Aliphatic amine discrimination by pentafluorophenyl dibromo BODIPY

Article abstract of DOI:10.1002/asia.201402389

Two new fluorescent BODIPY dyes have been designed and synthesized. They dyes differ in their meso substituents, which have different electronic properties. Their selective reactivity towards an Ar-S_N2 reaction has been explored as a potential

Full text of DOI:10.1002/asia.201402389

COMMUNICATION
DOI: 10.1002/asia.201402389
Aliphatic Amine Discrimination by Pentafluorophenyl Dibromo BODIPY**
Adiki Raja Sekhar, Masood Ayoub Kaloo, and Jeyaraman Sankar*[a]
Abstract: Two new fluorescent BODIPY dyes have been de-
signed and synthesized. They dyes differ in their meso sub-
stituents, which have different electronic properties. Their
selective reactivity towards an Ar-SN2 reaction has been ex-
plored as a potential basis for colorimetric and fluorescent
discrimination of primary, secondary and tertiary aliphatic
amines. This dual-mode, instantaneous recognition event is
unprecedented.
Molecular recognition provides an effective and promising
approach fulfilling most of the above requirements. It af-
fords fast and convenient read-out signals in the form of
color and fluorescence.[7] However, owing to the range of
sizes, conformations, and shapes of amines, besides their
high polarity, it is really challenging to design a molecular
scaffold providing aliphatic amine discrimination and analy-
sis in both aqueous and organic media.[8] So far, very few ef-
forts have been taken for the development of molecular sys-
tems for identification of aliphatic amines.[9] All these sys-
tems lack a clear-cut discrimination for various degrees of
aliphatic amines. The binding events are valid only in organ-
ic media and mostly suffer from time-delayed responses.
The recognitions display either a chromogenic or fluorogen-
ic output for a given interaction. Moreover, there are scarce
reports wherein any designed scaffold displays dual-mode
responses in the form of fluorescence and color through the
naked eye.[9] Our target was to achieve a molecular system
which exhibits fluorescence along with a chromogenic re-
sponse for amine discrimination. The BODIPY backbone
was chosen because of its excellent fluorescence and color,
and because it is structurally robust.
In our endeavor to develop the required molecular
system providing instantaneous aliphatic amine discrimina-
tion through visual diagnosis, a typical Ar-SN2 reaction of
BODIPYs at the 3- and 5-positions considered.[10] To ach-
ieve selective control over the nucleophilic substitutions
with various degrees of amines, we chose two new BODIPY
dyes (Ra and Rb), bearing electron-deficient and -rich moiet-
ies at meso-positions. The associated charge transfer (CT)
and electron transfer properties of the system are expected
to be strongly modulated through an ample variation.[11]
This can serve as a probable basis for discrimination with
fast and convenient signal transduction.
Aliphatic amines constitute one of the most important
and abundant classes of amines in nature.[1] Their impor-
tance can be felt by their widespread applications in textile,
cosmetic, chemical, medicinal, agricultural, plastic, leather,
metallurgical, pharmaceutical, and petroleum industries.[2]
They also play crucial roles in synthetic chemistry, biology,
and atmospheric sciences.[3] Apart from their vast diversity
and use in day-to-day life including modern technology, they
are usually associated with non-benignant, toxic, and carci-
nogenic properties, either in gaseous, aqueous, or non-aque-
ous media.[4] With these considerations along with character-
istic properties specified to various degrees of aliphatic
amines (primary, secondary, and tertiary), there should be
a potential need for direct discrimination of these amines in
a wide range of environments.
Over the past few decades, a number of methodologies
have been proposed for amine analysis, including gas chro-
matography (GC), liquid chromatography (LC), mass spec-
trometry (MS), capillary electrophoresis (CE), potentiome-
try, and ion chromatography (IC).[5] However, these tech-
niques involve tedious pre-concentration, which relies upon
extraction and separation, prior to their analysis. Besides
this disadvantage, current methodologies are expensive and
require a high level of expertise. Furthermore, none of these
techniques provide an in-situ amine discrimination and diag-
nosis with the naked eye, a quick and timely requirement in
clinical settings and in the food industry.[6]
The synthesis of Ra and Rb is outlined in Scheme 1. 5-pen-
tafluorophenyl-1,9-dibromodipyrromethene was obtained
through the reported procedure[12a] and further dissolved in
dry CH2Cl2 with subsequent addition of triethylamine and
BF3.Et2O at 08C. The reaction mixture was stirred at room
temperature for 2 h. The same strategy was utilized for the
synthesis of Rb, with 5-mesityl-1,9-dibromodipyrromethene
as starting material (see Scheme S1 and S2 in the Supporting
Information).[12b,c] The identities of compounds Ra and Rb
were confirmed by standard spectroscopic techniques in the
form of NMR (Figure S10 in the Supporting Information),
HR-LCMS (Figure S11 in the Supporting Information), and
single-crystal XRD (Figure 1).
[a] A. R. Sekhar, M. A. Kaloo, Prof. Dr. J. Sankar
Department of Chemistry
Indian Institute of Science Education and Research Bhopal
Indore bypass road, Bhouri, Bhopal, 462066 (India)
Fax : (+91)755-6692392
E-mail: sankar@iiserb.ac.in
[**] BODIPY=boron dipyrromethene (4,4-difluoro-4-bora-3a,4a-diaza-s-
indacene).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201402389.
Chem. Asian J. 2014, 9, 2422 – 2426
2422
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Jeyaraman Sankar et al.
In the emission spectra, striking changes in intensities and
wavelength shifts were observed upon addition of amines.
Ra shows a characteristic emission at 554 nm upon excitation
at 470 nm. Continuous addition of methylamine results in bi-
furcation of the 554 nm signal into peaks at 525 and 580 nm.
The changes further proceed with a blue shift of the former
and a red-shift of the later (Figure 3). These observations re-
flect the disappearance of the intrinsic BODIPY emission at
554 nm with predominance of newly existing strong charge
transfer emission at 580 nm as a result of intramolecular
charge transfer (ICT) from the amine nitrogen atom to the
pentafluorophenyl ring at the meso-position. The above
changes can be easily observed with the naked eye. In con-
trast, with diethylamine and triethylamine, quenching of
554 nm emission was observed as the reaction progressed
(Figure 3). This quenching is attributed to effective photoin-
duced energy transfer (PET) from amine nitrogen towards
the fluorophore.[13] The expected delay in the emission
changes with 38 amines was observed, similar to that in ab-
sorption spectra (Figure 4 and Figure S7 in the Supporting
Information). Hence instantaneous display of emission be-
havior and distinct variation in the output signals of Ra on
addition of various degrees of aliphatic amines serves as an-
other potential means of efficient and near-real time aliphat-
ic amine discrimination.
Scheme 1. Synthesis of BODIPYs (Ra and Rb). NBS=N-bromosuccini-
mide, DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone.
The absorption spectrum of Ra (e=10300mÀ1 cmÀ1, F=
0.37) in CH2Cl2 shows a characteristic S0 to S1 transition at
539 nm and a weak absorption at 510 nm. On interaction
with amines through Ar-SN2 reaction at the 3-position,
a strong modulation of ground-state electronic properties
was observed. Upon addition of various amounts of methyl-
amine and diethylamine, the absorption signal at 539 nm de-
creased with a concomitant increase in the intensity of the
510 nm band along with a slight blue shift. The given
changes proceed through appearance of clear isosbestic
points at 520 and 515 nm for primary and secondary amines
(Figure 2).
The difference of 5 nm shift in the absorption signal be-
tween Ra with primary (18) and secondary (28) amines leads
to their clear and visible discrimination with the appearan-
ces of respective yellow and pale yellow colors (Figure 4).
The interaction of 18 amines is instantaneous, followed by 28
amines, while tertiary (38) amines interact with a time delay
of about an hour for the completion of the reaction. Spectral
behavior finally resembles that with 28 amines and hence
similar visual appearances are observed (Figure 4 and Fig-
ure S7 in the Supporting Information). The delay in the che-
modosimetric reaction with 38 amines is attributed to the
facile Ar-SN2 reaction of 28 amines compared to 38.
The interaction of aliphatic amines was further probed
through NMR (1H, 11B, and 19F NMR) titration experiments.
Addition of methyl amine to Ra in CDCl3 results in the ap-
1
pearance of four distinct doublets in the H NMR spectrum
(Figure S8 in the Supporting Information), demonstrating
the unsymmetrical nature of the resulting species. Continu-
ing addition of amine result in clear distinction of doublets
1
and no further changes in the H NMR shifts. This result in-
dicates the reaction completeness and the sole existence of
3-substituted product.
The mechanism of interaction was also supported by
19F NMR titration of Ra with
amines. Addition of methyla-
mine results in up field and
down field shifts of pentafluor-
ophenyl ring signals (Figure S8
in the Supporting Information),
an indication of charge-transfer
modulations within the mole-
cule as a result of amine bind-
ing through chemodosimetric
Ar-SN2 reaction.
As a result, we demonstrate
that the resulting chemodosi-
metric behavior of Ra with the
aliphatic amines is an outcome
of the typical Ar-SN2 reaction
facilitated by an electron-defi-
cient moiety (pentafluorophen-
yl) at the meso-position. On re-
placing the pentafluorophenyl
moiety with a mesityl ring in Rb
Figure 1. ORTEP representation of crystal structures of a) Ra and b) Rb.
Chem. Asian J. 2014, 9, 2422 – 2426
2423
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Jeyaraman Sankar et al.
Figure 2. a) Absorption titration profile of Ra (1.6 mm) upon addition of
various amounts of methyl amine in CH2Cl2, and b) with various amounts
of diethylamine in CH2Cl2.
Figure 3. a) Emission titration profile of Ra (1.6 mm) upon addition of var-
ious equivalents of methylamine in CH2Cl2, and b) with diethylamine in
CH2Cl2, upon excitations at 470 nm.
(e=13204mÀ1 cmÀ1, F=0.30), sluggishness in the Ar-SN2 re-
action was observed, and with a time-delayed response in
both absorption and emission modes (Figures S3 and S4 in
the Supporting Information). This finding further supports
the role played by electron-deficient moieties at the meso-
position in the BODIPY system towards nucleophilic substi-
tutions at the 3- and 5-positions. The electronic effect of
substituents on the amine nitrogen atom and hence variation
in the electronic and charge-transfer processes act as the
basis for a selective discrimination of various degrees of ali-
phatic amines.
A 1:1 binding mode of the given interactions was evaluat-
ed via 1H NMR spectra of the products obtained through
a chemical reaction between Ra and two equivalents of ali-
phatic amines (methylamine and diethylamine) in ambient
conditions (Figure S11 in the Supporting Information). Rep-
etition of similar results even with excess amine concentra-
tions fully supported the 1:1 stoichiometry, which was also
confirmed through single-crystal XRD (Figure 5). For prac-
tical applicability of the system, a library of aliphatic amines
was tested, and similar trends were observed in various de-
grees of aliphatic amines (Table S2 in the Supporting Infor-
mation). Surprisingly, the recognition behavior of Ra with
amines was also observed in mixed CH2Cl2/aqueous media
(Figure 4), which signals potential utility of the system in
aqueous environments. Further, presence of Ra in a mixture
of all three (18, 28, and 38) amines revealed sole formation
(>95%) of the 18 amine substituted product. The ratiomet-
ric response at the two concomitant absorption wavelengths
can serve as an important means for calibrating and deter-
mining the respective amine concentrations in various
media under consideration.[14]
Further to emphasize the selectivity of the dibromo
BODIPY, we prepared a highly electron-deficient 3-fluoro-
Chem. Asian J. 2014, 9, 2422 – 2426
2424
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Jeyaraman Sankar et al.
ous media. The Ar-SN2 reaction of aliphatic amines results
in the selective modulation of charge-transfer properties of
the molecule. This in turn offers an unambiguous discern-
ment through dual-mode display in the form of color and
fluorescence. Besides a facile Ar-SN2 reaction at the 3- and
5-positions, the electron-deficient pentafluorophenyl ring
along with substituents present on the amine nitrogen atom
dictate excellent sensitivity and discrimination. Currently
the suitability of the chemodosimeter for environmental and
biological applications is being investigated and the results
will be communicated in due course.
Figure 4. Visible absorption and emission changes of Ra in CH2Cl2 upon
additions of various types of amines in organic and organic/aqueous
media. Pictures were taken immediately after amine additions at ambient
conditions. (See the Supporting Information for the figure in color.)
Experimental Section
General Information
Mass spectra were recorded on
1
a Bruker HR-LCMS spectrometer. H,
13C, 19F, and 11B NMR spectra were re-
corded using a Bruker instrument op-
erating at 400 MHz in CDCl3. UV/Vis
spectra were recorded on Shimadzu
spectrophotometry UV-1800. Fluores-
cence emission spectra were recorded
on a Horiba Jovin Vyon Fluoro log 3–
111 spectrophotometer.
Single-crystal data was collected on
a
Bruker APEX II diffractometer
equipped with a graphite monochro-
mator and MoKa (l=0.71073 ꢁ) radia-
tion. Data collection was performed
using f and w scans. The structures
was solved using direct method fol-
lowed by full matrix least square re-
finements against F2 (all data HKLF 4
format) using SHELXTL. All calcula-
tions were carried out using SHELXL
97, PLATON 99, and WinGXsystemV-
er-1.6414. CCDC 995505 (Rb), 995506
(Ra with diethylamine), 995507 (Rb
with propylamine), 995513 (Ra), and
1004955 (fluorine-substituted deriva-
tive) contain the supplementary crys-
Figure 5. ORTEP representation of crystal structures of a) Ra with diethylamine, b) Rb with propylethylamine,
confirming 1:1 stoichiometry.
tallographic 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.
5-bromo- pentafluorophenyl BODIPY derivative by the hal-
ogen exchange method. This is the first example to date of
a BODIPY derivative having a fluorine atom at the a-pyr-
rolic position. This fluorine-substituted derivative was char-
acterized by spectroscopic techniques (see the Supporting
Information) and single-crystal XRD. All efforts to obtain
difluoro-BODIPY failed due to the decomposition of the
monofluoro-BODIPY on prolonged heating. Upon addition
of various degrees of aliphatic amines to monofluorinated
BODIPY, there was no chromogenic or fluorogenic output
response, as shown in the Supporting Information. Thus, the
discrimination of various degrees of amines is selective only
for dibromo-BODIPY.
General synthetic procedure for 1,9-dibromodipyrromethene
N-bromosuccinimide (2 equiv) in THF (5 mL) was added dropwise to di-
pyrromethane (100 mg, 1 equiv) in dry THF (5 mL) at À788C. Reaction
progress was monitored by TLC. After reaction completion, excess bro-
mine was quenched with aqueous Na2S2O3. The organic phase was ex-
tracted with CH2Cl2 and dried over anhydrous Na2SO4. Brown oil was
obtained after evaporation of the solvent under reduced pressure. The
residue was dissolved in THF (10 mL), and DDQ (1.5 equiv) was added
to oxidize the dipyrromethane. The reaction mixture was stirred for
10 min at room temperature. The residue was then immediately subjected
to basic alumina column chromatography (hexane as elutant) to give the
desired product.
In conclusion, we have designed and synthesized two new
BODIPY dyes with strong emission behavior visible to the
naked eye. Pentafluorophenyl dibromo derivative Ra was
explored and developed as a promising analytical tool, pro-
viding in situ and instantaneous discrimination of primary,
secondary, and tertiary amines in organic and organic/aque-
5-Pentafluorophenyl-1,9-dibromodipyrromethene:
Dark red solid, 109 mg, 71% yield, 1H NMR (400 MHz; CDCl3): d=
6.37 ppm (s, 4H; b-pyrrole). 19F NMR (376 MHz; CDCl3): d=À160.28
(2F; meta), À151.15 (1F; para), À138.01 ppm (2F; ortho). MS (ESI-
Chem. Asian J. 2014, 9, 2422 – 2426
2425
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Jeyaraman Sankar et al.
HRMS, positive mode) found 468.8776, C15H5N2Br2F5 requires 468.8792.
UV/Vis (CH2Cl2): lmax =456 nm.
[1] a) K. I. Oberg, R. Hodyss, J. L. Beauchamp, Sens. Actuators B 2006,
115, 79–85; b) X. Liu, H. Wang, S.-C. Liang, H.-S. Zhang, Anal.
Chim. Acta 2001, 441, 45–52; c) N. Zhang, H. Wang, Y.-Z. Zhao,
K.-J. Huang, H.-S. Zhang, Microchim. Acta 2008, 162, 205–210.
[2] a) X. Li, Z. Zeng, J. Zhou, S. Gong, W. Wang, Y. Chen, J. Chroma-
togr. A 2004, 1041, 1–9; b) A. Mirmohseni, A. Oladegaragoze, Sens.
Actuators B 2003, 89, 164–172; c) W. Xiaofei, L. Shu, Y. Tingyun, C.
Yang, Eur. Chem. Bull. 2014, 3, 55–57.
5-Mesityl-1,9-dibromodipyrromethene
Orange solid, 127 mg, 80% yield, 1H NMR (400 MHz, CDCl3): d=2.07
(s, 6H; ortho-Me), 2.34 (s, 3H; para-Me), 6.27 (d, J=2 Hz, 4H; b-pyr-
role), 6.91 ppm (s, 2H; phenyl). MS (APCI-HR MS, positive mode)
found 420.9737, C18H16N2Br2 requires 420.9733. UV/Vis (CH2Cl2): lmax
=
445 nm.
[3] a) S. M. Murphy, A. Sorooshian, J. H. Kroll, N. L. Ng, P. Chhabra, C.
Tong, J. D. Surratt, E. Knipping, R. C. Flagan, J. H. Seinfeld, Atmos.
Chem. Phys. 2007, 7, 2313–2337; b) E. Agostinelli, M. P. M. Mar-
ques, R. Calheiros, F. P. S. C. Gil, G. Tempera, N. Viceconte, V. Bat-
taglia, S. Grancara, A. Toninello, Amino Acids 2010, 38, 393–403.
[4] a) F. W. Fifield, P. J. Haines, Environmental Analytical Chemistry,
2nd ed., Blackwell, London, 2000, p. 449; b) L. Pan, J. M. Chong, J.
Pawliszyn, J. Chromatogr. A 1997, 773, 249–260.
[5] a) L. Zhao, L. Zhu, H. K. Lee, J. Chromatogr. A 2002, 963, 239–
248; b) L. Zhu, C. B. Tay, H. K. Lee, J. Chromatogr. A 2002, 963,
231–237; c) M. M. Ayad N. L. Torad, Sens. Actuators B 2010, 147,
481–487; d) Z. Zeng, W. Qiu, H. Xing, Z. Huang, Anal. Sci. 2000,
16, 851–854; e) Y. Moliner-Martınez, R. Herraez-Hernandez, P.
Campıns-Falco, J. Chromatogr. A 2007, 1164, 329–333; f) A. Banel,
M. Wasielewska, B. Zygmunt, Anal. Bioanal. Chem. 2011, 399,
3299–3303; g) A. Bouchereau, P. Guenot, F. Larher, J. Chromatogr.
B 2000, 747, 49–67; h) G. J. Mohr, C. Demuth, U. E. Spichinger-
Keller, Anal. Chem. 1998, 70, 3868–3873.
General synthetic procedure for 3,5-dibromo BODIPY
1,9-dibromodipyrromethene (100 mg, 1 equiv) was dissolved in dry
CH2Cl2 (20 mL) at lower temperature (ice bath), followed by addition of
triethylamine (40 equiv) and dropwise addition of excess BF3·Et2O (40
equiv)). The reaction mixture was further stirred at room temperature
and the progress of reaction was monitored by TLC. After reaction com-
pletion, organic phase was extracted with CH2Cl2 and washed with aque-
ous NaHCO3. The organic layer was dried over anhydrous Na2SO4, and
solvent was evaporated under reduced pressure. The crude product was
subjected to silica gel (100–200 mesh) column chromatography (CH2Cl2
and hexane as eluent) to get desired product.
8-Pentafluorophenyl-3,5-dibromo BODIPY (Ra)
1
Brown shiny crystals, 87 mg, 79% yield, H NMR (400 MHz; CDCl3): d=
6.68 (d, J=4.27 Hz, 2H; b-pyrrole), 6.57 ppm (d, J=4.35 Hz, 2H; b-pyr-
role). 19F NMR (376 MHz; CDCl3): d=À158.74 (2F; meta), À148.41 (1F;
para), À146.92 (2F; Boron), À136.51 ppm (2F; ortho). 11B NMR
(128 MHz; CDCl3): d=0.62 ppm (t, 1B). MS (APCI-HRMS, positive
mode) found 515.8701. C15H4BBr2F7N2 requires 515.8700. UV/Vis
(CH2Cl2): lmax =539 nm. e=10300mÀ1 cmÀ1. m.p.=265.388C.
[6] a) E. Dadꢂkovꢂ, M. Krꢃzek, T. Pelikꢂnovꢂ, Food Chem. 2009, 116,
365–370; b) R. Kadnar, J. Chromatogr. A 1999, 850, 289–295; c) A.
ꢄnal, Food Chem. 2007, 103, 1475–1486.
[7] a) M. A. Kaloo, J. Sankar, Analyst 2013, 138, 4760–4763; b) R. M.
Duke, E. B. Veale, F. M. Pfeffer, P. E. Kruger, T. Gunnlaugsson,
Chem. Soc. Rev. 2010, 39, 3936–3953; c) R. B. P. Elmes, P. Turner,
K. A. Jolliffe, Org. Lett. 2013, 15, 5638–5641.
8-Mesityl-3,5-dibromo BODIPY (Rb)
Red solid, 100 mg, 90% yield, 1H NMR (400 MHz; CDCl3): d=2.07 (s,
6H; ortho-Me), 2.33 (s, 3H; para-Me), 6.44 (d, J=4.15, 2H; b-pyrrole),
6.53 (d, J=4.40, 2H; b-pyrrole), 6.92 ppm (s, 2H; phenyl). 13C NMR
(100 MHz; CDCl3): d=19.95, 21.13, 122.81, 128.3, 130.32, 132.64, 135.85,
139.24, 143.30 ppm. 19F NMR (376 MHz; CDCl3): d=À147.30 ppm (q,
2F; BF). 11B NMR (128 MHz; CDCl3): d=0.68 ppm (t, 1B). MS (APCI-
LR MS, negative mode) found 467.9473. C18H15BBr2F2N2 requires
[8] a) E. K. Feuster, T. E. Glass, J. Am. Chem. Soc. 2003, 125, 16174–
16175; b) S. Basurto, T. Torroba, M. Comes, R. Martinez-Manez, F.
Sancenon, L. Villaescusa, P. Amoros, Org. Lett. 2005, 7, 5469–5472;
c) M. Comes, M. D. Marcos, R. Martinez-Manez, F. Sancenon, J.
Soto, L. A. Villaescusa, P. Amoros, D. Beltran, Adv. Mater. 2004, 16,
1783–1786.
[9] a) M. R. Ajayakumar, P. Mukhopadhyay, Chem. Commun. 2009,
3702–3704; b) G. Lu, J. E. Grossman, J. B. Lambert, J. Org. Chem.
2006, 71, 1769–1776; c) J. H. Bang, S. H. Lim, E. Park, K. S. Suslick,
Langmuir 2008, 24, 13168–13172; d) H. Liu, J. Mack, Q. Guo, H.
Lu, N. Kobayashi, Z. Shen, Chem. Commun. 2011, 47, 12092–12094.
[10] a) L.-Y. Niu, Y.-S. Guan, Y.-Z. Chen, L.-Z. Wu, C.-H. Tung, Q.-Z.
Yang, J. Am. Chem. Soc. 2012, 134, 18928–18931; b) T. Rohand, M.
Baruah, W. Qin, N. Boens, W. Dehaen, Chem. Commun. 2006, 266–
268; c) A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891–4932.
[11] a) S. Erten-Ela, M. D. Yilmaz, B. Lcli, Y. Dede, S. Lcli, E. U.
Akkaya, Org. Lett. 2008, 10, 3299–3302; b) R. Guliyev, A. Coskun,
E. U. Akkaya, J. Am. Chem. Soc. 2009, 131, 9007–9013.
467.9641. UV/Vis (CH2Cl2): lmax =522 nm. e=13204mÀ1 cmÀ1
218.578C.
. m.p.=
8-Pentafluorophenyl-3-fluoro-5-bromo BODIPY
8-Pentafluorophenyl-3,5-dibromo BODIPY (200 mg, 0.427 mmol) was
dissolved in (20 mL) dichloromethane. Excess equivalents of tetrabutyl
ammonium fluoride were added to the reaction mixture and stirred over-
night at room temperature. The reaction mixture was concentrated under
reduced pressure and subjected to silica gel column to give 8-pentafluor-
ophenyl-3-fluoro-5-bromo BODIPY. This F-BODIPY was recrystallized
from pentane as a green solid (158 mg, 90% yield). 1H NMR (400 MHz;
[D6]DMSO): d=6.90 (d, J=5.26, 1H; b-pyrrole), 6.01 (d, J=3.37, 1H; b-
pyrrole), 5.94 (s, J=5.30, 1H; b-pyrrole), 5.75 ppm (d, J=2.95, 1H; b-
pyrrole). 19F NMR (376 MHz; [D6]DMSO): d=À139.51–139.75 (q, 2F;
[12] a) S. Shimizu, Y. Ito, K. Oniwa, S. Hirokawa, Y. Miura, O. Matsushi-
ta, N. Kobayashi, Chem. Commun. 2012, 48, 3851–3853; b) Y.
Matano, T. Shibano, H. Nakano, H. Imahori, Chem. Eur. J. 2012, 18,
6208–6216; c) during the preparation of this manuscript, there was
an interesting report on the structural characterization of Rb. See J.
Ahrens, B. Haberlag, A. Scheja, M. Tamm, M. Broring, Chem. Eur.
J. 2014, 20, 2901–2912.
BF), À139.85–139.94 (2F; ortho), À155.6–155.72(1F; para), À162.42–
G
162.57 ppm (2F; meta). 11B NMR (128 MHz; [D6]DMSO): d=0.79 ppm
(t, 1B). MS (ESI-LR MS, negative mode) found 450.9496. C15H2BBrF8N2
calcd. 450.9286.
[13] a) J. H. Chang, Y. Jeong, Y.-K. Shin, Bull. Korean Chem. Soc. 2003,
24, 119–122;b) H. Peng, W. Chen, Y. Cheng, L. Hakuna, R. Strong-
nin, B. Wang, Sensors 2012, 12, 15907–15946.
Acknowledgements
[14] a) Y. Qu, J. Hua, H. Tian, Org. Lett. 2010, 12, 3320–3323; b) X.-P.
Bao, P.-C. Zheng, Y. Liu, Z. Tan, Y.-H. Zhou, B.-A. Song, Supramol.
Chem. 2013, 25, 246–253.
We gratefully acknowledge DST (DST/TSG/PT/2009/115& DST/PHY/
2011/017) New Delhi, India for financial support and IISER Bhopal for
infrastructure.
Received: April 15, 2014
Published online: July 13, 2014
Keywords: amines
· chemodosimetry · dyes/pigments ·
fluorescence · sensors
Chem. Asian J. 2014, 9, 2422 – 2426
2426
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim