3,5-Bis(benzothiazolyl)-substituted BODIPY dyes

Article abstract of DOI:10.1002/ejoc.201000084

A number of new BODIPY dyes with benzothiazolyl substituents have been synthesized that exhibit long-wavelength absorption and act as strong fluorophores. The optical properties of the dyes were studied by using spectroscopic methods and quantum-chemical calculations. The structural peculiarities of the dyes obtained, in comparison to their analogues, were studied by X-ray analysis.

Full text of DOI:10.1002/ejoc.201000084

FULL PAPER
DOI: 10.1002/ejoc.201000084
3,5-Bis(benzothiazolyl)-Substituted BODIPY Dyes
Yevgen M. Poronik,[a] Viktor P. Yakubovskyi,[a] Mykola P. Shandura,[a] Yuriy G. Vlasenko,[a]
Alexander N. Chernega,[a] and Yuriy P. Kovtun*[a]
Keywords: BODIPY / Density functional calculations / Dyes/pigments / Fluorescence
A number of new BODIPY dyes with benzothiazolyl substitu-
ents have been synthesized that exhibit long-wavelength ab-
sorption and act as strong fluorophores. The optical proper-
ties of the dyes were studied by using spectroscopic methods
and quantum-chemical calculations. The structural peculiari-
ties of the dyes obtained, in comparison to their analogues,
were studied by X-ray analysis.
drance on changing from 6- to 5-membered rings. There-
fore, one of the main factors that affect the optical proper-
ties of such dyes is the efficient conjugation of the BODIPY
core with the π-system of the substituents; this can be partly
confirmed by comparing dyes 2 and 5.[3d]
Introduction
Borondipyrromethene dyes (4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene, BODIPY, BDP) have found numerous ap-
plications in biochemistry and molecular biology owing to
their excellent thermal, chemical, and photochemical sta-
bility, high molar absorptivity, high fluorescence quantum
yield and low sensitivity to both solvent polarity and pH.[1]
However, because the absorption maxima of the majority
of BODIPYs are below 600 nm, and because long-wave-
length dyes are important for both basic and applied re-
search,[2] many synthetic approaches have been developed
to modify the BODIPY core to obtain structures absorbing
at longer wavelengths.[1d] One of the most promising ap-
proaches to the modification of BODIPY is its peripheral
functionalization.
Substitution of BODIPY at the 3- and 5-positions with
aryl units usually results in a redshift of the absorption
maximum, and there are many 3,5-diaryl-substituted dyes
described in the literature.[3] In comparison to dye 1,[3a] the
bathochromic effect in compound 2[3b] is approximately
50 nm (Scheme 1). However, only a few BODIPYs substi-
tuted with heterocyclic rings at the 3- and 5-positions are
known.[4] The first representative, dye 3, which is substi-
tuted with benzothiophene moieties,[4a] shows a redshift of
the absorption maximum of near 30 nm, compared to
BODIPY 2.
This paper addresses the synthesis and study of bis-
(benzothiazolyl)-substituted BODIPY dyes.
Results and Discussion
The parent compound that was chosen for the synthesis
of the desired dyes, was 2-(pyrrol-2-yl)benzothiazole (6).[5]
According to the literature,[5a] it has been synthesized from
N-(ethoxycarbonyl)pyrrole-2-carbothioamide, and more re-
cently[5b] pyrrole 6 was prepared starting from 2-formylpyr-
role by using Sc(OTf)3 as the catalyst. We succeeded in the
synthesis of derivative 6 in good yield (91%) from accessible
2-cyanopyrrole[6] on a preparative scale (Scheme 2).
The condensation reaction of pyrroles with aromatic al-
dehydes occurred readily,[1,3] however, when electron-ac-
ceptor substituents were present on the pyrrole ring [e.g., 2-
(pyrrol-2-yl)pyridine] drastic reaction conditions were re-
quired.[7] In the latter case, the product was prepared in
poor yield and involved a tedious purification stage. We
found that heating of pyrrole 6 with benzaldehyde and 4-
methoxybenzaldehyde, in the presence of catalytic amounts
of acetic acid and aniline, gives rise to compounds 7a and
7b in good yields (Scheme 3).
The oxidation of compounds 7a and 7b with 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) led to di-
pyrromethenes 8a and 8b, respectively. Because the reaction
between (benzothiazolyl)pyrrole 6 and 4-hydroxybenzalde-
hyde did not succeed, dipyrromethene 8c was obtained by
cleaving methoxy derivative 8b with hydrobromic acid in
acetic acid. Compounds 8a–c were treated with boron tri-
fluoride–diethyl ether in the presence of Hünig’s base to
yield 3,5-bis(benzothiazolyl)-substituted BODIPY dyes 9a–
c (Scheme 3).
Another example is dye 4, with thienyl substituents in
the BODIPY core.[4b] As shown in Scheme 1, dye 4 demon-
strates a 69 nm redshift in comparison to 2. Given that the
electronic properties of thiophene rings are very similar to
those of the phenyl rings, the reason for such spectral differ-
ences could be explained in terms of the reduced steric hin-
[a] Institute of Organic Chemistry, National Academy of Sciences
of Ukraine,
5 Murmanska str., 02660 Kyiv, Ukraine
Fax: +380-44-5732643
E-mail: kovtun@ioch.kiev.ua
2746
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2746–2752

3,5-Bis(benzothiazolyl)-Substituted BODIPY Dyes
Scheme 1.
Scheme 2. Reagents and conditions: (i) 140 °C, 2 h.
For all BODIPYs synthesized, an intensive absorption
Besides long-wavelength absorption bands, dyes 9a–c
band near 620 nm was observed that showed almost no de- also exhibited relatively intensive short-wavelength absorp-
pendence on the solvent polarity. Molar absorption coeffi- tion bands (Figure 1).
cients of the dyes were in the range of 40000–
For a better understanding of the origin of the electronic
57000 –1 cm–1, which is comparable with another transitions, DFT/B3LYP/6-31 G(dp) calculations for dye 9b
BODIPYs.[1,3] Dyes 9a–c are fluorophores and exhibit were performed. The Firefly QC package,[9a] which is par-
strong emission near 640 nm (Figure 1, Table 1). Fluores- tially based on the GAMESS (US)[9b] source code, was used
cent quantum yields (Φ) are high and reach maximum val- to perform the calculations.
ues for 9b.
Analysis of the calculated absorption spectrum of dye 9b
Dye 9c, containing a hydroxy group at the terminal posi- shows that the long-wavelength band corresponds to the
tion, was further explored for the purpose of altering its electronic transition S0ǞS1. The short-wavelength band, lo-
optical properties by treatment with basic reagents. On ad- cated in the region of 460 nm, bears three electronic transi-
dition of excess pyridine to a solution of 9c, the absorption tions: S0ǞS2, S0ǞS3, and S0ǞS4, each roughly composed,
spectrum hardly changed, whereas the fluorescence of 9c to a considerable degree, by three transitions (H-1ǞL, H-
drastically decreased (Table 1). Similar effects were ob- 2ǞL, and H-3ǞL). HOMO–1, HOMO–2, and HOMO–3
served for other BODIPY hydroxy derivatives.[8]
are local orbitals that lie very close to one another in energy
Eur. J. Org. Chem. 2010, 2746–2752
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2747

Yu. P. Kovtun et al.
FULL PAPER
Figure 1. Absorption (––), fluorescence (----), and excitation anisot-
ropy (᭺) spectra of 9b in glycerol.
Table 1. Optical properties of the synthesized dyes.
ε·10–3
λem
Φ
[a]
[b]
Entry Dye
Solvent
λabs
[nm]
[–1cm–1]
[nm]
1
2
3
4
5
6
7
8
9a
9a
9a
9b
9b
9b
9c
9c
EtOH
CH2Cl2
DMF
619
403
623
399
620
406
616
460
624
460
617
468
618
448
616
48
13
48
14
40
12
47
18
57
21
44
18
54
18
54
639
0.43
0.86
0.66
0.94
1.00
0.81
0.53
0.11
643
642
637
643
641
639
638
EtOH
CH2Cl2
DMF
CH2Cl2
CH2Cl2 + Py
[a] c = 2ϫ10–5 . [b] Excitation at 550 nm.
Table 2. Calculated energy of molecular orbitals for dye 9b.
HOMO–3 HOMO–2 HOMO–1 HOMO LUMO
[eV]
[eV]
[eV]
[eV]
[eV]
9b
–6.26
–6.25
–6.18
–5.44
–3.06
Scheme 3. Reagents and conditions: (i) aniline, ArCHO, acetic
acid, 140 °C, 15 h; (ii) DDQ, CH2Cl2, room temp., 30 min; (iii)
BF3·Et2O, iPr2EtN, CH2Cl2, room temp., 1 h; (iv) R = OCH3, HBr
48%, acetic acid, reflux, 16 h; (v) BF3·Et2O, NiPr2Et, CH2Cl2,
room temp., 3 h.
the transition S0ǞS1. The anisotropy in both minimums
was –0.16 and, hence, according to the equation r =
(3cos2β – 1)/5,[10] the angles amount to approximately 75°
each.
To analyze the structural peculiarities of the synthesized
(Table 2); H-2 and H-3 are degenerate, with the electron dyes and their known analogous, the molecular structure of
density mainly localized on the benzothiazole substituent compound 9b was determined by single-crystal X-ray dif-
(Table 2, Figure 2).
fraction. A perspective view of molecule 9b is given in Fig-
The position of highest electronic transitions in the ure 3. The central six-membered ring B(1)N(3)C(13)C(12)-
short-wavelength region is illustrated by the fluorescence C(11)N(2) is not planar (the maximum deviation from the
excitation anisotropy spectrum (Figure 1). Two minimums least-square plane is 0.075 Å) and has a semi-boat confor-
at approximately 460 and 330 nm, were observed for dye 9b mation. The heterocycles C(8–11)N(2) and C(13–16)N(3)
in glycerol solution that correspond to electronic transitions are planar to within 0.001 Å, whereas the C(1–7)S(1)N(1)
with dipole moments at an angle to the dipole moment of and C(17–23)S(2)N(4) substituents are twisted around the
2748
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2746–2752

3,5-Bis(benzothiazolyl)-Substituted BODIPY Dyes
Figure 2. Molecular orbitals and electronic transitions for dye 9b.
central C(8–16)N(3)B(1)N(2) system by 43.86° and 50.41°,
To clarify the relationship between the structure and op-
respectively. Due to intramolecular steric interactions, sub- tical properties of the synthesized BODIPY, we have ana-
stituents C(1–7)S(1)N(1) and C(17–23)S(2)N(4) are almost lyzed the calculated dihedral angles around the bonds be-
orthogonal (the dihedral angle is 85.55°). The dihedral an- tween the BODIPY chromophore and the substituents for
gle between the C(24–29) and C(8–16)N(3)B(1)N(2) sys- a series of BODIPYs (2, 4, 5, and 9b).
tems is 48.43°.
In the pair of compounds 2 and 5, the substituents are
According to the literature,[4b] the dihedral angles be- equivalent in their electronic properties. The only difference
tween the BODIPY chromophore and the thienyl substitu- being that in dye 5 the rotation around the aryl–pyrrole
ents for dye 4 in the crystal state (Scheme 1) are 25.2° and bond is prevented by the ethylene bridge. For this pair, the
21.6°, respectively, leaving the sulfur atoms on the edges DFT calculations give dihedral angles of 34.6° and 18.0°,
turned out. Unlike compound 4, the X-ray analysis of respectively (Table 3), and the absorption band of dye 5 is
BODIPY 9b reveals that the sulfur atoms of the benzothia- 80 nm redshifted in comparison to 2.
zolyl substituents are turned towards the fluorine atom,
For dyes 4 and 9b, the calculations give the following
with interatomic distances of 2.92 Å and 3.10 Å, respec- conformations with the lowest energy: the thienyl substitu-
tively, which is shorter than the sum of sulfur and fluorine ents and the BODIPY system in 4 subtend an angle of
van der Waals radii.[11a] There is a report in the literature 22.1°, with the sulfur atoms twisted into different direc-
that refers to S–F intramolecular interactions[11b] and, evi- tions; in the case of 9b, the sulfur atoms are turned towards
dently, a weak intramolecular bonding of a similar type the fluorine atoms, the dihedral angles amounting to ap-
may also occur in this case.
proximately 16°.
However, the dihedral angles for such BODIPY dyes in
The fact that the optical properties of BODIPYs 4 and
the solid state cannot be responsible for the spectral proper- 9b are very similar can be explained on the basis of two
ties in solution due to the strong dependence upon the crys- factors: The first factor is the dihedral angle between the
tal packing (Figure 4).[3c,4b]
central framework and the substituents, which – as illus-
Since the synthesized dyes, like the majority of BODI- trated by the difference between the pair of 2 and 5 – plays
PYs, show very weak solvatochromism,[1,3] the optimized a crucial role. The second factor is the electronic effect of
calculated geometry in the gas phase could adequately the substituents, which is difficult to quantify correctly, ow-
model the optical properties of such dyes in solution.
ing to the different dihedral angles; however, the thienyl
Eur. J. Org. Chem. 2010, 2746–2752
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2749

Yu. P. Kovtun et al.
FULL PAPER
Conclusions
A synthesis of 2-(1H-pyrrol-2-yl)benzothiazole has been
developed that enabled a number of new BODIPY dyes
with benzothiazolyl substituents to be generated. Although
the molar absorption coefficients of the dyes are moderate,
they exhibit intense fluorescence (up to 100%). The dyes
obtained have relatively intense short-wavelength absorp-
tion bands arising from the three highest electronic transi-
tions. The substitution of BODIPY with benzothiazolyl
moieties leads to exactly the same optical properties as ob-
served for thienyl-substituted BODIPY. Unlike BODIPY 4,
in case of dye 9b, S–F intramolecular bonding occurs in the
solid state.
Experimental Section
General: Electronic absorption spectra were recorded with a Shim-
adzu UV-3100 spectrophotometer. Emission spectra were recorded
with a Solar 2303M instrument. The fluorescence quantum yields
were determined by using indodicarbocyanine iodide (Φ = 0.25,
EtOH) as a reference according to the literature.[12] 1H NMR spec-
tra were recorded with Varian VXR-300 and Bruker Avance DRX
500 instruments. LC/MS spectra were recorded with a chromatog-
raphy/mass spectrometric system that consisted of an Agilent 1100
Series high-performance liquid chromatograph equipped with an
Agilent LC\MSD SL diode-matrix and mass-selective detector.
Figure 3. Molecular structure of compound 9b. Selected bond
lengths [Å] and angles [°]: N(2)–C(8) 1.358(4), N(2)–B(1) 1.575(2),
N(3)–C(16) 1.363(4), N(3)–B(1) 1.553(2), C(1)–C(8) 1.461(4), C(8)–
C(9) 1.402(4), C(9)–C(10) 1.357(4), C(10)–C(11) 1.414(4), C(11)–
C(12) 1.399(4), C(12)–C(13) 1.401(4), C(12)–C(24) 1.482(4), C(13)–
C(14) 1.402(4), C(14)–C(15) 1.362(5), C(15)–C(16) 1.393(4), C(16)–
C(17) 1.457(4); C(27)–O(1)–C(30) 117.8(3), C(8)–N(2)–B(1)
128.2(2), C(16)–N(3)–B(1) 127.1(2), C(11)–C(12)–C(24) 121.7(3),
C(13)–C(12)–C(24) 118.2(3), N(2)–C(8)–C(1) 127.1(3), C(1)–C(8)–
C(9) 123.5(3), N(3)–C(16)–C(17) 127.0(3), C(15)–C(16)–C(17)
123.5(3).
2-(1H-Pyrrol-2-yl)benzothiazole (6): A mixture of 2-cyanopyrrole
(13.7 g, 0.15 mol) and 2-aminothiophenole (20 g, 0.16 mol) was
heated at 135–140 °C for 2 h. After cooling, the solid was filtered
and washed with hexane and iPrOH to give the title compound
(27 g, 90.6%); m.p. 155–156 °C (CCl4) (ref.[5a] 167–168 °C).
C11H8N2S (200.26): calcd. C 65.97, H 4.03, N 13.99; found C 66.09,
H 4.08, N 13.91. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 6.34 (dd,
3JH,H = 2.4, 2.7 Hz, 1 H, py-H4), 6.90 (br. s, 1 H, py-H5), 6.95 (br.
3
s, 1 H, py-H3), 7.33 (t, JH,H = 7.8 Hz, 1 H, benzo-H5), 7.44 (t,
3
3JH,H = 7.5 Hz, 1 H, benzo-H6), 7.85 (d, JH,H = 7.5 Hz, 1 H,
3
benzo-H7), 7.91 (d, JH,H = 8.1 Hz, 1 H, benzo-H4), 10.76 (br. s, 1
H, NH) ppm.
1,9-Bis(2-benzothiazolyl)-5-phenyl-5,10-dihydrodipyrrin (7a): A mix-
ture of compound
6 (4 g, 0.02 mol), benzaldehyde (1.18 g,
0.011 mol), acetic acid (1 g, 0.017 mol), and aniline (0.5 g,
0.005 mol) was heated at 140 °C under a flow of argon for 15 h.
After cooling, the product was solidified by the addition of acetoni-
trile and washed with toluene to give compound 7a (3.36 g, 69%);
m.p. 226–228 °C (toluene). C29H20N4S2 (488.64): calcd. C 71.28, H
4.13, N 11.47; found C 71.06, H 4.10, N 11.58. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 5.20 (br. s, 3 H, PhCH, 2 py-H),
6.55 (br. s, 2 H, py-H), 6.96–7.10 (m, 2 H, ArH), 7.15–7.35 (m, 7
Figure 4. Crystal packing of compound 9b.
3
H, 4 benzo-H, 3 ArH), 7.70 (d, JH,H = 7.5 Hz, 2 H, benzo-H),
3
7.80 (d, JH,H = 8.7 Hz, 2 H, benzo-H), 11.30 (br. s, 2 H, NH)
Table 3. Calculated bond lengths and dihedral angles between
BODIPY core and substituent in α-position.
ppm.
1,9-Bis(2-benzothiazolyl)-5-(4-methoxyphenyl)-5,10-dihydrodipyrrin
(7b): The product was synthesized as for 7a. Yield: 56%; m.p. 213–
214 °C (toluene). C30H22N4OS2 (518.66): calcd. C 69.47, H 4.28, N
10.80; found C 69.34, H 4.19, N 10.84. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 3.74 (s, 3 H, OCH3), 5.13 (s, 1 H, ArCH), 5.22
2
4
5
9b
Bond length (B3LYP) [Å]
Dihedral angle [°]
1.472
34.6
1.448
22.1
1.463
18.0
1.458
16.1
3
(br. s, 2 H, py-H), 6.52 (br. s, 2 H, py-H), 6.68 (d, JH,H = 9.3 Hz,
3
substituent probably has a larger polar effect. In the pair of
dyes 4 and 9b the combination of these factors results in
almost equal optical properties.
2 H, ArH), 6.90 (d, JH,H = 8.4 Hz, 2 H, ArH), 7.15–7.35 (m, 4 H,
3
3
benzo-H), 7.66 (d, JH,H = 7.5 Hz, 2 H, benzo-H), 7.77 (d, JH,H
= 9.0 Hz, 2 H, benzo-H), 11.23 (br. s, 2 H, NH) ppm.
2750
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2746–2752

3,5-Bis(benzothiazolyl)-Substituted BODIPY Dyes
1,9-Bis(2-benzothiazolyl)-5-phenyldipyrrin (8a): To a stirred solution
of compound 7a (0.75 g, 1.5 mmol) in CH2Cl2 (750 mL) at room
temp., DDQ (0.37 g, 1.6 mmol) was added. After 15 min, the solu-
tion was filtered to remove solid material. The solvent was distilled
off to afford 8a (0.74 g, 100%); m.p. 243 °C (toluene). C29H18N4S2
(486.62): calcd. C 71.58, H 3.73, N 11.51; found C 71.85, H 3.81,
3,5-Bis(2-benzothiazolyl)-4,4-difluoro-8-(4-hydroxyphenyl)-4-bora-
3a,4a-diaza-s-indacene (9c): Compound 8c (0.3 g, 0.6 mmol) was
suspended in anhydrous CH2Cl2 (300 mL), and a solution of boron
trifluoride–diethyl ether (1.42 g, 10 mmol) in CH2Cl2 (20 mL) was
added dropwise. The mixture was stirred for 1 h, then a solution
of Hünig’s base (1.1 g, 8.5 mmol) in CH2Cl2 (20 mL) was added
dropwise to the resulting mixture. The solution was stirred for 2 h,
and the solvent was distilled off. The residue was purified by
chromatography on silica gel by using ethyl acetate as eluent. The
solution was concentrated in vacuo almost to dryness, and then
diluted with an equal volume of hexane. The precipitate was filtered
to afford 9c (0.13 g, 39%); m.p. 205 °C (dec.). C29H17BF2N4OS2
(550.42): calcd. C 63.28, H 3.11, N 10.18; found C 63.61, H 3.23,
N 10.29. 1H NMR (300 MHz, [D6]DMSO, 25 °C): δ = 7.05 (d,
1
3
N 11.66. H NMR (300 MHz, CDCl3, 25 °C): δ = 6.81 (d, JH,H
=
3
4.2 Hz, 2 H, py-H), 7.18 (d, JH,H = 4.2 Hz, 2 H, py-H), 7.45–7.65
3
(m, 9 H, 5 ArH, 4 benzo-H), 8.03 (d, JH,H = 8.1 Hz, 2 H, benzo-
3
H), 8.17 (d, JH,H = 7.8 Hz, 2 H, benzo-H) ppm. MS (APCI): m/z
= 487 [M + H]+.
1,9-Bis(2-benzothiazolyl)-5-(4-methoxyphenyl)dipyrrin (8b): The
product was synthesized as for 8a. Yield: 90%; m.p. 208–209 °C
(toluene). C30H20N4OS2 (516.65): calcd. C 69.74, H 3.90, N 10.84;
found C 69.63, H 3.92, N 11.01. 1H NMR (300 MHz, CDCl3,
3
3JH,H = 7.5 Hz, 2 H, ArH), 7.15 (d, JH,H = 4.5 Hz, 2 H, py-H),
3
7.47 (d, JH,H = 4.5 Hz, 2 H, py-H), 7.50–7.70 (m, 6 H, 2 ArH +
3
25 °C): δ = 3.90 (s, 3 H, OCH3), 6.83 (d, JH,H = 4.2 Hz, 2 H, py-
3
3
4 benzo-H), 8.17 (d, JH,H = 7.5 Hz, 2 H, benzo-H), 8.26 (d, JH,H
= 8.1 Hz, 2 H, benzo-H), 10.44 (s, 1 H, OH) ppm. 19F NMR
(282 MHz, [D6]DMSO, CFCl3): δ = –131.36 (m) ppm. MS (APCI):
m/z = 503 [M – BF2].
3
3
H), 7.02 (d, JH,H = 8.7 Hz, 2 H, ArH), 7.16 (d, JH,H = 4.2 Hz, 2
3
H, py-H), 7.44 (t, JH,H = 7.5 Hz, 2 H, benzo-H), 7.48–7.58 (m, 4
H, 2 ArH + 2 benzo-H), 7.98 (d, JH,H = 8.1 Hz, 2 H, benzo-H),
3
3
8.13 (d, JH,H = 8.1 Hz, 2 H, benzo-H) ppm. MS (APCI): m/z =
517 [M + H]+.
X-ray Structure Determination for 9b: Crystal data:
¯
1,9-Bis(2-benzothiazolyl)-5-(4-hydroxyphenyl)dipyrrin (8c): A solu-
tion of 8b (1.4 g, 2.7 mmol) and hydrobromic acid (46%, 30 mL)
in acetic acid (140 mL) was refluxed for 16 h. The reaction mixture
was diluted with an equal volume of water, and aqueous ammonia
(25 mL) was added. The precipitate was filtered off to give the
crude material (0.89 g). Additional product (0.34 g) was obtained
from the mother liquor. The crude product was recrystallized from
acetic acid to afford 8c (0.87 g, 64%); m.p. 255–256 °C (HOAc).
C29H18N4OS2 (502.62): calcd. C 69.30, H 3.61, N 11.15; found C
C30H19B1F2N4O1S2; M = 564.45; system: triclinic; space group: P1
(no. 2); unit-cell dimensions: a = 6.712(2), b = 12.055(3), c =
15.570(5) Å, α = 82.844(8), β = 87.078(9), γ = 88.868(8)°; V =
1248.2(6) Å3;
Z = µ =
2; calculated density: 1.502 gcm–3;
0.263 mm–1; F(000) = 580; crystal size ca. 0.10ϫ0.20ϫ0.50 mm.
All crystallographic measurements were performed at 123 K with
a Bruker Smart Apex II diffractometer operating in the ω- and φ-
scan modes. The cell parameters were obtained from the least-
squares treatment of 2358 reflections in the θ range of 2.6–21.6°.
The intensity data were collected within the range of
2.1°ՅθՅ26.4° by using Mo-Kα radiation (λ = 0.71078 Å). The
intensities of 10821 reflections were collected (4832 unique reflec-
tions, Rint = 0.001). Data were corrected for Lorentz and polariza-
tion effects. The structure was solved by direct methods and refined
by the full-matrix least-squares technique in the anisotropic
approximation for non-hydrogen atoms by using the SHELXS97
and SHELXL97 programs[13,14] and CRYSTALS program pack-
age.[15] SADABS absorption correction was applied.[16] In the re-
finement, 4832 reflections [2429 reflections with IՆ3σ(I)] were
used. Convergence was obtained at R1 = 0.0372 and wR2 = 0.0359,
GOF = 1.165 (352 parameters; observed/variable ratio 6.90; largest
and smallest peaks in the final difference map 0.24 and –0.25 e/Å3).
In the refinement, the Chebychev weighting scheme[17] was used
(weighting coefficients: 0.924, –0.734, 0.756, –0.302, 0.136).
CCDC-755495 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
1
69.22, H 3.58, N 11.19. H NMR (500 MHz, [D6]DMSO, 25 °C):
3
3
δ = 6.91 (d, JH,H = 4.5 Hz, 2 H, py-H), 6.99 (d, JH,H = 8.5 Hz, 2
3
3
H, ArH), 7.27 (d, JH,H = 4.0 Hz, 2 H, py-H), 7.49 (d, JH,H
=
3
8.5 Hz, 2 H, ArH), 7.56 (t, JH,H = 7.5 Hz, 2 H, benzo-H), 7.64 (t,
3JH,H = 7.5 Hz, 2 H, benzo-H), 8.17 (d, 3JH,H = 8.0 Hz, 2 H, benzo-
3
H), 8.28 (d, JH,H = 8.0 Hz, 2 H, benzo-H), 10.20 (s, 1 H, OH),
13.76 (s, 1 H, NH) ppm. MS (APCI): m/z = 503 [M + H]+.
3,5-Bis(2-benzothiazolyl)-4,4-difluoro-8-phenyl-4-bora-3a,4a-diaza-
s-indacene (9a): Compound 8a (0.5 g, 1.03 mmol) was dissolved in
anhydrous CH2Cl2 (200 mL), and subsequently boron trifluoride–
diethyl ether (2.25 g, 2 mL, 16 mmol) and Hünig’s base (1.29 g,
10 mmol) were added. After 30 min of stirring, the solvent was dis-
tilled off, and the residue was purified by chromatography on silica
gel by using a mixture of ethyl acetate/hexane (1:3) to give BOD-
IPY 9a (0.61 g, 56%); m.p. 195–196 °C. C29H17BF2N4S2 (534.42):
calcd. C 65.18, H 3.21, N 10.48; found C 65.12, H 3.26, N 10.40.
3
1H NMR (300 MHz, CDCl3, 25 °C): δ = 6.96 (d, JH,H = 4.5 Hz,
3
3
2 H, py-H), 7.35 (d, JH,H = 4.5 Hz, 2 H, py-H), 7.47 (t, JH,H
=
7.8 Hz, 2 H, benzo-H), 7.52–7.65 (m, 7 H, 5 ArH + 2 benzo-H),
3
3
7.97 (d, JH,H = 7.8 Hz, 2 H, benzo-H), 8.21 (d, JH,H = 8.1 Hz, 2
H, benzo-H) ppm. 19F NMR (282 MHz, CDCl3, CFCl3): δ =
–135.63 (m) ppm. MS (APCI): m/z = 535 [M + H]+.
[1] a) A. Loudet, 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) A. B. Descalzo, H.-J. Xu, Z. Shen, K.
Rurack, Ann. N. Y. Acad. Sci. 2008, 1130, 164–171; e) R. P.
Haugland, The Handbook – A Guide to Fluorescence Probes
and Labeling Technologies, 10th ed., Invitrogen Corp., Eugene,
OR, 2005.
[2] a) J. Fabian, H. Nakazumi, M. Matsuoka, Chem. Rev. 1992,
92, 1197–1226; b) Near-Infrared Dyes for High Technology Ap-
plication (Eds.: S. Dahne, U. Resch-Genger, O. S. Wolfbeis),
Kluwer Academic, Dordrecht, 1998.
3,5-Bis(2-benzothiazolyl)-4,4-difluoro-8-(4-methoxyphenyl)-4-bora-
3a,4a-diaza-s-indacene (9b): The product was synthesized as for 9a.
Yield: 63%; m.p. 265–266 °C. C30H19BF2N4OS2 (564.45): calcd. C
1
63.84, H 3.39, N 9.93; found C 63.57, H 3.48, N 10.14. H NMR
3
(300 MHz, CDCl3, 25 °C): δ = 3.94 (s, 3 H, OCH3), 7.06 (d, JH,H
3
= 4.8 Hz, 2 H, py-H), 7.10 (d, JH,H = 8.7 Hz, 2 H, ArH), 7.47 (t,
3JH,H = 8.1 Hz, 2 H, benzo-H), 7.51–7.64 (m, 6 H, 2 ArH + 2 py-
3
H + 2 benzo-H), 8.03 (d, JH,H = 8.1 Hz, 2 H, benzo-H), 8.16 (d,
3JH,H = 7.8 Hz, 2 H, benzo-H) ppm. 19F NMR (282 MHz, CDCl3,
CFCl3): δ = –133.15 (m) ppm. MS (APCI): m/z = 565 [M + H]+.
Eur. J. Org. Chem. 2010, 2746–2752
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2751

Yu. P. Kovtun et al.
FULL PAPER
[3] a) R. W. Wagner, J. S. Lindsey, Pure Appl. Chem. 1996, 68,
1373–1380; b) T. Rohan, W. Qin, N. Boens, W. Dehaen, Eur. J.
Org. Chem. 2006, 4658–4663; c) A. Burghart, H. Kim, M. B.
Welch, L. H. Thoresen, J. Reibenspies, K. Burgess, F. Berg-
strom, L. B.-Å. Johansson, J. Org. Chem. 1999, 64, 7813–7819;
d) J. Chen, A. Burghart, A. Derecskei-Kovacs, K. Burgess, J.
Org. Chem. 2000, 65, 2900–2906; e) J. Chen, J. Reibenspies,
A. Derecskei-Kovacs, K. Burgess, Chem. Commun. 1999, 2501–
2502.
[9] a) A. A. Granovsky, FIREFLY, version 7.1.G, http://classic.-
chem.msu.su/gran/firefly/index.html; b) M. W. Schmidt, K. K.
Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen,
S. Koseki, N. Matsunaga, K. A. Nguyen, S. Su, T. L. Windus,
M. Dupuis, J. A. Montgomery, J. Comput. Chem. 1993, 14,
1347–1363.
[10] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd
ed., Kluwer Academic Plenum Publishers, New York, 1999.
[11] a) A. Bondi, J. Phys. Chem. 1964, 68, 441–451; b) D. J. Crouch,
P. J. Skabara, M. Heeney, I. McCulloch, S. J. Colesc, M. B.
Hursthouse, Chem. Commun. 2005, 1465–1467.
[4] a) E. Yu. Schmidt, B. A. Trofimov, A. I. Mikhaleva, N. V. Zor-
ina, N. I. Protzuk, K. B. Petrushenko, I. A. Ushakov, M. Yu.
Dvorko, R. Méallet-Renault, G. Clavier, T. T. Vu, H. T. T. [12] S. Fery-Forgues, D. Lavabre, J. Chem. Educ. 1999, 76, 1260–
Tran, R. B. Pansu, Chem. Eur. J. 2009, 15, 5823–5830; b) S.
Rihn, P. Retailleau, N. Bugsaliewicz, A. De Nicola, R. Ziessel,
Tetrahedron Lett. 2009, 50, 7008–7013; c) R. Haugland, H.
Kang, US Pat. 5248782, 1993.
1264.
[13] G. M. Sheldrick, SHELXS97 – Program for the Solution of
Crystal Structure, University of Göttingen, Germany, 1997.
[14] G. M. Sheldrick, SHELXL97 – Program for the Refinement of
crystal Structures, University of Göttingen, Göttingen, Ger-
many, 1997.
[15] D. J. Watkin, C. K. Prout, J. R. Carruthers, P. W. Betteridge,
CRYSTALS, Issue 10, Chemical Crystallography Laboratory,
University of Oxford, 1996.
[16] G. M. Sheldrick, SADABS – Program for scaling and correction
of area detector data, University of Göttingen, Germany, 1996.
[17] J. R. Carruthers, D. J. Watkin, Acta Crystallogr., Sect. A 1979,
35, 698–699.
[5] a) B. George, E. P. Papadopoulos, J. Org. Chem. 1977, 42, 441–
443; b) T. Itoh, K. Nagata, H. Ishikawa, A. Ohsawa, Heterocy-
cles 2004, 63, 2769–2783.
[6] H. J. Anderson, Can. J. Chem. 1959, 37, 2053–2058.
[7] R. J. P. Corriu, V. Huynh, J. Iqbal, J. J. E. Moreau, C. Vernhet,
Tetrahedron 1992, 48, 6231–6244.
[8] a) M. Baruah, W. Qin, N. Basaric´, W. M. De Borggraeve, N.
Boens, J. Org. Chem. 2005, 70, 4152–4157; A. Coskun, E. De-
niz, E. U. Akkaya, Org. Lett. 2005, 7, 5187–5189; T. Gareis, C.
Huber, O. S. Wolfbeis, J. Daub, Chem. Commun. 1997, 1717–
1718.
Received: January 22, 2010
Published Online: March 25, 2010
2752
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2746–2752