Selective and sensitive fluorescent chemosensors for Cu2+ ion based upon bis-1,8-naphthalimide dyads

Article abstract of DOI:10.1002/cjoc.201180481

A series of new fluorescent chemosensors 5a-5e, composed of two aminonaphthalimide fluorophores and 2,6-bis((N-aminoalkyl)aminocarboxy) pyridines, were prepared, characterized, and their fluorescent properties towards heavy and transition metal (HTM) ions were investigated. Chemosensors 5c-5e exhibited high selectivity and sensitivity for Cu²⁺ ion over other HTM ions with fluorescent quenching (green to colourless). It clearly demonstrated that the length of the linkers (diamines) between the aminonaphthalimides and 2,6-dicarboxypyridine of 5a-5e was very important for their sensitivity and selectivity for Cu²⁺ ion over other HTM ions. Three chemosensors 5c-5e exhibited high selectivity and sensitivity for Cu ²⁺ ion over other heavy and transition metal ions with fluorescent quenching (green to colourless). Copyright

Full text of DOI:10.1002/cjoc.201180481

FULL PAPER
DOI: 10.1002/cjoc.201180481
＋
Selective and Sensitive Fluorescent Chemosensors for Cu2
Ion Based upon Bis-1,8-naphthalimide Dyads
Dai, Huiling(代会苓)
Xu, Hui*(徐晖)
Laboratory of Pharmaceutical Design & Synthesis, College of Science, Northwest Agriculture & Forestry Univer-
sity, Yangling, Shaanxi 712100, China
A series of new fluorescent chemosensors 5a—5e, composed of two aminonaphthalimide fluorophores and
2,6-bis((N-aminoalkyl)aminocarboxy)pyridines, were prepared, characterized, and their fluorescent properties to-
wards heavy and transition metal (HTM) ions were investigated. Chemosensors 5c—5e exhibited high selectivity
＋
and sensitivity for Cu2 ion over other HTM ions with fluorescent quenching (green to colourless). It clearly dem-
onstrated that the length of the linkers (diamines) between the aminonaphthalimides and 2,6-dicarboxypyridine of
＋
5a—5e was very important for their sensitivity and selectivity for Cu2 ion over other HTM ions.
Keywords fluorescence, sensors, 1,8-naphthalimide, metal ion, selectivity
Introduction
prepare fluorescent chemosensors for metal cations and
protons in recent years.[3] Meanwhile, the fluorescent
properties of bis-1,8-naphthalimide derivatives have
also recently received much attention, for example, a
series of new kind of chemosensors A (Figure 1) have
been prepared and exhibited the excellent and selective
recognition for the HTM ions.[4] However, to our
knowledge, little attention has been paid to the fluores-
cent properties of another kind of chemosensors B based
upon the bis-1,8-naphthalimide dyads. Only Grabchev
and coauthors described the behavior and spectral char-
acteristics of B1 and B2 (Figure 1), two bis-1,8-naph-
thalimide derivatives linked by a diethylenetriamine
bridge, in the presence of different HTM ions.[5] Al-
though the selectivity of the reported sensors B1 and B2
for different HTM ions was not good, this encouraging
Since heavy and transition metal (HTM) ions play an
important role in many biological and environmental
processes, the design and synthesis of fluorescent sen-
sors with high selectivity and sensitivity for the detec-
tion and measurement of HTM ions nowadays are of
＋
significant importance.[1] For example, Cu2 ion has
been shown to have an important role in the enzymatic
defense against oxygen toxicity, and identified as an
environmental pollutant, consequently, the development
of fluorescent chemosensors with high selectivity and
＋
sensitivity for Cu2 ion over other HTM ions is still a
challenge.[2]
Due to their fluorescent properties and special inter-
actions with some biomolecules, mono-1,8-naphthal-
imides are frequently used as the fluoroionophores to
Figure 1 Chemical structures of chemosensors.
*
E-mail: orgxuhui@nwsuaf.edu.cn; Tel.: 0086-029-87091952; Fax: 0086-029-87091952
Received June 1, 2011; accepted September 28, 2011.
Chin. J. Chem. 2012, 30, 267—272
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Dai & Xu
FULL PAPER
results prompted us to further study other bis-1,8-naph-
thalimide derivatives of B as the fluorescent sensors.
Therefore, based on the aforementioned results, in the
present paper we designed a series of new chemosensors
5a—5e (Figure 2), which were composed of two ami-
nonaphthalimide fluorophores and 2,6-bis((N-amino-
alkyl)aminocarboxy)pyridines. We expected that 5a—5e
could adopt the semirigid V-shaped conformation,
which might be selectively binding with a metal cation.
Meanwhile, the nitrogen atoms of 2,6-bis((N-amino-
alkyl)aminocarboxy)pyridines and oxygen atoms of
aminonaphthalimides were both the ion receptors.
Moreover, according to the length of the linkers (dia-
mines) between the aminonaphthalimides and 2,6-di-
carboxypyridine of 5a—5e, the size of the cavity for
binding HTM ions could be regulated to some degree.
To our delight, 5a—5e displayed highly selective and
＋
sensitive response toward Cu2 ion over other HTM
ions. The synthetic route of 5a—5e was shown in
Scheme 1.
Figure 2 Chemical structures of target chemosensors 5a—5e.
Scheme 1 Synthetic routes of 5a—5e
268
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Chin. J. Chem. 2012, 30, 267—272

＋
Selective and Sensitive Fluorescent Chemosensors for Cu2 Ion
Experimental
2 (1.519 g) was obtained as a white solid. CAS:
499-83-2. Yield 91%, m.p. 226—227 ℃ (lit.[8] 227—
228 ℃).
All solvents and reagents were used as obtained from
commercial sources without further purification. The
solutions of metal ions were prepared from
Zn(ClO4)2•6H2O, Fe(ClO4)2•6H2O, Ca(ClO4)2•4H2O,
Synthesis of compound 3 A mixture of 2 (1.67 g,
10 mmol) and SOCl2 (7.1 mL) was refluxed for 3 d.
Then the excess SOCl2 was removed under normal
pressure. After the reaction mixture was cooled to room
temperature, methanol (50 mL) was added and the mix-
ture was refluxed for 3 h in the dry atmosphere. Finally,
some solvent was removed and 1.633 g of compound 3
was precipitated as a white solid. CAS: 5453-67-8. Yield
85%, m.p. 130—131 ℃ (lit.[9] 130—132 ℃); 1H NMR
(CDCl3, 400 MHz) δ: 8.33 (dd, J＝8.0, 1.6 Hz, 2H),
8.03—8.07 (m, 1H), 4.04 (s, 6H), EI-MS m/z: 195 (M＋,
2).
Mg(ClO4)2,
Ba(ClO4)2,
Pb(ClO4)2,
Cd(ClO4)2,
Cu(ClO4)2, Hg(ClO4)2, and AgPF4, respectively, and
were dissolved in distilled THF. Analytical thin-layer
chromatography (TLC) and preparative thin-layer
chromatography (PTLC) were performed with silica gel
plates using silica gel 60 GF254 (Qingdao Haiyang
Chemical Co., Ltd.). Melting points are uncorrected.
Nuclear magnetic resonance spectra (NMR) were re-
corded on a Bruker Avance DMX 300 or 400 MHz in-
strument in CDCl3 (1H at 300 or 400 MHz and 13C at 75
or 100 MHz) using TMS (tetramethylsilane) as the in-
ternal standard. High-resolution mass spectra (HR-MS)
and mass spectra (EI-MS) were carried out with APEX
II Bruker 4.7T AS instrument and HP 5988 instrument,
respectively. Electrospray iontrap mass spectrometry
(ESI-MS) was carried out with Thermo Scientific LCQ
Fleet mass spectrometer. Fluorescent spectra were de-
termined on a Hitachi F-4500 spectrophotometer.
UV-visible spectra were determined on a Hitachi
U-3310 spectrophotometer.
General procedure for the synthesis of 5a—5e
To a solution of diamine (5 mmol) in dried MeOH (5
mL) under argon at 0 ℃, a solution of 3 (97.5 mg, 0.5
mmol) in dried MeOH (20 mL) was added dropwise.
After adding, the above mixture was stirred for 12 h at
room temperature, and the solvent and excess of dia-
mine were removed under reduced pressure to give the
residues 4a—4c, which were used directly for the next
step without further purification. Then a mixture of 4a—
4c and 1a—1c (1.25 mmol) in EtOH (20 mL) was re-
fluxed under argon, and after 24 h, the solvent was
evaporated under reduced pressure to give the residue,
which was seperated by preparative thin-layer chroma-
tography (PTLC) to give the pure products 5a—5e.
Synthesis of compounds 1a—1c
A mixture of 4-bromo-1,8-naphthalic anhydride
(2.77 g, 10.0 mmol), and piperidine or morpholine or
pyrrolidine (20 mmol) in 2-methoxyethanol (25 mL)
was refluxed for 5 h, then the reaction mixture was
cooled to room temperature to afford a yellow solid after
filtration, which was purified by recrystallization from
ethanol to give 1a—1c in 85%—86% yields as the or-
ange needles.
1
5a: Yield 49%, yellow solid, m.p. 152—153 ℃; H
NMR (CDCl3, 400 MHz) δ: 9.04 (s, 2H), 8.20—8.38 (m,
8H), 7.91—7.95 (m, 1H), 7.55—7.59 (m, 2H), 7.02 (t,
J＝8.8 Hz, 2H), 4.02—4.03 (m, 4H), 3.83 (s, 4H), 3.17
(s, 8H), 1.86—1.87 (m, 8H), 1.71 (s, 4H); 13C NMR
(CDCl3, 100 MHz) δ: 164.9, 164.5, 163.9, 157.3, 148.3,
138.6, 132.7, 131.0, 130.7, 129.7, 125.9, 125.2, 124.0,
122.7, 115.3, 114.5, 54.4, 39.2, 39.0, 26.1 24.2; IR ν:
1a: CAS: 87223-12-9. m.p. 170—171 ℃ (lit.[6] 175
—176 ℃); 1H NMR (CDCl3, 400 MHz) δ: 8.58 (d, J＝
7.6 Hz, 1H), 8.50 (d, J＝8.4 Hz, 1H), 8.44 (d, J＝8.8 Hz,
1H), 7.73 (t, J＝7.6 Hz, 1H), 7.20 (d, J＝8 Hz, 1H),
3.31 (t, J＝5.6 Hz, 4H), 1.88—1.93 (m, 4H), 1.74—1.78
(m, 2H); EI-MS m/z: 281 (M+, 83 ), 280 ([M－1]+, 100).
1b: CAS: 31837-36-2. m.p. 210—212 ℃ (lit.[7] 220
—221 ℃); 1H NMR (CDCl3, 400 MHz) δ: 8.56 (d, J＝
7.2 Hz, 1H), 8.50 (d, J＝8.0 Hz, 1H), 8.46 (d, J＝8.8 Hz,
1H), 7.73 (t, J＝8 Hz, 1H), 7.26 (d, J＝1.6 Hz, 1H),
4.03 (t, J＝4.4 Hz, 4H), 3.31 (t, J＝4.8 Hz, 4H); EI-MS
m/z: 283 (M+, 48).
－
1
3456, 2936, 2852, 1690, 1649, 1588, 1533, 1235 cm .
HRMS (ESI) calcd for C45H44N7O6 [M＋H]＋ 778.3348,
found 778.3351.
1
5b: Yield 51%, yellow solid, m.p. 147—148 ℃; H
NMR (CDCl3, 400 MHz) δ: 9.36 (t, J＝5.6 Hz, 2H),
8.42 (d, J＝7.2 Hz, 2H), 8.36 (d, J＝7.6 Hz, 2H), 8.32
(d, J＝7.6 Hz, 2H), 8.21 (d, J＝8.4 Hz, 2H), 8.00 (t, J＝
7.6 Hz, 1H), 7.53 (t, J＝7.6 Hz, 2H), 7.06 (d, J＝8.4 Hz,
2H), 4.34 (t, J＝6.4 Hz, 4H), 3.58—3.62 (m, 4H), 3.16
(s, 8H), 2.12—2.15 (m, 4H), 1.87 (s, 8H), 1.72 (s, 4H);
13C NMR (CDCl3, 100 MHz) δ: 164.7, 164.3, 163.6,
157.2, 148.7, 138.6, 132.6, 130.9, 130.6, 129.7, 125.8,
125.1, 124.3, 122.6, 115.3, 114.5, 54.3, 37.5, 36.2, 27.9,
26.1, 24.2; IR ν: 3373, 2935, 2852, 1691, 1651, 1587,
1
1c: CAS: 99024-08-5. m.p. 220—222 ℃; H NMR
(CDCl3, 400 MHz) δ: 8.64 (d, J＝8.4 Hz, 1H), 8.51 (d,
J＝7.2 Hz, 1H), 8.33 (d, J＝8.4 Hz, 1H), 7.52 (t, J＝8.4
Hz, 1H), 6.77 (d, J＝8.8 Hz, 1H), 3.84 (s, 4H), 2.14 (s,
4H); MS (ESI-TRAP) m/z: 268 ([M+1]+, 100).
Synthesis of compound 2 A mixture of KMnO4
(8.848 g, 56 mmol) and 2,6-dimethylpyridine (1.2 mL,
10 mmol) in water (85 mL) was refluxed for 5 h, and
filtered. Then the filtrate was concentrated to the 1/5 of
original volum. Finally, when the pH value of the mix-
ture was adjusted to 2 by using 70% H2SO4, compound
－
1
1532, 1236 cm ; HRMS (ESI) calcd for C47H48N7O6
[M＋H]＋ 806.3661, found 806.3670.
1
5c: Yield 47%, yellow solid, m.p. 143—144 ℃; H
NMR (CDCl3, 300 MHz) δ: 8.61 (s, 2H), 8.32—8.46 (m,
8H), 7.96 (t, J＝7.6 Hz, 1H), 7.59 (t, J＝7.8 Hz, 2H),
7.12 (d, J＝8 Hz, 2H), 4.14 (s, 4H), 3.59—3.61 (m, 4H),
3.22 (m, 8H), 1.73—1.89 (m, 20H); 13C NMR (CDCl3,
Chin. J. Chem. 2012, 30, 267—272
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75 MHz) δ: 164.5, 164.1, 163.9, 157.2, 149.0, 138.6,
132.6, 130.9, 130.7, 129.7, 126.0, 125.2, 124.7, 122.8,
115.5, 114.6, 54.5, 39.5, 39.4, 26.1, 25.5, 24.3; IR ν:
－
1
3463, 2935, 2854, 1693, 1654, 1587, 1535 cm ; HRMS
(ESI) calcd for C49H52N7O6 [M＋H]＋ 834.3974, found
834.3982.
1
5d: Yield 41%, yellow solid, m.p. 141—142 ℃; H
NMR (CDCl3, 400 MHz) δ: 8.64 (s, 2H), 8.46 (d, J＝7.2
Hz, 2H), 8.41 (d, J＝7.2 Hz, 2H), 8.34—8.36 (m, 4H),
7.99 (s, 1H), 7.63 (t, J＝7.2 Hz, 2H), 7.18 (d, J＝7.2 Hz,
2H), 4.13 (s, 4H), 4.01 (s, 8H), 3.60 (s, 4H), 3.25 (s, 8H),
1.79 (s, 8H); 13C NMR (CDCl3, 100 MHz) δ: 164.3,
163.9, 163.8, 155.6, 148.9, 138.6, 132.4, 131.0, 130.1,
129.6, 125.9, 125.7, 124.7, 123.0, 116.7, 114.8, 66.8,
53.3, 39.5, 39.4, 26.1, 25.5; IR ν: 3462, 2958, 2856,
Figure 3 Absorbance intensities of 5a—5e (1×10－ mol•L－
in THF at 288 K.
)
6
1
－
1
1693, 1652, 1588, 1536, 1236 cm ; HRMS (ESI) calcd
for C47H48N7O8 [M＋H]＋ 838.3559, found 838.3550.
1
5e: Yield 34%, yellow solid, m.p. 146—147 ℃; H
NMR (CDCl3, 400 MHz) δ: 8.87 (s, 2H), 8.46 (d, J＝8
Hz, 2H), 8.38 (d, J＝6.8 Hz, 2H), 8.32 (d, J＝6.8 Hz,
2H), 8.22 (d, J＝8.4 Hz, 2H), 7.98 (s, 1H), 7.42—7.44
(m, 2H), 6.68 (d, J＝8 Hz, 2H), 4.11 (s, 4H), 3.74 (s,
8H), 3.6 (s, 4H), 2.09 (s, 8H), 1.78 (s, 8H); 13C NMR
(CDCl3, 100 MHz) δ: 164.7, 163.9, 152.9, 149.1, 138.4,
133.2, 131.8, 130.9, 130.8, 124.6, 122.8, 122.2, 110.2,
108.4, 53.1, 39.4, 39.3, 25.9, 25.5; IR ν: 3463, 2927,
2867, 1676, 1636, 1587, 1530; HRMS (ESI) calcd for
C47H48N7O6 [M＋H]＋ 806.3661, found 806.3647.
Figure 4 Variation of the fluorescent intensity at λmax (522 nm)
Results and Discussion
－
of 5a (1×10－ mol•L 1) in THF in the presence of 5.0 equiv. of
6
the respective metal cations.
As described in Scheme 1, 5a—5e were smoothly
obtained by the reaction of 4-piperidine/morpholine/py-
rrolidine-1,8-naphthalimides (1a—1c) with the corre-
sponding 2,6-bis((N-aminoalkyl)aminocarboxy)-
pyridines (4a — 4c), which were prepared from
2,6-dimethylpyridine and the corresponding diamines.
The chemical structures of 5a—5e were well character-
ized by IR, m.p., 1H NMR, 13C NMR, and HRMS.
Due to the good solubility for HTM ions and the
fluorescent quantun yields (ΦF), tetrahydrofuran (THF)
was chosen as the solvent for all the measurements. The
absorption spectra of 5a—5e in THF were shown in
Figure 3. The respective fluorescence responses of 5a—
＋
＋
＋
＋
＋
5e in the presence of Hg2 , Ag＋, Zn2 , Fe3 , Cd2 , Pb2 ,
＋
＋
＋
＋
Ca2 , Cu2 , Mg2 and Ba2 ions were presented in
Figures 4—8. When Cu2+ ion was added to the solution
of 5a—5e, respectively, a decrease of the fluorescent
intensity was detected. However, the addition of other
Figure 5 Variation of the fluorescent intensity at λmax (522 nm)
－
of 5b (1×10－ mol•L 1) in THF in the presence of 5.0 equiv. of
6
the respective metal cations.
metal ions, e.g., Hg2 , Ag＋, Zn2 , Fe3 , Cd2 , Pb2 ,
＋
＋
＋
＋
＋
＋
＋
＋
Ca2 , Mg2 and Ba2 ions, did not lead to a clear
change of the fluorescent intensity of 5a—5e. Especially
when Cu2+ ion was added to the solution of 5c—5e, all
with four carbon linkers, the significant changes in the
fluorescent intensity were observed. For example, after
addition of Cu2+ ion to the solution of 5c—5e, the cor-
responding fluorescent intensities were sharply de-
creased more than fivefold as compared with the
controls. It suggested that the length of the linkers (dia-
mines) between the aminonaphthalimides and
2,6-dicarboxypyridine of 5a—5e was very crucial for
＋
sensitivity and selectivity for Cu2 ion. But the effect of
substituents (e.g., 1-piperidinyl, 4-morpholinyl, and
1-pyrrolidinyl groups) at the 4-position of 5c—5e on
＋
their fluorescent intensity changes for Cu2 ion was not
obvious.
270
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Chin. J. Chem. 2012, 30, 267—272

＋
Selective and Sensitive Fluorescent Chemosensors for Cu2 Ion
in Figure 9 displayed the changes of fluorescent inten-
＋
sity (I513 nm) of 5e to the concentrations of Cu2 ion. The
photo in Figure 9 showed the colour change of 5e after
＋
addition of 10 equiv. of Cu2 ion (green to colourless).
＋
However, the increasing amounts of Cu2 ion had al-
most no effect on the absorption spectra in this paper
(Figure 10).
Figure 6 Variation of the fluorescent intensity at λmax (519 nm)
－
of 5c (1×10－ mol•L 1) in THF in the presence of 5.0 equiv. of
6
the respective metal cations.
Figure 9 Fluorescent spectra of 5e (1×10－ mol•L－1) in THF
6
in the presence of increasing amounts of Cu(ClO4)2 (from 0 to 7
equiv.). λex＝440 nm. Inset: (1) the plot of the fluorescent inten-
sity (I513 nm) vs. the concentration of Cu(ClO4)2; (2) the photo of
5e before and after addition of 10.0 equiv of Cu(ClO4)2 under UV
light illumination (365 nm).
Figure 7 Variation of the fluorescent intensity at λmax (516 nm)
－
of 5d (1×10－ mol•L 1) in THF in the presence of 5.0 equiv. of
6
the respective metal cations.
Figure 10 Variation of the absorbance intensity of 5e (1×10－
6
mol•L－1) in the presence of increasing amounts of Cu(ClO4)2
(from 0 to 7 equiv.) in THF at 288 K.
To explore further the utility of 5e as an ion-selective
fluorescent chemosensor for Cu2+ ion, the competition
experiments were conducted in the presence of Cu2+ ion
Figure 8 Variation of the fluorescent intensity at λmax (513 nm)
－
of 5e (1×10－ mol•L 1) in THF in the presence of 5.0 equiv. of
6
－
＋
＋
＋
＋
(5×10－ mol•L ) mixed with Hg2 , Ag , Zn2 , Fe3 ,
6
1
the respective metal cations.
＋
＋
＋
＋
＋
Cd2 , Pb2 , Ca2 , Mg2 , and Ba2 ions at 5×10－
6
mol•L－1, respectively. As outlined in Figure 11, as
Subsequently, the sensitivity of the fluorescent emis-
＋
compared with that only in the presence of Cu2 ion, no
＋
sion response of 5e toward Cu2 ion was typically in-
＋
vestigated with various Cu2 ion concentrations (0—7
obvious variation in its fluorescent intensity was de-
＋
tected in the presence of the mixture of Cu2 ion with
×10－ mol•L ) (Figure 9). The sensor exhibited high
－
6
1
＋
sensitivity for Cu2 ion probably attributed to the for-
other metal ions. It implied that the selectivity of 5e for
Cu2+ ion was remarkable.
＋
mation of a 5e-Cu2 ion complex (Figure 2). The inset
Chin. J. Chem. 2012, 30, 267—272
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www.cjc.wiley-vch.de
271

Dai & Xu
FULL PAPER
Acknowledgement
This work was supported by the program for New
Century Excellent University Talents, State Education
Ministry of China (No. NCET-06-0868), and the Special
Funds of Central Colleges Basic Scientific Research
Operating Expenses (No. QN2009045).
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cations (Mn＋, 5×10－6 mol•L－1). [Cu2＋]: 5×10－6 mol•L－
.
1
Conclusions
In summary, based on bis-1,8-naphthalimide dyads,
we have developed a novel series of fluorescent chemo-
＋
sensors 5c—5e for Cu2 ion with high sensitivity and
selectivity. It is noteworthy that the length of the linkers
(diamines) between the aminonaphthalimides and
2,6-dicarboxypyridine of 5a—5e was very important for
[6] Peters, A. T.; Bide, M. J. Dyes Pigm. 1985, 6, 349.
＋
their sensitivity and selectivity for Cu2 ion over other
[7] Krasovitskii, B. M.; Shevchenko, E. A.; Distanov, V. B. Zhurnal Organi-
cheskoi Khimii 1983, 19, 1305.
HTM ions. Moreover, it clearly demonstrated that an-
other kind of bis-1,8-naphthalimides B could also dis-
play the good selectivity for the HTM ions via introduc-
tion of the appropriate groups on the linker.
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