Abstract:
A benzimidazolium based thiourea conjugate (IL) receptor has been designed, synthesized and characterized
spectroscopically. The prepared receptor (IL) shows the sensitive and selective ratiometric sensing
for HSO4
over the other anions as evident by UV–visible absorption and fluorescence spectroscopy.
With the addition of HSO4
ion, the parent absorption band of IL in UV–visible absorption at 311 nm
was shifted to 261 nm having an isosbestic point at 294 nm, which clearly indicates an interaction
between HSO4
ion and the IL. Further, upon excitation at 310 nm, the fluorescence emission of IL at
455 nm was observed. Furthermore, the gradual addition of HSO4
ion results in a drastic decrease in
emission at 455 nm and simultaneous appearance of a new emission band at 379 nm with isosbestic
point at 430 nm was observed. The binding mechanism of HSO4
with IL was also explored with 1H
NMR titration, mass spectrometry and DFT calculations. These studies revealed the involvement of
hydrogen bonding with –NH (thiourea) and –CH (benzimidazolium) functionalities towards the recognition
of HSO4
ion. The association constant (Ka) and lowest detection limits for HSO4
were determined to
be 5.437 104 M 1 and 5.0 nM, respectively. The real sample analysis by synthesized sensor probe for
HSO4
was also performed which shows the practical applicability of the developed sensor system.
