A novel Bodipy-Dipyrrin fluorescent probe: Synthesis and recognition behaviour towards Fe (II) and Zn (II)

Article abstract of DOI:10.1016/j.dyepig.2012.02.006

We present the design, synthesis, characterization and spectral studies for a new Zn (II) and Fe (II) selective fluorescent probe, 4,4-Difluoro-8-{3-[(4- phenoxy-dipyrromethene)propoxy]}-4-bora-3a,4a-diazaindacene (DPYBODPY). DPBODPY consists of a terminal fluorophore and a selective ligand and was designed to detect significant changes in absorbance and/or fluorescence on metal ion binding. The fluorophore is based on the Bodipy unit due to its excellent photophysical properties, while the dipyrrin unit has specific recognition abilities for Fe²⁺ and Zn²⁺ ions. The combination of these two structures is optimised to achieve significant spectral changes in the presence of Fe²⁺ and Zn²⁺ ions.

Full text of DOI:10.1016/j.dyepig.2012.02.006

Dyes and Pigments 94 (2012) 496e502
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A novel Bodipy-Dipyrrin fluorescent probe: Synthesis and recognition behaviour
towards Fe (II) and Zn (II)
,
Ahmed Nuri Kursunlu a, Ersin Guler a, Halil Ismet Ucan a, Ross W. Boyle b
*
a Department of Chemistry, University of Selcuk Campus, 42075 Konya, Turkey
b Department of Chemistry, University of Hull, Kingston-upon-Hull, East Yorkshire HU6 7RX, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
We present the design, synthesis, characterization and spectral studies for a new Zn (II) and Fe (II)
selective fluorescent probe, 4,4-Difluoro-8-{3-[(4-phenoxy-dipyrromethene)propoxy]}-4-bora-3a,4a-
diazaindacene (DPYBODPY). DPBODPY consists of a terminal fluorophore and a selective ligand and was
designed to detect significant changes in absorbance and/or fluorescence on metal ion binding. The
fluorophore is based on the Bodipy unit due to its excellent photophysical properties, while the dipyrrin
unit has specific recognition abilities for Fe2þ and Zn2þ ions. The combination of these two structures is
optimised to achieve significant spectral changes in the presence of Fe2þ and Zn2þ ions.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 8 December 2011
Received in revised form
6 February 2012
Accepted 7 February 2012
Available online 16 February 2012
Keywords:
Bodipy
Florescent probe
Dipyrrin
Metal complex
Fluorophore
Photophysical property
1. Introduction
fluorescence due to an active quenching process (PET or ICT) in the
presence of some metal ions [14,15].
The design of fluorescent probes for metal cations is an important
field in organic chemistry, bioinorganic chemistry and the life
sciences due to their relatively high sensitivity, selectivity and short
response time [1e4]. Most fluorescent probes are designed to
incorporate either a structure wherein the receptor is part of the
Dipyrrins, which are closely structurally related to Bodipys, are
also efficient ligands for the formation of charge-neutral metal
complexes. Derivatives of dipyrrins complexed with a variety of
metal cations have been extensively investigated due to favourable
electrochemical and fluorescent properties [16,17]. Generally, the
dipyrrins have had a widespread impact on coordination chemistry,
and the first reports in the area date back to early last century
[18,19]. Examples include the work of Baudronet et al., who
reported homo- and hetero-metallic dipyrrin compounds [20] and
Catherine et al. who have shown that four cyclo-metallated Pd and
Pt complexes coordinated simultaneously to a dipyrrin derivative
could be synthesized [21].
p-electron system of the fluorophore, or a structure consisting of
a fluorophore and a receptor separated by a short alkyl chain [5,6]. In
the last decade, a range of Bodipy (borondifluorodipyrromethene)
fluorophores have been developed with excellent stability, high
fluorescence quantum yields, negligible triplet state formation,
intense absorptions, good solubility, and chemical robustness
[7e11]. Some similarities between Bodipys and porphyrins, which
are often assembled from dipyrromethane or dipyrromethene
building blocks, have been noted [12]. Due to these similarities,
novel Bodipy complexes (which can be converted into an energy
transfer cassette) have been synthesized in order to creating a large
Stoke shift [13]. Energy transfer cassettes typically rely on PET
(photoinduced electron transfer) and ICT (internal charge transfer)
processes for their activity. Bodipy compounds also show reduced
In this article, we investigate the binding properties of metal
ions [Fe (II), Co (II), Ni (II), Cu (II), Zn (II), Pb (II), Hg (II)] towards
DPYBODPY in methanol and describe a new fluorescent probe,
DPYBODPY, for Zn (II) and Fe (II).
2. Experimental
2.1. Instruments and chemicals
NMR spectra were recorded on a Jeol JNM ECP 400 spectrom-
* Corresponding author.
E-mail address: r.w.boyle@hull.ac.uk (R.W. Boyle).
eter, with TMS dH ¼ 0 as the internal standard or residual protic
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.02.006

A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
497
solvent. [CDCl3, dH ¼ 7.26]. Chemical shifts are given in ppm (
d
) and
PyH), 6.16 (d, 2H, PyH), 5.91 (d, 2H, PyH), 5.42 (s, 1H, meso-H), 4.08
(t, 2H, CH) 3.60 (t, 2H, CH), 2.30 (m, 2H, CH). 13C NMR [100 MHz,
CDCl3]: 161.4,143.3,134.8, 132.8, 131.4,126.3, 118.3,114.9, 65.0, 48.2,
28.5, 0.9. Anal. Calc. for (%)C18H19IN2O; C, 53.22; H, 4.71; N, 6.90;
Found; C, 53.41; H, 4.92; N, 6.81.
coupling constants (J) are given in Hertz (Hz). NMR measurements
were recorded at 400 MHz. UVevis spectra were obtained on
a
Perkin Elmer Lambda 25 UVevis spectrophotometer. The
percentages of carbon, hydrogen and nitrogen in all compounds
were determined using a TruSpec elemental analyser. Fluorescence
spectra were measured using a PerkinElmer LS 55 Fluorescence
spectrometer with a right angle illumination method. Compact UV
Lamps e UVGL-25 Compact UV Lamp was used to the visualization
of thin-layer chromatography (TLC).
4-Hyroxybenzaldehyde, was purchased from Merck. Pyrrole,
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 3-bromo-1-
chloropropane and sodium iodide, were purchased from Acros
Organics. All metal acetate salts were purchased from Fluka and
used as received. Other chemicals were purchased from Sigma
Aldrich or Alfa Aesar. All chemicals were used as received with the
exception of pyrrole, which was distilled before use. All solvents
were purchased from Fisher Scientific with the exception of buta-
none, which was purchased from Acros Organics.
2.2.4. Synthesis of 5-[4-((3-iodopropoxy)phenyl)]dipyrromethene (4)
To a solution of 3 (0.81 g, 2.00 mmol) in ether (35 mL), was
added DDQ (470 mg, 2.00 mmol) in ether/methanol (6 mL:4 mL),
the reaction was allowed to proceed at room temperature-dark
ambient under an inert atmosphere for 15 min. The solution was
then filtered and treated four times with ether (apart, 25 mL),
followed by filtration to yield a dark brown microcrystalline solid
(0.8 g, 99%). 1H NMR [400 MHz, CD3OD]: 8.00 (b, 1H, NH), 7.93
(d, 2H, PyH), 7.55 (d, 2H, ArH), 7.07 (d, 2H, ArH), 6.98 (d, 2H, PyH),
6.56 (d, 2H, PyH), 4.22 (t, 2H, CH) 3.65 (t, 2H, CH), 2.37 (m, 2H, CH).
13C NMR [100 MHz, CD3OD]: 161.4, 143.2, 134.8, 132.5, 131.4, 126.2,
118.7, 115.2, 65.1, 48.2, 28.5, 1.2. Anal. Calc. for (%)C18H17IN2O; C,
53.48; H, 4.24; N, 6.93; Found; C, 53.52; H, 4.43; N, 6.77.
TLC was performed with using Merck aluminium plates coated
with silica gel 60 F254 and visualized under UV light (254 nm or
372 nm). Column chromatography was performed with using MP
Silica 32-63, 60 Å. All solvent mixtures are given in v/v ratios.
2.2.5. Synthesis of 4,4-difluoro-8-[4-((3-iodopropoxy)phenyl)]-4-
bora-3a,4a-diazaindacene (5)
Toluene (100 mL) was degassed for 30 min with nitrogen. To this
was added 4 (0.8 g, 2.00 mmol), and 8 equivalents triethylamine.
The solution was heated to 70 ꢀC for 30 min after which 5 equiv-
alents boron triflouride etherate was added in four portions with
3 min between each addition. Intensive white fume was occurred
and the reaction was stirred at reflux for 3 h. The solution was
concentrated by evaporation and the black residue re-dissolved in
a minimal amount of dichloromethane and carefully purified by
column chromatography (SiO2 dichlormethane:ethyl acetate 7:1)
a single red-orange band was observed which yielded a vermilion
solid. Yield; 40% (0.36 g). 1H NMR [400 MHz, CDCl3]: 7.93 (bs, 2H,
PyH), 7.56 (d, 2H, ArH), 7.07 (d, 2H, ArH), 6.98 (d, 2H, PyH), 6.55
(t, 2H, PyH), 4.23 (t, 2H, CH), 3.65 (t, 2H, CH), 2.37 (m, 2H, CH).
11B-NMR [128.3 MHz, CDCl3]: ꢁ0.44 (s, 1B); 19F NMR [376.83 MHz,
CDCl3]: ꢁ145.0 (dd, 2F) ꢁ144.85 (dd,1F); 13C NMR [100 MHz CDCl3]:
180.7, 174.3, 146.8, 137.1, 133.9, 132.0, 127.8, 110.7, 104.3, 77.0, 33.6,
1.9. Anal. Calc. for (%) C18H16BF2IN2O; C, 47.83; H, 3.57; N, 6.20;
Found; C, 47.78; H, 3.77; N, 6.12.
2.2. Synthesis
2.2.1. Synthesis of 4-(3-chloropropyloxy)benzaldehyde (1)
1-Bromo-3-chloropropane (4.71 g, 30.00 mmol, 1.5 equiv.) was
added to
a
solution of 4-hydroxybenzaldehyde (2.44 g,
20.00 mmol, 1.0 equiv.) and K2CO3 (5.52 g, 40.00 mmol, 2.0 equiv)
in acetonitrile (100 mL). The mixture was refluxed for 18 h, then
cooled to r.t. and filtered through diatomaceous earth. The filtrate
was concentrated and the residue was purified by column chro-
matography (silica gel, ratio: 1:10, 1:9 and 1:8, ethyl acetate/
hexanes) to afford 2.58 g (65%) of 4-(3-chloropropyloxy)benzal-
dehyde. 1H NMR [400 MHz, CDCl3]: 9.88 (s, 1H, CHO), 7.84 (d, 2H,
ArH), 6.99 (d, 1H, ArH), 4.19 (t, 2H, CH), 3.59 (t, 2H, CH), 2.36 (m,
2H, CH). 13C NMR [100 MHz, CDCl3]: 191.2, 164.0, 132.0130.1, 115.5,
66.3, 32.1, 29.8. Anal. Calc. for (%) C10H11ClO2 C, 60.46; H, 5.58;
Found: C, 60.79; H, 5.92.
2.2.2. Synthesis of 4-(3-iodopropyloxy)benzaldehyde (2)
2.2.6. Synthesis of 5-(4-Hydroxyphenyl)dipyrromethane (6)
To a solution of freshly distilled and degassed pyrrole (150 mL)
was added 4-hydroxybenzaldehyde (2.44 g, 20.00 mmol) and tri-
fluoroacetic acid (0.15 mL, 2.00 mmol). The reaction was allowed to
proceed protected from light and under nitrogen for 15 min at room
temperature, yielding a red-orange solution. The excess pyrrole was
removed under reduced pressure to yield a black/brown oil, which
was purified by gravity percolation chromatography (silica, eluent:
dichloromethane:ethylacetate 19:1). The resulting ruby coloured
oil was triturated with hexanes yielding a white solid. The solid was
dried under vacuum to yield a pale pink solid [21]. Yield: 99%
1H NMR [400 MHz, CDCl3]: 7.92 (b, 2H, NH), 7.25 (bs, 2H, PyH), 7.06
(d, 2H, ArH), 6.76 (d, 2H, ArH), 6.68 (d, 2H, PyH), 6.15 (m, 2H, PyH),
5.90 (bs, 1H, ArOH), 5.41 (s, 1H, meso-H). 13C NMR [100 MHz,
CDCl3]: 156.2, 143.2, 138.8, 135.3, 133.7, 127.1, 118.7, 118.2, 102.4.
Anal. Calc. for (%); C15H14N2O; C, 75.61; H, 5.92; N,11.76; C, 75.72; H,
6.15; N, 11.71.
1 (1.99 g, 10 mmol) and 1.2-equivalent sodium iodide (1.8 g,
12 mmol) were heated in DMF (50 mL) at 80 ꢀC for 18 h. The
mixture was cooled to r.t. and water was added. The aqueous
mixture was extracted with ethyl acetate (three times) and the
combined extracts were dried (MgSO4), filtered, and concentrated.
The pale oil was obtained. Yield: 99% (2.88 g). 1H NMR [400 MHz,
CDCl3]: 9.87 (s, 1H, CHO), 7.84 (d, 2H, ArH), 7.04 (d, 1H, ArH), 4.19
(t, 2H, CH), 3.48 (t, 2H, CH), 2.36 (m, 2H, CH). 13C NMR [100 MHz,
CDCl3]: 191.2, 164.1, 132.1, 129.9, 115.5, 66.0, 29.5, 2.1. Anal. Calc. for
(%) C10H11IO2; C, 41.40; H, 3.82; Found:C, 41.62; H, 3.92.
2.2.3. Synthesisof5-[4-((3-iodopropoxy)phenyl)]dipyrromethane(3)
2 (1.45 g, 5 mmol) was dissolved in freshly distilled pyrrole
(100 mL) and degassed with nitrogen for 15 min. Then TFA (0.1 ml)
was added and the solution stirred at r.t. under nitrogen for 30 min.
The excess pyrrole was then removed by evaporation in vacuo and
the green oily residue was purified by column chromatography
eluting with 1:10 ethyl acetate:dichloromethane to give an oil. The
oil was triturated with hexanes and the material was obtained as an
off-white solid. The solid was dried under vacuum. The resulting
solid was recrystallized from methanol to yield the pure product as
an off-white dust. Yield: 76% (1.54 g) 1H NMR [400 MHz, CDCl3]:
7.90 (b, 2H, NH), 7.12 (d, 2H, ArH), 6.86 (d, 2H, ArH), 6.69 (d, 2H,
2.2.7. Synthesis of 5-(4-Hydroxyphenyl)dipyrromethene (7)
To a solution of 6 (480 mg, 2.00 mmol) in ether (25 mL), was
added DDQ (470 mg, 2.00 mmol) in ether/methanol (3 mL:2 mL),
the reaction was allowed to proceed at room temperature under an
inert atmosphere for 8 min. The solution was then filtered and
triturated with ether (35 mL), followed by filtration to yield a dark

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A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
NH H N
H
N
O
O
O
Br
Cl
NaI
K2CO3, MeCN
DMF
TFA
OH
O
O
O
I
Cl
I
(1)
(2)
(3 )
F
F
B
N
H N
N
N
BF3.OEt2
TEA
Methanol
Ether
3
DD Q
O
O
I
I
(4 )
(5)
O
NH H N
N
HN
H
N
TFA
DDQ
2
O H
OH
(6)
OH
(7 )
F
N
N
N
K2 CO 3
Butanone
B
O
O
(5)
(7 )
N H
F
(DPYBODPY)
Scheme 1. Synthesis of DPYBODPY.
Fig. 1. Absorption spectra of DPYBODPY-metal ion mixtures.
Fig. 2. Fluorescence spectra of DPYBODPY-metal ion mixtures.

A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
499
Fig. 4. Emission spectra (lex ¼ 450 nm) of DPYBODPY (1
m
M) upon addition of Zn2þ
Fig. 3. Emission spectra (lex ¼ 450 nm) of DPYBODPY (1
(1 M, 10 M, 20 M 30 M, 35 M, 40 M, 45 M, 50 M) in MeOH.
m
M) upon addition of Fe2þ
(1 M, 10 M, 20 M 30 M, 35 M, 40 M, 45 M, 50 mM) in MeOH.
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
CDCl3]: 8.15 (b, 1H, NH), 7.83 (d, 4H, PyH), 7.58 (d, 4H, ArH), 7.33
(d, 2H, PyH), 7.10 (d, 2H, ArH), 6.96 (d, 2H, ArH), 6.87 (d, 4H, PyH),
6.55 (t, 2H, PyH), 4.20 (t, 2H, CH), 4.18 (t, 2H, CH), 2.32 (m, 2H, CH).
11B-NMR [128.3 MHz, CDCl3]: ꢁ0.4891 (s, 1B). 19F NMR
[376.83 MHz, CDCl3]: ꢁ144.59 (dd, 2F), ꢁ144.74 (dd, 1F). 13C NMR
[100 MHz CDCl3]: 161.3, 159.3, 143.4, 140.2, 136.0, 133.7, 132.9, 131.4,
129.3, 127.0, 125.0, 123.8, 119.1, 118.4, 117.4, 115.1, 66.3, 31.3. Anal.
Calc. for (%); C33H27BF2N4O2; C, 70.73; H, 4.86; N, 10.00; Found; C,
70.64; H, 4.77; N, 9.90.
brown microcrystalline solid (475 mg, 99%) [21]. 1H NMR [400 MHz,
CD3OD]: 8.32 (b, 1H, NH), 7.94 (bs, 2H, PyH), 7.51 (d, 2H, ArH), 7.25
(d, 2H, PyH), 7.04 (d, 2H, ArH), 6.83 (m, 2H, PyH), 5.90 (bs, 1H,
ArOH). 13C NMR [100 MHz, CD3OD]: 154.7, 141.9, 139.6, 135.3, 133.7,
127.1, 118.9, 118.3, 102.0. Anal. Calc. for (%), C15H12N2O; C, 76.25; H,
5.12; N, 11.86; Found; C, 76.55; H, 5.33; N, 11.71.
2.2.8. Synthesis of DPYBODPY
5 (0.452, 1.00 mmol, 1 equiv.) was dissolved in butanone
(70 mL), 7 was added to this solution (0.354 g, 1.5 mmol, 1.5 equiv.)
followed by 5 equivalents K2CO3 as solid. The mixture was stirred at
60 ꢀC for 96 h. The butanone was then removed in vacuo and
dichloromethane (150 mL) was added to the residue. The
solution was extracted with dichloromethane (200 mL) and
water (2 ꢂ 200 mL) and brine (1 ꢂ 200 mL). The organic layer was
collected and dried over anhydrous sodium sulphate. Then, the
solvent of the filtration was removed, following the residue
3. Results and discussion
3.1. Synthesis and spectroscopic studies of DPYBODPY
Bodipy complexes have a strong chemical and photochemical
stability with excellent electron-transfer properties [22,23]. The
novel Bodipy-dipyrrin derivative (DPYBODPY) was synthesized by
an eight-step protocol as shown in Scheme 1. The DPYBODY dye
was prepared from Bodipy (5) and dipyrrin (7) containing
a phenolic eOH with halo-alkane as the solvent in good to excellent
yield. DPYBODPYand intermediates were characterized by 1H NMR,
was purified through
a column eluting with 10:1; dichlor-
omethane:ethyl acetate. The relevant fractions were collected and
the solvent was removed by evaporation. A crimson crystalline
material was obtained. Yield; 58% (0.325 g). 1H NMR [400 MHz,
Fig. 5. a) The selectivity of DPYBODPY (1
mM) towards iron ions (20 equiv.) in the presence of other metal ions on fluorescence spectra (in methanol). b) The selectivity of
DPYBODPY (1 M) towards zinc ions (20 equiv.) in the presence of other metal ions on fluorescence spectra (in methanol).
m

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A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
Table 1
Chemical shifts of 1H-NMR signals of DPYBODPY [in (CD3)2SO] in the free form and
in the presence of Zn2þ
.
Chemical shift (ppm)
DPYBODPY
DPYBODPY þ Zn2þ
Py-H1
Py-H2
Py-H3
Py-NH
7.83
6.87
6.55
8.15
7.64
6.92
6.65
e
attributed to the complexation between the electron-donating
nitrogen of dipyrrin group and metal ions in solution medium
[20]. As the inset in Fig. 1 clearly shows, above 20 equivalents of Zn
(II) or Fe (II), the change in the absorption wavelengths fall off very
quickly, indicating a strong affinity between the DPYBODPY (ligand)
and the Zn (II), Fe (II) ions (or Co (II)) in methanol. Additionally, no
remarkable change in maximum absorption intensities or wave-
lengths was observed with other DPYBODPY-metal cations (Ni, Cu,
Pb, Hg).
3.3. Fluorescence spectra of DPYBODPY with metal ions
The fluorescence spectra of DPYBODPYand DPYBODPY-Metal ion
mixtures were similarly measured in methanol at an excitation
wavelength of 450 nm and are shown in Fig. 2. The fluorescence peak
of the free dye was observed at 515 nm in methanol. By addition of Fe
(II) and Zn (II) solution, the maximum peak shifted towards the blue
with a concomitant increasing or quenching in emission intensity.
Fig. 6. Job’s plot for DPYBODPY/metal ions, 0.1 mM in CH3OH.
13C NMR, 19F NMR, 11B NMR (as appropriate) [NMR data in
supporting information].
UVevis absorption and fluorescence spectra were recorded at
room temperature in methanol, although the target DPYBODPY has
good solubility in a range of organic solvent. To investigate the
application of DPBODPY as a fluorescence probe, the effect of metal
ions was performed at 1 mM concentration. In this way complexa-
tion reactions of DPYBODPYand the binding properties of the metal
ions (Fe, Co, Ni, Cu, Zn, Pb, Hg) were studied. From this data it was
concluded that Zn (II) and Fe (II) are the ions most successfully
detected by DPYBODPY.
3.2. UVevis absorption spectra of DPYBODPY with metal ions
The recognition behaviour of DPYBODPY towards various metal
ions was investigated. Briefly methanolic solutions of DPYBODPY
(1 mM) and metal acetate salt (20 mM) were prepared. UVevisible
absorption spectra were then obtained. DPYBODPY and DPY-
BODPY-metal ion complexes, present a strong absorption transition
in the 475e500 nm range, which can be attributed to the S0eS1
transition of the Bodipy component (Fig. 2) [24,25]. The Zn and Fe
complexes were detected at 472 nm and 479 nm, respectively;
although the wavelength of metal free DPYBODPY was observed at
495 nm in the absorption spectra, representing hyspsochromic shifts
of 23 nm for DPYBODPY-Zn (II) and 16 nm for DPYBODPY-Fe (II)
relative to metal free DPBODPY. DPYBODPY-metal ion mixtures
showed no significant changes relative to metal free DPYBOPPY,
with the exception of Co (II). The remarkable hypsochromic shift of
the maximum absorption wavelengths of DPYBODPY were
Fig. 7. SterneVolmer plot for the fluorescence quenching and enhancement of metal
ions by DPYBODPY in CH3OH.

A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
501
The bands shifted 25 nm and 21 nm for Zn (II) and Fe (II) respectively.
In addition, the fluorescence emission intensity of DPYBODPY is
remarkably enhanced upon the addition of Zn (II) and quenched
upon the addition of Fe (II) which is attributed to the formation of
complex (1:2 or 1:3; metal:ligand) [21].
Fig. 3 indicates that starting with a 1
m
M concentrations of Fe (II),
a decrease in the fluorescence intensity occurred with a 10e12 nm
bathochromic shift. In order to ascertain the selectivity of DPY-
BODPY for Fe (II), we repeated the experiments for Zn (II). In
contrast to DPYBODPY þ Fe (II) mixtures, the wavelength of
DPYBODPY þ Zn (II) mixtures is hypsochromically shifted and
the fluorescence intensity increases with increasing Zn (II)
concentration.
To confirm DPYBODPYas an ion-selective fluorescence probe for
iron and zinc ions the effect of competing metal ions was deter-
mined. DPYBODPY 1 mM was treated with 20 equiv. iron and zinc
In contrast, the emission of DPYBODPY-Co (II) mixture occurred at
lower intensity and other transition metal ions such as Hg (II), Ni (II), Cu
(II) and Pb (II) gave only a minor quenching of the fluorescence of
DPYBODPY. This quenching effect is often attributed to electron
transfer from ligand to metal cations (generally for heavy metal cation).
The enhancement or decrease in fluorescence intensity can be
ascribed to the planarity and stability of the dipyrrin group induced
by chelation of Zn (II) or Fe (II). The geometry of Zn (II) complex is
slightly distorted tetrahedral [26] and the geometries of Fe (II) e Fe
(II) are distorted tetrahedral-octahedral, respectively. There, the
valance of iron depends on the stability of the ion in solution. It has
been generally reported that iron complexes have an octahedral
geometry. Similarly, cobalt complexes have the same geometry and
coordination as iron complexes [27,28]. In summarily, the basis of
the selectivity and affinity depends on the match between the
valence of the metal cation and the electron donating ability of
the nitrogen on the dipyrrin. Moreover, it can be considered that
the expected trends between ligand and metal ion are observed as
hardesoft acidebase effects.
metals in the presence of other metal ions (20 equiv), respectively.
As shown in Fig. 5, the presence of other metal ions on the detec-
tion of Zn2þ and Fe2þhad little effect, except in the case of Co2þ
which showed a significant perturbation.
3.4. Determination of complex stoichiometry
In order to determine the stoichiometry of the Zn (II) and Fe
(II)/Fe (III) complexes, the Job’s plot method of continuous varia-
tion was also used. The total concentration of the compound
DPYBODPY and metal ions were constant (0.1 mM), with
a continuous variable molar fraction of guests. Fig. 5 shows the
Job plot of DPYBODPY with metal ions. The DPYBODPY/Zn and
The gradual addition of Fe (II) and Zn (II) to DPYBODPY resulted
in significant quenching or enhancement, respectively as shown
Figs. 3 and 4. Due to the interaction between DPYBODPY and metal
ions, suggesting that DPYBODPY could be used as a quantitative
chemosensor for Fe (II) and Zn (II).
DPYBODPY/Fe complex concentrations approach
a maximum
when the molar fraction of iron and zinc ions are 0.27and 0.34,
respectively, (which means DPYBODPY with complex forms w1:3
and 1:2,respectively).
Fig. 8. The estimated perspective of DPYBODPY-metal ions combination with four or six coordination.

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A.N. Kursunlu et al. / Dyes and Pigments 94 (2012) 496e502
[4] Zhang Z, Xu B, Su J, Shen L, Xie Y, Tian H. Color-tunable solid-state
3.5. SterneVolmer analysis
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I0=I ¼ 1 þ Ksv½Mꢃ
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constant. For both metal ion, linear behaviour was shown in both
graphics. But, while the line of slope to upward in iron ion; towards
down in zinc ion. The static quenching constants (Ksv) are calcu-
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3.6. Analysis of 1H-NMR spectrum of Zn complex
We carried out the 1H-NMR experiments of DPYBODPY in the
absence of zinc ions in order to understand the binding behaviour.
The data of complex obtained are shown in supporting information.
The two proton signals of dipyrrin were shifted to downfield and
one proton signal was shifted to up field (see Table 1 and support.
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4. Conclusion
In conclusion, a novel selective fluorescent probe for Zn (II) and
Fe (II) with high selectivity has been reported. The Bodipy-dipyrrin
conjugate presented in this work give a rapid, sensitive and selec-
tive response to Fe (II) and Zn (II), but gives little response when
associated with a range of other metal cations. We believe the
BPYBODPY probe therefore has a number of potential applications
for the qualitative and quantitative detection of Zn (II) and iron (II)
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This work was supported by the Scientific Research Projects
Foundation of Selcuk University (SUBAP-Grant Number 2011-
11601191 and 11601195).
Appendix. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.dyepig.2012.02.006.
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