Highly selective colorimetric signaling of iron cations based on fluoran dye

Article abstract of DOI:10.1080/15421400902946319

A highly selective colorimetric chemosensor based on fluoran dye for iron cations, 2′-anilino-3′methyl-6′-dibuthylamino-N-(2′- (2″-hydroxybenzylideneamino)ethyl) iso-indolin-1-one-fluoran (5), was designed and synthesized. The chemical structures of all t

Full text of DOI:10.1080/15421400902946319

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Highly Selective Colorimetric
Signaling of Iron Cations Based
on Fluoran Dye
Sheng Wang a b , Seon-Yeong Gwon a , Yong-A Son c ,
Shinya Matsumoto d , In Jeong Hwang a & Sung-Hoon
Kim a
a Department of Textile System Engineering ,
Kyungpook National University , Daegu, Korea
b School of Chemistry Science & Technology,
Zhanjiang Normal University , Zhanjiang, P.R. China
c BK21 FTIT, Department of Organic Materials and
Textile System Engineering , Chungnam National
University , Daejeon, South Korea
d Department of Environmental Sciences , Faculty of
Education and Human Sciences, Yokohama National
University , Yokohama, Japan
Published online: 25 Jun 2009.
To cite this article: Sheng Wang , Seon-Yeong Gwon , Yong-A Son , Shinya Matsumoto ,
In Jeong Hwang & Sung-Hoon Kim (2009) Highly Selective Colorimetric Signaling of
Iron Cations Based on Fluoran Dye, Molecular Crystals and Liquid Crystals, 504:1,
155-163, DOI: 10.1080/15421400902946319
To link to this article: http://dx.doi.org/10.1080/15421400902946319
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Mol. Cryst. Liq. Cryst., Vol. 504, pp. 155–163, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902946319
Highly Selective Colorimetric Signaling of Iron Cations
Based on Fluoran Dye
Sheng Wang1,2, Seon-Yeong Gwon1, Yong-A Son3,
Shinya Matsumoto4, In Jeong Hwang1, and
Sung-Hoon Kim1
1Department of Textile System Engineering, Kyungpook National
University, Daegu, Korea
2School of Chemistry Science & Technology, Zhanjiang Normal
University, Zhanjiang, P.R. China
3BK21 FTIT, Department of Organic Materials and Textile System
Engineering, Chungnam National University, Daejeon, South Korea
4Department of Environmental Sciences, Faculty of Education and
Human Sciences, Yokohama National University, Yokohama, Japan
A highly selective colorimetric chemosensor based on fluoran dye for iron cations,
20-anilino-30methyl-60-dibuthylamino-N-(20-(200-hydroxybenzylideneamino)ethyl)
iso-indolin-1-one-fluoran (5), was designed and synthesized. The chemical struc-
tures of all the intermediates and fluoran dye 5 were characterized by 1H-NMR,
13C-NMR, MS and elemental analysis. And its sensing behavior toward metal ions
was investigated by UV-visible absorption spectroscopes. The fluoran dye 5 chemo-
sensor showed an extreme selectivity for Fe2þ and Fe3þ in acetonitrile solution.
Whereas other ions including Mg2þ, Pd2þ, Ni2þ, Hg2þ, Cd2þ, Agþ, Cu2þ, Zn2þ
and Al3þ induced basically no spectral change, which constituted a Fe2þ highly
sensitive and selective colorimetric chemosensor from colorless to black by ‘‘naked
eyes.’’ Spectral responses at kmax ¼ 653 nm reveals that dye 5 can function as OR
logic gate with Fe2þ and Fe3þ as input variables.
Keywords: chemosensor; colorimetric; fluoran dye; iron cation; selective; sensitive
This research was supported by Kyungpook National University Research Fund,
2008. This work was supported by Korea Science & Engineering Foundation through
the Joint Research Program (Grant No. F01-2007-000-10014-0).
Address correspondence to Sung-Hoon Kim, Department of Textile System Engineer-
ing, Kyungpook National University, Daegu 702-701, Korea. E-mail: shokim@knu.ac.kr
155

156
S. Wang et al.
INTRODUCTION
The development of sensitive chromogenic probes has been receiving
much attention in recent years because of the potential application in
clinical biochemistry and environment. There are already many chro-
mogenic 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 important elements among heavy metals
for metabolic processes, being indispensable for plants and animals and
therefore it is extensively distributed in environmental and biological
materials [4]. If iron concentration exceeds the normal level it may
become potential health hazard. Iron deficiency leads to anemia. There-
fore, 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 ana-
lyses 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 interesting topic.
Fluoran dyes have the remarkable feature of giving a wide variety
of colors depending on their substituents [13]. In particular, fluoran
type dyes are very important in theirs ability to yield singly black color
on the addition of an acidic compound. The fluoran dyes are only
applied for use in thermosensitive recording paper. No one almost care
about the fluoran chromophore as metal recognization chromophore.
From the fluoran dyes parents structures can be seen that it is closely
resembles the Rhodamine dye. Rhodamine is a dye used extensively as
a chemosensor reagent due to its excellent photophysical properties,
SCHEME 1 The synthesis routes of fluoran dye 5.

Highly Selective Colorimetric Signaling of Iron Cations
157
SCHEME 2 Proposed binding mode and color change of fluoran dye 5 with Fe2þ
.
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]. To be their enlightened, we designed
and synthesized a highly selective chemosensor based on fluoran dye
5 for iron ion as shown in Scheme 1.
To the best of our knowledge, there have no report on fluoran dye as
colorimetric chemosensor that show the black color for highly sensitive
and selective Iron metal cations.
EXPERIMENTAL
Melting points were determined using an Electrothermal IA 900 and
are uncorrected. Elemental analyses were recorded on a Carlo Elba
Model 1106 analyzer. UV-visible absorption spectra were measured
on an Agilent 8453 spectrophotometer. Mass spectra were recorded
on a Shimadzu QP-1000 spectrometer using electron energy of 70 eV
and the direct probe EI method. 1H NMR, 13C NMR spectra were
recorded using a Varian Inova 400 MHz FT-NMR spectrometer with
TMS as internal standard.
Fluoran Dye 3
Fluoran dye 3 was synthesized according to thþe literature method [17].
Yield: 58%, m.p. 187ꢀC; mass (m=z) 532(M ); 1H NMR (400 MHz,
DMSO-d6): d (ppm) 7.93 (d, J ¼ 7.56, 1H), 7.76 (t, J ¼ 7.56, 1H), 7.66
(t, J ¼ 7.36, 1H), 7.41 (s, 1H), 7.26 (t, J ¼ 7.84, 1H), 7.22 (s, 1H), 6.99
(t,
J ¼ 7.84,
2H),
6.62
(t,
J ¼ 7.04,
1H),
6.55
(d, J ¼ 7.6, 2H), 6.49 (d, J ¼ 8.08, 2H), 6.43 (s, 1H), 6.41 (d, J ¼ 9.08,
1H), 3.25 (t, J ¼ 7.6, 4H), 2.21 (s, 3H), 2.07 (s, 1H), 1.48 (m, 4H),
1.29 (m, 4H), 0.87 (t, 6H).

158
S. Wang et al.
13C NMR (400 MHz, DMSO-d6): d (ppm), 13.78, 17.84, 19.63, 28.86,
30.59, 49.89, 83.55, 96.98, 104.1, 108.5, 114.63, 116.99, 118.32, 118.53,
119.49, 123.92, 124.45, 126.24, 128.59, 128.77, 129.94, 134.92, 135.40,
136.85, 145.25, 146.58, 149.63, 152.43, 152.49, 168.66.
Fluoran Dye 4
Fluoran dye 3 (1.0 g, 1.9 mmol) was dissolved in 100 mL of ethanol,
followed by addition of ethylenediamine (2.0 mL, 24.7 mmol). The
reaction mixture was refluxed for 12 hours. After cooling to the room
temperature, the solvent was evaporated in vacuo. The CH2Cl2 and
water (200 mL) were added, and the 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 þof dye 4.
Yield: 91%, m.p. 223–225ꢀC; mass (m=z) 574 (M ); 1H NMR
(400 MHz, DMSO-d6): d (ppm) 7.72 (d, J ¼ 7.08, 1H), 7.54 (t, J ¼ 6.8,
1H), 7.48 (t, J ¼ 7.32, 1H), 7.16 (s, 1H), 7.04 (d, J ¼ 7.32, 1H), 6.99(d,
J ¼ 7.84, 2H), 6.61 (t, J ¼ 7.32, 1H), 6.49 (d, J ¼ 7.84, 2H), 6.38 (s,
1H), 6.33 (d, J ¼ 7.56, 4H), 3.42 (m, 2H), 3.22 (t, J ¼ 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).
13C NMR (400 MHz, DMSO-d6): d (ppm), 13.89, 17.76, 18.59, 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,
167.10.
Fluoran Dye 5
Fluoran dye 4 (0.2 g, 0.35 mmol) was dissolved in 15 mL absolute
ethanol. An excessive 2-hydroxybenzaldehyde (0.171 g, 1.4 mmol)
was added then the mixture was refluxed for 6 h. After that, the
solution was cooled (concentrated to 10 mL) and allowed to stand at
room temperature overnight. The precipitate was filtered and washed
3 times with 10 mL cold ethanol to obtain the crude product. Then, the
crude product was purified by column chromatography on silica gel
(CHCl3=EtOH: 8=1 (v=v)) to give 0.14 g white powder.
Yield: 59%, m.p. 169–171ꢀC; mass (m=z) 678 (Mþ); 1H NMR
(400 MHz, DMSO-d6): d (ppm) 12.93 (s, 1H), 8.02 (s, 1H), 7.72 (d,
J ¼ 7.56, 1H), 7.55 (t, J ¼ 7.6, 1H), 7.50 (t, J ¼ 7.32, 1H), 7.32 (s, 1H),

Highly Selective Colorimetric Signaling of Iron Cations
159
7.18 (d, J ¼ 5.32, 1H), 7.09 (d, J ¼ 7.32, 1H), 6.95 (t, J ¼ 7.60, 2H), 6.81
(t, J ¼ 7.84, 2H), 6.58 (t, J ¼ 5.32, 1H), 6.48 (d, J ¼ 8.36, 2H), 6.36 (s,
1H), 6.29 (d, J ¼ 9.8, 2H), 3.4 (m, 2H), 3.26 (m, 2H), 3.23 (t, J ¼ 7.6,
4H), 2.17 (s, 3H), 2.08 (s, 1H), 1.48 (m, 4H), 1.29 (m, 4H), 0.89 (t, 6H).
13C NMR (400 MHz, DMSO-d6): d (ppm), 13.82, 17.78, 20.49, 28.91,
40.47, 49.86, 56.63, 63.97, 97.16, 97.43, 103.92, 108.44, 114.32, 116.32,
117.20, 118.19, 118.36, 118.48, 118.66, 119.73, 122.51, 123.62, 128.42,
128.57, 128.78, 130.10, 131.56, 132.20, 132.95, 133.97, 136.68, 145.30,
147.0, 148.97, 152.55, 152.96, 160.32, 166.27, 167.12, 173.71.
Anal. Cald. for C44H46N4O3: C, 77.84; H, 6.83; N, 8.25 Found; C,
77.11; H, 7.14; N, 8.16%.
RESULTS AND DISCUSSION
Fluoran dye 5 was synthesized according to the Scheme 1. At first, the
intermediate fluoran dye 3 was synthesized from 2-(4-(dibutylamino)-
2-hydroxybenzoyl) benzoic acid
1
and 4-methoxy-2-methyl-N-
phenylbenzenamine 2 as starting materials using H2SO4 as catalyst.
Then, fluoran dye 3 was transferred to fluoran dye 4 via condensation
reaction. At last, fluoran dye 5 was prepared from fluoran dye 4 and
2-hydroxybenzaldehyde by Schiff’s base condensation.
The recognition between fluoran dye 5 and different metal cations
were investigated by UV-vis spectroscopy in the CH3CN solution.
The solution of fluoran dye 5 is at a concentration of 1.0 ꢁ 10ꢂ5 mol=L.
From the absorption spectrum of fluoran dye 5 in the CH3CN solution,
it was not found that an absorption band appeared in visible region,
fluoran dye 5 solution is colorless. Variation of absorption spectra of
fluoran dye 5 upon addition of different metal cations including
Cd2þ, Mg2þ, Pd2þ, Hg2þ, Ni2þ, Cu2þ, Fe2þ, Fe3þ, Hþ, alkali metal
and alkaline earth metal cations, are shown in Figures 1 and 2.
Figure 1 show the UV-vis spectra of fluoran dye 5 (1.0 ꢁ 10ꢂ5mol ꢃ Lꢂ1
)
,
upon addition of ClOꢂ4 salt of X ¼ Cd2þ, Mg2þ, Pd2þ, Hg2þ, Ni2þ
Cu2þ, Fe2þ, Fe3þ, Hþ (10 equiv) in CH3CN solution. The absorption
maximum show no obvious change upon the addition of the metal ions
Cd2þ, Mg2þ, Pd2þ, Hg2þ, Ni2þ, and Hþ. A small increase at 565 nm was
observed in the presence of Cu2þ. While upon addition of Fe2þ, we also
found new absorption bands appeared including the absorption at
wavelength peaked at 433 nm and 653 nm. The color changed from
colorless to black. The color of 433nm is complementary to the color
of 653 nm. As a result, a black color hue can be obtained by use of only
one chromophore. While upon addition of Fe3þ, we also found new
absorption bands appeared including the absorption at wavelength
peaked at 640 nm, which is similar to Fe2þ (Fig. 1). Figure 2 show the

160
S. Wang et al.
FIGURE 1 The UV-vis spectra of fluoran dye 5 (1.0 ꢁ 10ꢂ5 mol ꢃ Lꢂ1) upon
addition of ClO4ꢂ salt of X ¼ Hþ, Cd2þ, Mg2þ, Pd2þ, Hg2þ, Ni2þ, Cu2þ, Fe2þ
,
Fe3þ (10 equiv) in CH3CN solution.
FIGURE 2 The absorbance response of fluoran dye 5 to 1.0 mM 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. no cation (blank: dye 5), 2. Mg2þ, 3. Cu2þ, 4. Co2þ, 5.
Hg2þ, 6. Zn2þ, 7. Pd2þ, 8. Ni2þ, 9. Fe2þ, 10. Al3þ, 11. Fe3þ, 12. Agþ, 13. Kþ.

Highly Selective Colorimetric Signaling of Iron Cations
161
FIGURE 3 The color changes of fluoran dye 5 (1.0 ꢁ 10ꢂ5 mol ꢃ Lꢂ1) upon addi-
tion of ClOꢂ4 salt of X ¼ Mg2þ, Pd2þ, Ni2þ, Hg2þ, Cd2þ, Fe2þ,Cu2þ, Fe3þ, Zn2þ
,
Al3þ, Ba2þ, Kþ in CH3CN solution (10 equiv).
absorbance intensities at 653 nm (A653 nm) over the absorbance intensity
of the blank fluoran dye 5 solution. With the addition of Fe2þ, the absor-
bance intensity of fluoran dye 5 at 653nm was increased. With the addi-
tion of the other metal ions, the absorbance intensity of fluoran dye 5 at
653 nm was almost no evidently changed. While upon addition of Fe3þ
,
we also found new absorption bands appeared including the absorption
at wavelength peaked at 650 nm, which is similar to Fe2þ. Figure 3
show the color change photographs of fluoran dye
5
(1.0 ꢁ
10ꢂ5 mol ꢃ Lꢂ1) upon addition of ClOꢂ4 salt of X ¼ Mg2þ, Pd2þ, Ni2þ
,
Hg2þ, Cd2þ, Fe2þ, Cu2þ, Fe3þ, Zn2þ, Al3þ, Ba2þ, Kþ in CH3CN solution
(10 equiv).
These results indicate that fluoran dye 5 shows sensing ability for
Iron cations (Scheme 2). It has high-sensitivity and selectivity toward
Fe2þ ions. The dependence of absorption spectroscopy of fluoran dye 5
in the solution on the concentration of Fe2þ was investigated by the UV
titration method. With the addition of Fe2þ, the 290 nm was decreased
accomplished with the increase of the wavelength at 443 nm and
653 nm. An isosbestic point in the titration curves shows new specie
appeared with the addition of Fe2þ, which could be assigned to the for-
mation of the Fe2þ complex of fluoran dye 5 as shown in Figure 4.
Figure 4 set shows the absorbance intensities change at 443 nm
(A443 nm) and 653 nm (A653 nm) over the absorbance intensity of the
blank fluoran dye 5 solution. With the addition of Fe2þ, the absorbance
intensity of fluoran dye 5 at 443 nm and 653 nm was all increased. So
the color of solution gradually became black from the colorless.
Actually, an obvious color change from colorless to black was observed
by the naked eyes.
These behaviours may be conveniently described using logic nota-
tion [18,19]. The input signals are Fe2þ and Fe3þ. The presence of
Fe2þ and Fe3þ can be characterized by the typical absorption band

162
S. Wang et al.
FIGURE 4 The absorbance spectra of fluoran dye 5 in the presence of Fe2þ in
CH3CN solution. The Fe2þ concentration is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mM,
respectively. Inset: absorbance at 433 nm and 653 nm change with Fe2þ
concentration change.
at 653 nm. The absorption band with kmax ¼ 653 nm can be considered
as output signals: output ¼ 0 when the absorbance at 653 nm is low
(<0.4); output ¼ 1 when the absotbance at 653 nm is high (>0.4).
TABLE 1 (a) Truth Table; (b) Physical
Electronic Symbol of 2-Input OR Logic Gate
(a)
Input1 (Fe2þ
)
Input2 (F3þ
)
Output (A653)
0
0
1
1
0
1
0
1
0 (low, <0.4)
1 (high, >0.4)
1 (high, >0.4)
1 (high, >0.4)
(b)

Highly Selective Colorimetric Signaling of Iron Cations
163
Due to the dependence of the absorption intensity of adding Fe2þ and
Fe3þ, it is possible to mimic the function of the truth table of an OR
gate (see Table 1).
CONCLUSION
In conclusion, a new chromogenic chemosensor based on fluoran dye
derivative was developed. It shows a good selectivity and sensitivity
for Fe2þ and Fe3þ. An obvious color change from colorless to black
was observed by the naked eyes, in other words, a colorimetric signal
could be easily read by the naked eye without resort to any spectro-
scopic instrumentation. This is a very simple and effective method
for detecting the Iron cations.
These responses follow the truth table of an OR logic gate.
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