Spectroscopic characterization of heptamethine cyanine dyes for the interaction with the CN- and F-

Article abstract of DOI:10.1080/15421406.2012.701121

The selectivity and sensitivity of a benzoindolium heptamethine cyanine dyes toward CN^- and F^- in DMSO are described. These anions interact with Dye-1 and Dye-2 forming anion-Dye adducts, the formation of which was supported by the Pariser-Parr-Pople molecular orbital (PPP MO) calculation. The different optical responses in Dye-1 stimulated by addition of CN ^- (blue to pale yellow) and F^- (blue to pink) allow simultaneous estimation of CN^- and F^-.

Full text of DOI:10.1080/15421406.2012.701121

Mol. Cryst. Liq. Cryst., Vol. 566: pp. 61–66, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.701121
Spectroscopic Characterization of Heptamethine
Cyanine Dyes for the Interaction with the CN- and F-
YU WANG,1 SEON-YEONG GWON,1 YOUNG-A SON,2,∗
AND SUNG-HOON KIM1,∗
1Department of Advanced Organic Materials Science and Engineering,
Kyungpook National University, Daegu 702-701, S. Korea
2Department of Advanced Organic Materials and Textile System Engineering,
Chungnam National University, Daejeon 305-764, S. Korea
The selectivity and sensitivity of a benzoindolium heptamethine cyanine dyes toward
CN- and F- in DMSO are described. These anions interact with Dye-1 and Dye-2
forming anion-Dye adducts, the formation of which was supported by the Pariser-
Parr-Pople molecular orbital (PPP MO) calculation. The different optical responses in
Dye-1 stimulated by addition of CN- (blue to pale yellow) and F- (blue to pink) allow
simultaneous estimation of CN- and F-.
Keywords Heptamethine cyanine dye; Anion recognition; Orbital calculation; Optical
responses; Chemosensing; F- and CN-.
1. Introduction
Cyanine dyes absorb in a wide range of wavelengths. The color-structure relationships
of cyanines and related dyes have been quantitatively evaluated by the Pariser-Parr-Pople
molecular orbital method by Fabian and Hartmann [1]. The structural changes affecting the
color of cyanine dyes have also been summarized by Griffiths [2]. Especially, indolenine
cyanine dyes are expected from their superior solubility and their strong absorption in
near infrared (NIR) region. The use of an ion binding dye with chromophore activity in
the near NIR region has the advantage of greatly reduced background interference since
most biomolecules do not have absorbance in this wavelength region [3–4]. A number of
colorimetric and fluorescence-based chemosensors have been reported recently including
heptamethine cyanine dyes [5]. Anions are key to many processes, both industrial and
biological, playing crucial roles in both health and the environment. In particular, cyanide
is a detrimental anion causing poisoning in biology and the environment [6]. As fluoride is
the smallest anion and has unique biological and chemical properties, its recognition and
detection are of great interest because of its well-known usage in dental care [7, 8] and
∗Address correspondence to Prof. Young-A Son, Department of Advanced Organic Materi-
als and Textile System Engineering, Chungnam National University, Daejeon 305-764, S. Korea.
Tel: +82-42-821-6620; Fax : +82-42-823-3736. E-mail: yason@cnu.ac.kr
∗Address correspondence to Prof. Sung-Hoon Kim, Department of Advanced Organic Materials
Science and Engineering, Kyungpook National University, Daegu 702-701, S. Korea. Tel: +82-53-
950-5641; Fax : +83-53-950-6617. E-mail: shokim@knu.ac.kr
61

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Y. Wang et al.
osteoporosis [9] as well as its potentially damaging nephrotoxic effect in humans that can
result from overly high concentrations of fluoride [10]. The development of colorimetric
signaling chemosensors for the selective recognition of anions has received considerable
attention in recent decades owing to their key role in host-guest chemistry, especially from
both biological and environmental perspectives [11]. The molecular design of chemosens-
ing receptor system is an additional interesting area in anion recognition chemistry. The
chemosensing effect involves binding a specific target anion (A-) to receptor molecules
(R) as a result of which, the chemosensor chromophore displays changes of optical signal
(eg absorbance) owing to the formation of a receptor: sensing anion complex. Currently,
colorimetric chemosensors are popular due to their capability to detect analytes by naked
eye without resorting to any expensive instruments. Therefore, to develop simple-to-use
and naked eye diagnostic tool for selective detection of anion is a hot and interesting topic.
Our work aims to construct a heptamethine cyanine dye-based near infrared probes with
colorimetric assay to specifically detect the presence of CN− and F−.
2. Experimental
All chemicals, including the tetrabutylammonium salts of various anions, namely CN−,
F−, H2PO4−, NO3−, HSO4−, ClO4−, Br−, Cl− and solvents were of the highest purity
grade available and were used without further purification. Measurements of UV-Visible
absorption were performed by the addition of anions to dye solutions. And then the samples
were well mixed to test for 10 min using Vortex mixer. UV-Visible absorption spectra were
measured on an Agilent 8453 spectrophotometer. Dye-1 and Dye-2 were synthesized ac-
cording to the literature method [12]. The absorption maxima wavelengths of π-conjugated
molecules were calculated by the Pariser-Parr-Pople molecular orbital (PPP-MO) method.
Two center electron repulsion integrals were determined by the Nishimoto-Mataga relation-
ship, and electronic excitation energies were refined by a limited configuration interaction
(CI) treatment involving the first nine singly excited singlet configurations obtained by
promoting an electron from the three highest occupied orbitals to the three lowest unoccu-
pied orbitals. The calculated configuration interaction vectors indicate that in most cases
the contribution of the HOMO-LUMO electron transition to the visible absorption band is
about 95%.
3. Results and Discussion
The synthetic route of indolenine heptamethine cyanine dyes shown in Scheme 1.
Scheme 1. Synthesis of Dye-1 and Dye-2.

Heptamethine Cyanine Dyes
63
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0 equi.
-
[CN ]
5 equi.
300
400
500
600
700
800
900
Wavelength (nm)
Figure 1. Effect of cyanide ion concentration on the absorbance of 1.0 × 10–5 M solution of Dye-1
in DMSO.
The indolenine heptamethine cyanine dyes can be synthesized by the reaction of 2,3,3-
trimethyl indolenine salt 2 with glutaconaldehyde 1. These dyes also can be synthesized by
a stepwise procedure as shown in Scheme 1. This present work is aimed at the interaction of
Dye-1 and Dye-2 with the anions. In our present experiments, tetrabutylammonium salts of
various anions, namely CN−, F−, H2PO4−, NO3−, HSO4−, ClO4−, Br−, Cl− were gradually
added to the solution of cyanine dyes in DMSO as anion source, and the interaction abilities
of cyanine dyes with anions were invested by UV-Vis spectroscopy.
Figure 1 showed the absorption spectral changes of Dye-1 as a function of the CN−
concentration in DMSO at room temperature; as the CN− concentration increased, the
absorbance of Dye-1 at 756 nm progressively decreased in intensity and peak at 408 nm
increased. An isobestic point at 560 nm also developed and the solution changing from blue
to pale yellow. From the titration to a solution of Dye-1, we notice the stoichiometry of the
Dye-1: CN− is 1:5, in Fig. 1. The effect of F− concentration on the absorbance of Dye-1
is shown in Fig. 2. Likewise the addition of F− to the solution of Dye-1, the absorption
band at 756 nm abruptly decreased in intensity, while new bands with a peak at around 400
and 542 nm appeared. The color changed from blue to pink. However, addition of other
anions such as, H2PO4−, NO3−, HSO4−, ClO4−, Br−, Cl− under similar condition does not
0.6
0 equi.
0.5
[F-]
0.4
80 equi.
0.3
0.2
0.1
0.0
300
400
500
600
700
800
900
Wavelength (nm)
Figure 2. Effect of fluoride ion concentration on the absorbance of 1.0 × 10–5 M solution of Dye-1
in DMSO.

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Y. Wang et al.
have any significant effect on the absorption spectrum of Dye-1. The superior selectivity of
Dye-1 for CN− and F− in DMSO solution is evident from the absorbance response of the
anions.
Strekowski and co-workers studied the addition reaction of hydroxide or ethoxide
ion with benzindolium heptamethine cyanine dyes [13]. They reported that the simple
reaction of heptamethine cyanine dye, 2-ꢀ7ꢀ-(3ꢀꢀ-butyl)-1,1-dimethyl-2ꢀꢀ,3ꢀꢀ-dihydro-1ꢀꢀH-
benz[e]indol-2ꢀꢀ-ylidene)-4ꢀ-chloro-3ꢀ,5ꢀ-(propane-1ꢀꢀꢀ,3ꢀꢀꢀ-diyl)-1ꢀ,3ꢀ,5ꢀ-heptatrien-1ꢀ-yl]-
3-butyl-1,1-dimethyl-1H-benz[e]indolium iodide, in aqueous MeOH in the presence of
KOH, which gave the hydroxyl adduct. The presence of the hydroxyl group in the adduct
at the heterocyclic nuclei was established. For this reason, our results can be explained
in terms of the addition reaction of nucleophiles such as CN− and F− with Dye-1. We
propose that these spectral changes are due to the interaction of the anions such as CN−
and F− with the Dye-1 and the subsequent perturbation of the π system (Scheme 2).
Scheme 2. A possible structure and calculation results of Dye-1 with CN− and F−.
Dye-1 absorbs at 756 nm and produces a new band at 408 nm by the introduction of a
two CN−. On the other hand, the introduction of a F− to indole moiety of Dye-1 produced
a new band at 542 and 400 nm which correspond to the mono- and di-introduced adducts.
We quantitatively evaluated the color-structure relationship before and after addition of
1.2
0 equi.
1.0
[CN-]
0.8
1 equi.
0.6
0.4
0.2
0.0
300
400
500
600
700
800
900
Wavelength (nm)
Figure 3. Effect of cyanide ion concentration on the absorbance of 1.0 × 10−5 M solution of Dye-2
in DMSO.

Heptamethine Cyanine Dyes
65
CN− and F− to Dye-1 by means of PPP MO method. The calculation result show that the
absorption maximum wavelength of the compounds depend markedly on the number of
anions such as CN− and F− (λmax: 405 nm in Dye-1(2CN) and Dye-1(2F), λmax: 510 nm
in Dye-1(F)). This result was in well agreement with theoretical calculation as shown in
Scheme 2. The different optical responses in Dye-1 stimulated by addition of CN− (blue to
pale yellow) and F− (blue to pink) allow simultaneous estimation of CN− and F−. As Fig.
3 shows, upon the addition of CN− to the DMSO solution of Dye-2, the absorption band at
751 nm decreased and a new peak at 413 nm appeared; an isobestic point at 500 nm also
developed. The appearance of this isobestic point suggests that at least one stable Dye-2-
CN− species is present in solution and is indicative that a stable adduct formed between
Dye-2 and CN−. However, none of the other anions investigated, namely F−, H2PO4
,
−
NO3−, HSO4−, ClO4−, Br− and Cl− had any noticeable effect on absorption.
4. Conclusions
In conclusion, we synthesized and characterized new dyes which are Dye-1 and Dye-2 based
on heptamethine cyanine dyes. Dye-1 showed highly selective functions toward CN− and
F− recognition in DMSO with compared to other examined anions. An obvious sensing
effect for CN− was also observed with Dye-2. Moreover, these dyes exhibited significant
sensing responses accompanying color changes; CN− (blue to pale yellow) and F− (blue to
pink).
Acknowledgments
This work was supported by the Basic Science Research Program through the Na-
tional Research Foundation (NRF) grant funded by the Korea government (MEST) (No.
2011–0001084). This research was supported by a grant from the Fundamental R&D Pro-
gram for Core Technology of Materials funded by the Ministry of Knowledge Economy,
Republic of Korea.
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