm; 13
C
NMR δ 156.0, 132.0, 127.9, 121.0, 120.4, 13.4, 10.4 ppm; MS (EI, 70 eV;
m/z) 404, 406, 408; HRMS (m/z) calcd for C13H13BF2N2Br2 406.974 13,
found 406.973 46 (45.56%).
2,3,5,6-Tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-in-
dacene (6c). The compound was obtained according to General
Procedure for the Decarbonylative Condensation as a purple solid
1
(149 mg, 60%): mp 229À232 °C; H NMR δ 6.82 (s, 1H), 6.65 (s,
2H), 2.50 (s, 6H), 2.02 (s, 6H) ppm; 13C NMR δ 156.3, 133.1, 128.0,
124.5, 12.8, 11.1 ppm; MS (EI, 70 eV; m/z) 248; HRMS (m/z) calcd for
C13H15BF2N2 248.129 64, found 248.129 69.
1,7-Diphenyl-2,3,5,6-tetramethyl-4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (7a). General Procedure for the Suzuki Reaction.
BODIPY 6b (40.6 mg, 0.1 mmol) was dissolved in toluene (1 mL),
followed by the addition of benzene boronic acid (26 mg, 0.22 mmol, 2.2
equiv), Pd(PPh3)4 (11 mg, 0.01 mmol, 10%), and aqueous Na2CO3 (1 mL
of a 1 M solution). The resulting mixture was flushed with nitrogen and
refluxed for 3 h or until TLC analysis showed complete reaction. The
mixture was extracted with diethyl ether (200 mL), and the organic layer
was collected, dried over MgSO4, and evaporated to dryness. The crude
solid was purified chromatographically to yield the target compound as a
purple solid (32 mg, 81%): mp 238À241 °C; 1H NMR δ 7.43À7.33 (m,
8H), 7.27 (d, 2H, J = 1.53 Hz), 2.60 (s, 6H), 2.03 (s, 6H) ppm; 13C NMR δ
155.2, 141.9, 133.2, 132.7, 129.8, 128.7, 127.9, 124.9, 124.1, 13.0, 9.8 ppm;
MS (EI, 70 eV; m/z) 400; HRMS (m/z) calcd for C25H23BF2N2
400.192 24, found 400.192 24.
General Procedure for the Stille Reaction. To a solution of 1,7-
dibromoBODIPY 6b in dioxane (1 mL) was added Pd2(dba)3 (5 μmol,
4.5 mg, 5%), tris(2-furyl)phosphine (5 mmol, 1.2 mg, 5%), fenyltribu-
tyltin (0.22 mmol, 72 mL, 2.2 equiv), and Na2CO3 (0.30 mmol, 32 mg,
3 equiv). The reaction mixture was heated to reflux until TLC analysis
indicated complete reaction. The mixture was cooled to room tempera-
ture and evaporated to dryness. After purification via column chroma-
tography (silica; petroleum ether/CH2Cl2, 1/1 (v/v)), the compound
was obtained as a purple solid (38 mg, 96%).
1-(4-tert-Butylphenyl)-2,3,5,6-tetramethyl-7-bromo-4,4-
difluoro-4-bora-3a,4a-diaza-s-indacene (8). Obtained from
General Procedure for the Suzuki Reaction on 1,7-dibromoBODIPY
(6b; 22 mg, 48%): mp 216À219 °C; 1H NMR δ 7.52 (d, 2H, J = 8.32
Hz), 7.27 (d, 2H, J = 8.32 Hz), 6.96 (s, 1H), 2.57 (s, 3H), 2.53 (s, 3H),
2.05 (s, 3H), 2.05 (s, 3H), 2.00 (s, 3H), 1.38 (s, 9H) ppm; 13C NMR δ
158.5, 152.6, 151.5, 143.3, 133.4, 131.4, 129.8, 129.5, 126.2, 126.1, 125.8,
122.5, 31.9, 31.4, 13.2, 13.1, 10.3, 9.9 ppm; LRMS (EI, 70 eV; m/z): 458;
HRMS (m/z) calcd for C23H26BBrF2N2 458.134 05, found 458.134 87.
1-(4-tert-Butylphenyl)-2,3,5,6-tetramethyl-7-(phenyl-
ethynyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (9). Ob-
tained from General Procedure for the Sonogashira Reaction (see under
1
7c) on monobromoBODIPY (8; 40 mg, 83%): mp 242À247 °C; H
NMR δ 7.52 (d, 2H, J = 8.28 Hz), 7.46 (m, 2H), 7.33 (m, 6H), 7.11 (s,
1H), 2.60 (s, 3H), 2.52 (s, 3H), 2.12 (s, 3H), 2.07 (s, 3H), 1.39 (s, 9H)
ppm; 13C NMR δ 158.2, 152.8, 151.4, 143.1, 134.8, 133.6, 131.7, 130.0,
139.6, 128.8, 128.7, 128.5, 125.9, 125.7, 123.2, 122.1, 99.3, 82.5, 34.9, 31.4,
13.2, 12.7, 10.2, 9.9 ppm; LRMS (EI, 70 eV; m/z): 480; HRMS (m/z)
calcd for C31H31BF2N2 480.254 84, found 480.256 81.
1,7-Bis(phenylsulfenyl)-2,3,5,6-tetramethyl-4,4-difluoro-
4-bora-3a,4a-diaza-s-indacene (10). Nucleophilic Substitution
Procedure. To a solution of BODIPY 6a (0.1 mmol) in acetonitrile
(1.5 mL) were added triethylamine (0.5 mmol, 50.6 mg, 5 equiv) and
thiophenol (0.5 mmol, 55 mg, 5 equiv). The resulting mixture was
stirred at room temperature until the reaction was complete, as indicated
by TLC analysis. The reaction mixture was poured into diethyl ether
(200 mL) and repeatedly washed with aqueous Na2CO3. The organic
layer was dried over MgSO4, filtered, and evaporated to dryness. After
purification via column chromatography (silica, petroleum ether/
CH2Cl2, 2/1 (v/v)), the compound was obtained as a purple solid in
near-quantitative yield (46 mg): mp 188À191 °C; 1H NMR δ 7.34 (s,
1H), 7.25À7.19 (m, 4H), 7.14À7.11 (m, 6H), 2.56 (s, 6H), 1.92 (s, 6H)
ppm; 13C NMR δ 156.3, 136.3, 135.6, 132.1, 131.5, 129.2, 127.9, 126.2,
121.2, 13.2, 10.1 ppm; MS (EI, 70 eV; m/z) 464; HRMS (m/z) calcd for
C25H23BF2N2S2 464.136 38, found 464.134 54.
1,7-Bis(2-thienyl)-2,3,5,6-tetramethyl-4,4-difluoro-4-bora-
3a,4a-diaza-s-indacene (7b). The compound was obtained accord-
ing to General Procedure for the Suzuki Reaction and General Procedure
for the Stille Reaction as a purple solid (37 mg, 90%): mp 240À242 °C;
1H NMR δ 7.47 (s, 1H), 7.42 (d, 2H, J = 5.04 Hz), 7.14 (t, 2H, J = 5.04
Hz), 7.08 (d, 2H, J = 2.76 Hz), 2.58 (s, 6H), 2.14 (s, 6H) ppm; 13C NMR
δ 155.6, 134.4, 132.8, 128.1, 128.0, 127.8, 127.2, 125.0, 123.7, 13.0, 10.3
ppm; MS (EI, 70 eV; m/z) 412; HRMS (m/z) calcd for C21H19BF2N2S2
412.105 08, found 412.10742.
1,7-Bis(phenylethynyl)-2,3,5,6-tetramethyl-4,4-difluoro-4-
bora-3a,4a-diaza-s-indacene (7c). General Procedure for the
Sonogashira Reaction. 1,7-DibromoBODIPY 6b (0.1 mmol, 40.6 mg),
Pd2(dba)3 (5 mmol, 4.6 mg, 5%), tris(2-furyl)phosphine (5 μmol, 2.4
mg, 10%), and CuI (10 μmol, 10%) were dissolved in a mixture of DMF
and triethylamine (8/2 (v/v), 1 mL) and flushed with nitrogen.
Phenylacetylene (0.26 mmol, 27 mg, 28.5 μL, 2.6 equiv) was added,
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The Journal of Organic Chemistry
ARTICLE
1,7-Dichloro-2,3,5,6-bis(dihydronaphthyl)-4,4-difluoro-
4-bora-3a,4a-diaza-s-indacene (11a). Obtained by following
General Procedure for the Decarbonylative Condensation of pyrrolic
aldehydes to symmetric BODIPY dyes, as a deep blue, metallic solid
(2) (a) Kim, T. G.; Castro, J. C.; Loudet, A.; Jiao, J. G.-S.;
Hochstrasser, R. M.; Burgess, K.; Topp, M. R. J. Phys. Chem. A 2006,
110, 20. (b) Cakmak, Y.; Akkaya, E. U. Org. Lett. 2009, 11, 85.
(3) (a) Thivierge, C.; Bandichhor, R.; Burgess, K. Org. Lett. 2007, 9,
2135. (b) Chen, J.; Mizumura, M.; Shinokubo, H.; Osuka, A. Chem. Eur.
J. 2009, 15, 5942.
1
(111 mg, 48%): mp >300 °C; H NMR δ 8.70 (d, 2H, J = 7.92 Hz),
7.46À7.24 (m, 7H), 2.94 (, 4H, J = 6.39 Hz), 2.73 (, 4H, J = 3.69 Hz)
ppm; 13C NMR δ 151.8, 140.8, 133.3, 130.6, 129.8, 128.6, 128.5, 128.3,
127.7, 127.6, 117.6, 34.2, 20.2 ppm; LRMS (EI, 70 eV; m/z): 464;
HRMS (m/z) calcd for C25H17BCl2F2N2 464.082 99, found 464.0765.
1,7-Dibromo-2,3,5,6-bis(dihydronaphthyl)-4,4-difluoro-4-
bora-3a,4a-diaza-s-indacene (11b). Obtained by following the
General Procedure for the Decarbonylative Condensation of pyrrolic
aldehydes to symmetric BODIPY dyes, as a bronze metallic solid (153 mg,
55%): mp 282À283 °C; 1H NMR δ 8.70 (d, 2H, J = 7.71 Hz), 7.45À7.24
(m, 7H), 2.95 (t, 4H, J = 6.39 Hz), 2.72 (t, 4H, J = 5.67 Hz) ppm; 13C
NMR δ 152.4, 141.5, 135.1, 133.2, 131.0, 129.0, 128.7, 128.5, 128.4, 127.7,
127.7, 120.3, 117.0, 30.1, 21.7 ppm; LRMS (EI, 70 eV; m/z): 556; HRMS
(m/z) calcd for C25H17BBr2F2N2 553.979 92, found 553.982 03.
1,7-Bis(2-thienyl)-2,3,5,6-bis(dihydronaphthyl)-4,4-difluoro-
4-bora-3a,4a-diaza-s-indacene (12). Obtained from General Proce-
dure for Stille Coupling, as a blue metallic solid (36 mg, 64%): mp
>300 °C; 1H NMR δ 8.30 (d, 2H), 7.77 (s, 1H), 7.48 (m, 4H), 7.34À7.16
(m, 8H), 2.95-.289 (m, 8H) ppm; 13C NMR δ 140.6, 133.9, 130.1, 128.5,
128.4, 128.3, 128.2, 128.1, 128.0, 127.6, 127.3, 31.0, 21.5 ppm; LRMS (EI,
70 eV; m/z): 560; HRMS (m/z) calcd for C33H23BF2N2S2 560.136 38,
found 560.139 48.
1,7-Bis(phenylsulfenyl)-2,3,5,6-bis(dihydronaphthyl)-4,4-
difluoro-4-bora-3a,4a-diaza-s-indacene (13). Obtained from
Nucleophilic Substitution Procedure with triethylamine as base and 4
equiv of thiophenol, as a golden metallic solid (22 mg, 36%): mp 214 °C
dec; 1H NMR δ 8.76 (d, 2H, J = 7.92 Hz), 7.58 (s, 1H), 7.43 (t, 2H, J =
7.53 Hz), 7.36À7.13 (m, 14H), 2.87 (t, 4H, J = 6.57 Hz), 2.58 (t, 4H, J =
7.53 Hz) ppm; 13C NMR δ 152.5, 140.9, 138.4, 136.7, 136.1, 130.4,
129.3, 128.9, 128.5, 128.0, 127.9, 127.7, 126.3, 123.1, 120.0, 30.0, 21.3
ppm; HRMS (m/z) calcd for C37H27BF2N2S2 612.167 68, found
612.168 62.
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: Wim.Dehaen@chem.kuleuven.be.
(16) Fron, E.; Couti~no-Gonzalez, E.; Pandey, L.; Sliwa, M.;
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’ ACKNOWLEDGMENT
The continuing support from the KU Leuven, the “Fonds voor
Wetenschappelijk Onderzoek” (FWO), and the “Ministerie voor
Wetenschapsbeleid (Belgium)” is gratefully acknowledged. V.L.
thanks the “Instituut voor de aanmoediging van innovatie door
Wetenschap en Technologie in Vlaanderen” (IWT) for a doc-
toral grant. A.F. and J.M.N. are grateful for financial support
through GOA 2006-2 and IAP 6/27.
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