A simple AIE-based chemosensor for highly sensitive and selective detection of Hg2+and CN?

Article abstract of DOI:10.1016/j.tet.2016.07.054

A novel red-emitting chemosensor BCTT has been developed for the detection of Hg²⁺and CN^?in DMF-water solution with high sensitivity and selectivity. It exhibited a ‘turn-on’ fluorescence upon binding with Hg²⁺based on its

Full text of DOI:10.1016/j.tet.2016.07.054

Tetrahedron 72 (2016) 5620e5625
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A simple AIE-based chemosensor for highly sensitive and selective
detection of Hg2þ and CNꢀ
,
Yiru Li a, Haitao Zhou a, Wei Chen a, Guangchen Sun a, Lu Sun b, Jianhua Su a
*
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai, 200237, PR China
b Institute of Modern Optics, Nankai University, Tianjin, 300071, PR China
a r t i c l e i n f o
a b s t r a c t
A novel red-emitting chemosensor BCTT has been developed for the detection of Hg2þ and CNꢀ in DMF-
water solution with high sensitivity and selectivity. It exhibited a ‘turn-on’ fluorescence upon binding
with Hg2þ based on its AIE properties and a ‘turn-off’ response to CNꢀ due to the nucleophilic addition of
CNꢀ to the dicyanovinyl group with visible color changing from yellow to colorless. Remarkably, the
Article history:
Received 23 May 2016
Received in revised form 11 July 2016
Accepted 22 July 2016
Available online 22 July 2016
detection limits for Hg2þ and CNꢀ were 6.6 nM and 0.11
mM, respectively, which are much lower than the
regulated limits in drinking water, promoting BCTT as a promising candidate in practical applications.
Keywords:
AIE
Ó 2016 Published by Elsevier Ltd.
Chemosensor
Hg2þ
CNꢀ
1. Introduction
(AAS), atomic fluorescence spectrometry (AFS), and inductively
coupled plasmamass spectrometry (ICP-MS) for Hg2þdetection,6
Among the various metal ions and anions, Hg2þ and CNꢀ are
considered to be especially deleterious to human health and nat-
ural environment. Hg2þ, one of the most toxic heavy metal ions,
mostly released by human activities such as coal-fired power sta-
tions, primary metals production, and the chlor-alkali industry,1 is
known to be accumulated over time through the food chain,
causing significant damage to organs such as brain, kidneys, liver
and nervous system.2 Similarly, cyanide is a kind of extremely
poisonous compounds, existing in certain plants, such as cassava,
the seeds of several fruits, cigarette smoke, and the combustion
products of synthetic materials,3 and is commonly utilized in in-
dustries such as precious metal mining, metal plating shops, steel
mills, and plastic and fertilizer plants.4 Cyanide ions can form
a stable complex with cytochrome c oxidase, which disrupts the
function of this enzyme, resulting in cytotoxic hypoxia and cellular
asphyxiation. Moreover, anaerobic metabolism induced by cyanide
leads to accumulation of lactate in the blood. The combined effects
of hypoxia and lactate acidosis disturb the central nervous system,
resulting in respiratory arrest and even death.3e5
and potentiometric, chromatographic, and flow injection tech-
niques for CNꢀ analysis are usually high cost, time-consuming and
require sophisticated instruments.7,8 In contrast, optical detection
based on absorption or fluorescence which takes advantages of
simplicity and low detection limit has been widely studied and
developed in recent years.9 Consequently, tremendous sensors for
detecting Hg2þ or CNꢀ have been reported, however, sensors with
responsibility for both are relatively rare to date.10 Considering the
fluorescence quenching effect of Hg2þ, the turn-on fluorescent
chemosensors based on AIE phenomenon induced by metal ion
complexation are more favorable for sensitive detection and wide
use.11e14 Otherwise, cyanide chemosensors are tended to take ad-
vantage of the unique nucleophilicity of cyanide to realize recog-
nition through the bond-formation reaction between the probing
molecule and cyanide anions, minimizing the interference of other
anions.15 Herein, thymine was chosen as an acceptor for its affinity
with Hg2þ and the dicyano-vinyl group was selected as a reactive
moiety for CNꢀ. Moreover, due to the strong electron-withdrawing
property, the dicynao-vinyl group can also cause a considerable
bathochromic-shift of emission, making it feasible in biological
applications.16 It is because that blue florescence is strongly at-
tenuated by a biological specimen while red fluorescence corre-
sponds to the biological specimen’s transparency window,
producing high penetration depth.
Thus, given the widespread occurrence and extreme toxicity of
Hg2þ and CNꢀ, the selective and sensitive determination of both
ions in various samples is of great importance for lives on the earth.
Traditional methods including atomic absorption spectroscopy
Hence a novel TPA-based red emitting probe BCTT with AIE
properties was designed and synthesized for detecting both Hg2þ
* Corresponding author. E-mail address: bbsjh@ecust.edu.cn (J. Su).
http://dx.doi.org/10.1016/j.tet.2016.07.054
0040-4020/Ó 2016 Published by Elsevier Ltd.

Y. Li et al. / Tetrahedron 72 (2016) 5620e5625
5621
and CNꢀ, which contains two thymine groups and a dicyano-vinyl
group as coordination/reaction sites. The probe was expected to
be a dual-functional detector with high selectivity and sensitivity,
which has potential in practical applications.
2. Results and discussion
2.1. Synthesis
The synthetic route of BCTT was depicted in Scheme 1. The in-
termediates 1 and 2 were synthesized according to the reported
literature.17,18 Compounds 3, 4 and 5 were obtained through simple
reactions. The target compound BCTT was synthesized and con-
firmed by 1H NMR, 13C NMR and High-resolution mass spectros-
copy (HRMS).
Fig. 1. a) The fluorescence spectra of BCTT (10.0
mM) in DMF-water mixtures with
different water fractions (fw). b) Plots of relative PL intensity (I/I0) of BCTT at 645 nm
versus the composition of DMF-water mixtures of BCTT. I0¼PL intensity in pure DMF
solution (fw¼0). Inset: fluorescence photos of BCTT in DMF-H2O mixtures at fw¼0 (left)
and 80% (right) taken under 365 nm UV illumination from a hand-held UV lamp.
was proved to be the best choice as test solution. Besides, SDS (So-
dium Dodecyl Sulfonate) (1.0 mM) was added to make the com-
plexing between probe and Hg2þ faster and more easily.19
Scheme 1. Structure and synthetic route of BCTT.Scheme 1
The fluorescence spectra of the probe in the presence of a seri-
ous of concentrations of Hg2þ was shown in Fig. 2a. The probe has
a weak emission at ca. 600 nm, then upon the addition of Hg2þ, the
fluorescence intensity of BCTT started to increase gradually ac-
companied by a bathochromic shift of 50 nm, and reached the
maximum, which was about 20 times stronger than the original
value, after the treatment of 1.0 equiv Hg2þ (Fig. S3a). A red fluo-
rescence could be observed by naked eye under a UV lamp at
360 nm. Moreover, an approximate linear relationship between the
fluorescence intensity of probe and the concentration of Hg2þ in the
2.2. AIE performance of BCTT
To investigate the AIE property of BCTT, we tested its absorption
and emission spectra in DMF-H2O mixtures with different water
fraction. As shown in Fig. 1a, BCTT was almost nonemissive in pure
DMF solution and low water content solution. However, the fluo-
rescence intensity at 650 nm increased dramatically when water
content increased to 60 vol %, and reached its maximum with 120-
fold enhancement in intensity when the water fraction reached 80
vol %. BCTT was therefore AIE active. Further increase in water
fraction resulted in a slight decrease of fluorescence intensity,
which could be ascribed to the formation of amorphous aggregates.
What’s more, a slight red shift and intensity decrease could be
observed in absorption spectra (Fig. S1), which may be caused by
the increasing solvent polarity and accumulation of molecules.
range of 1.5e8.8
mM was exhibited in Fig. 2b. Remarkably, the de-
tection limit of BCTT was calculated to be 6.6 nM by the formula 3
s
/
jkj, which is much lower than the limit of Hg2þ in drinking water
(2 ppb, ca. 10 nM) set by the US EPA,20 indicating the high sensi-
tivity of the probe towards Hg2þ. As for the change of absorbance of
probe under the titration of Hg2þ, a slight red shift and about
a quarter intensity decline caused by the aggregation of BCTT and
reduced solubility was observed when complexation arrived at the
saturation point (Fig. S3b).
2.3. Optical response to Hg2D
The probes with fluorescence enhancement due to aggregation
induced by coordination of thymine units with Hg2þ have been
reported previously,13,14 and the proposed mechanism is sche-
It is known that thymine can bind with Hg2þ sensitively and
selectively, therefore we investigated the absorbance and fluores-
cence responses of the probe to different amounts of Hg2þ. Con-
sidering the requirement of the test solvent with low biotoxicity and
high water content but not affecting the probe’s fluorescence for
further biological application, we tested the sensing behavior of
BCTT towards Hg2þ in DMF-H2O solutions with different water
percentage(Fig. S2, Fig. 2a), and the mixtureof DMF-H2O (13:12, v/v)
matically illustrated in Scheme 2. Firstly, after addition of Hg2þ
,
BCTT aggregated in the solution causing the fluorescence increase,
which could be proved by corresponding absorption spectrum and
SEM analysis. Fig. S3b shows the absorption changes after titration
with mercury ion. The absorption band at 440 nm became weak
and intensity in the range of 480e580 nm increased gradually,

5622
Y. Li et al. / Tetrahedron 72 (2016) 5620e5625
In order to examine the selectivity of this assay for Hg2þ, we
measured the fluorescent responses of the probe to various metal
ions. It can be seen from Fig. 3, the addition of 1.0 equiv of Hg2þ
could produce a notable fluorescence enhancement of the probe,
while 50.0 equiv of other metal ions did not induce the apparent
fluorescence increase. Subsequently, competition experiments
were carried out to ensure the potential application of the probe for
practical use. The fluorescent intensity of BCTT in the presence of
1.0 equiv Hg2þ and 50.0 equiv competing metal ions changed little
comparing to that with the addition of Hg2þ only, indicating that
our proposed probe is highly selective for Hg2þ
.
2.4. Optical response to CNL
In order to investigate the ability of BCTT to detect CNꢀ, the cy-
anide titration experiment was carried out in DMF-H2O solutions
with different water fraction (Figs. S7ꢀS10, Fig. 4), with the assis-
tance of CTAB (Hexadecyl trimethyl ammonium Bromide) (1.0 mM).
According to results, BCTT was most sensitive towards CNꢀ in DMF-
H2O (1:19, v/v). As shown in Fig. 4, the initial solution emitted red
fluorescence located at 645 nm because of the AIE property of BCTT.
The visual color of yellow corresponding to main absorption band
centered at 440 nm could be observed distinctly by naked eye as
well. Afterwards, the sensor immediately responded with dramatic
color and fluorescence changes when cyanide was added to the
solution of BCTT. As shown in Fig. 4a, the absorption band at 440 nm
gradually decreased with the addition of CNꢀ and eventually dis-
appeared after 7.8 equiv of CNꢀ was added, which was accompanied
by the color change from yellow to colorless, suggesting the com-
plete addition reaction between dicyanovinyl and CNꢀ.
Meanwhile, the fluorescence intensity reduced gradually with
increasing amounts of CNꢀ. As expected, the red fluorescence fi-
nally quenched when the titration reached its end point (Fig. 4b).
Notably, the detection limit for CNꢀ using fluorescence intensity
Fig. 2. a) Fluorescence spectra of BCTT in DMF-H2O (13:12, v/v) (10.0 mM) upon ad-
dition of 0e1.2 equiv of aqueous Hg2þ
,
lex¼440 nm. Inset: fluorescence photos of BCTT
with different amount of Hg2þ (left: none; right: 1.2 equiv Hg2þ). b) The fluorescence
intensity (I645 as M),
linear function of Hg2þ concentration (from 1.5 to 8.8
lex¼440 nm, lem¼645 nm, ¼0.10. The standard deviation ( ) was obtained by fluo-
rescence intensity (10-times scanning without addition of Hg2þ). The detection limit
was calculated to be 6.6 nM by the formula (3
/jkj).
changes was estimated to be 0.11
mM, which is far lower than the
WHO guideline of 1.9
m
M (Fig. S10a).21
The reaction process of CNꢀ undergoing conjugate addition to
the 1,1-dicyano-vinyl group to produce a stabilized anionic adduct
has been studied in previous literature.22,23 Thus, the 1H NMR ti-
tration of BCTT upon addition of 0e1.0 equiv of cyanide in DMSO-d6
was performed to confirm this sensing process. It can be seen from
Fig. 5 that the vinylic proton (Ha) at 8.14 ppm gradually decreased
with progressive addition of CNꢀ and eventually vanished when
1.0 equiv of cyanide was added, implying the completion of nu-
)
a
m
s
s
s
indicating the aggregation of the probe. Moreover, the SEM image
(Fig. S4) reveals the formation of aggregate in the solution of BCTT
with 1.0 equiv of Hg2þ. In addition, the Job’s plot (Fig. S5) presented
a maximum fluorescence intensity as the ratio x was 0.5, and
MALDI-TOF mass spectrum (Fig. S6) of probe in the presence of
Hg2þ showed a signal at m/z¼970.3216, coinciding with that of
[BCTT/Hg2þꢀHþ]. Above evidence suggested a 1:1 stoichiometry of
cleophilic addition. Concurrently,
a new signal appeared at
4.41 ppm attached to Hb. Naturally, the aromatic proton signals all
upfield shifted due to the broken conjugation between the diac-
yanovinyl group and triphenylamine framework. What’s more, the
the complexes between probe and Hg2þ
.
Fig. 3. PL Intensities at 645 nm of BCTT (10.0 mM) in DMF-H2O (13: 12, v/v) in the
absence of Hg2þ and in the presence of various ions (1.0 equiv for Hg2þ and 50.0 equiv
Scheme 2. Proposed schematic illustration of the coordination between BCTT and
for other ions, lex¼440 nm, black bar portion) and in the mixture of 50.0 equiv of other
Hg2þ.Scheme 2
metal ions with 10.0 m
M of Hg2þ (gray bar portion).

Y. Li et al. / Tetrahedron 72 (2016) 5620e5625
5623
group appeared at 140 ppm, implying the nucleophilic addition of
CNꢀ with dicyano-vinyl group. Furthermore, 1:1 stoichiometric
reaction between BCTT and cyanide could be proved by Benesi-
Hildebrand plot of absorbance at 440 nm upon addition of cya-
nide (Fig. S10b), which revealed a linear correlation between 1/
D
A440 and 1/[CNꢀ], and MS (ESI) spectra after treatment of CNꢀ,
showing a signal of m/z¼795.3624 which was exactly coincided
with that of [BCTTþCN] (Fig. S12).
Moreover, the interference studies were undertaken in the
identical condition to examine the selectivity of BCTT. As described
in Fig. 6, the absorbance intensity at 440 nm and fluorescence in-
tensity at 645 nm remained almost unchanged in the presence of
400.0 equiv of those ions, sufficiently showing the excellent se-
lectivity for CNꢀ. In addition, the sensing abilities of BCTT for cya-
nide was not affected by the treatment of excessive other anions,
indicating its potential political application for cyanide sensing in
aqueous medium.
3. Conclusion
In summary, a novel fluorescent probe BCTT with red emission
centered at 645 nm, combining a dicyanovinyl group and triphe-
nylamine skeleton with thymine, has been successfully synthesized
for the detection of mercury and cyanide ions in DMF-water solu-
tion containing SDS and CTAB, respectively. BCTT exhibited a fluo-
rescence enhancement upon addition of Hg2þ due to the
coordination between thymine groups and Hg2þ based on its AIE
Fig. 4. a) Absorption and b) fluorescence spectra of BCTT in DMF-H2O (1:19,v/v)
(10.0
M) upon addition of 0e7.8 equiv of aqueous CNꢀ
m
;
lex¼440 nm. Inset: photos of
BCTT with different amount of cyanide (left: none; right: 7.8 equiv of cyanide).
Fig. 5. Partial 1H NMR spectra of BCTT (5 mM) in DMSO-d6 with different equivalent of
CNꢀ
.
13C NMR spectra of BCTT in CDCl3 after addition of 1.0 equiv CNꢀ
was conducted (Fig. S11). It can be seen that signals at around 157
and 73 ppm belonging to vinylic carbons disappeared and shifted to
23 and 17 ppm after addition of CNꢀ and the signal of added cyano
Fig. 6. a) Absorbance intensities at 440 nm and b) PL Intensities at 645 nm of BCTT
(10.0 m
M) in DMF-H2O (1:19, v/v) in the absence of CNꢀ and in the presence of various
ions (8.0 equiv for CNꢀ and 400.0 equiv for other anions, lex¼440 nm, gray bar portion)
and in the mixture of 4 M of other anions with 80.0 mM of CNꢀ (black bar portion).

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Y. Li et al. / Tetrahedron 72 (2016) 5620e5625
properties. What’s more, the probe could detect CNꢀ with the
quenched red fluorescence and decreased absorbance intensity,
presenting a color change from yellow to colorless, which could be
observed by naked eye. Both the sensing processes were monitored
by 1H NMR or MS spectra to reveal the mechanisms of Hg2þ in-
duced aggregation and CNꢀ triggered nucleophilic addition. It is
mentionable that BCTT showed superb selectivity and sensitivity
towards Hg2þ and CNꢀ in the presence of other interfering ions,
which were also proved by the competition experiments. It is
therefore that probe BCTT could serve as a high sensitive and se-
lective detector for both Hg2þ and CNꢀ, with the detection limits as
(DMSO-d6, 400 MHz, TMS), d: 9.67 (s, 1H), 9.59 (s, 2H), 7.61 (d,
J¼9.2 Hz, 2H), 7.09 (d, J¼8.8 Hz, 4H), 6.81 (d, J¼8.8 Hz, 4H), 6.62 (d,
J¼8.8 Hz, 2H). 13C NMR (DMSO-d6, 100 MHz),
d: 189.99, 155.81,
154.15, 136.70, 131.45, 128.82, 126.68, 116.66, 114.76. HRMS (m/z):
[MþH]þ calcd for: C19H16NO3, 306.1130, found: 306.1129.
4.3.4. 4-(Bis(4-((6-bromohexyl)oxy)phenyl)amino)benzaldehyde
(4). The solution of 3 (1.80 g, 5.90 mmol) and 1,6-dibromohexane
(7.20 g, 29.48 mmol) in acetonitrile (50 mL) added with K2CO3
(4.07 g, 29.48 mmol) was refluxed overnight under N2 atmosphere.
The reaction mixture was concentrated, dissolved in dichloro-
methane, washed with water, dried over anhydrous NaSO4, and
concentrated. The residue was chromatographed on silica gel with
petroleum/ethyl acetate (7:1) to get compound 4 (2.50 g) as a yel-
low as 6.6 nM and 0.11 m
M for Hg2þ and CNꢀ, respectively. Our work
opens up a new avenue for the research of dual-functional fluo-
rescent probes for cations and anions.
low liquid. Yield: 67.2%. 1H NMR (DMSO-d6, 400 MHz, TMS),
d: 9.69
4. Experimental section
4.1. Materials
(s, 1H), 7.63 (d, J¼9.2 Hz, 2H), 7.16 (d, J¼8.8 Hz, 4H), 6.96 (d,
J¼9.2 Hz, 4H), 6.68 (d, J¼8.8 Hz, 2H), 3.94 (t, J¼6.4 Hz, 4H), 3.52 (t,
J¼6.8 Hz, 4H), 1.85e1.78 (m, 4H), 1.72e1.69 (m, 4H), 1.47e1.39 (m,
8H). 13C NMR (DMSO-d6, 100 MHz),
d: 190.07, 156.60, 153.66, 137.89,
Compound 1 and 2 were synthesized according to previous
literature. Other reactants were purchased commercially and used
as received without further handling. The salts used in stock solu-
tions of metal ions were NaCl, KCl, AlCl3, AgNO3, CaCl2, CoCl2$6H2O,
131.29, 128.35, 127.00, 115.68, 115.26, 67.50,35.03, 32.16, 28.49,
27.27, 24.66. HRMS (m/z): [MþH]þ calcd for: C31H38Br2NO3,
630.1218, found: 630.1220.
CrCl3$6H2O,
CuCl2$2H2O,
FeCl3$6H2O,
Hg(ClO4)2$3H2O,
4.3.5. 4-(Bis(4-((6-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-
1(2H)-yl)hexyl)oxy)phenyl)amino)benzaldehyde (5). To the solution
of 4 (2.50 g, 3.96 mmol) in DMF was added 5-methyluracil (3.00 g,
23.40 mmol) and K2CO3 (5.47 g, 39.60 mmol), and stirred at 60 ꢁC
under N2 atmosphere for 36 h. After the reaction, DMF was re-
moved under reduced pressure. The mixture was dissolved in
dichloromethane and washed with water for three times. The oil
layer was dried (anhydrous Na2SO4), concentrated, and chromato-
graphed on silica gel with ethyl acetate/petroleum (3: 1) to give
compound 5 (1.50 g) as bright yellow liquid. Yield: 52.4%. 1H NMR
MnCl2$4H2O, NiCl2$6H2O, PbCl2, ZnCl2, and the solutions of anions
were prepared from the corresponding sodium salts except that the
hydroxide ion and cyanide anion were in the form of tetrabuty-
lammonium (TBA) salts. Water used in tests was double distilled
water. All the organic solvents were dried with 4 A molecular sieves
prior to use and DMF treated with calcium hydride was further
distilled under reduced pressure for main experiments.
ꢀ
4.2. Instruments
(DMSO-d6, 400 MHz, TMS), d: 11.22 (s, 2H), 9.70 (s, 1H), 7.65 (d,
1H NMR and 13C NMR spectra were recorded on Brucker AM-400
spectrometers using DMSO-d6 as solvent and tetramethylsilane
J¼8.8 Hz, 2H), 7.54 (s, 2H), 7.18 (d, J¼9.2 Hz, 4H), 6.97 (d, J¼9.2 Hz,
4H), 6.68 (d, J¼8.8 Hz, 2H), 3.95 (t, J¼6.4 Hz, 4H), 3.62 (t, J¼7.2 Hz,
4H), 1.74 (s, 6H), 1.73e1.68 (m, 4H), 1.63e1.56 (m, 4H), 1.45e1.40 (m,
(TMS,
d
¼0 ppm) as internal standard. Mass spectra (MS) were ob-
tained on a Waters LCT Premier XE spectrometer. The UVevis ab-
sorption spectra and PL spectra were performed on a Varian Cray
500 spectrophotometer and a Varian Cray Eclipse, respectively.
4H), 1.35e1.27 (m, 4H). 13C NMR (DMSO-d6, 100 MHz),
d: 190.13,
164.26, 156.62, 153.69, 150.84, 141.42, 137.88, 136.18, 131.34, 128.41,
126.97, 115.69, 115.22, 108.34, 107.13, 67.52, 47.04, 28.46, 28.37,
25.52, 25.16, 11.90. HRMS (m/z): [MþH]þ calcd for: C41H48N5O7,
722.3554, found: 722.3550.
4.3. Synthesis
4.3.1. 4-Methoxy-N-(4-methoxyphenyl)-N-phenylaniline
(1). 4-
4.3.6. 2-(4-(Bis(4-((6-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-
1(2H)-yl)hexyl)oxy)phenyl)amino)benzylidene)malononitrile
(BCTT). Ammonium acetate (58.59 mg, 0.76 mmol) was added tothe
solution of compound 5 (0.50 g, 0.69 mmol) and malononitrile
(0.46 g, 6.91 mmol) in acetic acid. The mixturewas refluxed under N2
atmosphere for 12 h. Upon cooling, the mixturewas poured into cold
water to give a red precipitate. The crude product was collected by
suction filtration and purified by silica gel column chromatography
(petroleum ether/ethyl acetate¼1:3 v/v) to afford the compound
BCTT as a dark red solid (0.30 g). Yield: 56.4%. 1H NMR (DMSO-d6,
iodoanisole (7.20 g, 30.76 mmol) and aniline (1.14 mL, 12.49 mmol)
were dissolved in a round-bottom flask in 50 mL toluene, and o-
phenanthroline (0.45 g, 2.30 mmol), cuprous iodide (0.48 g,
2.52 mmol) and potassium hydroxide (5.60 g, 100.00 mmol) were
added to the solution. The mixture was refluxed under N2 atmo-
sphere for 12 h and then treated according to previous literature to
obtain the compound 1 as a white solid (2.50 g). Yield: 65.6%.17
4. 3 . 2. 4 - ( B i s ( 4 - m e t h o xy p h e nyl) m e t hyl ) b e nza l de hy de
(2). Compound 1 (2.00 g, 6.55 mmol) was treated with POCl3 in
DMF according to the reported method to afford the compound 2 as
a yellow liquid (2.00 g). Yield: 91.7%.18
400 MHz, TMS),
d
: 11.20 (s, 2H), 8.14 (s, 1H), 7.77 (d, J¼9.2 Hz, 2H),
7.54 (s, 2H), 7.22 (d, J¼9.2 Hz, 4H), 6.99 (d, J¼8.8 Hz, 4H), 6.68 (d,
J¼8.8 Hz, 2H), 3.96 (t, J¼6.4 Hz, 4H), 3.62 (t, J¼7.2 Hz, 4H),1.74 (s, 6H),
1.71e1.68 (m, 4H), 1.63e1.55 (m, 4H), 1.47e1.40 (m, 4H), 1.34e1.29
4.3.3. 4-(Bis(4-hydroxyphenyl)amino)benzaldehyde (3). A solution
of compound 2 (2.00 g, 6.00 mmol) in dichloromethane was added
with BBr3 (4.51 g, 6.00 mmol) (1.0 M solution in dichloromethane)
at 0 ꢁC and stirred under N2 atmosphere for 30 min. The reaction
mixture was stirred for another 24 h at room temperature and
poured into water and then extracted with ethyl acetate (3ꢂ50 mL).
The extract was dried (NaSO4) and concentrated. The residue was
chromatographed on silica gel with ethyl acetate/petroleum (2: 1)
to give compound 3 (1.80 g) as a yellow liquid. Yield: 98.3%. 1H NMR
(m, 4H). 13C NMR (CDCl3, 100 MHz),
d: 164.28, 157.83, 157.36, 154.17,
150.94, 140.33, 137.63, 133.20, 128.18, 121.66, 116.54, 115.72, 115.57,
110.70, 73.89, 67.90, 48.41, 29.07, 28.98, 26.14, 25.71,12.36. HRMS(m/
z): [MþH]þ calcd for: C44H48N7O6, 770.3666, found: 770.3674.
Acknowledgements
This work was supported by National Natural Science Founda-
tion of China (20772031), the National Basic Research 973 Program

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Supplementary data
Supplementary data (The characterization (NMR and MS) of
BCTT) related to this article can be found in the online version, at
http://dx.doi.org/10.1016/j.tet.2016.07.054.
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P.; Fichou, M. T. ChemBioChem 2007, 8, 424e433.
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