Synthesis of 3,5-diaryl substituted indole derivatives and its selective iodide ion chemosensing

Article abstract of DOI:10.1016/j.saa.2011.10.067

In this contribution, we have synthesized series of 1-ethyl-3,5-bis[2- (aryl)ethenyl]-1H-indole based derivatives with different functional groups using Wadsworth-Emmons coupling. The sensing ability of the receptors has been studied for halides like tetrabutylammonium fluoride, chloride, bromide, iodide and bisulphate by UV-vis spectroscopy methods. In THF solution, compound A-E exhibits excellent selectivity with iodide ions over the other ions like tetrabutylammonium bromide (TBABr), tetrabutylammonium chloride (TBACl), tetrabutylammonium fluoride (TBAF) and tetrabutylammonium bisulphate (TBAHSO₄). The indole cores were observed effectively and selectively recognized biologically important iodide was reported. Significant absorption change was observed only for tetrabutylammonium iodide and no change with other anions. The absorption spectra indicated the formation of complex between host and guest is in 1:1 stoichiometric ratio. The association constants of A-E for iodide ions were found to be 3.2 × 10⁴ M^-1, 3.9 × 10⁴ M^-1, 4.2 × 10³ M ^-1, 2.9 × 10³ M^-1 and 2.14 × 10³ M^-1, respectively.

Full text of DOI:10.1016/j.saa.2011.10.067

Spectrochimica Acta Part A 86 (2012) 640–644
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Short communication
Synthesis of 3,5-diaryl substituted indole derivatives and its selective iodide ion
chemosensing
Krishnaswamy R. Rathikrishnana, Vellore K. Indirapriyadharshinia,∗, Seeram Ramakrishnab,c,d
,
Rajendiran Muruganb,∗∗
a Department of Chemistry, SRM University, Chennai 600026, Tamil Nadu, India
b HEM Laboratory, NUSNNI, National University of Singapore, 2 Engineering Drive 3, 117576, Singapore
c Institute of Material Research and Engineering, Singapore 117602, Singapore
d King Saud University, Riyadh 11451, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 July 2011
Received in revised form 17 October 2011
Accepted 30 October 2011
In this contribution, we have synthesized series of 1-ethyl-3,5-bis[2-(aryl)ethenyl]-1H-indole based
derivatives with different functional groups using Wadsworth–Emmons coupling. The sensing ability of
the receptors has been studied for halides like tetrabutylammonium fluoride, chloride, bromide, iodide
and bisulphate by UV–vis spectroscopy methods. In THF solution, compound A–E exhibits excellent
selectivity with iodide ions over the other ions like tetrabutylammonium bromide (TBABr), tetrabutylam-
monium chloride (TBACl), tetrabutylammonium fluoride (TBAF) and tetrabutylammonium bisulphate
(TBAHSO4). The indole cores were observed effectively and selectively recognized biologically important
iodide was reported. Significant absorption change was observed only for tetrabutylammonium iodide
and no change with other anions. The absorption spectra indicated the formation of complex between
host and guest is in 1:1 stoichiometric ratio. The association constants of A–E for iodide ions were found
to be 3.2 × 104 M−1, 3.9 × 104 M−1, 4.2 × 103 M−1, 2.9 × 103 M−1 and 2.14 × 103 M−1, respectively.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Indole derivatives
Iodide sensors
Chemosensors
1. Introduction
the elemental iodine has been frequently used in many areas of
chemistry for synthesizing valuable molecules/intermediates such
Molecular recognition of anionic species plays an essential role
in a large number of chemical, biological and environmental pro-
cesses [1–3]. The search of a chemosensor for recognition and
sensing of specific anionic analytes through naked eye, electro-
chemical and optical responses are emerging research areas of
considerable importance [4]. The practical recognition of anions
has continued to be a more challenging issue than the recogni-
tion of cations, which has been fully developed for nearly forty
years [5]. The variety of geometry shapes of anions and synthetic
difficulty in building selective anionic receptive sites make the
design and synthesis of anion sensor intellectually more demand-
ing and practically less predictable [6]. Among various important
anionic analytes, the iodide ion is one of the most significant,
since play an essential role in biological activities, such as thyroid
function and neurological activity. In many systems the iodide con-
tent of milk and urine is often required for metabolic, nutritional,
and epidemiological studies of thyroid disorder [7]. In addition
as drugs, dyes and molecular electronics. There are few reports
on the fluorescent recognition of iodide using small molecules
and conjugated polymers [8]. In most cases, hydrogen bonding
between the N–H of the molecule and anions was used for the
recognition, without the involvement of hydrogen bonds, quater-
nized ammonium hosts [9], azamacrocycles[10], and phosphonium
hosts [11] are known to form anion complexes. A cyclic peptide
has been reported for the anion sensing includes iodides, bro-
mides, chlorides and fluorides, but there is no selectivity [12].
Bis-imidazolinium [13], adenine [14], trifluoroacetyl aminoph-
thalimide based derivatives [15], benzimidazole based tripodal
receptor [16], pyrenyl-appended triazole-based calix[4]arene [17],
silver nanoparticles [18], N-fused tetraphenylporphyrin [19], 4,7-
diaryl indole-based derivatives [20] and macrocyclic binuclear
copper (II) complex [21] are reported for the selective iodide
sensors. The present receptors are designed based on quater-
nized ammonium hosts bonds in the receptor aligned in parallel;
it may effectively make a complex with iodide ions. Herein we
report the synthesis of new indole based sensors containing
conjugated moieties and their selective sensing of iodide ions.
The electronic nature of its substituent was used to tune the
selectivity and the photophysical properties of the chemosen-
sors.
∗
Corresponding author.
Corresponding author. Tel.: +65 65196593; fax: +65 84317476.
E-mail addresses: doctorindira@gmail.com (V.K. Indirapriyadharshini),
∗∗
mperajen@nus.edu.sg (R. Murugan).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.10.067

K.R. Rathikrishnan et al. / Spectrochimica Acta Part A 86 (2012) 640–644
641
2. Experimental
2.2.3. 1-Ethyl-3,5-bis[(E)-2-(quinolin-8-yl)]-1H-indole (C)
Yellow solid; 100 mg, 44%; 1H NMR (400 MHz, DMSO–d6): ı 1.44
(t, J = 7.12 Hz, 3H), 4.28 (q, J = 7.12 Hz, 2H), 7.57–7.68 (m, 7H), 7.47 (s,
1H), 7.84–7.91 (m, 3H), 8.22–8.24 (m, 2H), 8.36–8.51 (m, 3H), 9.01
(s, 2H); 13C NMR (100 MHz, DMSO–d6): ı 149.74, 149.58, 145.07,
144.86, 136.53, 136.30, 135.52, 131.64, 129.74, 128.68, 128.36,
128.33, 127.03, 126.68, 126.53, 126.20, 124.69, 123.75, 123.13,
121.64, 121.54, 121.30, 120.85, 119.45, 118.80, 114.36, 110.80,
15.48; m/z 452.34 (M+). Anal. Calcd. for C32H25N3: C, 85.11; H, 5.58;
N, 9.31%. Found: C, 85.08; H, 5.67; N, 9.38%.
2.1. Materials and methods
All reagents were purchased from Aldrich, Fluka and/or Merck
and were used without further purification unless otherwise stated.
All reactions were carried out with dry, freshly distilled sol-
vents under anhydrous conditions or in an inert atmosphere.
THF was purified by distillation from sodium in the presence
of benzophenone under nitrogen atmosphere. The NMR spec-
tra were collected on a Bruker ACF 400 spectrometer with
DMSO–d6 as solvent. Elemental analyses were done in VarioMi-
cro analyzer. UV–vis spectra were recorded on a PG Instrument
Ltd. spectrophotometer. Compounds N-ethyl indole [22] and N-
ethyl indole-5-carboxyaldehyde [23] were prepared according
to the published procedures. Phosphonates A1–D1 diethyl ben-
zylphosphonate [24], diethyl (quinolin-8-ylmethyl) phosphonate
[25], diethyl (3-methoxybenzyl) phosphonate [26], diethyl (3-
fluorobenzyl) phosphonate [27] required for stilbene synthesis
were prepared by Arbusov reaction between the appropriate aro-
matic methyl bromide and trietylphosphite. Tetrahydrofuran of
HPLC grade was purchased from Aldrich and used throughout the
experiments as solvent for chemosensor studies. All the titration
measurements were carried at room temperature. The THF solu-
tions of anions were prepared from their tetrbutylammonium salts
of analytical grade and used for titration. The anion binding behav-
iors of 3,5-diaryl substituted indole derivatives were determined
by UV–vis spectroscopic studies.
2.2.4. 1-Ethyl-3,5-bis[(E)-2-(3-methoxyphenyl)ethenyl]-1H
-indole (D)
Off brown solid; 40 mg, 49%; 1H NMR (400 MHz, DMSO-d6):
ı 1.39 (t, J = 7.20 Hz, 3H), 3.80 (s, 6H), 4.21 (q, J = 7.24 Hz, 2H),
6.76–6.82 (m, 2H), 7.08 (s, 1H), 7.13 (s, 4H), 7.24–7.30 (m, 2H),
7.42–7.54 (m, 2H), 7.70 (s, 1H), 8.19 (s, 1H); 13C NMR (100 MHz,
DMSO–d6); ı 159.64, 159.62, 139.95, 139.20, 136.14, 130.23,
129.63, 129.54, 129.14, 128.62, 126.11, 125.53, 123.61, 122.04,
120.23, 119.25, 118.71, 113.46, 112.84, 111.08, 110.69, 110.54,
55.04, 15.36; m/z 410.23 (M+). Anal. Calcd. for C28H27NO2: C, 82.12;
H, 6.65; N, 3.42%. Found: C, 82.14; H, 6.71; N, 3.38%.
2.2.5. 1-Ethyl-3,5-bis[(E)-2-(3-fluorophenyl)ethenyl]-1H-indole
(E)
Brown oil; 38 mg, 62%; 1H NMR (400 MHz, DMSO–d6): ı 1.38 (t,
J = 7.16 Hz, 3H), 4.22 (q, J = 7.16 Hz, 2H), 6.99–7.06 (m, 2H), 7.10 (d,
J = 15.92 Hz, 1H), 7.27 (d, J = 16.40 Hz, 1H), 7.35–7.55 (m, 10H), 8.24
(s, 1H); 13C NMR (100 MHz, DMSO–d6): ı 163.97, 163.89, 161.56,
141.31, 141.23, 140.52, 140.44, 136.33, 131.51, 130.56, 130.47,
130.43, 130.34, 129.21, 128.94, 126.08, 124.41, 123.37, 122.42,
121.80, 120.58, 119.39, 113.64, 113.43, 113.25, 112.91, 112.69,
112.13, 111.92, 111.39, 110.62, 15.34; m/z 386.45 (M+). Anal. Calcd.
for C26H21F2N: C, 81.02; H, 5.49; N, 3.63%. Found: C, 81.06; H, 5.41;
N, 3.65%.
2.2. General experimental procedure for the synthesis of the A–E
To diethyl phenyl methyl phosphonate A1 (0.471 g, 2.06 mmol)
in dry THF (10 mL) was added NaH (0.043 g, 1.72 mmol). After ini-
tial effervescence the suspension was stirred for 1 h at 85 ◦C under
nitrogen. To this 1-ethyl indole-3,5-carboxyaldehyde 6 (0.100 g,
0.689 mmol) in dry THF (10 mL) was added drop wise and the
mixture heated to reflex at 85 ◦C for 12 h. Then cooled to room
temperature and poured in to water and extracted with ethylac-
etate (2× 20 mL). The organic layer was added brine solution (2×
10 mL) and layer was separated and dried with Na2SO4, filtered
and concentrated. The crude product was purified by column chro-
matography using hexane:ethylacetate (60:40) as eluent.
3. Results and discussion
The synthetic route to the 1-ethyl-3,5-bis[2-(aryl)ethenyl]-1H-
indole derivatives A–E is outlined in Scheme 1. Treatment of
indole 1 with ethyl bromide in dry THF in the presence of sodium
hydroxide afforded N-ethyl indole 2 which was Vilsmeier–Haack
formylation with phosphorous oxychloride in DMF to the N-ethyl
indole-5-carboxyaldehyde. The Wadsworth–Emmons condensa-
tion of N-ethyl indole-3-carboxyaldehyde was treated with
corresponding triethylphosphite salts A1–D1 in the presence of
2.5 equiv of sodium hydride in THF, the reaction mixture was
refluxed for 12 h which gave compound A. A similar sequence fol-
lowed by preparation of compounds B–E. All the reactions are
very straight forward. The alkyl chain in A–E led to a reasonable
level of solubility in a variety of organic solvents such as CH2Cl2,
CHCl3, MeOH and THF. All the phosphonates A1–D1 required for
stilbene synthesis were prepared by Arbusov reaction between
the appropriate aromatic methyl bromide and trietylphosphite
(Scheme 1). They were well characterized by MS, elemental and 1H,
13C, NMR spectroscopic methods before using them in application.
NMR spectroscopy is one of the principal techniques which give
us the structural information about receptor molecules. NMR spec-
tra were obtained using DMSO–d6 as solvent. Compound E gave
a multiple at around ı 6.99–7.06 ppm corresponding to the vinyl
proton indicating the formation of conjugated and ı 7.35–7.55 ppm
corresponding to the aromatic protons.
2.2.1. 1-Ethyl-3-[(E)-2-phenylethenyl]-1H-indole (A)
Brown solid; 80 mg, 47%; 1H NMR (400 MHz, DMSO–d6): ı
1.38 (t, J = 3.32 Hz, 3H), 4.23 (q, J = 7.20 Hz, 2H), 7.06–7.11 (m, 4H),
7.33–7.44 (m, 3H), 7.52 (d, J = 8.04 Hz, 1H), 7.58 (d, J = 7.84 Hz, 2H),
7.72 (s, 1H), 8.02 (d, J = 7.88 Hz, 1H); 13C NMR (100 MHz, DMSO–d6):
ı 138.92, 136.83, 129.05, 128.63, 126.70, 126.20, 125.90, 123.83,
122.40, 122.25, 120.51, 120.24, 113.45, 110.61, 15.77; m/z 248.32
(M+). Anal. Calcd. for C18H17N: C, 87.41; H, 6.93; N, 5.66%. Found:
C, 87.37; H, 6.90; N, 5.78%.
2.2.2. 1-Ethyl-3,5-bis[(E)-2-phenylethenyl]-1H-indole (B)
Brown solid; 25 mg, 44.4%; 1H NMR (400 MHz, DMSO–d6): ı
1.41 (t, J = 7.24 Hz, 3H), 4.22 (q, J = 7.20 Hz, 2H), 7.13–7.18 (m, 5H),
7.23–7.29 (m, 5H), 7.39 (q, J = 7.64 Hz, 2H), 7.47–7.64 (m, 4H), 7.73
(s, 1H), 8.22 (s, 1H); 13C NMR (100 MHz, DMSO–d6): ı 138.94,
138.21, 136.61, 130.44, 129.67, 129.14, 129.06, 128.97, 127.43,
126.79, 126.64, 126.55, 126.06, 126.01, 124.19, 122.18, 120.78,
119.54, 113.99, 110.97, 15.82; m/z 350.46 (M+). Anal. Calcd. for
C26H23N: C, 89.36; H, 6.63; N 4.01%. Found: C, 89.39; H, 6.70; N,
4.06%.

642
K.R. Rathikrishnan et al. / Spectrochimica Acta Part A 86 (2012) 640–644
Ph
O
O
P
CHO
O
, NaH
THF, reflux
EtBr
DMF/POCl3
0oC - rt
NaOH
THF, reflux
N
N
N
H
N
1
4
3
6
2
5
A
O
O
P
CHO
O
OHC
OHC
OHC
, NaH
THF, reflux
DMF/POCl3
0oC - rt
EtBr
NaOH
THF, reflux
N
N
H
N
N
B - E
OMe
F
B - E
N
P(OEt3)
180oC
O
P
OEt
=
Br
OEt
B
A1 - D1
7
D
E
C
Scheme 1. Synthesis of 1-ethyl-3,5-bis[2-(aryl)ethenyl]-1H-indole derivatives A–E.
3
2
1
0
a
b
D
B
2
1
0
A-E In Acetronitrile
A- E in THF
E
D
E
B
C
A
C
A
250
300
350
400
250
300
350
400
450
Wavelength(nm)
Wavelength (nm)
Fig. 1. Absorption spectra of A–E in acetronitrile and THF solution.
3.1. Photophysical study of 3,5-diaryl indoles A–E
fluorescence spectra of the A–E were recorded with the exci-
tation wavelength corresponding to their maximum absorption
wavelength. The titration experiments of A–E performed by a
UV–vis spectroscopic method using tetrabutylammonium halides
and bisulphate at room temperature. Fig. 1 shows the absorption
spectra of compounds A–E in different solvents. The calculated
HOMO–LUMO energy gaps are in good agreement with the exper-
imental values obtained from the UV–vis spectra (Table 1). All the
new compounds were characterized using various analytical tech-
niques.
The optical properties of A–E were investigated by UV–vis
spectroscopy on THF solutions (10−5 M) at room temperature.
Absorption spectra of these derivatives show two maxima (ꢀmax),
one in the range 300–330 nm and another above 300 nm. All the
receptor shows absorption band at (ꢀmax) 336, 339, 379, 306
and 310 nm in the absence of an anion. Since there is no signifi-
cant difference in the conjugation length, there are no significant
changes in the ꢀmax with changes in the functional group. The
Table 1
Photophysical properties of 1-ethyl-3,5-bis[2-(aryl)ethenyl]-1H-indoles A–E.
Compound
Absorption ꢀmax
Emission ꢀem
ꢀonset
Band gapa
εmax
(eV)
THF
MeoH
CH3CN
Toluene
A
B
C
D
E
336
339
379
306
310
331
300
376
303
307
332
301
368
308
302
337
306
312
278
281
415
410
413
408
423
356
381
417
346
350
3.48
3.25
2.97
3.58
3.54
5.3 × 105
1.1 × 105
1.8 × 105
1.3 × 105
1.2 × 105
a
Calculated from onset wavelength.

K.R. Rathikrishnan et al. / Spectrochimica Acta Part A 86 (2012) 640–644
643
2.5
2.0
1.5
1.0
0.5
0.0
a
b
E + TBAI
60
E + TBA salts
1.0
I-
0.5
Br-, Cl-, F-, HSO4-
0
0.0
300
350
400
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Fig. 2. (a) Absorption spectra of E in THF after addition of various tetrabutylammonium salts in 1 M solution. The concentration of E was 2.67 × 10−5 M. (b) Change in the
absorption spectra of E at different concentration of tetrabutylammonium iodide in THF solution: (i) 0 ␮M, (ii) 10 ␮M, (iii) 30 ␮M, and (iv) 60 ␮M.
1.0
0.5
0.0
1.0
0.5
0.0
a
b
E + TBAF
A + TBACl
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Fig. 3. (a) Change in the absorption spectra of A at different concentration of tetrabutylammonium chloride in THF solution: (i) 10 ␮M, (ii) 30 ␮M, and (iii) 60 ␮M. (b) Change
in the absorption spectra of E at different concentration of tetrabutylammonium fluoride in THF solution: (i) 10 ␮M, (ii) 30 ␮M, and (iii) 60 ␮M.
3.2. UV–vis titration study of A–E with anions
changes observed on the absorption spectra of E (60 ␮M in THF)
upon titrating with a solution of tetrabutylammonium solution like
iodide, bromide, chloride, fluoride and bisulphate. The change was
observed only with iodide not other anions like fluoride, bromide,
chloride and bisulphate (Fig. 2a).
The variation of indole through the introduction of UV–vis active
aryl groups at 3, 5 position is expected to improve the photophysical
properties for the chemosensing studies. Considering the biologi-
cal, environmental analytical relevance of anions, such as F−, Cl−,
Br− and I− the sensing properties of A–E were investigated using the
corresponding tetrabutylammonium salts in THF solution. Interest-
ingly, these A–E detect only iodide among other common anions
such as fluorides, chlorides, bromides and bisulphate. In the case of
addition of fluoride, chloride, bromide and bisulphate ions into the
A–E solution, no significant changes in absorption (see supporting
data) however the addition of the iodide ion results in a blue shift
in the absorption spectra (Fig. 2a and b). The absorption changes
of A with a solution of tetrabutylammonium chloride and E with
solution of tetrabutylammonium fluoride were shown in Fig. 3.
It is interesting to note that the absorption spectra of A–E can be
modulated by addition of iodide ion. The quenching effects of the all
0.9
0.6
0.3
0.0
3.3. Job’s plot
The association constants ka of A–E for iodide were calcu-
lated on the basis of Benesi–Hildebrand plot [28] and were found
to be 3.2 × 104 M−1, 3.9 × 104 M−1, 4.2 × 103 M−1, 2.9 × 103 M−1
and 2.14 × 103 M−1, respectively. The stoichiometry of the com-
plex formed was determined by Job’s plot [29] and turned out
to be 1:1 stoichiometry in Fig. 4. This indicated that sensors had
reached a saturation level as it binds to its anions guest. The nature
of other anions, such as tetrabutylammonium halides (F−, Cl−,
Br− and HSO4−) does not influence the absorption changes. The
0.0
0.2
0.4
0.6
0.8
1.0
molar fraction of E + iodide ion
Fig. 4. Job’s plots for complexation of E with iodide determined by UV–vis spec-
troscopy in THF.

644
K.R. Rathikrishnan et al. / Spectrochimica Acta Part A 86 (2012) 640–644
References
E
0.9
0.6
0.3
[1] (a) K. Ghosh, I. Saha, Supramol. Chem. 22 (2010) 311–317;
(b) J.L. Sessler, J.M. Davis, Acc. Chem. Res. 34 (2001) 989–997;
(c) A.P. de Silva, H.Q.N. Gunaratne, T.L. Gunalaugsson, A.J.M. Hauxley, C.P.
McCoy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515–1566;
(d) P. Rajakumar, M.G. Swaroop, Tetrahedron Lett. 45 (2004) 6165–6169.
[2] (a) R.H. Yang, W.H. Chan, A.W.M. Lee, P.F. Xia, H.K. Zhang, K.A. Li, J. Am. Chem.
Soc. 125 (2003) 2884–2885;
(b) K. Hanaoka, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, J. Am. Chem. Soc.
126 (2004) 12470–12476;
(c) Z. Xu, Y. Xiao, X. Qian, J. Cui, D. Cui, Org. Lett. 7 (2005) 889–892;
(d) P. Chen, B. Greenberg, S. Taghavi, C. Romano, D. Van der Lelie, C. He, Angew.
Chem., Int. Ed. 44 (2005) 2715–2719.
[3] (a) T. Wang, X.-P. Yan, Chem. A: Eur. J. 16 (2010) 4639–4649;
(b) Z.-Q. Hu, C.-L. Cui, H.-Y. Lu, L. Ding, X.-D. Yang, Sens. Actuators B: Chem.
B141 (2009) 200–204;
(c) F.S. Raad, A.O. El-Ballouli, R.M. Moustafa, M.H. Al-Sayah, B.R. Kaafarani,
Tetrahedron 66 (2010) 2944–2952;
(d) F. Wang, J. Wu, X. Zhuang, W. Zhang, W. Liu, P. Wang, S. Wu, Sens. Actuators
B: Chem. B146 (2010) 260–265;
0
3
6
9
(e) A.N. Swinburne, M.J. Paterson, A. Beeby, J.W. Steed, Org. Biomol. Chem. 8
(2010) 1010–1016;
Equivalent of Iodide
(f) J.M. Suk, M.K. Chae, N.K. Kim, U.I. Kim, K.S. Jeong, Pure Appl. Chem. 80 (2008)
599–608.
[4] P.A. Gale, Coord. Chem. Rev. 213 (2001) 79–128.
[5] (a) K. Hanaoka, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, J. Am. Chem. Soc. 126
(2004) 12470–12476;
Fig. 5. Relative UV–vis absorption responses of E in the presence of tetrabutylam-
monium iodide at various concentrations in THF.
Table 2
(b) Z. Xu, Y. Xiao, X. Qian, J. Cui, D. Cui, Org. Lett. 7 (2005) 889–892;
(c) R.H. Yang, W.H. Chan, A.W.M. Lee, P. Xia, H.K. Zhang, K.A. Li, J. Am. Chem.
Soc. 125 (2003) 2884–2885;
Absorption responses of A–E upon addition of iodides.
Compounds
ꢀmax (nm)
ꢁꢀmax
(d) P. Chen, B. Greenberg, S. Taghavi, C. Romano, D. Van der Lelie, C. He, Angew.
Chem., Int. Ed. 44 (2005) 2715–2719.
I− free a
Presence of I− b
[6] (a) F.P. Schmidtchen, M. Berger, Chem. Rev. 97 (1997) 1609–1646;
(b) P.D. Beer, P.A. Gale, Angew. Chem. Int. Ed. 40 (2001) 486–516.
[7] (a) G. Aumont, J. Tressol, Analyst 3 (1986) 841–857;
(b) F. Jalai, M.J. Rajabi, G. Bahrami, C. Shamsipur, Anal. Sci. 21 (2005) 1533–
1535;
(c) N. Singh, D.O. Jang, Org. Lett. 9 (2007) 1991–1994.
[8] (a) H.A. Ho, M. Leclerc, J. Am. Chem. Soc. 125 (2003) 4412–4413;
(b) M. Vetrichelvan, R. Nagarajan, S. Valiyaveettil, Macromolecules 39 (2006)
8303–8310;
A
B
C
D
E
336
339
379
306
310
295
295
289
293
291
−41
−44
−90
−13
−19
a
Absorption in THF.
Addition of iodides.
b
(c) A. Kumar, R.K. Chhatra, P.S. Pandey, Org. Lett. 12 (2010) 24–27.
[9] F.P. Schmidtchen, Angew. Chem. Int. Ed. 16 (1977) 720–721.
[10] E. Garcia−Espana, P. Diaz, J.M. Llinares, A. Bianchi, Coord. Chem. Rev. 250 (2006)
2952–2986.
[11] R. Pomecko, Z. Asfari, V. Hubscher-Bruder, M. Bochenska, F. Arnaud-Neu,
Supramol. Chem. 19 (2007) 459–466.
[12] Z. Rodriguez-Docampo, S.I. Pascu, S. Kubik, S. Otto, J. Am. Chem. Soc. 128 (2006)
11206–11210.
[13] H. Kim, J. Kang, Tetrahedron Lett. 46 (2005) 5443–5445.
[14] K. Ghosh, T. Sen, Tetrahedron Lett. 49 (2008) 7204–7208.
[15] H. Okamoto, H. Konishi, M. Kohno, K. Satake, Org. Lett. 10 (2008) 3125–3128.
[16] P.A. Gale, Chem. Commun. (2008) 4525–4540.
the derivatives absorption in the presence of tetrabutylammonium
iodide salts have been investigated in detail (see supporting data).
Comparative UV–vis absorption responses of E in the presence of
tetrabutylammonium iodide at various concentrations are shown
in Fig. 5. The addition of iodide salts to A–E produced a significant
shift in the absorption spectra and the results are summarized in
Table 2.
4. Conclusions
[17] J.S. Kim, S.Y. Park, S.H. Kim, P. Thuery, R. Souane, S.E. Matthews, S.J. Vicens, Bull.
Kor. Chem. Soc. 31 (2010) 624–629.
[18] A. Kumar, R.K. Chhatra, P.S. Pandey, Org. Lett. 12 (2010) 24–27.
[19] K. Ariga, T. Kunitake, H. Furuta, J. Chem. Soc., Perkin Trans.
667–672.
[20] K.R. Rathikrishnan, V.K. Indirapriyadharshini, S. Ramakrishna, R. Murugan,
Tetrahedron 67 (2011) 4025–4030.
[21] J.S. Mendy, M.A. Saeed, F.R. Fronczek, D.R. Powell, M.A. Hossain, Inorg. Chem.
49 (2010) 7223–7225.
[22] B.S. Lane, M.A. Brown, D. Sames, J. Am. Chem. Soc. 127 (2005) 8050–8057.
[23] P.K. Dubey, B. Babu, N.M. Venkata, Ind. J. Heterocy. Chem. 15 (2006)
205–208.
[24] A. Winter, C. Friebe, M.D. Hager, U.S. Schubert, Eur. J. Org. Chem. 6 (2009)
801–809.
In summary, we have synthesized and structurally character-
ized indole based chemosensors, as an ideal receptor for iodide.
The receptor binds iodide strongly, showing good selectivity for it
over other halides. The new receptors are capable of discriminat-
ing anions that can be monitored from their ꢀmax and absorption
intensity.
2 (1996)
Acknowledgements
[25] V. Jagodic, L.J. Tusek-Bozic, B. Bozic, M.J. Herak, J. Heterocy. Chem. 17 (1980)
685–688.
We would like to thank technical support from HEM Laboratory,
National University of Singapore. We thank the reviewers for their
constructive comments and suggestion.
[26] G.H. Chen, S. Wang, F.H. Wu, Chin. Chem. Lett. 21 (2010) 287–289.
[27] U. Weis, J.T. Andersson, Polycycl. Aromat. Compd. 22 (2002) 71–85.
[28] (a) H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703–2707;
(b) O. Stern, M. Volmer, Phys. Z 20 (1919) 183–188.
[29] (a) T.D. Thangadural, N.J. Singh, I.C. Hwang, J.W. Lee, R.P. Chandran, K.S. Kim, J.
Org. Chem. 72 (2007) 5461–5464;
Appendix A. Supplementary data
(b) M.M. Linn, D.C. Poncio, V.G. Machado, Tetrahedron Lett. 48 (2007)
4547–4551.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.10.067.