A highly selective and sensitive colorimetric chemosensor for Fe2+ based on fluoran dye

Article abstract of DOI:10.1016/j.saa.2009.12.018

A highly selective chemosensor based on fluoran dye for Fe²⁺, 2′-anilino-3′-methyl-6′-dibuthylamino-N-((2′-(2″-ethylimino) methyl) naphthalen-2-ol) iso-indolin-1-one-fluoran (5), was designed and synthesized. The chemical structures of all the intermediates and the fluoran dye 5 are characterized by ¹H NMR, ¹³C NMR, Ms and elemental analysis. Upon addition of Fe²⁺, the fluoran dye 5 shows a new peak around 658 nm in its absorption spectra, and the color of solution changed from colorless to greenish black. Whereas other ions including Mg²⁺, Pb²⁺, Ni²⁺, Hg²⁺, Cd²⁺, Fe³⁺, Cu²⁺, Zn²⁺ and Al³⁺ and so on induced basically no spectral change, which constituted a Fe²⁺ highly sensitive and selective colorimetric chemosensor by naked eyes .

Full text of DOI:10.1016/j.saa.2009.12.018

Spectrochimica Acta Part A 76 (2010) 293–296
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
2
+
A highly selective and sensitive colorimetric chemosensor for Fe based on
fluoran dye
Sheng Wanga,b, Seon-Yeong Gwon , Sung-Hoon Kima,∗
a
a
Department of Textile System Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea
School of Chemistry Science & Technology, Zhanjiang Normal University, Development Center for New Materials Engineering & Technology in Universities of Guangdong,
b
Zhanjiang 524048, PR China
a r t i c l e i n f o
a b s t r a c t
2
+
ꢀ
ꢀ
ꢀ
Article history:
Received 2 March 2009
Received in revised form
A highly selective chemosensor based on fluoran dye for Fe , 2 -anilino-3 -methyl-6 -dibuthylamino-
ꢀ
ꢀꢀ
N-((2 -(2 -ethylimino) methyl) naphthalen-2-ol) iso-indolin-1-one-fluoran (5), was designed and
synthesized. The chemical structures of all the intermediates and the fluoran dye 5 are char-
3
0 November 2009
1
13
2+
acterized by H NMR,
dye shows new peak around 658 nm in its absorption spectra, and the color of solu-
tion changed from colorless to greenish black. Whereas other ions including Mg , Pb2+, Ni
C NMR, Ms and elemental analysis. Upon addition of Fe , the fluoran
Accepted 3 December 2009
5
a
2+
2+
,
Keywords:
Chemosensor Fe2 recognition
Fluoran
2
+
2+
3+
2+
2+
3+
Hg , Cd , Fe , Cu , Zn
and Al
and so on induced basically no spectral change, which
+
+
constituted
a
Fe2 highly sensitive and selective colorimetric chemosensor by “naked eyes”.
Colorimetric
Metal cation
© 2009 Elsevier B.V. All rights reserved.
Selectivity
1
. Introduction
The development of sensitive chromogenic probes has been
Fluoran dyes have the remarkable feature of giving a wide vari-
ety of colors depending on their substituents [13]. In particular,
fluoran type dyes are very important in their ability to yield singly
black color on the addition of an acidic compound. The fluoran
dyes as a color former are only applied for use in thermosensi-
tive recording paper. The color formers used in thermal paper are
essentially colorless organic compounds that develop an intense
color when brought into contact with an acid. Black is the most
important color in thermal printing, and the most widely used color
formers for producing a black color are fluoran derivatives. No one
almost care about the fluoran chromophore as metal recognition
chromophore. The structure of fluoran dye is very resemble the rho-
damine dye. Rhodamine is a dye used extensively as a chemosensor
reagent due to its excellent photophysical properties, such as long
absorption and emission wavelengths elongated to visible region,
high absorption coefficient and high fluorescence quantum yield
[14]. Various rhodamines fluorescent probes for heavy metal have
been developed [15,16]. Several organic dye-based chemosensors
for Fe3+ have recently been reported. However, despite the urgent
need for Fe2+ sensing, there have been only limited studies on Fe
selective sensors. We designed and synthesized a highly selec-
tive chemosensor based on fluoran dye 5 for Fe2+ as shown in
Scheme 1. To the best of our knowledge, this is the first exam-
ple of fluoran dye as colorimetric chemosensor that show the
greenish black color for highly sensitive and selective Fe2+ metal
cation.
receiving much attention in recent years because of the poten-
tial application in clinical biochemistry and environment. There are
already many chromogenic chemosensors developed for selective
recognition of different species so far due to their high selectivity,
sensitivity and simplicity [1–3]. Iron is one of the most impor-
tant elements among heavy metal for metabolic processes, being
indispensable for plants and animals and therefore it is exten-
sively distributed in environmental and biological materials [4]. If
iron concentration exceeds the normal level it may become poten-
tial health hazard. Iron deficiency leads to anemia. Therefore, it is
important to explore new chromogenic chemosensors for selec-
tive detection of iron. Over the past years, some examples for
iron detection, including chromogenic [5] and fluorescent [6–10]
chemical sensors, electrochemical devices [11] have been reported.
Currently, colorimetric sensors are popular due to their capability
to detect analyses by naked eye without resorting to any expensive
instruments [12]. Therefore, to develop simple-to-use and naked
eye diagnostic tool for selective detection of iron is a hot and inter-
esting topic.
2+
∗ Corresponding author. Tel.: +82 53 950 5641; fax: +82 53 950 6617.
E-mail address: shokim@knu.ac.kr (S.-H. Kim).
1
386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.12.018

2
94
S. Wang et al. / Spectrochimica Acta Part A 76 (2010) 293–296
Scheme 1. Proposed binding mode and color change of fluoran dye 5 with Fe2+
.
2
. Experimental
129.94, 134.92, 135.40, 136.85, 145.25, 146.58, 149.63, 152.43,
1
52.49 and 168.66.
2.1. Materials and methods
2.4. Synthesis of fluoran dye 4
Most of chemicals were purchased from Aldrich Chemical Co.
and TCI. Solvents were purified by normal procedures and used
under moisture free atmosphere. The other materials were com-
mercial products and were used without further purification.
Fluoran dye 3 (1.0 g, 1.9 mmol) was dissolved in 100 mL of
ethanol solution, followed by addition of ethylenediamine (2.0 mL,
24.7 mmol). The reaction mixture was refluxed for 12 h. After
cooling to the room temperature, the solvent was evaporated in
2.2. Instruments and spectral measurements
vacuum. The CH Cl2 and water (200 mL) were added, and the
2
organic layer was separated, washed twice with water and dried
over anhydrous sodium sulfate. After filtration of sodium sulfate,
the solvent was removed under reduced pressure. Then 1 M HCl
(50 ml) was added to the solid in the flask to generate a clear red
solution. After that, 2 M NaOH was added slowly with stirring until
the pH of the solution reached 7–8. The resulting pink solid was
filtered and obtained 1.1 g of fluoran dye 4.
Melting points were determined using an Electrothermal IA
00 and are uncorrected. Elemental analyses were recorded on a
9
Carlo Elba Model 1106 analyzer. UV–vis absorption spectra were
measured on an Agilent 8453 spectrophotometer. Mass spectra
were recorded on a Shimadzu QP-1000 spectrometer using elec-
1
13
tron energy of 70 eV and the direct probe EI method. H NMR,
C
Yield: 91%, m.p. 223–225 C; mass (m/z) 574(M ); 1H NMR
◦
+
NMR spectra were recorded using a Varian Inova 400 MHz FT-NMR
spectrometer with TMS as internal standard.
(400 MHz, DMSO-d6): ␦ (ppm) 7.72 (d, J = 7.08, 1H), 7.54 (t, J = 6.8,
1
H), 7.48 (t, J = 7.32, 1H), 7.16 (s, 1H), 7.04 (d, J = 7.32, 1H), 6.99 (d,
J = 7.84, 2H), 6.61 (t, J = 7.32, 1H), 6.49 (d, J = 7.84, 2H), 6.38 (s, 1H),
.33 (d, J = 7.56, 4H), 3.42 (m, 2H), 3.22 (t, J = 6.8, 4H), 3.0 (m, 2H),
2.17 (s, 3H), 2.08 (s, 1H), 1.48 (m, 4H), 1.30 (m, 4H), 0.9 (t, 6H).
2
.3. Synthesis of fluoran dye 3
6
The fluoran dye 3 was synthesized according to the literature
13
method [17].
C NMR (400 MHz, DMSO-d6): ı (ppm), 13.89, 17.76,18.59,
1
H NMR Yield: 58%, m.p. 187 C; mass (m/z) 532(M ); 1H NMR
◦
+
19.69, 25.24, 28.95, 32.14, 43.58, 49.88, 63.89, 97.11, 103.91, 108.41,
114.48, 117.35, 118.32, 118.18, 118.60, 119.70, 122.38, 123.57,
128.38, 128.86, 130.14, 132.81, 133.81, 136.58, 145.43, 146.32,
146.86, 152.39, 153.35 and 167.10.
(
400 MHz, DMSO-d6): ␦ (ppm) 7.93 (d, J = 7.56, 1H), 7.76 (t, J = 7.56,
1
1
6
4
6
H), 7.66 (t, J = 7.36, 1H), 7.41 (s, 1H), 7.26 (t, J = 7.84, 1H), 7.22 (s,
H), 6.99 (t, J = 7.84, 2H), 6.62 (t, J = 7.04, 1H), 6.55 (d, J = 7.6, 2H),
.49 (d, J = 8.08, 2H), 6.43 (s, 1H), 6.41 (d, J = 9.08, 1H), 3.25 (t, J = 7.6,
H), 2.21 (s, 3H), 2.07 (s, 1H), 1.48 (m, 4H), 1.29 (m, 4H), 0.87 (t,
H).
2.5. Synthesis of fluoran dye 5
13C NMR (400 MHz, DMSO-d6): ı (ppm), 13.78, 17.84, 19.63,
8.86, 30.59, 49.89, 83.55, 96.98, 104.1, 108.5, 114.63, 116.99,
18.32, 118.53, 119.49, 123.92, 124.45, 126.24, 128.59, 128.77,
Fluoran dye 4 (0.2 g, 0.35 mmol) was dissolved in 15 mL abso-
lute ethanol. An excessive 2-hydroxy-1-naphthaldehyde (0.171 g,
1.4 mmol) was added then the mixture was refluxed for 6 h. After
2
1
Scheme 2. The synthetic route of fluoran dye 5.

S. Wang et al. / Spectrochimica Acta Part A 76 (2010) 293–296
295
3. Results and discussion
The fluoran dye 5 was synthesized according to the Scheme 2.
At first, the intermediate the fluoran dye 3 was synthesized
from 2-(4-(dibutylamino)-2-hydroxybenzoyl) benzoic acid 1 and
4
-methoxy-2-methyl-N-phenylbenzenamine 2 as starting mate-
rials using H SO4 as catalyst. Then, the fluoran dye 3 was
2
transferred to the fluoran dye 4 via condensation reaction. At
last, the fluoran dye 5 was prepared from the fluoran dye 4
and 2-hydroxy-1-naphthaldehyde by Schiff’s base condensation.
The chemical structures of all the intermediates and the dye
are characterized by 1H NMR,
13
C NMR, MS and elemental
5
analysis.
The recognition between the fluoran dye 5 and different metal
cations were investigated by UV–vis spectroscopy in the CH CN
3
solution. The solution of the fluoran dye 5 is at a concentration
−
5
of 1.0 × 10 mol/L. From the absorption spectrum of the fluoran
dye 5 in the CH CN solution, it was not found that an absorp-
tion band appeared in visible region, the fluoran dye 5 solution
is colorless. Variation of absorption spectra of the fluoran dye 5
3
−
5
−1
2+
Fig. 1. The UV–vis spectra of fluoran dye 5 (1.0 × 10 mol L ) upon addition of
−
2+
2+
2+
2+
2+
2+
2+
3+
3+
ClO4 salt of X = Cd , Mg , Pd , Hg , Ni , Cu , Fe , Fe , Zn and Al (10 equiv.)
in CH3CN solution.
2
+
2+
2+
upon addition of different metal cations including Cd , Mg , Pd
,
2+
2+
2+
2+
3+
2+
3+
Hg , Ni , Cu , Fe , Fe , Zn , Al , alkali metal and alkaline
earth metal cations, are shown in Figs. 1 and 2. Fig. 1 show the
that, the solution was cooled (concentrated to 10 mL) and allowed
to stand at room temperature overnight. The precipitate was fil-
tered and washed 3 times with 10 mL cold ethanol to obtain the
crude product. Then, the crude product was purified by column
−5
−1
2+
UV–vis spectra of fluoran dye 5 (1.0 × 10 mol L ) upon addi-
−
2+
2+
2
2+
+
3+
2+
tion of ClO
salt of X = Mg , Cu , Hg , Ag , Zn , Fe , Fe ,
4
2+
3+
Pb , Al , Ni (10 equiv.) in CH CN solution. The absorption max-
3
chromatography on silica gel (CHCl /EtOH: 8/1 (v/v)) to give 0.14 g
3
imum show no obvious change upon the addition of the metal
white powder of fluoran dye 5.
2+
2+
2+
2+
2+
3+
2+
2+
ions Cd , Mg , Pd , Hg , Ni , Fe , Ca and Co . While upon
Yield: 59%, m.p. 193–195 C; mass (m/z) 728 (M ); 11H NMR
400 MHz, CDCl ) ı: 0.95 (t, J = 7.32 Hz, 6H), 1.33 (sextet, J = 7.32 Hz,
H), 1.56 (quintet, J = 7.32 Hz, 4H), 2.10 (s, 3H) 3.22 (t, J = 7.8 Hz, 4H),
.42 (m, 4H), 5.23 (s, 1H), 6.25 (d, J = 9.08 Hz, 1H), 6.38 (m, 4H), 6.45
s, 1H), 6.66 (t, J = 7.32 Hz, 1H), 6.86(d, J = 7.32 Hz, 1H), 6.99(d, 2H),
.09 (m, 2H), 7.23 (t, J = 7.08 Hz, 1H), 7.44 (m, 3H), 7.59(d, J = 7.84,
H), 7.66 (d, J = 9.32 Hz, 1H), 7.80 (d, J = 8.60 Hz, 1H), 7.87 (m, 1H),
.52 (d, J = 7.08 Hz, 1H), 13.98 (s, 1H, –OH).
◦
+
2+
addition of Fe , we found new absorption bands appeared includ-
(
3
ing the absorption at wavelength peaked at around 658 nm. The
color changed from colorless to greenish black. While upon addi-
4
3
(
3+
tion of Fe , we do not found new absorption bands appeared
including the absorption at wavelength peaked. Fig. 2 shows the
absorbance intensities at 658 nm (A658 nm) over the absorbance
intensity of the blank fluoran dye 5 solution. With the addition
7
1
8
2+
of Fe , the absorbance intensity of the fluoran dye 5 at around
13
C NMR (400 MHz, CDCl ) ı: 14.18, 18.13, 20.50, 29.53, 32.36,
3
6
58 nm was increased. With the addition of the other metal ion,
3
1
1
1
1
8.26, 41.28, 50.86, 50.94, 65.10, 97.91, 103.92, 107.08, 108.69,
14.77, 117.67, 118.29, 119.14, 121.99, 122.93, 123.33, 123.90,
25.00, 126.40, 128.16, 128.59, 128.72, 129.23, 129.32, 130.77,
32.98, 133.92, 135.18, 136.29, 137.28, 145.18, 148.41, 149.61,
53.35, 153.47, 158.71, 168.79, 172.00 and 176.02.
the absorbance intensity of the dye 5 at 658 nm was almost no
evidently changed.
These results indicate that fluoran dye 5 has high-sensitive and
2+
selective toward Fe . The dependence of absorption spectroscopy
2+
of dye 5 in CH CN solution on the concentration of Fe was inves-
3
Anal. Cald. for C48H48N O : C 79.09, H 6.64, N 7.68; found: C
4
3
tigated by the absorption spectroscopy titration method. With the
7
8.61, H 6.80, N 7.68.
Fig. 2. The absorbance response of fluoran dye 5 to 1.0 ␮M of various cations in
CH3CN solution. The bar represent the absorbance intensities at 653 nm (A653 nm)
over the absorbance intensity of the blank dye 5 solution. From left to right: (1) dye
−
5
−1
Fig. 3. The absorbance spectra of fluoran dye 5 (cal. 10 mol L ) in the presence
2
+
2+
of Fe in CH3CN solution. The Fe concentration is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,
0.8, 0.9 and 1.0 equiv., respectively. Inset: absorbance at 658 nm change with Fe
2+
2+
3+
2+
2+
+
2+
3+
2+
2+
5
, (2) Mg , (3) Fe , (4) Fe , (5) Cu , (6) Hg , (7) Ag , (8) Zn , (9) Al , (10) Pb
,
2
+
2+
+
2+
(
11) Ni , (12) Ca , (13) K and (14) Co
.
concentration change.

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96
S. Wang et al. / Spectrochimica Acta Part A 76 (2010) 293–296
4. Conclusions
In conclusion, a new chromogenic chemosensor based on flu-
oran derivative was developed. It shows a good selectivity and
sensitivity for Fe2+. An obvious color change from colorless to
greenish black was observed by the naked eyes, in other words,
a signal could be easily read by the naked eye without resort to any
spectroscopic instrumentation. This is a very simple and effective
method for detecting the Fe2+
.
Acknowledgements
This work was supported by the Korean Science and Engineering
Foundation (KOSEF) grant funded by the Korea government (MEST)
(No. 2009-0063408). This research was supported by Kyungpook
National University Fund, 2008. This work was also supported by
the National Natural Science Foundation of China (No. 20802065).
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+
are shown in Fig. 4, which shows the recognition of fluoran dye 5
with Fe2+ to form a stable complex.