Sandip Banthia

A two-dimensional chromogenic sensor as well as fluorescence inverter: selective detection of copper(II) in aqueous medium

A new chromogenic sensor (1) has been synthesized that shows simultaneous blue shift and intensity loss of the absorption maximum as well as quenching of fluorescence, selectively, in the presence of Cu2+ ions at physiological pH.

Calix[4]azacrown and 4-aminophthalimide-appended calix[4]azacrown: synthesis, structure, complexation and fluorescence signaling behaviour

The synthesis and single crystal structure of 25,27-(diamidomonoazacrown-5)-calix[4]arene (L), calix[4]arene capped by a diamide bridge in the 1,3-position on the lower rim, which forms a supramolecular dimer in the solid state via intermolecular hydrogen bonding, are described. A 4-aminophthalimide (AP) fluorophore has been regioselectively linked to the secondary amino function of the azacrown unit with a dimethylene spacer to construct N-(4-aminophthalimidoethyl)calix[4]azacrown (APL), a fluorescent sensor, via a fluorophore-spacer-receptor architecture. Fluorescence quantum yield and lifetime of APL have been measured to be lower than those of the bare fluorophore (AP) due to the photoinduced intramolecular electron transfer (PIET) between the fluorophore and the receptor moieties of the molecule. In the presence of transition metal ions, fluorescence enhancement of is observed suggesting the binding of the metal ion to the sensor. Complexation properties of APL with transition metal ions are investigated using UV-vis spectroscopy. A 1 : 1 stoichiometry of the complex is determined from a Job plot and the corresponding association constants for the various metal ions are evaluated. Fe(3+) and Cu(2+) ions have the largest association constants (K= 2.3 x 10(5) M(-1) and 1.6 x 10(5) M(-1) respectively) compared to other metal ions indicating that they form complexes selectively with APL.

Fluorescence signaling of transition metal ions: a new approach

Fluorescence signaling of transition metal ions by the fluorophore-spacer-receptor systems I and II is based on an unconventional mechanism.

Fluorescence signalling of the transition metal ions: Design strategy based on the choice of the fluorophore component

Transition metal ions are notorious for their fluorescence quenching abilities. In this paper, we discuss the design strategies for the development of efficientoff-on fluorescence signalling systems for the transition metal ions. It is shown that even simplefluorophore-spacer-receptor systems can display excellentoff-on fluorescence signalling towards the quenching metal ions when the fluorophore component is chosen judiciously.

pH-Regulated Off-On" fluorescence signalling of d-block metal ions in aqueous media and realization of molecular IMP logic function

The potential of an anionic receptor moiety in “Off–On” fluorescence signalling of d-block metal ions has been exploited with the demonstration of a two-input IMP function.

Photophysical and transition metal ion signaling properties of some 4-amino-1,8-naphthalimide derivatives

Photophysical and transition metal ion signaling behaviour of several 4-amino-1,8-naphthalimide derivatives in aprotic solvents, tetrahydrofuran and acetonitrile, are reported. The weakly fluorescent nature of the fluorophore–spacer–receptor systems (1a, 1b) compared to the parent fluorophore is shown to be due to photoinduced electron transfer (PET) between the terminal moieties of the systems. PET is found to be more efficient in polar medium. These systems show reasonably good ‘off–on’ fluorescence signaling in the presence of the transition metal ions. On the other hand, 2, 3a and 3b show unusual absorption and fluorescence behavior in acetonitrile in the presence of Cu2+. These spectral changes have been found to be particularly useful for specific signaling of Cu2+ in acetonitrile. The present study also reveals that reduction of Cu2+ to Cu+ in this solvent aided by the hydrogen atom of the 4-amino group of the fluorophore leads to the observed spectral changes.