For ratiometric “naked eye” detection of CN⁻, an ESIPT exhibiting benzothiazole receptor (BHI) is designed having one aldehyde group ortho and the other aldehyde para to the OH group respectively. Due to RAHBs, the ortho aldehyde group is highly reactive undergoing nucleophilic cyanide addition selectively, which hampered ESIPT. This is also supported by DFT and TD-DFT calculations.

A spirobenzopyran-quinoline (SBPQ) based sensor was synthesized which selectively detects trivalent ions viz. Al³⁺, Fe³⁺ and Cr³⁺ through a fluorescence turn on signal in the red region (∼675 nm) with the detection limit in the order of 10⁻⁸ M. The potentiality of the probe was confirmed by employing it for fluorescence bio-imaging with Al³⁺ in three different types of live-cells.

In this study, we have synthesized a simple Schiff base type isophthaloyl salicylaldehyde hydrazone (ISH) moiety which selectively detects Al(III) and PPi with a fluorescence enhancement at two different wavelengths in aqueous solution. The sensing phenomenon is also reversible and thus the sensor beautifully mimics logic gates (INHIBIT and EXOR gates).

A new naphthalimide–quinoline based probe (NAQ) is designed and synthesized and its structure is confirmed through single crystal analysis. It detects the trivalent ions (Fe³⁺ or Al³⁺ or Cr³⁺) selectively among other alkali and transition metal ions studied. NAQ shows a distinct ratiometric fluorescence behavior upon addition of trivalent metal ions in CH₃CN–HEPES buffer solution (40/60, v/v, pH = 7.4). This fluorogenic sensing of NAQ to M³⁺ (M³⁺ = Fe³⁺ or Al³⁺ or Cr³⁺) can be observed by the naked eye, when illuminated under the UV light.

A new rhodamine–quinoline based dyad has been synthesized. It shows a highly selective response to Cd²⁺ in the presence of other competing metal ions in aqueous media (pH = 7.1). The detection limit of the sensor is in the 10⁻⁷ M level.