A highly selective and sensitive probe based on benzo[1,2-b:4,5-b′]dithiophene: Synthesis, detection for Cu(II) and self-assembly

Article abstract of DOI:10.1016/j.tet.2016.03.029

A novel turn-off probe for copper(II) containing benzo[1,2-b:4,5-b′]dithiophene (BDT) and two picolinamide units was synthesized. In this probe, two picolinamide units complex with one Cu²⁺ ion and two nitrogen atoms in each picolinamide unit coordinate with Cu²⁺, which is verified by DFT calculation. Its fluorescence quantum yield is 0.43 and the detection limit is as low as 2.4×10^-8 mol/L. The results show that the probe displays good selectivity for Cu²⁺ over other ions (Mn²⁺, Pb²⁺, Cr³⁺, Zn²⁺, Ni²⁺, K⁺, Ca²⁺, Ag⁺, Mg²⁺, Fe³⁺, Fe²⁺, Hg²⁺, Al³⁺, Cd²⁺, Pd²⁺, Co²⁺). Furthermore, the probe induced by Cu²⁺ and the π-π interaction of the aromatic unit can also form rod structure assembly, which can be observed by scanning electron microscopy (SEM).

Full text of DOI:10.1016/j.tet.2016.03.029

Tetrahedron 72 (2016) 2219e2225
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A highly selective and sensitive probe based on benzo[1,2-b:4,5-b0]
dithiophene: synthesis, detection for Cu(II) and self-assembly
,
Yuwen Ma a, Taohua Leng b, Guoqiao Lai c, Zhifang Li c, Xiaojia Xu a, Jianwei Zou d
*
,
,
Yongjia Shen a, Chengyun Wang a
*
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237, PR China
b National Food Quality Supervision and Inspection Center (Shanghai)/Shanghai Institute of Quality Inspection and Technical Research, Shanghai
200233, PR China
c Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, PR
China
d Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, PR China
a r t i c l e i n f o
a b s t r a c t
A novel turn-off probe for copper(II) containing benzo[1,2-b:4,5-b0]dithiophene (BDT) and two picoli-
namide units was synthesized. In this probe, two picolinamide units complex with one Cu2þ ion and two
nitrogen atoms in each picolinamide unit coordinate with Cu2þ, which is verified by DFT calculation. Its
fluorescence quantum yield is 0.43 and the detection limit is as low as 2.4ꢀ10ꢁ8 mol/L. The results show
Article history:
Received 8 January 2016
Received in revised form 3 March 2016
Accepted 8 March 2016
Available online 10 March 2016
that the probe displays good selectivity for Cu2þ over other ions (Mn2þ, Pb2þ, Cr3þ, Zn2þ, Ni2þ, Kþ, Ca2þ
,
Agþ, Mg2þ, Fe3þ, Fe2þ, Hg2þ, Al3þ, Cd2þ, Pd2þ, Co2þ). Furthermore, the probe induced by Cu2þ and the
interaction of the aromatic unit can also form rod structure assembly, which can be observed by
scanning electron microscopy (SEM).
Keywords:
pep
Fluorescent dyes
Benzo[1,2-b:4,5-b0]dithiophene
Picolinamide
Ó 2016 Elsevier Ltd. All rights reserved.
Turn-off probe
Self-assembly
1. Introduction
At the same time, molecular self-assembly based on rational
control of non-covalent interactions such as hydrophobic in-
teractions, hydrogen bonding, aromatic stacking or metal co-
ordination interactions, provides the design of self-assembly
molecules from nanometer to micrometer scale.25 Among these
non-covalent interactions for molecular self-assembly, co-ordina-
tion compounds of metal ions with the organic ligands can result in
interesting structures such as spherical particles,26 rigid rods,27
nanotubes28 and springs29 of micro to even nano dimension.
In this work, a novel probe was designed and synthesized, in
which benzo[1,2-b:4,5-b0]dithiophene (BDT) unit is used as fluo-
rophore and two picolinamide units are used as metal-binding
The design and synthesis of efficient artificial receptors for var-
ious ions have received much interest in the last decade due to their
essential roles in many places.1e10 Among these ions, copper(II) is
the third most abundant transition-metal ion in the human body,
and it plays an important role in many biological and environmental
processes.5 Up to now, much effort has been made to detect cop-
per(II) ions based on different analytical strategies,11e22 among
which fluorometric methods have attracted considerable attention.
Benzo[1,2-b:4,5-b0]dithiophene (BDT) unit has been the most
popular donor for designing bulk heterojunction solar cells for its
favor light harvesting and thermal stability.23 In our previous work,
BDT unit was formed copolymer with benzodithiophene and its
photoelectric properties were studied.24 Then we found that BDT
unit has strong fluorescence. However, to the best of our knowl-
edge, there are few researches for designing probe containing BDT
as fluorophore.
sites. To develop the probe of fluorophored
rdreceptor form, phenyl group is elongated the
p
conjugate space-
-conjugation.
p
Picolinamide unit has been utilized as a receptor and a suitable p-
conjugated bridge. It is anticipated that the external metallic cat-
ions stimulus with picolinamide unit could modulate the intra-
molecular charge transfer, resulting in changes in the absorption
spectra and fluorescence emission, thus the compound can be used
as turn-off sensor for Cu2þ in a flash way, furthermore, transition
metal Cu2þ can induce the compound to form metal-
losupramolecular assembly.
* Corresponding authors. Tel./fax: þ86 21 64252967 (C.-Y.W.); e-mail addresses:
jwzou@nit.net.cn (J. Zou), yjshen@ecust.edu.cn (Y. Shen), cywang@ecust.edu.cn
(C. Wang).
http://dx.doi.org/10.1016/j.tet.2016.03.029
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.

2220
Y. Ma et al. / Tetrahedron 72 (2016) 2219e2225
2. Results and discussion
the fluorescence intensity at a particular concentration of Cu2þ, the
ratio of the final fluorescence intensity to the initial fluorescence
intensity was found to be 0.03.
2.1. Synthesis
From the titration experiment, it can be estimated that Cu2þ and
picolinamide unit formed complex with a ratio of 1:2, and the ratio
was confirmed by the Job’s Plot (Fig. 4). The change in Job’s Plot
happened at [Cu2þ]/([Cu2þ]þ[BDT-BPBA])¼0.33, which meant that
Cu2þ and BDT-BPBA formed a complex with a ratio of 1:2. It can be
deduced that two picolinamide units of two BDT-BPBA molecules are
in complex with one Cu2þ and two nitrogen atoms in each picoli-
The synthesis route of BDT-BPBA was shown in Scheme 1. BDT-
BPBA was synthesized by Suzuki coupling reaction of 4-bromo-N-
(pyridin-2-yl)benzamide
and
N-(pyridin-2-yl)-4-(4,4,5,
5-
tetramethyl-1,3,2-dioxaborolan-2-yl)benzamide in 54% yield. The
chemical structure of BDT-BPBA was confirmed by 1H NMR, 13C
NMR and mass spectroscopic data (As shown in Fig. S1eS9).
(i) CH2Cl2, r.t., overnight. (ii) CH2Cl2, r.t., 30min, 84%. (iii) THF/n-BuLi, r.t., 30min, 71%. (iv) H2O/Zn/NaOH/TBAB, relux, 7h, 74%. (v) CH2Cl2, r.t.,
6h, 87%. (vi) DMF/CuI, 80°C, 24h, 63%. (vii) dioxane/KOAc/ Pd(dppf)Cl2, 100°C, overnight, 72%. (viii) toluene/H2O/K2CO3/ Pd(PPh3)4, reflux, 24h,
54%.
Scheme 1. The synthesis of BDT-BPBA.
2.2. Sensing response of BDT-BPBA for Cu2D
The UVevis spectra of BDT-BPBA with different amount of Cu2þ
were investigated. As shown in Fig. 1, BDT-BPBA in DMSO/H2O
(v:v¼4:1) showed that two absorption peaks were centered at
358 nm and 422 nm. Upon additional of 0.5 equiv Cu2þ into the
solution of BDT-BPBA, the two peaks were red-shift to 380 nm and
440 nm. The change of the UVevis spectra can be explained by
internal charge transfer (ICT) mechanism, which refers to the
pushepull effect of the electron-donating and electron-
withdrawing groups. That is, the red shift indicates that the en-
ergy gap of ICT band decreases, upon binding Cu2þ to the electron
withdrawing moieties.30
For fluorescence spectra (Fig. 2a), the emission wavelength of
BDT-BPBA was appeared at 546 nm in DMSO/H2O (v:v¼4:1) when
excited by 410 nm photon. The fluorescence quantum yield can
reach at 0.43. The fluorescence intensity was found to quench with
the addition of Cu2þ. The quenching continues till addition of
0.5 equiv Cu2þ and remains constant thereafter. Under the common
TLC-UV light,
l
¼365 nm, the yellow fluorescence quenching was
observed by naked eyes when 0.5 equiv of Cu2þ was added to
a
2ꢀ10ꢁ5 mol/L BDT-BPBA solution in DMSO/H2O (v:v¼4:1)
(Fig. 2b). The plot of F/F0 as a function of Cu2þ concentration was
Fig. 1. UVevis spectra of BDT-BPBA in DMSO/H2O (v:v¼4:1) (2ꢀ10ꢁ5 mol/L) upon
addition of 0.1e1.0 equiv of CuCl2.
shown in Fig. 3, where F0 is the initial fluorescence intensity and F is

Y. Ma et al. / Tetrahedron 72 (2016) 2219e2225
2221
namide unit coordinate with Cu2þ (Fig. 5). The detection limit can be
calculated to be as low as 2.4ꢀ10ꢁ8 mol/L using 3
s/K (Fig. S10).
Fig. 5. The possible detection mechanism of Cu2þ by BDT-BPBA.
To further understand the fluorescence character of BDT-BPBA
and the effect of metal ion titration, density functional theory
(DFT) calculations at the B3LYP/Lanl2dz level were performed for
BDT-BPBA and its 2:1 complex with Cu2þ, BDT-BPBA/Cu2þ (for the
sake of simplicity, the OC8H17 group attached to the BDT unit was
replaced by methoxy group in the actual calculations). The frontier
molecular orbitals (HOMO and LUMO) of the BDT-BPBA monomer
Fig. 2. (a) Fluorescence emission spectra of BDT-BPBA in DMSO/H2O (v:v¼4:1)
(2ꢀ10ꢁ5 mol/L) upon addition of 0.1e1.0 equiv of CuCl2 (b) Naked-eye fluorescent
(
lex¼365 nm) images of BDT-BPBA (2ꢀ10ꢁ5 mol/L) in DMSO/H2O (v:v¼4:1) solution
upon the addition of 0.5 equiv of CuCl2.
are shown in Fig. 6. As can be seen, both the HOMO (
and LUMO (
p
) (ꢁ5.42 eV)
p
*) (ꢁ2.18 eV) mainly reside at the BDT fragment, and
the pyridine units have almost no distribution. The DFT calculation
reveals that a lowest energy singlet transition of HOMO-LUMO
characters with an energy gap of 3.24 eV. According to the fluo-
rescence emission mechanism, the excited electron of BDT unit is
back to the ground state and radiates strong fluorescence.
Fig. 3. The plot of F/F0 for BDT-BPBA complex with Cu2þ
.
Fig. 6. DFT calculated molecular orbitals of BDT-BPBA.
For the 2:1 BDT-BPBA and Cu2þ coordination complex, geo-
metrical optimizations show that four nitrogen atoms from two
picolinamide units of BDT-BPBA ligands are coordinated with Cu2þ
in the stable structure, while the carbonyl oxygen atoms do not
participate in the coordination (Fig. 7a). Fig. 7b displays the con-
tours of HOMO (
p
) (ꢁ5.55 eV) and LUMO ( *) (ꢁ3.61 eV) of the
p
complex BDT-BPBA/Cu2þ. It can be seen that the HOMO and LUMO
are located in two different BDT-BPBA ligands. As compared to the
monomer, the HOMO energy level keeps almost unchanged,
whereas the LUMO energy level is significantly lower. As a result,
a lowest energy singlet transition of HOMOeLUMO characters the
energy of 1.94 eV for BDT-BPBA/Cu2þ. The decrease of energy gap
can interpret that the two absorption peaks are red-shift after the
addition of Cu2þ. On the other hand, as the frontier molecular or-
bitals are spreading over two different ligands in the BDT-BPBA/
Cu2þ complex, the excited electron of a BDT unit is back to the
Fig. 4. Job’s Plot for the complex of Cu2þ with BDT-BPBA determined by Fluorescence
emission spectra.

2222
Y. Ma et al. / Tetrahedron 72 (2016) 2219e2225
ground state of another BDT unit, and therefore leads to the
In fluorescence spectra, BDT-BPBA alone has fluorescence
quenching of the fluorescence.
emission at 546 nm with an excitation of 410 nm. When 0.5 equiv of
various ions (Mn2þ, Pb2þ, Cr3þ, Zn2þ, Ni2þ, Kþ, Ca2þ, Agþ, Mg2þ
,
Fe3þ, Fe2þ, Hg2þ, Al3þ, Cd2þ, Pd2þ, Co2þ) were added to BDT-BPBA
solution, respectively, it was found that the solution of BDT-BPBA
exhibited no or small significant decrease of the fluorescence. The
addition of 0.5 equiv Cu2þ resulted in drastic decrease of emission
intensities at 546 nm (Fig. 9a). As shown in Fig. 9b, the fluorescence
quenching could be observed only by additional of 0.5 equiv Cu2þ
,
while the fluorescence not changed when other ions were exit
under the TLC-UV light,
¼365 nm.
l
Fig. 7. (a) DFT optimized structure of BDT-BPBA/Cu2þ complex. (Ball color: Green¼Cu,
Blue¼N, Red¼O, Gray¼C, White¼H) (b) DFT calculated molecular orbitals of BDT-BPBA/
Cu2þ complex.
2.3. Selective detection studies of Cu2D by BDT-BPBA
The selectivity of BDT-BPBA towards a variety of metal ions
Fig. 9. (a) Fluorescence emission spectra of BDT-BPBA in DMSO/H2O (v:v¼4:1)
(2ꢀ10ꢁ5 mol/L) upon addition of CuCl2, MnCl2, PbCl2, CrCl3, ZnCl2, NiCl2, KCl, CaCl2,
AgNO3, MgCl2, FeCl3, FeCl2, Hg(ClO4)2, AlCl3, CdCl2, PdCl2, CoCl2 (0.5 equiv) (b) Naked-
eye fluorescent (lex¼365 nm) images of BDT-BPBA (2ꢀ10ꢁ5 mol/L) in DMSO/H2O
(v:v¼4:1) solution upon the addition of CuCl2, MnCl2, PbCl2, CrCl3, ZnCl2, NiCl2, KCl,
CaCl2, AgNO3, MgCl2, FeCl3, FeCl2, Hg(ClO4)2, AlCl3, CdCl2, PdCl2, CoCl2 (0.5 equiv).
(Mn2þ, Pb2þ, Cr3þ, Zn2þ, Ni2þ, Kþ, Ca2þ, Agþ, Mg2þ, Fe3þ, Fe2þ, Hg2þ
,
Al3þ, Cd2þ, Pd2þ, Co2þ) was examined through UVevis spectra and
fluorescence emission in DMSO/H2O (v:v¼4:1). As shown in Fig. 8,
the absorption peaks were centered at 358 nm and 422 nm without
further change when 0.5 equiv other ions were in presence. Upon
the addition of 0.5 equiv Cu2þ, these two peaks were red-shifted to
380 nm and 440 nm clearly, indicating the formation of the only
species between BDT-BPBA and Cu2þ. The results indicated that
only Cu2þ could influence the electron transfer in BDT-BPBA
molecule.
At the same time, the competition experiments were conducted
in the presence of Cu2þ mixed with other relevant ions (Mn2þ, Pb2þ
Cr3þ, Zn2þ, Ni2þ, Kþ, Ca2þ, Agþ, Mg2þ, Fe3þ, Fe2þ, Hg2þ, Al3þ, Cd2þ
,
,
Pd2þ, Co2þ) (Fig. 10). When BDT-BPBA was treated with 0.5 equiv
Cu2þ in the presence of 0.5 equiv other ions, the coexistent ions had
Fig. 8. UVevis spectra of BDT-BPBA in DMSO/H2O (v:v¼4:1) (2ꢀ10ꢁ5 mol/L) upon
addition of CuCl2, MnCl2, PbCl2, CrCl3, ZnCl2, NiCl2, KCl, CaCl2, AgNO3, MgCl2, FeCl3,
FeCl2, Hg(ClO4)2, AlCl3, CdCl2, PdCl2, CoCl2 (0.5 equiv).
Fig. 10. The selectivity of BDT-BPBA in DMSO/H2O (v:v¼4:1) (2ꢀ10ꢁ5 mol/L) for Cu2þ
in the presence of other metal ions (CuCl2, MnCl2, PbCl2, CrCl3, ZnCl2, NiCl2, KCl, CaCl2,
AgNO3, MgCl2, FeCl3, FeCl2, Hg(ClO4)2, AlCl3, CdCl2, PdCl2, CoCl2) (0.5 equiv).

Y. Ma et al. / Tetrahedron 72 (2016) 2219e2225
2223
a little effect on the emission intensity, Cu2þ can also influence the
4. Experimental section
intermolecular electron transfer of BDT-BPBA and the fluorescence
of the solution was reduced.
4.1. Materials and measurements
2.4. Self-assembly studies of BDT-BPBA/Cu2D
All chemical reagents and solvents were purchased from com-
mercial suppliers and were used without further purification un-
less otherwise note. Dioxane was dried with metal sodium and
distilled immediately prior to use. All moisture-sensitive and air-
sensitive reactions were carried out under argon atmosphere.
1H NMR and 13C NMR spectra were measured on a Bruker AM-
400 spectrometer using d-chloroform or d8-THF as a solvent and
The assembly properties of BDT-BPBA/Cu2þ was also studied by
scanning electron microscopy (SEM) due to the characters of BDT-
BPBA. Through the fluorescence titration and the theoretical cal-
culations, it could be proved that picolinamide units of BDT-BPBA
could form complex with Cu2þ and the binding constant between
Cu2þ and picolinamides units is 3.93ꢀ103 L/mol according to
UVevis spectrum (Fig. S11). We inferred that Cu2þ may promote
metal-assisted coordinative self-assembly of BDT-BPBA. As shown
tetramethylsilane (TMS,
d¼0 ppm) as an internal standard. The
UVevis spectra were recorded on a Varian CARY 100 spectropho-
tometer at room temperature. Fluorescence-emission was detected
on Varian Cary Eclipse spectrophotometer at room temperature.
Scanning electron microscopy (SEM) was tested on Hitachi S-
3400N SEM.
in Fig. 11, the molecules formed self-assembly in line with Cu2þ
furthermore, the BDT unit functionalized with phenyl-amide
groups may also give directionality to the stacked assembly of
,
p
metal coordinated ligands.31 In order to confirm it, a tetrahydrofu-
ran solution of the Cu2þ (0.1 mol/L, 0.1 mL) was dropped into the
tetrahydrofuran solution of BDT-BPBA (0.01 mol/L, 2.0 mL). Then
red precipitate was appeared gradually. A SEM image of the pre-
cipitate showed that many short rod structures are created (Fig. 12).
The rod structure may be formed by the Cu2þ induced orientation
4.2. Synthetic procedures and characterizations
Compound 1e5 was synthesized similar to the literature.23
4.2.1. Thiophene-3-carbonyl chloride (1). Thiophene-3-carboxylic
acid (8.00 g, 62.43 mmol) were dissolved in 80 mL CH2Cl2 and
cooled to 0 ꢂC, then oxalyl chloride (12.0 mL, 140.87 mmol) was
added into the reaction system. The reactant was stirred overnight
at room temperature, and a light yellow solution was obtained.
After removing the solvent, unreacted oxalyl chloride was removed
under vacuum, yellow solid was obtained. It was dissolved into
20 mL of CH2Cl2 and used for the next step without further purified.
and by the pep interaction of the aromatic unit synchronously.
Fig. 11. Schematic representation of possible metal-directed self-assembly of BDT-
BPBA.
4.2.2. N,N-Diethylthiophene-3-carboxamide
(2). Diethylamine
(28.0 mL, 271.82 mmol) and 160 mL CH2Cl2 were mixed at 0 ꢂC, and
the solution of 1 was added into the reagent slowly. After all of the 1
solution was added, the reactant was stirred at room temperature
for 30 min. Then, the reactant was washed by water (3ꢀ60 mL), and
the organic layer was dried over Na2SO4. After removing solvent,
the crude product was purified by distillation under vacuum, and
pale yellow oil was obtained in 84% yield. 1H NMR (400 MHz, CDCl3)
d
(ppm): 7.47 (s, 1H), 7.33e7.31 (m, 1H), 7.18 (d, J¼4.0 Hz, 1H),
3.51e3.29 (m, 4H), 1.23e1.17 (m, 6H).
4.2.3. 4,8-Dihydrobenzo[1,2-b;4,5-b0]dithiophen-4,8-dione
(3). 2
(2.00 g, 10.9 mmol) was dissolved in 30 mL THF under argon at-
mosphere. The solution was cooled to 0 ꢂC, and n-butyllithium
(5.2 mL, 2.5 mol/L) was added dropwise within 30 min. Then, the
reactant was stirred at room temperature for 30 min. The reactant
was poured into 100 mL ice water and stirred for another 2 h. The
mixture was filtrated, and the precipitate was washed by 10 mL
water, 5 mL of methanol. 3 was obtained as yellow powder in 71%
Fig. 12. SEM image of BDT-BPBA/Cu2þ
.
3. Conclusions
In summary, a new fluorescence probe BDT-BPBA containing
yield. Mp >200 ꢂC 1H NMR (400 MHz, CDCl3),
J¼4.2 Hz, 2H), 7.65 (d, J¼4.2 Hz, 2H).
d (ppm): 7.69 (d,
benzo[1,2-b:4,5-b0]dithiophene (BDT) and two picolinamide units
was synthesized through Suzuki coupling. To elongate the
p con-
jugate spacer of the compound, phenyl was introduced. As a result,
the fluorescence quantum yield of BDT-BPBA can achieve at 0.43.
Through the titration test, the two absorption peaks centered at
358 nm and 422 nm red-shifted to 380 nm and 440 nm and the
fluorescence intensity was almost quenched when addition of
0.5 equiv Cu2þ. The complex ratio is 1:2 between Cu2þ and BDT-
BPBA, which was proved by Job’s Plot and theoretical calculations.
So, BDT-BPBA can be used as a turn-off probe for Cu2þ in a flash way
and the detection limit is as low as 2.4ꢀ10ꢁ8 mol/L. It displayed well
selectivity to Cu2þ over other ions (Mn2þ, Pb2þ, Cr3þ, Zn2þ, Ni2þ, Kþ,
Ca2þ, Agþ, Mg2þ, Fe3þ, Fe2þ, Hg2þ, Al3þ, Cd2þ, Pd2þ, Co2þ) as well. On
the other hand, it could form assembly in rod structure by the Cu2þ
induced orientation, which can be confirmed by SEM.
4.2.4. 4,8-Didodecyloxybenzo[1,2-b;3,4-b]dithiophene (4). 3 (1.00 g,
4.5 mmol), zinc powder (0.71 g, 10.88 mmol), and 15 mL of water
were mixed, then sodium hydroxide (2.73 g, 68.23 mmol) was
added into the mixture. The mixture was well stirred and heated to
reflux for 1 h. During the reaction, the color of the mixture changed
from yellow to red and then to orange. Then, 1-bromododecane
(2.4 mL, 13.67 mmol) and tetrabutylammonium bromide
(293 mg, 0.91 mmol) were added. The color of the reactant should
be yellow or orange. Then, the reactant was refluxed for 6 h. After
completion of the reaction, the reactant was poured into water and
extracted by CH2Cl2 (3ꢀ10 mL). The organic layer was dried over
Na2SO4. After removing solvent, the crude product was purified by
silica column (eluent petroleum ether: CH2Cl2¼15:1). White solid

2224
Y. Ma et al. / Tetrahedron 72 (2016) 2219e2225
was obtained in 74% yield. MP 46.0e47.1 ꢂC 1H NMR (400 MHz,
CDCl3)
J¼6.6 Hz, 4H), 1.87 (q, J¼6.9 Hz, 4H), 1.57e1.54 (m, 4H), 1.34e1.25
(m, 16H), 0.88 (t, J¼7.0 Hz, 6H).
2ꢀ10ꢁ5 mol/L solution (DMSO:H2O¼4:1(v/v)). CuCl2$2H2O
(17.0 mg) was dissolved in 10 mL deionized water to get 0.01 mol/L
solution. 2.5 mL 2ꢀ10ꢁ5 mol/L BDT-BPBA solution was in cuvette,
d
(ppm): 7.47 (d, J¼5.5 Hz, 2H), 7.36 (d, J¼5.5 Hz, 2H), 4.27 (t,
then 0.5
mL (0.1 equiv), 1.0
mL (0.2 equiv), 1.5
mL (0.3 equiv), 2.0
mL
L
(0.4 equiv), 2.5
mL (0.5 equiv), 3.0
mL (0.6 equiv), and 5.0
m
4.2.5. 2,6-Dibromo-4,8-didodecyloxybenzo[1,2-b;3,4-b]dithiophene
(5). 4 (1.37 g, 3.08 mmol) was dissolved into 30 mL of CH2Cl2.
Bromine (0.93 g, 6.15 mmol) was dissolved into 20 mL CH2Cl2,
slowly dropped into the reactant at 0 ꢂC, and then the reactant was
stirred for 6 h at room temperature. After the reaction was over, the
solvent was removed under vacuum. The residue was purified by
silica column (eluent petroleum ether: CH2Cl2¼10:1) to get a white
solid in 87% yield. Mp 58.9e59.3 ꢂC 1H NMR (400 MHz, CDCl3)
(1.0 equiv) Cu2þ was added, respectively. After mixing them for
a few seconds, UVevis and fluorescence spectra were taken at room
temperature.
4.4. UVevis and fluorescence for selectivity
ZnCl2 (0.0136 g), PbCl2 (0.0278 g), FeCl3 (0.0162 g), AgNO3
(0.0170 g), NiCl2$6H2O (0.0238 g), CaCl2 (0.0111 g), MgCl2
(0.0095 g), KCl (0.0075 g), CrCl3$6H2O (0.0266 g), MnCl2$4H2O
(0.0198 g), FeCl2$4H2O (0.0199 g), Hg(ClO4)2$3H2O (0.0399 g) CdCl2
(0.0183 g), CoCl2$6H2O (0.0238 g), AlCl3 (0.0133 g), PdCl2 (0.0177 g)
were dissolved in 10 mL deionized water to get 0.01 mol/L solution,
d
(ppm): 7.42 (s, 2H), 4.19 (t, J¼6.6 Hz, 4H), 1.85e1.82 (m, 4H),
1.55e1.51 (m, 4H), 1.37e1.31 (m, 16H), 0.90 (t, J¼6.8 Hz, 6H).
4.2.6. 4-Bromo-N-(pyridin-2-yl)benzamide
(6).32 4-
Bromobenzaldehyde (200 mg, 1.09 mmol), pyridin-2-amine
(153 mg, 1.63 mmol) and CuI (21 mg, 0.11 mmol) were dissolved
in 5 mL DMF. The reaction mixture was stirred at 80 ꢂC for 24 h.
Then the reactant was extracted with CH2Cl2 (3ꢀ10 mL) and then
washed by water (3ꢀ10 mL). The organic layer was dried by Na2SO4.
After removing the solvent, the crude product was purified by silica
column (eluent petroleum ether:ethyl acetate¼10:1) to get white
solid in 63% yield. Mp 133.2e135.0 ꢂC 1H NMR (400 MHz, CDCl3)
respectively. Then 2.5 mL (0.5 equiv) ion solution was added into
2.5 mL 2ꢀ10ꢁ5 mol/L BDT-BPBA solution. After mixing them for
a few seconds, UVevis and fluorescence spectra were taken at room
temperature.
4.5. Job’s plot measurements
500
m
L, 450
mL, 400 mL, 350 mL, 300 mL, 250 mL, 200 mL, 150 mL,
100 L, 50
m
mL and 0 m
L 1ꢀ10ꢁ4 mol/L BDT-BPBA solution were taken
d
(ppm): 8.64 (s, 1H) 8.37 (d, J¼8.4 Hz, 1H) 8.30 (d, J¼5.9 Hz, 1H)
7.81 (d, J¼8.6 Hz, 2H) 7.77 (dd, J1¼8.4 Hz, J1¼1.8 Hz, 1H) 7.67e7.63
(m, 2H) 7.10e7.08 (m, 1H).
and transferred to cuvette. 0
mL, 0.5
mL, 1.0 mL, 1.5 mL, 2.0 mL, 2.5 mL,
3
m
L, 3.5 L, 4.0 L, 4.5
m
m
mL and 5.0 mL 0.01 mol/L CuCl2 solution was
added into each cuvette, and 0.5 mL deionized water was added
into each cuvette. Then each cuvette was dilute to 2.5 mL. After mix
4.2.7. N-(Pyridin-2-yl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)benzamide (7). 6 (200 mg, 0.72 mmol), bis(pinacolato)diboron
(367 mg, 1.44 mmol) were combined in anhydrous dioxane. Po-
tassium acetate (213 mg, 2.16 mmol) and Pd(dppf)Cl2 (53 mg,
0.07 mmol) were added to the mixture under argon atmosphere.
The mixture was stirred at 100 ꢂC overnight. After evaporation of
the solvent, the residue was purified by silica column (eluent pe-
troleum ether:ethyl acetate¼5:1) to get brown oil in 72% yield. 1H
a
few seconds, fluorescence spectra were taken at room
temperature.
4.6. Calculation of detection limit
The detection limit was determined from the fluorescence ti-
tration data based on 3
BDT-BPBA were tested and
s
/K. Ten times of fluorescence intensity of
can be calculated. According to the
NMR (400 MHz, CDCl3)
d
(ppm): 8.82 (s, 1H) 8.42 (d, J¼8.4 Hz, 1H)
s
8.31 (d, J¼3.6 Hz, 1H) 7.94 (s, 4H) 7.78 (t, J¼8.8 Hz, 1H) 7.09(dd,
result of fluorescence titrating experiment, the fluorescent in-
tensity data of BDT-BPBA were normalized between the minimum
intensity and the maximum intensity, respectively when excited by
410 nm. The linear regression curve was then fitted to these nor-
malized fluorescent intensity data, and the slop K of line could be
calculated.
J1¼6.6 Hz, J1¼5.0 Hz, 1H) 1.37 (s, 12H).
4.2.8. 4,40-(4,8-Didodecyloxybenzo[1,2-b;3,4-b]dithiophene)bis(N-
(pyridin-2-yl)benzamide) [BDT-BPBA]. 5 (133 mg, 0.21 mmol), 7
(207 mg, 0.64 mmol) and K2CO3 (236 mg, 1.68 mmol) were dis-
solved in toluene (20 mL) and water (5 mL). Then Pd(PPh3)4 (25 mg,
0.021 mmol) was added under Argon atmosphere. The reaction
mixture was heated to reflux and stirred for 24 h. After completion
of the reaction, CH2Cl2 (10 mL) and water (10 mL) were added into
the reaction mixture. Then the organic layer was washed by water
(10 mLꢀ3) and dried over Na2SO4. After the solvent was removed,
the residue was purified by silica column (eluent petroleum
ether:ethyl acetate¼3:1) to get a yellow solid in 54% yield. Mp
Acknowledgements
The authors are grateful to financial support from the National
Natural Science Foundation of China (Nos. 20872035, 21576087),
Key Laboratory of Organosilicon Chemistry and Material Technol-
ogy of Ministry of Education, Hangzhou Normal University, and the
East China University of Science and Technology.
199.4e201.9 ꢂC 1H NMR (400 MHz, CDCl3)
d (ppm): 8.63 (s, 2H) 8.42
(d, J¼8.3 Hz, 2H) 8.34 (d, J¼5.7 Hz, 2H) 8.02 (d, J¼8.4 Hz, 3H)
7.90e7.87 (m, 3H) 7.81e7.77 (m, 4H) 7.65 (s, 1H) 7.13e7.06 (m, 2H)
4.36 (t, J¼6.6 Hz, 4H) 1.98e1.94 (m, 4H) 1.63e1.61 (m, 4H)
Supplementary data
Supplementary data (1H NMR, 13C NMR, and MS of BDT-BPBA
are available. Additional graph for calculation of detection limit and
binding constant can be found in ESI) associated with this article
can be found in the online version, at http://dx.doi.org/10.1016/
j.tet.2016.03.029.
1.33e1.25 (m, 16H). 13C NMR (100 MHz, d8-THF)
d (ppm): 164.81,
152.80, 147.80, 144.61, 142.55, 137.55, 137.17, 134.49, 132.85, 129.90,
128.49, 125.93, 119.14, 117.29, 114.02, 73.86, 31.88, 30.55, 29.66,
29.64, 29.34, 26.05, 22.60, 13.49. ESI-MS [MþHþ] calcd 839.3665,
Found 839.3665.
References and notes
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