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.