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A coumarin-based Schiff base (receptor 1) exhibited fluorescence enhancement selectively with Zn(2+) at a nanomolar level in near-aqueous medium (EtOH-H2O; 1:1, v/v). The response was instantaneous with a detection limit of 3.26 × 10(-9) M. The sensing event is supposed to incorporate a combinational effect of intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF) and C[double bond, length as m-dash]N isomerization mechanisms. Various spectroscopic methods, viz. IR, UV-visible, fluorescence and NMR in association with single crystal XRD studies, were used for thorough investigation of the structure of receptor 1 as well as of the sensing event. The Zn(2+) complex of receptor 1 exhibited a very nice 1D chain coordination polymeric framework in its single crystal XRD.

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A simple Schiff base (RC) has been explored as a smart example of fluorescent material for the selective detection, differentiation and bioimaging of methanol. The nucleophilic attack of methanol on the cyclic control unit of RC leads to its opening and formation of a highly fluorescent moiety, RO. The RC displays a good sensitivity for MeOH with a detection limit of 0.042 wt% in water.

In this work, a 2-(2-hydroxyphenyl)benzothiazole (HBT)-based ratiometric fluorescent probe exhibiting coupling between the ICT and ESIPT mechanisms was exploited for the optical sensing of cysteine and successfully utilised in the bio-imaging of cysteine in HeLa cells.

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The present communication outlined for the first time a novel combination of chromogenic near-infrared (NIR) and ratiometric fluorescence responses for Fe(3+) by a symmetric chalcone analogue (receptor 1). The key step behind NIR chromogenic response was attributed to chelation of Fe(3+) with receptor 1 upon its unfolding in aprotic, low viscosity solvents. The receptor 1 also exhibited Fe(3+) selective ratiometric changes at 538 nm and 463 nm. The chromogenic detection limit of the receptor 1 for Fe(3+) is the lowest ever (5.8 × 10(-8) M). The mechanistic details of NIR/fluorescence sensing of receptor 1 along with its solvent dependency have been discussed in detail.