An air stable, water soluble, and efficient ionic liquid-tagged Schiff base palladium complex was prepared. The synthesized complex was well characterized by NMR, mass spectrometry, FT-IR, UV-visible spectroscopy and powder X-ray diffraction. The complex was used as a catalyst for the Suzuki and Heck cross-coupling reactions in water. Good to excellent yields were achieved using a modest amount of the catalyst. In addition, the catalyst can be easily reused and recycled for six steps without much loss in activity, exhibiting an example of sustainable and green methodology.

Recyclable nickel(ii) catalyst promoted sulfenylation of aryl halides with sulfonyl hydrazides in water using microwave irradiation under mild conditions is reported.

An imidazolium-based quinoline Schiff base ImSB was developed and fully characterized by FT-IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and X-ray crystallography. The fluorescence behaviour of ImSB in solution and in the solid state, keto–enol stability at different concentrations and pH in aqueous medium were investigated. The UV-visible and fluorescence studies were performed to determine the response of ImSB towards different ions in aqueous medium. ImSB showed a turn-on fluorescence behaviour with high selectivity towards Al³⁺ over various cations and anions due to chelation-enhanced fluorescence (CHEF), inhibition of photoinduced electron transfer (PET) and restriction of CN isomerization. The low detection limit for Al³⁺ was 54 nM and Job's plot confirmed 1 : 1 stoichiometry between ImSB and Al³⁺ with a high binding constant value of 4.16 × 10⁶ M⁻¹. Monitoring of Al³⁺ was also demonstrated in real water samples (mineral, river and tap water). The structural and electronic parameters of ImSB and ImSB-Al³⁺ were also studied theoretically.

Sensing nitroaromatic explosives has gained significant attention due to both increased terrorist threats and a need for environmental protection. In this regard, a fluorescent chemosensor, 1-benzyl-3,5-di(thiophen-2-yl)pyrazin-1-ium bromide (BTPyz), was synthesized and characterized via spectroscopic methods. The photophysical properties were investigated using absorption and emission spectral analysis. As a fluorescent chemosensor, BTPyz exhibited a selective response towards 2,4,6-trinitrophenol (TNP) with a detection limit of 11.6 nM and quenching constant (K_SV) of 3.8 × 10⁴ M⁻¹. The fluorescence quenching mechanism was attributed to ground-state charge-transfer complex formation and resonance energy transfer, as evident from Uv-visible, fluorescence and NMR spectroscopy, single-crystal XRD studies, and density functional theory calculations. BTPyz was also employed for the contact mode detection of TNP on paper strips. The detection of TNP in real water and soil samples demonstrated BTPyz to be a promising detection tool toward environmental specimens.

A fluorescent pyrazinium-based 1-benzyl-3,5-diphenylpyrazin-1-ium bromide (BPPyz) chemosensor was synthesized and well-characterized. A significant reduction in blue emission of BPPyz was observed in the presence of TNP as compared to other nitroaromatic compounds, indicating high selectivity towards TNP. In the presence of sulfite ions, BPPyz showed fluorescence quenching and rapid naked-eye detection with a significant color change. The sensing mechanism was investigated through UV–visible studies, time-resolved fluorescence results, and density functional theory (DFT) calculations. The quenching constants (K_SV) are 4.12 × 10⁵ M⁻¹ for TNP and 3.8 × 10⁵ M⁻¹ for sulfite with the detection limits of 9.5 nM and 46.17 nM for TNP and sulfite, respectively. The selectivity of BPPyz towards TNP was ascribed to the ground state charge transfer complex (GSC) formation and resonance energy transfer. Sulfite ion detection involved the formation of a GSC through hydrogen bonding with the pyrazinium proton.