A new diketopyrrolopyrrole (DPP) derivative bearing boronate group as fluorescent probe for fluoride ion

Article abstract of DOI:10.1016/j.dyepig.2013.02.015

A new diketopyrrolopyrrole (DPP) derivative bearing pinacol boronate group has been synthesized via Suzuki-Miyaura reaction under mild conditions in good yield. The product could act as a colorimetric and ratiometric fluorescent probe for fluoride ion with high sensitivity and selectivity. The recognition mechanism was attributed to unique fluoride-boron interaction, which blocked the charge transfer (CT) between DPP chromophore and the empty p orbitals of boron atoms, and proved by the fluorescence spectra, ¹⁹F NMR spectra and ¹H NMR spectra titration experiments.

Full text of DOI:10.1016/j.dyepig.2013.02.015

Dyes and Pigments 98 (2013) 232e237
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A new diketopyrrolopyrrole (DPP) derivative bearing boronate group
as fluorescent probe for fluoride ion
*
Guanjun Zhang, Limin Wang , Xiaofei Cai, Liang Zhang, Jianjun Yu, Aili Wang
Shanghai Key Laboratory of Functional Materials Chemistry, Institute of Fine Chemicals, East China University of Science and Technology,
Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new diketopyrrolopyrrole (DPP) derivative bearing pinacol boronate group has been synthesized via
SuzukieMiyaura reaction under mild conditions in good yield. The product could act as a colorimetric
and ratiometric fluorescent probe for fluoride ion with high sensitivity and selectivity. The recognition
mechanism was attributed to unique fluorideeboron interaction, which blocked the charge transfer (CT)
between DPP chromophore and the empty p orbitals of boron atoms, and proved by the fluorescence
spectra, 19F NMR spectra and 1H NMR spectra titration experiments.
Received 6 September 2012
Received in revised form
31 January 2013
Accepted 22 February 2013
Available online 14 March 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Diketopyrrolopyrrole (DPP)
Fluoride ion
Boronate group
Fluorogenic chemosensor
Anion sensing
BenesieHildebrand (BeH) method
1. Introduction
Recently, considerable studies have been made to use DPP-
containing materials in polymer solar cells (PSCs), organic field ef-
Fluoride ion is the smallest anion with a high charge density and
a hard Lewis basic nature, which results in unusual chemical
properties. It is biologically important because of their roles in a
wide range of chemical and biological processes, for example,
dental care and the treatment of osteoporosis [1e5]. In this regard,
the sensing of fluoride ion has attracted growing attention, and
considerable effort has been devoted to the development of probes
for fluoride ion [6e10].
fect transistors (OFETs), organic light-emitting diodes (OLEDs), two-
photon excitation, fluorescent sensor, and dye sensitizing solar cell
applications [27e35].
Herein, we would like to report a novel DPP derivative bearing a
pinacol boronate group through operationally mild process and in
satisfied yield compared with reference (as shown in Scheme 1)
[36]. This compound displayed selective fluorescent change for
fluoride ion among the other halide ions.
In most cases, hydrogen bond between amide or lactam
hydrogen (NH) and fluoride was usually used for fluoride ion
recognition. For examples, the 1,4-diketo-3,6-diphenylpyrrolo[3,4-
c]pyrrole (DPP) chromophore as fluorescent sensor for fluoride
ion was reported because that the strong HeF interaction could
result in deprotonation of the DPP amide moiety and huge change
both in color and fluorescence [11,12]. However, there have been
few reports regarding fluoride ion detection utilizing unique fluo-
rideeboron interaction [13e16].
2. Materials and methods
2.1. Experimental
2.1.1. General
Unless otherwise stated, reagents were commercially obtained
and used without further purification. All solvents were freshly
distilled: THF from Na/benzophenone, anhydrous DMF, CH2Cl2 from
CaH2. Reactions were monitored by TLC. Flash chromatography
separations were carried out using silica gel (200e300 mesh).
NMR and 13C NMR spectra were collected on a Bruker Avance DPS-
300 spectrometer using CDCl3 or DMSO-d6 as solvent and tetra-
methylsilane as internal reference, respectively. Mass spectrometry
was performed by Bruker Biflex III MALDI-TOF (both positive and
DPP and its derivatives represent a class of brilliant red and
strong fluorescent high performance pigments that have prominent
light-resistant, weather-resistant, and solvent-resistant [17e26].
1H
* Corresponding author. Tel./fax: þ86 21 64253881.
E-mail addresses: wanglimin@ecust.edu.cn, wangliminecust@msn.cn (L. Wang).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.02.015

G. Zhang et al. / Dyes and Pigments 98 (2013) 232e237
233
Br
O
O
Na
O
HN
O
Br
CN
O
NH
t-Amyl alcohol
O
Br
1
O
O
B
Br
O
O
K2CO3,DMF
120 °C
Pd(PPh3)2Cl2, KOAc
Bis(pinacolato)diboron
N C12H25
N
C12H25
N C12H25
N
C12H25
O
O
B
O
Br
O
3
2
Scheme 1. The synthetic route of probe.
negative ion reflector mode). Absorption spectra were measured on
Thermo UVeVis spectrophotometer. Fluorescence spectra were
obtained on Thermo fluorescence spectrophotometer. Both excita-
tion and emission slit widths were 2.5 nm.
Subsequently, the resulting suspension was stirred for 3 h at 120 ꢀC,
the reaction mixture was then cooled to 50 ꢀC. Glacial acetic acid
was slowly added and refluxed for 30 min, 100 mL methanol and
water (1/2) were added, the mixture was refluxed for another 2 h.
After filtration and dry, a bluish-red solid was obtained. (7 g, yield:
65%). (The decomposition temperature of compound 1 was proved
to be greater than 400 ꢀC according to TGA results, which were
consistent with reported literature.) [11].
2.2. Synthesis
2.2.1. Synthesis of compound 3,6-bis(4-bromophenyl)pyrrolo[3,4-c]
pyrrole-1,4(2H,5H)-dione (1) [11]
2.2.2. Synthesis of compound 3,6-bis(4-bromophenyl)-2,5-
didodecylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2)
Sodium (2.3 g, 100 mmol) dissolved in 50 mL t-amyl alcohol at
about 90 ꢀC over 1 h with catalytic amount of FeCl3. The solution
was cooled to 50 ꢀC, 4-bromobenzonitrile was added, and the
mixture was heated to 90 ꢀC, then diisopropylsuccinate (5.05 g,
25 mmol) in 20 mL t-amyl alcohol was added drop-wisely over 2 h.
Compound 1 (0.223 g, 0.5 mmol), K2CO3 (0.276 g, 2 mmol) and
50 mL DMF were added into a three-necked flask, heated to 120 ꢀC
30000
28000
26000
4 eq
24000
22000
0 eq
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
F
500
550
600
650
700
Wavelength (nm)
Fig. 1. The absorption spectra of 3 (5 ꢁ10ꢂ5 mol/L in CH2Cl2) upon addition of 0e2 equiv.
Fig. 2. The emission spectra of 3 (5 ꢁ 10ꢂ5 mol/L in CH2Cl2) upon addition of 0e
TBAF.
2 equiv. TBAF.

234
G. Zhang et al. / Dyes and Pigments 98 (2013) 232e237
Fig. 3. The photograph of color and fluorescence change between probe and probe with fluoride ion. (a): color change; b): fluorescence change excited at 365 nm).
for 30 min,1-bromododecane (2 mL, 5 mmol) was added slowly. The
mixture was kept at 120 ꢀC for 3 h. After cooled, 50 mL water was
poured to quench the reaction, the mixture were filtered. The cake
was dried under vacuum, resolved in 50 mL CH2Cl2. The mixture was
purified by column chromatography (silica gel, petroleum ether/
ethyl acetate 20/1) to give a dark red solid as the product. (0.234 g,
yield: 60%) 1H NMR (400 MHz, CDCl3): 0.875 (t, J ¼ 6.8 Hz, 6H), 1.23
(m, 40H), 3.70 (t, J ¼ 7.6 Hz, 4H), 7.61 (d, J ¼ 8.4 Hz, 4H), 7.64 (d,
J ¼ 8.4 Hz, 4H). 13C NMR (400 MHz, CDCl3): 14.08, 22.66, 28.99, 29.31,
29.40, 29.49, 29.59, 31.89, 41.78, 109.88, 125.78, 126.93, 130.10,
132.15, 147.41, 162.34. HRMS: m/z ¼ 781.2939. (calcd. 780.2865).
4H), 7.74 (d, J ¼ 8.0 Hz, 4H), 7.97 (d, J ¼ 8.0 Hz, 4H). 13C NMR
(400 MHz, CDCl3): 14.13, 22.69, 25.03, 26.71, 29.06, 29.34, 29.44,
29.51, 31.91, 38.72, 41.93, 83.52, 110.17, 127.73, 130.63, 134.74, 135.11,
148.50, 162.61. HRMS: m/z ¼ 877.6434. (calcd. 876.6359).
3. Results and discussions
The emission change could be monitored at 527 nm and
596 nm. Stock solutions (1 mmol/L) of tetrabutylammonium salts
of Fꢂ, Clꢂ, Brꢂ, and Iꢂ in CH2Cl2 were prepared. Stock solutions of
probe (0.1 mmol/L) were prepared in CH2Cl2. Test solutions were
prepared by placing 2 mL stock solution of the probe into test
tube, adding an appropriate aliquot of each ion stock. For all
measurements, excitation was at 486 nm; emission was at
527 nm. Excitation and emission spectra were carried out by
adding stock solutions of TBAF in CH2Cl2 to the solutions of probe
in CH2Cl2.
As depicted in Figs. 1 and 2, in presence of two equiv. fluoride
ion, both the maximum absorption and emission wavelength of 3
were a little blue shift. Upon addition of fluoride ion, the intensity
at 486 nm, 350 nm and 250 nm were gradually increased, and a
little blue shift also could be observed. Meanwhile, the intensity at
596 nm, 285 nm decreased. In addition, the emission intensity at
535 nm experienced an approximated 5 folds increase with a blue
shift of the emission band from 535 nm to 527 nm, meanwhile the
band at 596 nm decreased gradually. With respect to the spectra
2.2.3. Synthesis of compound 2,5-didodecyl-3,6-bis(4-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (3)
Compound
2 (0.39 g, 0.5 mmol), bis(pinacolato)diboron
(0.28 g, 1.1 mmol), potassium acetate (117 mg, 1.2 mmol), and
bis(triphenylphosphine) palladium dichloride (17 mg, 0.025 mmol)
were added to 25 mL distilled 1,4-dioxane, then heated to 85 ꢀC and
reacted for 2 h. After cooled, 20 mL water was added and the
mixture was extracted with 80 mL CH2Cl2. The organic layer was
combined and dried over Na2SO4. The solvent was removed by ro-
tary evaporation in vacuum, and the residue was purified by column
chromatography (silica gel, petroleum ether/ethyl acetate 10/1) to
give an orange solid. (0.175 g, yield: 40%) 1H NMR (400 MHz, CDCl3):
0.90 (t, J ¼ 6.6 Hz, 6H), 1.28 (m, 40H),1.37 (s, 24H), 3.75 (t, J ¼ 7.2 Hz,
200
180
160
140
120
100
80
60
40
20
0
-20
0
5000
10000
15000
20000
25000
1/[TBAF]
Fig. 4. Plot of CP0/ΔA466 vs (1/CB) of the titration data.
Fig. 5. Plot of CP0/ΔA466 vs (1/CB)2 of the titration data.

G. Zhang et al. / Dyes and Pigments 98 (2013) 232e237
235
Fig. 6. 19F NMR spectra of sensor in CDCl3 in the presence of (a) 0.5 equiv, (b) 1 equiv, (c) 2 equiv, and (d) 4 equiv TBAF.
changes, an obvious fluorescence color change from yellow-green
to green was observed, as shown in Fig. 3. However, other halide
ions produced no changes in both absorption and emission
spectra.
Benesi-Hildebrand (B-H) method was a widely used approach
for determining the stoichiometry and equilibrium constants
of nonbonded interactions, particularly 1:1 and 1:2 interac-
tions [37].
Fig. 7. Partial 1H NMR spectra of (a) only probe, (b) probe with 2 equiv TBAF.

236
G. Zhang et al. / Dyes and Pigments 98 (2013) 232e237
O
F
O
O
F
B
HO
B
O
B
ChargeTransfer
F
ChargeTransfer
O
O
O
TBAF
TBAF
N
C12H25
N
C12H25
N
C12H25
N
O
C12H25
N
C12H25
N
C12H25
O
O
O
F
B
F
O
B
OH
B
O
O
F
4b
3
4a
Scheme 2. Hypothesized binding mode of probe with F-.
When absorption intensity of 466 nm was used, let us assume
that a chromophore-containing molecule P interacts with anion B
to form a 1:n complex PBn.
points of both absorption and emission spectra change reached
after addition of two equiv. fluoride ion, 1:2 interactions between
probe and Fꢂ was introduced.
To further prove the binding mode and mechanism, titration
experiment with 19F and 1H NMR spectroscopy were studied. Fig. 6
showed the 19F NMR spectra of probe 3, upon the addition of Fꢂ.
According toliterature reported, the bands at ꢂ132.8 and ꢂ128 ppm,
correspond to 4a and free Fꢂ, with excess fluoride ions, 4b was more
stable species, correspond to the band at ꢂ139.5 ppm, the band
arising from 4a still existed alongside the band of 4b, which were a
little weak. 1H NMR spectra titration results proved that H chemical
shift of phenyl ring shift to up-filed after fluoride ion added, in
addition, 1H NMR spectra of phenyl ring revealed that two different
compounds existed in system. Combined with 19F NMR spectra, the
two compounds were speculated as 4a and 4b. (as shown in Fig. 7
and Scheme 2).
K
%
P þ nB
PBn
To be concise, we further assumed that the BeereLambert law
could be expressed in the form of A ¼
3
C. Then, the 1:1 B-H equation
was as follows:
Cp0
1
1
ꢀ
ꢁ
ꢀ
ꢁ
¼
þ
n
D
A
ðCBÞ k
3
ꢂ
3
p
3
ꢂ
3
p
pBn
pBn
where
CB0 were the initial concentrations of P and B,
absorption coefficients of P and PBn, respectively [38].
It was generally believed that the CP0
A466 vs (1/CB)n plot
DA was change in absorbance during complexation. CP0 and
3
P and PBn were the
3
The 19F NMR spectroscopy in Fig. 6 and the 1H NMR spectroscopy
data in Fig. 7 assumed the formation of 4a, and 4b, finally 4b was
more stable component. On the basis of the above facts, the binding
mode of probe with Fꢂ was hypothesized as shown in Scheme 2.
The mechanism for the fluorescent change upon the addition of
fluoride ion could be attributed to the interaction of the boron
center and fluoride, a complex formed between boron atom and
fluoride ion. To our best knowledge, tri-substituted boron atoms
have a sp2 trigonal planar geometry with an empty p orbital. Before
addition of Fꢂ, the charge of flurophore could be transferred to the
/D
would yield a straight line for a 1:n complexation. On the basis of
these hypothetic values, the binding stoichiometry could be
determined according to the linearity of the B-H plots in the form of
either n ¼ 1 or n ¼ 2, evaluated by the correlation coefficient R2. As
shown in Figs. 4 and 5, for 1:1 binding interactions, the plot showed
nonlinear correlation; however, when used the B-H equation as
n ¼ 2, CP0
/
D
A vs (1/CB)2 plot gave a straight line with R2 ¼ 0.99917,
binding constant was 2.4 ꢁ 107[M]ꢂ2. Combination with saturation
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2.5
2.0
1.5
1.0
0.5
0.0
none
F
Cl
Br
I
none
F
Cl
Br
I
Fig. 8. Absorbance ratiometric response of probe 3 between 330 and 280 nm to the
Fig. 9. Emission ratiometric response of probe 3 to the halide ions. The emissions were
halide ions.
at 510 and 596 nm and excited at 490 nm.

G. Zhang et al. / Dyes and Pigments 98 (2013) 232e237
237
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In conclusion, a new DPP derivative bearing pinacol boronate
group was synthesized for the first time via SuzukieMiyaura re-
action under mild conditions in good yield. The compound showed
selective fluorescent enhancement for fluoride ion among the other
halide ions because unique fluorideeboron interaction blocked the
charge transfer (CT) between DPP and the boron center. On the
other hand, the recognition mechanism was confirmed successful
by the fluorescence spectra, 19F NMR spectra and 1H NMR spectra
titration experiments. In addition, the compound 3 bearing boro-
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optoelectronic materials.
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This research was financially supported by the National Nature
Science Foundation of China (20672035), the Opening Foundation
of Zhejiang Provincial Top Key Discipline, the Fundamental
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