Synthesis and spectral properties of a highly selective D-π-S based dye chemosensor

Article abstract of DOI:10.1080/15421406.2011.564507

A novel chromogenic and fluorogenic dye chemosensor was computationally designed using MO theory calculation and synthesized based on donor-π-acceptor unit. This prepared dye sensor showed the selective Ni ²⁺ metal ion sensing effects in optica

Full text of DOI:10.1080/15421406.2011.564507

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Synthesis and Spectral Properties of
a Highly Selective D-π-A Based Dye
Chemosensor
Young-A Son a , Seon-Yeong Gwon b & Sung-Hoon Kim b
a Department of Advanced Organic Materials and Textile System
Engineering , Chungnam National University , Daejeon, S. Korea
b Department of Textile System Engineering , Kyungpook National
University , Daegu, S. Korea
Published online: 16 May 2011.
To cite this article: Young-A Son , Seon-Yeong Gwon & Sung-Hoon Kim (2011) Synthesis and Spectral
Properties of a Highly Selective D-π-A Based Dye Chemosensor, Molecular Crystals and Liquid Crystals,
538:1, 327-332, DOI: 10.1080/15421406.2011.564507
To link to this article: http://dx.doi.org/10.1080/15421406.2011.564507
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Mol. Cryst. Liq. Cryst., Vol. 538: pp. 327–332, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2011.564507
Synthesis and Spectral Properties of a Highly
Selective D-p-A Based Dye Chemosensor
YOUNG-A SON,1 SEON-YEONG GWON,2 AND
SUNG-HOON KIM2
1Department of Advanced Organic Materials and Textile System
Engineering, Chungnam National University, Daejeon, S. Korea
2Department of Textile System Engineering, Kyungpook National
University, Daegu, S. Korea
A novel chromogenic and fluorogenic dye chemosensor was computationally
designed using MO theory calculation and synthesized based on donor-p-acceptor
unit. This prepared dye sensor showed the selective Ni2þ metal ion sensing effects
in optical properties with UV-vis absorption and fluorescence emission. Dye sensor
displayed evident absorption changes with Ni2þ ion and highly selective fluorescence
quenching effect was determined. But it showed no significant changes upon the
addition of other metal ions such as Cd2þ, Na2þ, Mg2þ, Pb2þ, Fe2þ, Fe3þ, Ca2þ
Cu2þ, Hg2þ and Zn2þ
,
Keywords Absorption; D-p-A; dye sensor; fluorescence; metal cation; spectral
properties
1. Introduction
The sensing of metal cations using dye sensor has attracted much attention owing to
its application in both chemical and environmental processes [1–4]. The synthesis of
chemical sensors or receptors capable of recognizing metal cations selectively con-
tinues to attract research interest. There are already many chromogenic dye sensors
developed for selective recognition of different species so far due to their high selec-
tivity, sensitivity and simplicity [5–7]. The design of chemical sensors that are sensi-
tive towards specific target ions is a great challenge for dye chemists [8]. For various
metal ions, even though there are many research reports and works are introduced
[9–18] to detect Hg2þ, Cd2þ, Pb2þ, Cu2þ, Fe2þ and so on, few findings are reported
for the sensing of Ni2þ ions. Herein, we have designed and synthesized the chromo-
genic and fluorephoric dye sensor to respond the presence of Ni2þ ions.
Intramolecular charge transfer (ICT) system based on donor-p-acceptor molecu-
lar conjugation has been widely attracted [1–7] for ions sensing, molecular switching
and fluorescent labeling due to the clear changes of absorption and emission
Address correspondence to Sung-Hoon Kim, Department of Textile System Engineering,
Kyungpook National University, Daegu 702-701, S. Korea. Tel.: þ82 53 950 5641; Fax: þ82
53 950 6617; E-mail: shokim@knu.ac.kr
327

328
Y.-A. Son, S.-Y. Gwon, and S.-H. Kim
properties. In dye sensor 3, we have selected 2-(3,5,5-trimethylcyclohex-2-enylidene)-
malononitrile 1 as electron withdrawing acceptor and 4-(bis(pyridin-2-ylmethyl)
amino)benzaldehyde 2 as electron pushing donor, which also considered as Ni2þ
receptor. A vinyl group between the receptor (and ICT donor) and isophorone
acceptor can induce longer wavelengths in absorption and fluorescence emission
spectra. This paper concerns the synthesis of a dye sensor for metal ions, especially
designed for Ni2þ ion, based on a donor-p-acceptor, intramolecular charge transfer
system. And the potential function of dye sensor 3 to recognize Ni2þ ion, HOMO=
LUMO energy levels, electron distribution in molecular structure and the corre-
sponding changes in its absorption=emission properties were determined.
2. Experimental
All reagents and solvents were purchased from Aldrich and were used without
further purification. Mass spectra were obtained using a Shimadzu QP-1000 and
1H NMR spectra were recorded on a Varian Inova 400 MHz FT-NMR using
TMS as internal standard. UV-Vis absorption spectra were measured on an Agilent
8453 spectrophotometer whilst fluorescecne spectra were measured on a Shimadzu
RF-5301PC fluorescence spectrophotometer. Melting points were determined using
an Electrothermal IA900. 2-(3,5,5-Trimethylcyclohex-2-enylidene)-malononitrile 1
and 4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde 2 were prepared using the pre-
viously described procedure [19,20].
Synthesis of Dye Sensor 3
2-(3,5,5-Trimethylcyclohex-2-enylidene)-malononitrile 1 (0.31 g, 1.65 mmol) and
4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde 2 (0.5 g, 1.65 mmol) were dissolved
in 1-propanol (10 ml) with piperidine (0.1 ml) as catalyst and refluxed for 4 h. After
which, the reaction mixture was cooled down to room temperature. Via column
chromatography (silica, ethlyacetate=ethanol, 40=1. v=v), the desired product was
1
obtained in 50% yield. H NMR (400 MHz, CDCl3): d 0.98 (s, 6H), 2.35 (s, 2H),
2.49 (s, 2H), 4.86 (s, 4H), 6.75 (m, 4H), 6.91 (d, J ¼ 15.88, 1H), 7.28 (m, 5H), 7.65
(t, J ¼ 7.84, 2H), 8.57 (d, J ¼ 3.84, 2H). Mþ ¼ 471. mp: 173ꢀC.
3. Results and Discussion
Dye sensor 3 was designed and synthesized readily from commercially available start-
ing materials using a one-step reaction (Fig. 1). Due to its well-defined intramolecular
Figure 1. Synthetic route for dye sensor 3.

Synthesis and Spectral Properties of a Highly Selective D-p-A
329
charge transfer theory, donor-p-acceptor structure that contains an electron rich
donating (N) atom, it was anticipated that dye sensor 3 could function as a host mol-
ecule for the recognition of metal cations via coordinating interaction. This was inves-
tigated by adding various metal cations (Cd2þ, Na2þ, Mg2þ, Pb2þ, Fe2þ, Fe3þ, Ca2þ
,
Cu2þ, Hg2þ, Zn2þ and Ni2þ) to a 1 ꢁ 10ꢂ5 mol solution of dye sensor 3 in CH3CN and
recording the changes in absorption and emission spectra that occurred during the
titration of the solution of dye sensor 3 with between 0 and 1.0 equiv of Ni2þ cation.
As Figure 2 shows, upon the addition of Ni2þ to the solution of dye sensor 3, the
absorption band at 396 nm progressively increased in intensity and a peak at 479 nm
decreased; an isobestic point at 432 nm also developed. The appearance of this iso-
bestic point in absorption band changes suggests that at least one stable dye-Ni2þ
cation species is present in solution and is indicative that a stable complex formed
between dye sensor 3 and Ni2þ. However, none of the other cations investigated,
Figure 2. Effect of Ni2þ cation concentration on the absorbance and emission intensity of a
1 ꢁ 10ꢂ5 mol solution of dye sensor 3 in CH3CN.

330
Y.-A. Son, S.-Y. Gwon, and S.-H. Kim
namely Cd2þ, Na2þ, Mg2þ, Pb2þ, Fe2þ, Fe3þ, Ca2þ, Cu2þ, Hg2þ and Zn2þ had any
noticeable effect on absorption, as shown in Figure 3.
When Ni2þ cations and the dye sensor formed a complex via the –N electron
donors of the 4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde, the large intramolecu-
lar charge transfer system within dye sensor 3, namely the donor-acceptor electron
stream, was changed, resulting in the observed changes in UV-Vis absorption and
fluorescence emission.
In the context of the ability of dye sensor 3 to act as a fluorescence sensor toward
metal cation detection, the marked quenching of fluorescence emission imparted by
Ni2þ cations (Fig. 2) can be explained on the basis that, as a result of the formation
of an ꢂN, coordination binded complex between Ni2þ and dye sensor 3, both the
intramolecular charge transfer system and the excited state were greatly modified,
resulting in reduced fluorescence emission. When a fluorophore acceptor contains
an electron-donating group, e.g., amino group, conjugating to a fluorophore unit,
it undergoes ICT from the donor to the fluorophore acceptor on light excitation,
which shows a red-shifted emission. If the donor receptor is coordinated with metal
ion, the amino group loses its donating ability [19]. Thus, the ICT is inhibited and
the emission is quenched. This observation is in well agreement with the UV-Vis
absorption behavior (Fig. 2) insofar as, colorimetric changes due to the coordination
binding of ꢂN, which is directly influenced by the chromophore and the fluoro-
phore, have been employed in the design of a chemosensor for Ni2þ cation.
For the interpretation of the complexation and electronic structure of dye sensor
3-Ni2þ, the quantum chemical DMol3 approach was used. All the theoretical calcula-
tions were performed by DMol3 program in the Materials Studio 4.2 package [21,22]
which is the quantum mechanical code using density functional theory. Perdew-
Burke-Ernzerhof (PBE) function of generalized gradient approximation (GGA) level
[23] with double numeric polarization basis set was used to calculate the energy level
of the frontier molecular orbital. The optimized dye sensor 3-Ni2þ bidentate
Figure 3. Comparison of absorption ratio for various cations (A and A0 are the absorbance in
the presence and the absence of metal cations, respectively at 396 nm).

Synthesis and Spectral Properties of a Highly Selective D-p-A
331
Figure 4. Optimized structure of dye sensor 3-Ni2þ complex.
Figure 5. Electron distribution of HOMO and LUMO energy levels of dye sensor 3.
structure is shown in Figure 4; Ni2þ cation is bridged between two nitrogen atoms in
electrong donor unit.
Figure 5 shows the calculated structural energy levels of dye sensor 3 and the elec-
tron distribution of its HOMO and LUMO. Comparison of the electron distribution
in the frontier MOs reveals that HOMO-LUMO excitation moved the electron
distribution from 4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde to the isophorone
moiety, which shows a strong migration of intramolecular charge-transfer character-
istic of dye sensor 3. Therefore, the electron donating moiety of 4-(bis(pyridin-2-
ylmethyl)amino)benzaldehyde in HOMO energy level is important for effective
complexation with Ni2þ in this system. As a result, the complexation of Ni2þ to nitro-
gen atoms reduces the electron density on the nitrogen atoms and lowers the electron
donating ability of 4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde.
4. Conclusions
A novel, chromogenic and fluorescent dye senor based on 4-(bis(pyridin-2-ylmethyl)-
amino)benzaldehyde as donor unit and 2-(3,5,5-trimethylcyclohex-2-enylidene)malo-
nonitrile as acceptor unit exhibited marked changes in UV-Vis absorption peak and
fluorescence emission intensity upon the addition of Ni2þ ion. Dye sensor displayed
evident spectral changes with Ni2þ ion and highly selective fluorescence quenching
effect was determined. But it showed no significant changes upon the addition of

332
Y.-A. Son, S.-Y. Gwon, and S.-H. Kim
other metal ions such as Cd2þ, Na2þ, Mg2þ, Pb2þ, Fe2þ, Fe3þ, Ca2þ, Cu2þ, Hg2þ
and Zn2þ. For the interpretation of the complexation and electronic structure of
dye sensor 3-Ni2þ, the optimized dye sensor 3-Ni2þ bidentate structure is bridged
between two nitrogen atoms in electron donor unit. For the electron distribution
of its HOMO and LUMO, HOMO-LUMO excitation has changed the electron dis-
tribution from 4-(bis(pyridin-2-ylmethyl)amino)benzaldehyde to the isophorone
moiety, which shows a strong migration of ICT characteristic of dye sensor 3.
Acknowledgment
This work was supported by the Basic Science Research Program through the
National Research Foundation (NRF) grant funded by the Korea government
(MEST) (No. 2010-0001885). This research was supported by a grant from the Fun-
damental R&D Program for Core Technology of Materials funded by the Ministry
of Knowledge Economy, Republic of Korea (2010).
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