Boradipyrromethenecyanines

Article abstract of DOI:10.1002/ejoc.200900192

A series of meso-polymethine-substituted BODIPY compounds have been synthesized by the reaction of mesomethyl-3,5-diphenylboradipyrromethene with a number of hemicyanine derivatives. The dyes obtained exhibit: intense long-wavelength absorption, but weak

Full text of DOI:10.1002/ejoc.200900192

FULL PAPER
DOI: 10.1002/ejoc.200900192
Boradipyrromethenecyanines
Viktor P. Yakubovskyi,[a] Mykola P. Shandura,[a] and Yuriy P. Kovtun*[a]
Keywords: BODIPY compounds / Boron dipyrromethene dye / Merocyanine / Polymethine dye / Long-wavelength dye /
Heterocycles
A series of meso-polymethine-substituted BODIPY com-
pounds have been synthesized by the reaction of meso-
methyl-3,5-diphenylboradipyrromethene with a number of
hemicyanine derivatives. The dyes obtained exhibit intense
long-wavelength absorption, but weak fluorescence. Upon
protonation of the dyes the long-wavelength band disap-
pears and the intensity of the short-wavelength band in-
creases significantly. It has been shown that the properties of
the dyes obtained, which we call boradipyrromethenecyan-
ines, are closely related to those of merocyanine dyes rather
than those of boron dipyrromethenes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
For example, distyryl-substituted derivatives A exhibit a
bathochromic shift of the absorption maximum of 79 nm
compared with diphenyl-substituted analogues (see Scheme
1). The bathochromic shift of phenylethynyl analogues B is
somewhat smaller, however, both A and B are typical BOD-
IPYs and demonstrate high fluorescence quantum yields
that are fairly insensitive to the nature of the solvent.[3] The
introduction of additional 4-(dialkylamino) substituents
into A (structure C[4]) results in even more pronounced
spectral changes, with bathochromic shifts of around
80 nm. The structures C exhibit very small solvatochro-
mism and considerable positive solvatofluorochromism.
The fluorescence intensity increases significantly with
decreasing solvent polarity. Protonation of the dialk-
ylamino groups in C leads to optical properties that are
very similar to those of A. Although the charge-separated
mesomeric form C2 is typical of merocyanine dyes, the
properties of the structures C (e.g., easy protonation, weak
solvatochromism, and relatively low molar absorptivity) as
Introduction
Boradipyrromethene dyes (4,4-difluoro-4-bora-3a,4a-diaza-
s-indacenes, BODIPY, BDP) have attracted considerable at-
tention over the past two decades. The ever increasing inter-
est in this type of compound is due to their excellent ther-
mal, chemical, and photochemical stability, high molar ab-
sorptivity, high fluorescence quantum yields, insensitivity to
solvent polarity and pH, long excited-state lifetimes, a large
two-photon cross-section for multiphoton excitation, lack
of ionic charge, and good solubility.[1] However, the absorp-
tion maxima of the majority of BODIPYs are below
600 nm. Long-wavelength dyes are important for both basic
and applied research[2] and therefore many synthetic ap-
proaches exist for modifying the BODIPY core to give
structures that absorb at longer wavelengths. One of the
most promising approaches to the modification of BOD-
IPY is its peripheral functionalization with conjugated
chromophores.
Scheme 1.
[a] Institute of Organic Chemistry, National Academy of Sciences
of Ukraine,
a whole do not correspond to those of merocyanines. Thus,
the dialkylamino groups in structures C provide consider-
able spectral changes, but do not change the color of the
5 Murmanska Street, 02094 Kyiv, Ukraine
E-mail address: kovtun@ioch.kiev.ua
Eur. J. Org. Chem. 2009, 3237–3243
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3237

V. P. Yakubovskyi, M. P. Shandura, Y. P. Kovtun
FULL PAPER
BODIPY core. Therefore in this case they cannot be re-
ferred to as true “end groups” as defined in the ideology of
polymethine dyes.
Results and Discussion
The selection of a BODIPY derivative suitable for fur-
This statement is even more evident for structures ther derivatization to obtain dyes G was based on the fol-
D.[3a,4b,5] In this case the dialkylamino group leads to a lowing. We assumed that the methyl group in the meso
small hypsochromic shift of the BODIPY absorption maxi- position of structure H should be active enough for Knoe-
mum. The fluorescence quantum yields are quenched in po- venagel-type condensations. In addition, the positions next
lar solvents but not in nonpolar media. Protonation of the to the meso-methyl group should not be substituted to
dialkylamino groups in D results in both a small bathoch- avoid steric problems. Therefore, the readily available 2-
romic shift of the BODIPY absorption maximum and the phenylpyrrole (1)[7] was used in the first synthetic step. As
appearance of fluorescence. For steric reasons the conjuga- shown in Scheme 3 the salt 2 was prepared by treating 1
tion of the dialkylaminophenyl fragment with the BODIPY with triethyl orthoacetate and p-toluenesulfonic acid. This
chromophore in D is rather inefficient, but fluorescence approach is more convenient compared with other re-
quenching occurs in the planar structure E[6] (see Scheme ported methods that use chloroacetaldehyde[8] or acetyl
2). Compounds of type F (n = 0, 1) were also described in chloride.[9]
this report. Thus far this is the only example of a meso-
The salt p-toluenesulfonate·2 partly dissociates in polar
1
vinyl-substituted BODIPY reported in the literature. Intro- solvents, so its H NMR spectrum in [D6]DMSO reveals
duction of an additional vinyl unit into the meso position signals of both the protonated form and the free base 3. The
of BODIPY does not influence its absorption maximum, latter was prepared from 2 by the action of triethylamine.
but leads to a bathochromic shift of 26 nm in the emission Compound 3 is quite stable in ambient conditions, in con-
spectrum.
trast to some alkyl-substituted dipyrrolylethylenes that are
In this paper we report the synthesis and spectral study susceptible to oxidation.[8] Compound 3 exists in an equilib-
of a new series of dyes of type G that combine the poly- rium of two tautomeric forms, an ethylenic form 3a and a
methine and dipyrromethene chromophoric fragments. It meso-methyldipyrromethene form 3b, which can be ob-
1
was our expectation that such a combination of chromo- served in the H NMR spectra. The ethylenic form prevails
phores would have a considerable effect on spectral proper- in polar [D6]DMSO, whereas the meso-methyldipyrrome-
ties enabling the design of deeply colored dyes.
thene tautomer is the major component in CDCl3.
Scheme 2.
Scheme 3. Synthetic route to the key compound 4. Reagents: i) CH3C(OEt)3, TsOH; ii) Et3N; iii) TsOH; iv) BF3·OEt2, Et3N.
3238 Eur. J. Org. Chem. 2009, 3237–3243
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Boradipyrromethenecyanines
The reaction of either 3 or 2 with BF3–OEt2 in the pres- product. This is perhaps due to the low electron-with-
ence of a base led to the fluorescent boron difluoride com- drawing ability of the terminal boradipyrromethene nu-
plex 4, a key intermediate in the synthesis of meso-polyme- cleus, which makes the betaine mesomeric form G2 unfa-
thine-substituted BODIPY derivatives.
vorable. The contribution of the G2 form increases with
The methyl group in the dye 4 is not highly reactive, how- increasing electron-donating effect of the second terminal
ever, it is still able to participate in some condensation reac- nucleus, whereas the stability of the boron complex de-
tions (Scheme 4). Attempts to prepare the formyl deriva- creases. The unfavorable formation of the anionic form of
tives 5 and 6 failed. Nevertheless, a standard Vilsmeier-type the dipyrromethene nucleus is probably the main obstacle
formylation of 4 gave rise to the disubstituted product 7. in the synthesis of symmetrical dyes of type 10 (at least for
Even though diformylation under the given conditions is given substituents).
known,[10] in our case, as well as in the case described in
In the case of a terminal pyran nucleus with weak elec-
ref.[10b], it turned out to be impossible to stop the reaction tron-donating properties (dye 11) a broad band with only a
at the monoformylation stage. A mixture of the diformyl- small short-wavelength shoulder is observed in the absorp-
ated derivative 7 and the unreacted 4 was formed when the tion spectrum in acetonitrile (Figure 1, Table 1). The ab-
Vilsmeier reagent and 4 were used in a 1:1 or lower ratio. sorption band becomes narrower and more intense with in-
Nevertheless, the monoformylated product 8 was obtained creasing electron-donating ability of the second terminal
by the reaction of compound 4 with DMF acetal. The reac- nucleus. This behavior is typical of merocyanine dyes that
tion of intermediate 8 with aniline resulted in the hemicyan- contain weak electron-acceptor terminal nuclei[11] and is a
ine 6. However, further synthetic transformations of 6 (e.g., result of an increase in the polarization of the donor–ac-
reactions with quaternary salts of heterocycles) were not ceptor system through the increasing electron-donating
efficient.
properties of another nucleus, that is, the increased contri-
An attempt to prepare the styryl derivative 9 by the reac- bution of the mesomeric form G2. The opposite trend is
tion of BODIPY derivative 4 with p-(dimethylamino)benz- observed at short wavelengths.
aldehyde failed (Scheme 5). At the same time, the reactions
Dichloromethane and DMF are the optimal solvents for
of 4 with more active phenyliminovinyl derivatives of evaluating the solvatochromic properties of the dyes from
heterocycles of low and medium basicity (e.g., 4-pyran, in- the standpoint of solvent polarity with a minimum of other
doline, benz[c,d]indole, and benzothiazole) proceeded effects.[11] The data obtained with these solvents are given
smoothly to give the corresponding dyes 11–15 in good in Table 1.
yields (Scheme 5). The reaction of 4 with phenyliminobuta-
Positive and negative solvatochromism is observed for
dienyl-substituted indolenine yielded the vinylogue dye 12b. the long- and short-wavelength absorption bands, respec-
In principle, it is possible to obtain other butadienyl deriva- tively (Table 1, Figure 2). Extension of the polymethine
tives of this type; in fact, they were observed in the reaction chain (dyes 12a and 12b) leads to a bathochromic shift of
mixtures, but were not isolated as individual compounds. the long-wavelength absorption band by 98 nm in DMF,
The reaction of 4 with a 2-(anilidovinyl)quinoline derivative although the band becomes less intense.
proved more complicated. In this case a mixture of dyes
The starting boron difluoride complex 4 shows a narrow
was obtained and the desired dye 14 was isolated by column fluorescence band and a high quantum yield, which is typi-
chromatography. In an attempt to condense 4 with a 4-sub- cal of BODIPYs (see Figure 3 and Table 1). BODIPY de-
stituted analogue to produce 16, the latter lost the borondi- rivative 7 also exhibits good fluorescent properties. How-
fluoride fragment to form salt 17. Apparently, in the case ever, the BODIPY derivatives 6 and 8 do not fluoresce be-
of the reaction of 4 with the 2-(phenyliminovinyl)quinoline cause of photoinduced electron transfer, which has also
derivative, a dye of this type was also formed as a side- been reported for similar systems.[12] As expected, acidifica-
Scheme 4. Reagents: i) CH(OEt)3, Ac2O; ii) PhN=CHOEt, Ac2O; iii) POCl3, DMF, HClO4; iv) (CH3)2NCH(OCH3)2, Ac2O; v) PhNH2.
Eur. J. Org. Chem. 2009, 3237–3243
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3239

V. P. Yakubovskyi, M. P. Shandura, Y. P. Kovtun
FULL PAPER
Scheme 5. Reagents: i) p-(dimethylamino)benzaldehyde, Ac2O; ii) CH(OEt)3 or PhN=CHOEt, Ac2O, Et3N; iii) Het=(CH–CH)n=NPh,
TsOH, Ac2O, Et3N.
tion of solutions of 6 and 8 leads to bathochromic shifts in
Similarly, polymethine-substituted BODIPYs as well as
the absorption spectra of 2 and 55 nm, respectively, and to their enamine-type analogues are weakly fluorescent, par-
the appearance of fluorescence. In the case of compound ticularly in polar solvents. However, in contrast to the stan-
8, the fluorescence vanishes quickly and the solution turns dard BODIPYs, the polymethine-substituted BODIPYs be-
yellow. This process is irreversible, which we assume is a have differently upon protonation; the long-wavelength ab-
result of a hydrolytic cleavage of the boron complex and/or sorption band completely disappears and an increase in the
the enamine fragment.
intensity of the short-wavelength band is observed (Fig-
Table 1. Optical properties of the prepared compounds.
Dye
CH2Cl2
fwhm
CH3CN
DMF
λabs [nm]
λem [nm]
(Φf)
λabs [nm]
(ε)·[10–3 –1 cm–1]
fwhm
[cm–1]
λem [nm]
(Φf)
λabs [nm]
(ε)·[10–3 –1 cm–1]
fwhm
λem [nm]
(Φf)
(ε)·[10–3

–1 cm–1][cm–1]


[cm–1]
4
6
7
544 (57)
1631
2904
577 (64)
536 (35)
1732
2915
543 (47)
1684
2923
53 2 (65)
305 (48)
564 (54)
501 (57)
692 (65)
547 (31)
543 (65)
305 (50)
572 (54)
501 (58)
712 (69)
557 (34)
306 (49)
572 (54)
501 (67)
674 (66)
562 (40)
604 (32)
1635
3155
4306
1685
3159
4531
1738
3163
4403
8
11
12a
–
–
–
736
712 (0.6)
720 (Ͻ0.1)
(Ͻ0.1)
661 (108)
587 (38)
743 (98)
558 (33)
1631
1683
671 (111)
572 (29)
771 (116)
539 (26)
1656
1915
682 (116)
582 (27)
784 (107)
549 (25)
1634
1777
12b
13
726 (0.5)
745 (0.4)
–
727 (Ͻ0.1)
743 (Ͻ0.1)
–
729
(Ͻ0.1)
679 (110)
560 (23)
2289
683 (116)
534 (17)
1595
693 (105)
548 (21)
1558
14
15
754
(Ͻ0.1)
710 (125)
610
737 (73)
1432
2353
705 (117)
597 (23)
752 (74)
1403
2184
718 (128)
614 (24)
762 (78)
1334
2071
–
3240
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 3237–3243

Boradipyrromethenecyanines
The optical properties of the cationic dye 17 cannot be
discussed in direct comparison with those of the boron
difluoride complexes 11–15 because it is a different type of
dye. Such dyes have not been investigated systematically;[9]
however, their properties will be reported in the due
course.
Conclusions
The reported compounds 11–15 are specific polymethine
merocyanine dyes, even though they can be formally re-
ferred to as BODIPY derivatives. The merocyanine nature
of these dyes manifests itself in the existence of two charac-
teristic bands in their absorption spectra. The long-wave-
length band belongs to the polymethine fragment and is
more intense than the short-wavelength band that stems
from the dipyrromethene unit. This is also confirmed by
the spectral changes that occur upon protonation of these
dyes, that is, the long-wavelength band disappears and the
short-wavelength absorption increases. The prepared dyes
show intense long-wavelength absorption and weak fluores-
cence. These dyes have only a few known formal analogues,
the cyanine-like chromophoric systems that contain another
dye as a terminal nucleus.[13] By reference to conventional
cyanine nomenclature,[14] we refer to them as boradipyrro-
methenecyanines.
Figure 1. Absorption spectra of compounds 4 and 11–14 in aceto-
nitrile (C = 1ϫ10–5 ).
Experimental Section
General: The absorption spectra were recorded with a Shimadzu
UV-3100 spectrophotometer. 1H (300 MHz, 25 °C, TMS as internal
standard) and 13C NMR (75 MHz, CDCl3 as internal standard)
spectra were obtained with a Varian VXR-300 spectrometer. LC–
MS measurements were performed with a liquid chromatography–
mass spectrometric system consisting of an Agilent 1100 Series
HPLC instrument equipped with a diode matrix detector and an
Agilent LC/MSD SL mass-selective detector. The atmospheric
pressure chemical ionization (APCI) technique with detection of
positive ions was used. Fluorescence spectra were recorded with a
Solar CM 2203 fluorescence spectrophotometer. Fluorescence
quantum yields (Φ) for compounds 4 and 7 were determined rela-
tive to Rhodamine 6G (Φ = 0.95, EtOH), whereas for compounds
11, 12a, 13, and 14 they were determined relative to pentamethine-
dioxaborinate (Φ = 0.57, CH2Cl2).[15]
Figure 2. Absorption spectra of compounds 12a (solid line) and
12b (dotted line) (C = 1ϫ10–5 ).
5-Phenyl-2-[1-(5-phenyl-1H-pyrrol-2-yl)ethylidene]-2H-pyrrolium
Tosylate (2): A solution of 2-phenylpyrrole (2.14 g, 15 mmol) and
toluene-4-sulfonic acid (1.35 g, 7.8 mmol) in triethyl orthoacetate
(8 mL, 45 mmol) was stirred for 30 min at room temp. The solution
was diluted with EtOAc (30 mL), filtered, and the precipitated solid
was washed with EtOAc and hexane. Yield 2.65 g, 73%; m.p. 212–
1
214 °C. H NMR ([D6]DMSO, 300 MHz; mixture of 2 and 3a in a
ratio of 1:2): δ = 12.68 (s, NH; 2), 11.14 (s, NH; 3a), 8.12 (d, J =
7.2 Hz), 7.79 (d, J = 7.8 Hz), 7.74 (d, J = 7.2 Hz), 7.58 (d, J =
7.8 Hz), 7.47 (d, J = 7.2 Hz), 7.44 (d, J = 4.2 Hz), 7.36 (t), 7.1–7.2
(m), 6.54 (s), 6.26 (s), 5.42 (s, CH2; 2), 3.02 (s, CH3; 2), 2.29 (s,
CH3) ppm. C29H26N2O3S (482.60): calcd. C 72.18, H 5.43, N 5.80;
found C 72.30, H 5.31, N 5.89.
Figure 3. Normalized emission spectra of the dyes 4, 7, and 12a–
14 in CH2Cl2.
ure 1). At the same time, no fluorescence appears in these
dyes upon protonation.
1,1-Bis(5-phenyl-1H-pyrrol-2-yl)ethene (3): Triethylamine (0.5 g,
5 mmol) was added to a solution of compound 2 (0.97 g, 2 mmol)
Eur. J. Org. Chem. 2009, 3237–3243
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3241

V. P. Yakubovskyi, M. P. Shandura, Y. P. Kovtun
FULL PAPER
in EtOH (15 mL) and the reaction mixture was stirred for 30 min
at room temp. The crude product was filtered and washed with
EtOH. Yield 0.46 g, 74%; m.p. 142–144 °C. Form 3a: 1H NMR
([D6]DMSO, 300 MHz): δ = 11.18 (s, 2 H, NH), 7.74 (d, J = 7.8 Hz,
4 H, ArH), 7.35–7.39 (m, 6 H), 6.55 (s, 2 H, pyrrole H), 6.27 (s, 2
4,4-Difluoro-8-[2-(dimethylamino)ethenyl]-3,5-diphenyl-4-bora-
3a,4a-diaza-s-indacene (8): N,N-Dimethylformamide dimethyl ace-
tal (0.5 g, 4.2 mmol) was added to compound 4 (0.36 g, 1 mmol) in
Ac2O (2 mL) and the reaction mixture was heated at reflux for 2–
3 min. After cooling to room temperature, the crude product was
H, pyrrole H), 5.43 (s, 2 H, CH2) ppm. Form 3a: 1H NMR (CDCl3, filtered and washed with AcOH. Yield 0.29 g, 70 %; m.p. 249–
1
300 MHz): δ = 13.96 (br. s, 1 H, NH), 7.88 (d, J = 7.2 Hz, 4 H,
251 °C. H NMR ([D6]DMSO, 300 MHz): δ = 8.22 (d, J = 12 Hz,
ArH), 7.36–7.48 (m, 6 H, ArH), 7.20 (d, J = 4.2 Hz, 2 H, pyrrole 1 H, CH), 7.63 (d, J = 7.2 Hz, 4 H, ArH), 7.25–7.37 (m, 8 H), 6.49
H), 6.84 (d, J = 4.2 Hz, 2 H, pyrrole H), 2.56 (s, 3 H, CH3) ppm. (d, J = 3.9 Hz, 2 H, pyrrole H), 6.40 (d, J = 12 Hz, 1 H, CH), 3.42
13C NMR ([D6]DMSO, 75 MHz): δ = 106.7, 107.3, 111.0, 124.6, (s, 3 H, CH3), 3.30 (s, 3 H, CH3) ppm. 13C NMR ([D6]DMSO,
126.3, 129.1, 132.3, 133.0, 133.1, 133.2 ppm. LC–MS: m/z = 311
75 MHz): δ = 39.1, 46.6, 97.9, 116.0, 127.7, 128.2, 129.0, 135.0,
146.1, 14.4, 159.4 ppm. C25H22BF2N3 (413.27): calcd. C 72.63, H
5.33, N 10.17; found C 72.47, H 5.51, N 10.26. LC–MS: m/z 394
[M – 19]+.
[M + H]+.
4,4-Difluoro-8-methyl-3,5-diphenyl-4-bora-3a,4a-diaza-s-indacene
(4): Triethylamine (1.94 g, 15 mmol) was added to compound 3
(1.45 g, 3 mmol) in BF3·OEt2 (6 mL) and the reaction mixture was
stirred for 15 min at room temp. Then the reaction the mixture was
diluted with CH2Cl2. The mixture was washed with water
(4 ϫ 50 mL) and the organic layer was separated, dried with
Na2SO4, and the solvents evaporated to dryness. Yield 0.98 g, 91%;
General Procedure for the Synthesis of Dyes 11, 12a,b, 13–15, and
17: Triethylamine (0.65 mmol) was added to compound 4
(0.5 mmol) and the corresponding hemicyanine (0.65 mmol) in
Ac2O (2 mL) and the reaction mixture was heated at reflux for 2–
3 min. After cooling to room temperature, the crude product was
filtered and washed with AcOH.
1
m.p. 231–233 °C. H NMR ([D6]DMSO, 300 MHz): δ = 7.79–7.82
(m, 4 H, ArH), 7.72 (d, J = 4.5 Hz, 2 H, pyrrole H), 7.44–7.47 (m,
6 H, ArH), 6.83 (d, J = 4.5 Hz, 2 H, pyrrole H), 2.76 (s, 3 H,
CH3) ppm. 13C NMR (CDCl3, 75 MHz): δ = 16.5, 120.7, 127.7,
128.5, 129.8, 133.1, 137.1, 142.2, 158.6 ppm. LC–MS: m/z 340 [M –
19]+.
8-[3-(2,6-Diphenylpyran-4-ylidene)propenyl]-4,4-difluoro-3,5-diphen-
yl-4-bora-3a,4a-diaza-s-indacene (11): Yield 0.14 g, 44%; m.p. 163–
165 °C. 1H NMR ([D6]DMSO, 300 MHz): δ = 8.32 (t, J = 12.9 Hz,
1 H, CH), 8.11 (d, J = 7 Hz, 2 H, ArH), 8.02 (d, J = 7 Hz, 2 H,
ArH), 7.74 (d, J = 6.6 Hz, 5 H, ArH), 7.55–7.58 (m, 8 H, ArH),
7.27–7.45 (m, 8 H, ArH), 6.72 (d, J = 3.9 Hz, 2 H, pyrrole H), 6.37
(d, J = 12.3 Hz, 1 H, CH) ppm. 13C NMR ([D6]DMSO, 75 MHz):
δ = 104.8, 106.2, 110.0, 118.2, 118.9, 119.1, 121.3, 125.7, 126.0,
128.5, 128.9, 129.3, 129.4, 129.6, 131.2, 131.9, 132.1, 133.9, 134.5,
142.6, 143.1, 145.1, 152.7, 155.5, 155.7 ppm. LC–MS: m/z 596 [M –
19]+.
4,4-Difluoro-3,5-diphenyl-8-[2-(phenylamino)ethenyl]-4-bora-3a,4a-
diaza-s-indacene (6): Aniline (0.37 g, 4 mmol) and acetic acid
(0.5 mL) were added to a solution of compound 8 (0.082 g,
0.2 mmol; prepared as described below) in CH2Cl2 (5 mL) and the
reaction mixture was allowed to stand overnight. Then the reaction
mixture was diluted with CH2Cl2. The mixture was washed with
water (4ϫ30 mL) and the organic layer was separated, dried with
Na2SO4, and the solvents evaporated to dryness. The residue was
purified by chromatography on silica gel (eluent hexane/EtOAc,
8-[3-(1,3,3-Trimethylindolin-2-ylidene)propenyl]-4,4-difluoro-3,5-di-
phenyl-4-bora-3a,4a-diaza-s-indacene (12a): Yield 0.16 g, 60%; m.p.
242–244 °C. 1H NMR ([D6]DMSO, 300 MHz): δ = 8.31 (t, J =
12.9 Hz, 1 H, CH), 7.69 (d, J = 7.2 Hz, 4 H, ArH), 7.51 (d, J =
6.6 Hz, HetH), 7.14–7.39 (m, 12 H), 6.63 (d, J = 3.9 Hz, 2 H, pyr-
role H), 6.38 (d, J = 12.9 Hz, 1 H, CH), 3.56 (s, 3 H, NCH3), 1.65
(s, 6 H, 2 CH3) ppm. 13C NMR (CDCl3, 75 MHz): δ = 28.3, 29.7,
47.2, 99.7, 107.9, 117.2, 118.1, 121.9, 122.3, 123.7, 128.0, 128.3,
129.2, 133.9, 134.3, 139.4, 143.8, 144.7, 153.3, 166.5 ppm. LC–MS:
m/z 522 [M – 19]+.
1
4:1, then hexane/EtOAc, 1:1). Yield 0.07 g, 76%. H NMR ([D6]-
DMSO, 300 MHz): δ = 11.31 (d, J = 12 Hz, 1 H, NH), 8.46 (t, J
= 12.3 Hz, 1 H, CH), 7.69 (d, J = 7.2 Hz, 4 H, ArH), 7.33–7.45
(m, 13 H), 6.75 (d, J = 12 Hz, 1 H, CH), 6.61 (d, J = 4.5 Hz, 2 H,
pyrrole H) ppm. 13C NMR ([D6]DMSO, 75 MHz): δ = 101.3,
117.6, 123.0, 124.9, 128.3, 129.2, 130.3, 132.8, 134.4, 140.2, 145.5,
149.3, 150.2 ppm. LC–MS: m/z 442 [M – 19]+.
2-(4,4-Difluoro-3,5-diphenyl-4-bora-3a,4a-diaza-s-indacen-8-yl)-3-
(dimethylamino)propenylidene(dimethyl)ammonium Perchlorate (7):
The Vilsmeier complex was prepared by the dropwise addition of
freshly distilled POCl3 (0.27 g, 17.5 mmol) to dry N,N-dimethyl-
formamide (5 mL) with stirring and cooling in an ice bath. The
complex was warmed to room temperature and then was added
dropwise to a stirred solution of compound 4 (0.18 g, 0.5 mmol) in
dry DMF (3 mL). The mixture was stirred at 60 °C until comple-
tion of the reaction (50–60 min). The mixture was poured into ice–
water and extracted with CH2Cl2 (3ϫ25 mL). The combined ex-
tracts were washed with water and dried with anhydrous Na2SO4.
The solvent was removed under reduced pressure and the residue
was dissolved in iPrOH (25 mL). Perchloric acid (3 mL) was added
to the solution and left to stand overnight. The crude product was
filtered and washed with iPrOH. Yield 0.1 g, 34 %. 1H NMR
(CDCl3, 300 MHz): δ = 8.22 (s, 2 H, CH), 7.85–7.87 (m, 4 H, ArH),
8-[4-(1,3,3-Trimethylindolin-2-ylidene)-1,3-butadienyl]-4,4-difluoro-
3,5-diphenyl-4-bora-3a,4a-diaza-s-indacene (12b): Yield 0.18 g,
1
64%; m.p. 215–217 °C. H NMR (CDCl3, 300 MHz): δ = 7.82 (d,
J = 6.9 Hz, 4 H, ArH), 7.54 (t, J = 14.1 Hz, 1 H, CH), 7.2–7.42
(m, 13 H), 6.95 (t, J = 8.1 Hz, 1 H, CH), 6.87 (d, J = 14.4 Hz, 1
H, CH), 6.74 (d, J = 8.1 Hz, 1 H, CH), 6.58 (d, J = 3.9 Hz, 2 H,
pyrrole H), 6.37 (t, J = 12.3 Hz, 1 H, CH), 3.25 (s, 3 H, NCH3),
1.64 (s, 6 H, CH3) ppm. 13C NMR (CDCl3, 300 MHz): δ = 28.4,
29.5, 46.7, 97.9, 107.2, 118.7, 120.0, 121.3, 121.8, 125.1, 125.5,
128.0, 128.3, 128.6, 129.3, 133.7, 134.7, 139.4, 140.5, 142.6, 144.3,
148.1, 154.5, 162.9 ppm. LC–MS: m/z = 567 [M]+.
8-[3-(3-Methyl-3H-benzothiazol-2-ylidene)propenyl]-4,4-difluoro-
3,5-diphenyl-4-bora-3a,4a-diaza-s-indacene (13): Yield 0.16 g, 62%;
1
m.p. 226–229 °C. H NMR ([D6]DMSO, 300 MHz): δ = 8.09 (t, J
= 13.2 Hz, 1 H, CH), 8.02 (d, J = 8 Hz, 1 H, HetH), 7.76 (d, J =
7.44–7.47 (m, 6 H, ArH), 7.17 (d, J = 3.8 Hz, 2 H, pyrrole H), 6.75 8.1 Hz, 1 H, HetH), 7.66 (d, J = 6.9 Hz, 4 H, ArH), 7.57 (t, J =
(d, J = 3.8 Hz, 2 H, pyrrole H), 3.44 (s, 6 H, 2 CH3), 2.97 (s, 6 H, 8.1 Hz, 1 H, HetH), 7.26–7.45 (m, 8 H), 7.12–7.18 (m, 3 H), 6.84
2 CH3) ppm. 13C NMR ([D6]DMSO, 75 MHz): δ = 49.3, 122.8,
128.9, 130.6, 131.4, 132.1, 138.4, 159.8, 165.1 ppm. LC–MS: m/z
551 [M – 19]+.
(d, J = 13.2 Hz, 1 H, CH), 6.52 (d, J = 4.2 Hz, 2 H, pyrrole H),
3.89 (s, 3 H, CH3) ppm. 13C NMR ([D6]DMSO, 75 MHz): δ = 34.0,
104.0, 114.1, 114.8, 116.3, 119.3, 123.5, 125.6, 125.9, 127.7, 128.2,
3242
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 3237–3243

Boradipyrromethenecyanines
[2] For reviews, see: a) J. Fabian, H. Nakazumi, M. Matsuoka,
Chem. Rev. 1992, 92, 1197–1226; b) S. Dahne, U. Resch-
Genger, O. S. Wolfbeis (Eds.), Near-Infrared Dyes for High
Technology Application, Kluwer Academic, Dordrecht, 1998.
[3] a) K. Rurack, M. Kollmannsberger, J. Daub, New J. Chem.
2001, 25, 289–292; b) A. Coskun, E. U. Akkaya, Tetrahedron
Lett. 2004, 45, 4947–4949; c) T. Rohald, W. Qin, N. Boens, W.
Dehaen, Eur. J. Org. Chem. 2006, 4658–4663.
[4] a) K. Rurack, M. Kollmannsberger, J. Daub, Angew. Chem. Int.
Ed. 2001, 40, 385–387; b) Y.-H. Yu, A. B. Descalzo, Z. Shen,
H. Rohr, Q. Li, Y.-W. Wang, M. Spieles, Y.-Z. Li, K. Rurack,
X.-Z. You, Chem. Asian J. 2006, 1–2, 176–187; c) N. Saki, T.
Dinc, E. U. Akkaya, Tetrahedron 2006, 62, 2721–2725; d) X.
Peng, J. Du, J. Fan, J. Wang, Y. Wu, J. Zhao, S. Sun, T. Xu, J.
Am. Chem. Soc. 2007, 129, 1500–1501.
128.5, 129.0, 129.4, 133.3, 135.0, 140.9, 142.5, 146.9, 147.7,
165.3 ppm. LC–MS: m/z = 512 [M – 19]+.
8-[3-(1-Methyl-1H-quinolin-2-ylidene)propenyl]-4,4-difluoro-3,5-di-
phenyl-4-bora-3a,4a-diaza-s-indacene (14): The product was puri-
fied by chromatography on silica gel (100 mesh, CHCl3) to give the
pure dye. Yield 0.07 g, 26%; m.p. Ͼ250 °C. 1H NMR ([D6]DMSO,
300 MHz): δ = 8.51 (t, J = 13.2 Hz, 1 H, CH), 8.19 (m, 2 H, HetH),
8.06 (d, J = 9.3 Hz, HetH), 7.95 (d, J = 7.8 Hz, 1 H, HetH), 7.83
(t, J = 7.5 Hz, 1 H, HetH), 7.65 (d, J = 7.2 Hz, 4 H, ArH), 7.55
(t, J = 6.9 Hz, 1 H, HetH), 7.32 (t, J = 7.8 Hz, 4 H, ArH), 7.18–
7.28 (m, 3 H), 7.13 (d, J = 3.6 Hz, 2 H, pyrrole H), 6.91 (d, J =
12.9 Hz, 1 H, CH), 6.46 (d, J = 3.6 Hz, 2 H, pyrrole H), 4.11 (s, 3
H, CH3) ppm. LC–MS: m/z = 507 [M – 19]+.
[5] a) T. Werner, C. Huber, S. Heinl, M. Kollmannsberger, J. Daub,
O. Wolfbeis, Fresenius’ J. Anal. Chem. 1997, 359, 150–154; b)
M. Kollmannsberger, T. Gareis, S. Heils, J. Brue, J. Daub, An-
gew. Chem. Int. Ed. Engl. 1997, 36, 1333–1335; c) M.
Kollmannsberger, K. Rurack, U. Resch-Genger, J. Daub, J.
Phys. Chem. A 1998, 102, 10211–10220; d) K. Rurack, M.
Kollmannsberger, U. Resch-Genger, J. Daub, J. Am. Chem.
Soc. 2000, 122, 968–969; e) Z. Shen, H. Rohn, K. Rurak, H.
Uno, M. Spieles, B. Schulz, G. Reck, N. Ono, Chem. Eur. J.
2004, 10, 4853–4871.
[6] T. Venkateshwar Goud, A. Tutar, J.-F. Biellmann, Tetrahedron
2006, 62, 5084–5091.
[7] Th. Severin, B. Bruck, Chem. Ber. 1965, 98, 3847–3853.
[8] H. Hie, D. A. Lee, D. M. Wallace, M. O. Senge, K. M. Smith,
J. Org. Chem. 1996, 61, 8508–8517.
8-[3-(1-Butyl-1H-benzo[c,d]indol-2-ylidene)propenyl]-4,4-difluoro-
3,5-diphenyl-4-bora-3a,4a-diaza-s-indacene (15): The product was
dissolved in CH2Cl2 and purified by flash column chromatography
(CH2Cl2). Yield 0.18 g, 60 %; m.p. 245–247 °C. 1H NMR ([D6]-
DMSO, 300 MHz): δ = 8.53 (t, J = 12.5 Hz, 1 H, CH), 8.08 (d, J
= 6.9 Hz, 1 H, HetH), 8.02 (d, J = 8.1 Hz, 1 H, HetH), 7.75–7.8
(m, 6 H), 7.52–7.59 (m, 6 H), 7.37–7.45 (m, 6 H), 7.23 (d, J =
6.3 Hz, 1 H, CH), 6.81 (d, J = 12.6 Hz, 1 H, CH), 6.75 (d, J =
4.2 Hz, 2 H, pyrrole H), 4.17 (q, 2 H, CH2), 1.8 (q, 2 H, CH2),
1.48 (q, 2 H, CH2), 0.96 (t, J = 7.5 Hz, 3 H, CH3) ppm. 13C NMR
([D6]DMSO, 75 MHz): δ = 14.3, 20.3, 30.7, 43.2, 79.7, 118.9, 124.7,
125.8, 128.5, 128.7, 129.2, 134.0, 151.9 ppm. LC–MS: m/z 572 [M –
19]+.
[9] a) A. Treibs, K. Hintermeier, Justus Liebigs Ann. Chem. 1958,
592, 11–25; b) A. Treibs, F. Reisam, Justus Liebigs Ann. Chem.
1958, 611, 205–223.
1-Methyl-4-[4,4-bis(5-phenyl-1H-pyrrol-2-yl)-1,3-butadienyl]quinoli-
nium p-Toluenesulfonate (17): Yield 0.08 g, 23%; m.p. Ͼ250 °C.
ˇ
[10] a) J. Ciernik, Collect. Czech. Chem. Commun. 1972, 37, 2273–
2281; b) M. Shandura, Ye. Poronik, Yu. Kovtun, Dyes Pigm.
2007, 73, 25–30.
[11] A. Kulinich, N. Derevianko, A. Ishchenko, Russ. Chem. Bull.
2005, 54, 2820–2830.
[12] a) H. Sunahara, Y. Urano, H. Kojima, T. Nagano, J. Am.
Chem. Soc. 2007, 129, 5597–5604; b) Y. Gabe, Y. Urano, K.
Kikuchi, H. Kojima, T. Nagano, J. Am. Chem. Soc. 2004, 126,
3357–3367.
UV/Vis (CH3CN
+
5% AcOH): λmax (ε)
=
620 nm
(39000 –1 cm–1). 1H NMR ([D6]DMSO, 300 MHz): δ = 11.76 (s,
2H NH), 8.91 (d, J = 6 Hz, 1 H, ArH), 8.78 (d, J = 15 Hz, 1 H,
CH),8.31 (d, J = 9 Hz, 1 H, ArH), 8.08–8.22 (m, 2 H), 7.75–8.02
(m, 7 H), 7.39–7.5 (m, 5 H), 7.25–7.33 (m, 3 H), 7.11 (d, J = 6 Hz,
2 H, pyrrole H), 6.8 (d, J = 12 Hz, 2 H, pyrrole H), 6.58 (s, 1 H,
ArH), 6.48 (s, 1 H, ArH), 4.4 (s, 3 H, CH3), 2.3 (s, 3 H, CH3) ppm.
[13] M. Shandura, Ye. Poronik, Yu. Kovtun, Dyes Pigm. 2005, 71,
171–177.
[1] For recent reviews, see: a) A. Louder, K. Burgess, Chem. Rev.
2007, 107, 4891–4932; b) G. Ulrich, R. Ziessel, A. Harriman,
Angew. Chem. Int. Ed. 2008, 47, 1184–1201; c) T. E. Wood, A.
Thompson, Chem. Rev. 2007, 107, 1831–1861; d) R. P.Haug-
land, The Handbook. A Guide to Fluorescence Probes and La-
beling Technologies, 10th ed., Invitrogen, Eugene, OR, 2005.
[14] F. M. Hamer, The cyanine dyes and related compounds, Intersci-
ence (Wiley), New York, 1964.
[15] A. Gerasov, M. Shandura, Yu. Kovtun, Dyes Pigm. 2008, 77,
598–607.
Received: February 24, 2009
Published Online: May 14, 2009
Eur. J. Org. Chem. 2009, 3237–3243
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3243