A new selective fluorescent chemosensor for Cu(II) ion based on zinc porphyrin-dipyridylamino

Article abstract of DOI:10.1016/j.inoche.2006.12.023

A new fluorescent chemosensor 5-(p-N,N′-bis(2-pyridyl)amino)phenyl-10,15,20-tris(p-methoxyphenyl)porphyrin zinc has been designed and synthesized by the Ullmann-type coupling. It displays high selectivity for Cu²⁺ ion and exhibits fluorescence quenching upon binding of Cu²⁺ ion with an on-off type fluoroionophoric switching property, and its fluorescence can be revived by addition of EDTA disodium solution.

Full text of DOI:10.1016/j.inoche.2006.12.023

Inorganic Chemistry Communications 10 (2007) 443–446
www.elsevier.com/locate/inoche
A new selective fluorescent chemosensor for Cu(II) ion based on
zinc porphyrin-dipyridylamino
*
Yan-Qin Weng, Ying-Lai Teng, Fan Yue, Yong-Rui Zhong, Bao-Hui Ye
MOE Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University,
Guangzhou 510275, China
Received 29 November 2006; accepted 25 December 2006
Available online 10 January 2007
Abstract
A new fluorescent chemosensor 5-(p-N,N0-bis(2-pyridyl)amino)phenyl-10,15,20-tris(p-methoxyphenyl)porphyrin zinc has been
designed and synthesized by the Ullmann-type coupling. It displays high selectivity for Cu2+ ion and exhibits fluorescence quenching
upon binding of Cu2+ ion with an ‘‘on–off’’ type fluoroionophoric switching property, and its fluorescence can be revived by addition
of EDTA disodium solution.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Ullmann-type coupling; Porphyrin; Fluorescence sensor; Cu2+ ion
The development of high selective, sensitive and low
detection limit fluorescent sensors for Cu2+ ion has been
actively investigated [1–7], since copper is a significant
metal pollutant due to its widespread use [8], but it is also
required as a cofactor in nearly 20 enzymes and an essential
micronutrient for all known life forms. Fluorescent sensor
of Cu2+ ion is used to clarify the physiological role of the
metal in vivo as well as to monitor its concentration in
the metal-contaminated sources due to its high detection
sensitivity and intrinsic operation simplicity.
Porphyrins have been widely utilized as fluorophores
due to their high absorption coefficients at visible region,
tunable fluorescence emission, high stability against light
and chemical reactions [9]. Metalloporphyrins can also be
used as colorimetric sensors for detection of metalligating
vapours and organic molecules because of their open coor-
dination sites for axial ligation, their large spectral shifts
upon ligand binding, and their color change [10,11]. On
the other hand, molecular sensors based on porphyrins or
metalloporphyrins can also be constructed by modification
of the porphyrin meso-positions with appropriately func-
tional groups that create both the recognition and binding
sites for the analytes. Such interactions may lead to the
analyte-dependent changes in the absorption and/or fluore-
sence properties of the sensors. Following this strategy,
several sensors have been developed for certain analytes
[12–15]. Herein, we designed and synthesized a new metal
fluorescent sensor 5-(p-N,N0-bis(2-pyridyl)amino)phenyl-
10,15,20-tris(p-methoxyphenyl)porphyrin zinc (1, Scheme
1). The sensor is constructed via two functional moieties:
zinc porphyrin acts as a fluorophore for its excellent photo-
physical property, and 2,20-dipyridylamine (dpa) linked to
zinc porphyrin provides the recognition and binding site
for metal ions [16–18]. Indeed, 1 displays high selectivity
for Cu2+ ion among the metal ions examined and exhibits
fluorescence quenching upon binding of Cu2+ ion with an
‘‘on–off’’ type fluoroionophoric switching property. Its
fluorescent signal can be revived by the addition of EDTA
disodium solution.
The targeted product 1 was synthesized by the direct
reaction of 5-(p-bromophenyl)-10,15,20-tris(p-methoxy-
phenyl)porphyrin zinc with dpa via the Ullmann-type cou-
pling using copper powder as a catalyst and K2CO3 as base
in the dry DMF solvent at 150 ꢁC [19].
*
Corresponding author.
E-mail address: cesybh@mail.sysu.edu.cn (B.-H. Ye).
1387-7003/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.12.023

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Y.-Q. Weng et al. / Inorganic Chemistry Communications 10 (2007) 443–446
OCH3
10
8
6
N
N
N
N
N
N
Zn
N
H3CO
4
2
fluorophore
binding site
0
OCH3
Scheme 1. Structure of 1.
Fig. 2. Responses of sensor 1 in CHCl3 (25 lM) to different metal ions in
MeOH (125 lM). Excitation at 435 nm and emission at 608 nm. Final
solvent composition is CHCl3:MeOH = 20:1 in volume.
Absorption spectra of 1 in CHCl3 exhibits a Soret band
at 427 nm, which is slightly red shift compared with that of
the tetraphenylporphyrin zinc at 423 nm (Fig. S1). To
observe the optical sensor property of 1 for metal ions,
intensity loss in 1:1 molar ratio. Continuous addition of
Cu2+ ion, emission intenstity of 1 decreased slowly and
was about 10% of the original one when the molar ratio
of Cu2+ to 1 increased to 2. The mole ratio method was
applied to examine the stoichiometry [22], indicating a
1:1 complex formed (Fig. S3), which was further con-
firmed by ESI-MS (Fig. S4) [23]. The binding constant,
K, determined by fluorescence titration is appropriate
6.31 · 105 Mꢀ1, comparable to the report [22,24].
Quantum yield of 1 was 5.8% measured at room temper-
ature in CHCl3 solution, which is larger than that of zinc
tetraphenylporphyrin (2.8%) [25]. Luminescence decay
experiment was performed in chloroform solution at room
temperature. The lifetime yield in 1.53 ns by fitting the data
to a single exponential decay function (Fig. S5).
the tested metal ions representative of Na+, Mg2+, Cr3+
,
Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+
and Fe3+ were added to the solution of 1, respectively.
The spectra showed negligible changes, when the metal
ions (four equivalent) were added to the solution of 1,
respectively.
Emission spectrum of 1 in CHCl3 displays a sharp band
at 608 nm with a shoulder at 656 nm upon excition at
435 nm (Fig. S2). To screen the fluorescent sensor prop-
erty, the responses of 1 to the aforementioned metal ions
were examined. Only Cu2+ ion caused a significant fluores-
cence quenching as shown in Figs. 1 and 2. Such a signifi-
cant difference in fluorescence intensity between Cu2+ and
other metal ions indicates that the function group dpa of
1 is more suitable to bind Cu2+ than other metal ions
observed. This may be attributed to complex formation
with the metal ion in preference over others following
Irving–Williams order of stability [20]. The fluorescence
quenching was most probably caused by the binding of
Cu2+ at dpa moiety [21].
1.0
0.8
0.6
0.4
0.2
0.0
0
To examine the binding properties of 1 toward Cu2+
ion, titration experiments were carried out and the results
are shown in Fig. 3. Addition of Cu2+ to the solution of 1
caused a decrease of emission intensity, and about 76%
49 μM
550
600
650
700
wavelength/nm
Fig. 3. Fluorescent titrations emission spectra of 1 (25 lM) in CHCl3
solution upon addition of Cu2+ in MeOH solution [Cu2+] = 0, 4, 8, 12, 16,
20, 24, 28, 32, 37, 41, 45, 49 lM. The excitation wavelength was 435 nm.
Final solvent composition is CHCl3:MeOH = 50:1 in volume.
Fig. 1. The fluorescence responses of 1 (25 lM) in CHCl3 upon addition
of (160 lM) metal ions in MeOH excited at 365 nm using UV lamp. Final
solvent composition is CHCl3:MeOH = 18:1 in volume.

Y.-Q. Weng et al. / Inorganic Chemistry Communications 10 (2007) 443–446
445
To examine the reversibility of sensor 1 to Cu2+ ion,
aqueous solution of EDTA disodium was added to the
complexed solution of 1 (25 lM) and Cu2+ (50 lM) in
methanol. As expected, fluorescence signal with a maxi-
mum at 608 nm was completely recovered (Fig. S6), dem-
onstrating the binding is really chemically reversible. This
is very important for the preparation of sensor device.
The detection limit for Cu2+ ion with 1 is determined to
be 1.5 · 10ꢀ6 M under the present conditions (3s blank)
[26]. These results indicate that 1 can function as a fluores-
cence sensor for Cu2+ ion.
of sensor 1 would help to extend the development of fluo-
rescent sensors for metal ions.
Acknowledgement
This work was supported by the NSFC (No. 20371052)
and NSF of Guangdong (No. 06023086).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2006.
12.023.
The competition experiments of Cu2+and other metal
ions were also performed. As shown in Fig. 4, when the
mixed solution of Cu2+ ion (25 lM) with other metal ions
(125 lM) were added to the solution of 1 (25 lM), respec-
tively, only Co2+, Zn2+, Cd2+ and Fe2+ ions had a slight
disturbance under their much excess. The results indicate
that the binding of Cu2+ ion to 1 is much stronger than that
of other metal ions, though the latter is fivefold to Cu2+
ion.
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Y.-Q. Weng et al. / Inorganic Chemistry Communications 10 (2007) 443–446
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