Helicenoid-based bis-1,2,3-triazole tweezer: Synthesis and selective iodide sensing

Article abstract of DOI:10.1080/00397911.2019.1710212

Novel helicenoid based 1,2,3-triazole tweezer 4 was synthesized using a multistep synthetic protocol with high yields from 2,7-Dihydroxynaphtlene 3 as a precursor. This helicenoid-based bis-1,2,3-triazole tweezer 4 selectively causes non-covalent interact

Full text of DOI:10.1080/00397911.2019.1710212

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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Helicenoid-based bis-1,2,3-triazole tweezer:
Synthesis and selective iodide sensing
Siddharth B. Kamble, Prashant M. Gawade, Purav M. Badani & Anil V. Karnik
To cite this article: Siddharth B. Kamble, Prashant M. Gawade, Purav M. Badani & Anil V. Karnik
(2020): Helicenoid-based bis-1,2,3-triazole tweezer: Synthesis and selective iodide sensing,
Synthetic Communications, DOI: 10.1080/00397911.2019.1710212
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https://doi.org/10.1080/00397911.2019.1710212
Helicenoid-based bis-1,2,3-triazole tweezer: Synthesis and
selective iodide sensing
Siddharth B. Kamble , Prashant M. Gawade, Purav M. Badani , and
Anil V. Karnik
Department of Chemistry, University of Mumbai, Mumbai, India
ABSTRACT
ARTICLE HISTORY
Novel helicenoid based 1,2,3-triazole tweezer 4 was synthesized
using a multistep synthetic protocol with high yields from 2,7-
Dihydroxynaphtlene 3 as a precursor. This helicenoid-based bis-1,2,3-
triazole tweezer 4 selectively causes non-covalent interaction with
iodide anion. The UV-vis absorption exhibited enhancement while
Received 26 September 2019
KEYWORDS
Fluorescence; helicenoid;
iodide sensor; 1,2,3-
triazoles; tweezer
1
fluorescence spectra exhibited significant quenching. H NMR titra-
tion showed shift of 1,2,3-triazole C–H signal with an increase in iod-
4
ꢁ1
ide concentration. Association constant of 3.818ꢀ 10
M
was
recorded for the host interaction with iodide ions. This value of asso-
ciation constant for iodide sensing using 1,2,3-triazole is the best
reported so far for hosts with 1,2,3-triazole moiety and suggests that
the helicenoid geometry is responsible for this remarkable behavior.
GRAPHICAL ABSTRACT
Introduction
[
1]
BINOL 1 is one of the most successful atropisomeric systems in chiral chemistry.
BINOL can be converted to the corresponding helicenoid 2 by co-joining the free
[
2]
hydroxyl groups by di-O-alkylation reaction. This simple transformation changes the
molecule with a presence of the chiral axis to a molecule with helical chirality
(
Figure 1). Helicenes and helicenoids are a group of crowded molecules endowed with
[
3]
helical geometry and a groove. Their characteristic geometry has attracted many
CONTACT Anil V. Karnik
avkarnik@chem.mu.ac.in
Department of Chemistry, University of Mumbai, Vidyanagari,
Kalina, Mumbai 400098, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher’s website
ß 2020 Taylor & Francis Group, LLC

2
S. B. KAMBLE ET AL.
Figure 1. Examples of BINOL 1 and helicenoid 2.
research groups to explore applications of these molecules in the field of asymmetric
[
4]
transformations and as a supramolecular host for selective detection of cations,
[
5,6]
[7–9]
anions
and chiral guest molecules.
The conversion of BINOL 1 to the corre-
sponding helicenoid 2 with helical molecular geometry brings the aromatic rings closer.
Tweezers are a group of hosts used in supramolecular chemistry and in organo-
catalysis. The flexible arms of the tweezer remove limitation associated with the com-
patibility of guest species size matching the cavity size, encountered in macrocyclic
[
9]
hosts. Helicenes and helicenoids have terminal aryl rings in the close proximity.
There appears a reason to believe that the geometrical feature of helical molecule-based
tweezers can cause the new system with helical platform become more efficient in cap-
turing the guest species. Additionally, supramolecular hosts have been mainly used for
[
4]
[5,6]
detecting cations, and in comparison, anion
Triazole derivatives have been found to be useful as halide sensors along with some
sensors are few in numbers. 1,2,3-
[
5,6]
other anions.
1,2,3-Triazole derivatives can be accessed through “click” chemis-
[
10]
try
protocol.
With this background, we envisaged the formation of bis-1,2,3-triazole derivatives
with helical geometry as shown in Scheme 1. The two naphthalene rings in BINOLs are
almost perpendicular to each other and hence it was gathered that the tweezer arms
would be projecting away from each other. Once the BINOL is transformed into helice-
noids, the flexible arms could be manipulated to be closer, enhancing the chances of
trapping of suitable guests with stronger binding. We found that the helicenoid-based
bis-1,2,3-triazole tweezer 4 as shown in Figure 2, was highly selective toward iodide and
4
ꢁ1
exhibited high binding constant 3.8 ꢀ 10 M . It is worthwhile to note that a
[
6]
binaphthyl-based bis-1,2,3-triazole derivative was reported to exhibit a binding con-
3
ꢁ1
stant of 2.5 ꢀ 10 M .
Iodine is an essential micronutrient that plays a key role in thyroid hormone synthe-
sis and brain development. Iodine deficiency disorder (IDD) is a major world health
problem that leads to increased perinatal mortality, birth defects, hypothyroidism and a
[
11]
host of other functional and developmental abnormalities.
Thus, reliable methods for
the estimation of iodide are vital from several health aspects and the development of an
efficient iodide sensor would certainly be a welcome prospect. In this work, we present
the synthesis of a new family of cyclic helicenoid based bis-1,2,3-triazole 4 and its sub-
ꢁ
sequent use as a fluorescent sensor for iodide ions. This receptor recognizes I with
1
excellent levels of selectivity. The spectral analysis, including UV, Fluorescence and H
ꢁ
NMR titrations, established the selective sensing of I ions by the host 4.

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Scheme 1. Synthesis of helicenoid based Bis-1,2,3-triazole tweezer 4.
Figure 2. Helicenoid based bis-1,2,3-triazole tweezer 4.
Results and discussion
Synthesis of helicenoid based bis-1,2,3-triazoles 4 (Scheme 1) was carried out using 2,7-
Dihydroxynaphthalene 3 as the precursor. The first step was alkylation of 2,7-dihydrox-
ynaphthalene 3 with propargyl bromide in basic condition. Both mono and di alkylated
products were formed, which, in turn, were separated by column chromatography.
Mono alkylated product 5, was subjected to an oxidative coupling reaction in the pres-
[
10]
ence of FeCl to give a new BINOL derivative 6. Further, the “Click” reaction
on
3
product 6 afforded compound 7 with two 1,2,3-triazole rings. Formation of helicenoid 4
could be achieved by the conjoining of the two hydroxyl groups of 7 reacting it with
Chloroiodomethane. (Scheme 1) Change of geometry while the formation of helicenoid
1
4
from BINOL derivative 7 caused a shift of C–H protons of triazoles in the H NMR
spectrum. In BINOL based bis-1,2,3-triazoles 7, the C–H proton of 1,2,3-triazoles

4
S. B. KAMBLE ET AL.
Figure 3. Fluorescence spectra of helicenoids 4 (10mM) upon addition of tetrabutylammonium salts
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
of Cl , Br , F , I , ClO , CN , HO , and Ac–O (4 equiv.) in CH CN, k ¼ 250 nm.
4
3
ex
appears as a singlet at d 8.51 ppm, but in case of helicenoid 4, the same C–H protons of
triazoles gives singlet at d 7.97 ppm suggesting further deshielding. The singlet of –OH
from BINOL 7 at d 9.24 ppm disappears in helicenoid 4, and the newly introduced
methylene group signal appears at 5.66 ppm.
After successful synthesis of helicenoid–based bis-1,2,3-triazole tweezer molecule 4, we
studied the interaction of the same with different anions such as tetra butyl ammonium
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
salts of I , Cl , Br , CN , F ClO , HO , Ac–O in CH CN and were delighted to see
4
3
the results. A significant decrease in fluorescence was observed on the interaction of 4 with
ꢁ
I ions as shown in (Figure 3) whereas the same interaction was found to cause enhance-
ꢁ
ꢁ
ꢁ
ment of UV-vis signals as shown in (Figure 4). The addition of 4 equiv. of Cl , Br , F ,
ꢁ
ꢁ
ꢁ
ClO , CN, HO and Ac–O had no obvious effect on the fluorescence emission (k
50 nm) and, however, when 4 equiv. of I ions was added to the solution of 4, fluores-
¼
4
ex
ꢁ
2
cence intensity was quenched approximately to 30% of the initial fluorescence intensity
Figure 3) and at the same time, UV-vis intensity was found enhanced to 50% (Figure 4).
(
UV and fluorescence studies indicated non-covalent interaction between iodide ions
and the helicenoid 4. It was of interest to know the exact point of interactions between
the iodide ions and the structural unit of helicenoid 4. NMR is a powerful technique to
study the polar interactions between two species. Thus, it was of interest to study the
changes that occur in the chemical shifts of signals of different sets of protons of helice-
1
noid 4, upon the gradual addition of the iodide ions. Figure 5 represents the H NMR
titration studies between the helicenoid 4 and different molar equivalents of tetrabuty-
1
lammonium iodide. The H NMR (300 MHz, CD CN) spectrum of compound 4 mainly
3
displays 7 sets of signals by naphthalene and benzene which appeared at d ¼ 6.94, 7.02,

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ꢁ
Figure 4. UV-vis spectra of helicenoids 4 (10 mM) upon addition of tetrabutylammonium salts of Cl ,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Br , F , I , ClO , CN , HO , and Ac–O (4 equiv.) in CH CN.
4
3
1
Figure 5. H NMR, 300 MHz, (CD CN); titration studies: spectra for parent helicenoid 4 and mixtures
3
of helicenoid 4 with addition of 2, 4, 6, 8, 10, 12 equiv. of tetrabutylammonium iodide, respectively.

6
S. B. KAMBLE ET AL.
ꢁ
ꢁ
Figure 6. Fluorescence of helicenoids 4 (10mM) addition of tetrabutylammonium salts of Cl , Br ,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
F , I , ClO , CN , HO and Ac–O (4 equiv.) in CH CN, k ¼ 250 nm (0, 0.5, 1.5, 2.5, 3.5, 4.5, 6, 8,
4
3
ex
10, 12, 15, 19 equiv.) kex ¼ 250 nm.
7
.12, 7.36, 7.58, 7.90 and 7.97 ppm. The –CH proton of 1,2,3-triazole ring appears as a
singlet at d 7.97 ppm which is merged with a doublet signal of aryl protons of naphtha-
lene ring at d 7.97 ppm. After the addition of tetrabutylammonium iodide, the signals at
–CH proton of 1,2,3-triazole appears as a singlet, separated from aryl protons of naph-
thalene ring. The signal of –CH proton of 1,2,3-triazole was found to undergo gradual
ꢁ
downfield shift with an increase in I ions concentration of 2, 4, 6, 8, 10, 12 equiv. and
1
appears at d ¼ 8.01, 8.04, 8.07, 8.11, 8.16, 8.19 ppm, respectively. H NMR titration stud-
ꢁ
ies confirm the non-covalent, polar interaction of –CH proton of 1,2,3-triazole and I
ions resulting in the downfield signals for the C–H proton of the 1,2,3-triazolyl part.
The shift of 1,2,3-triazole C–H signal was found to be ᭝d
þ0.03, þ0.06, þ0.09,
¼
ꢁ
þ0.13, þ0.18, and þ0.21 ppm for 2, 4, 6, 8, 10, and 12 equiv. of I ions. The other sig-
ꢁ
nals do not appear to get affected due to the addition of I ions.
ꢁ
When fluorescence titration of different concentrations of I ions into the CH CN
3
solution of Helicenoid 4 was performed, it exhibited a gradual decrease in the fluores-
ꢁ
cence intensity of 4 with the increase of I ions concentration (Figure 6). The fluores-
ꢁ
cence intensity was quenched completely after the addition of 22 equiv. of I ions.
Quenching of fluorescence intensity was observed at 376–389 nm. The efficiency of
quenching was further studied by plotting F /F vs. [Q] and the fluorescence quenching
o
[
12]
Ksv was further calculated from the Stern–Volmer equation as follows:
F =F ¼ 1 þ K ½Qꢂ,
o
sv

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Figure 7. UV-vis spectra of helicenoids 4 (10mM) in CH CN upon addition of increasing concentra-
3
ꢁ
tions I .
ꢁ
Where F and F represent fluorescence intensity in the absence and presence of I
0
ꢁ
ions, respectively, [Q] is the molar concentration of quencher I ions. Stern–Volmer
4
ꢁ1
plot K was found to be 3.818 ꢀ 10 M . This high binding constant confirmed strong
sv
ꢁ
ꢁ
affinity between I ions and the proton of 1,2,3-triazole ring. The effect of increasing I
ions concentration on UV-vis signal intensity was studied by the titration of helicenoid
ꢁ
4
with iodide. Upon addition of I ions the band at 239 nm showed a slight redshift of
8
ꢁ 10 nm, which may be ascribed to the interaction of the Iodide ions with the 1,2,3-
triazole ring. The titration graph of UV spectra is provided, which shows concentration-
dependent enhancement of UV signal at around 248–250 nm for compound 4 with the
ꢁ
increase of I ions (Figure 7). The saturation of UV intensity enhancement was seen
after the addition of 22 equiv. iodide.
Conclusions
Helicenoid based Bis-1,2,3-triazole tweezer 4 was synthesized to study its anions binding
ability and showed remarkable selectivity toward iodide ions in comparison to many
ꢁ
other anions studied. The selective sensing and effect of I ions concentration on sig-
1
nals observed in fluorescence, UV and H NMR were studied by carrying out suitable
4
ꢁ1
experiments, including titrations. Binding constant of 3.818 ꢀ 10 M was determined
using fluorescence titration experiment. The helicenoid-based bis-1,2,3-triazole host
functions as a highly selective and exhibiting high binding constant for iodide ions. No
other host with 1,2,3-triazole moiety is reported to exhibit such high binding constant
for iodide sensing. It is proposed that the helicenoid geometry is responsible for this
remarkable behavior.

8
S. B. KAMBLE ET AL.
Experimental part
All reagents were obtained from commercial suppliers and were used without further
purification Analytical thin-layer chromatography was performed using Silica Gel 60
1
13
F254 plates (Merck). The H and C NMR spectra were recorded with Bruker AM 300
300 MHz) spectrometers. Chemical shifts are expressed in parts per million with
(
residual CDCl as reference. Low- and high-resolution mass spectra were recorded
3
under fast atom bombardment (FAB) conditions
Preparation of 7-(prop-2-yn-1-yloxy) naphthalen-2-ol (5): To a solution of 2,7-dihy-
droxynaphthalene 3 (10 g, 62.4 mmoles) in DMF (100 mL) was added K CO (12.9 g,
2
3
ꢃ
9
3.6 mmoles) and Propargyl Bromide (5.7 mL, 74.9 mmoles) at 0–5 C. The reaction
mixture was then stirred at room temperature for 24 h. After completion of the reaction
mixture, The mixture was poured in cold water and further, it was extracted with ethyl
acetate and dried over sodium sulfate and concentrated. The resulting residue was puri-
fied by silica column chromatography. (Pet - ethyl acetate, 90:10!80:20) to give 5 as a
white solid.
ꢃ
1
Yield: 60%; mp: 90–92 C; H NMR (300 MHz, CDCl ) d (ppm): 2.54–2.57 (t, 1H),
3
4
2
1
.77–4.78 (d, 1H), 5.15 (s, 1H), 6.94–6.97 (dd, 1H), 7.00–7.01 (d, 1H), 7.04–7.06 (dd,
1
3
H), 7.66–7.68 (dd, 2H); C NMR (75 MHz, CDCl ): 55.81, 75.67, 78.50, 106.32,
3
15.66, 116.30, 124.75, 129.46, 129.62, 135.68, 154.02, 156.17.
Supporting information
Procedure for synthesis of compounds 6, 7, 8, and 4 is provided in the supporting
1
13
information. Full experimental detail, IR, H NMR, and C NMR, and HRMS spectra
can be found via the “Supplementary Content” section of this article’s webpage
Acknowledgments
SBK acknowledges to CSIR-UGC for JRF and SRF funding and Center for Nano Science and
Nano Technology, University of Mumbai for UV-vis and Fluorescence study.
ORCID
Siddharth B. Kamble
Purav M. Badani
http://orcid.org/0000-0002-2158-774X
http://orcid.org/0000-0002-5270-5227
Anil V. Karnik
http://orcid.org/0000-0001-9701-6516
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