Several amino acid-based photo-active monomeric iron(III) complexes of the general formula,[Fe(L)₂]PP^-, where L= Schiff base ligands (salisalidene arginine, salicylidenetryptophan, 3,5-di-tert-butyl benzalidine arginine and salicylidene tryptophan) were synthesized, characterized and explored for photoactivated anticancer activity to Chang Liver Cells, HeLa and MCF-7 cells. Complexes exhibited remarkable photo-cytotoxicity with IC₅₀ value to the extent of 0.7 μM to Chang Liver Cells in visible light and there wasa 40-fold enhancement in cytotoxicity in comparison to the cytotoxicity in dark. Complexes were non-toxic to MCF-10A (normal cells) in dark and visible light (IC₅₀ > 100 μM in dark; IC₅₀ > 80 μM in visible light) signifying target-specific nature of the anti-tumour activity of the complexes. Increased ROS concentration,as probed by DCFDA assay, in the cancer cells was responsible for apoptotic cell death. Decarboxylation or phenolate-Fe(III) charge transfer of photo-activated iron(III) complexes generating • OH radicals (ROS) were responsible for the apoptosis. Overall, the tumour-selective photo-activated anticancer activity of the amino acidbased iron(III) complexes have shown a promising aspect in developing iron-based photo-chemotherapeutics as the next generation PDT agents.

Temperature-driven, highly sensitive and selective ^''TURN-ON^'' fluorometric detection of Zn²⁺ by benzothiazole-based probes (L¹ and L²) was reported in physiological pH in the present work. Iron(II) acted as the reversible switch or trigger for the reversible detection of Zn²⁺ ions by the probes resulting in

^''TURN-OFF^'' fluorescence at room temperature. However, selective detection of Zn²⁺ in the presence of Fe²⁺ was irreversible at 0–5 ^°C. Such temperature dependence on reversible fluorometric detection of Zn²⁺ in the presence of Fe²⁺ was explained from the thermodynamic perspective as well as DFT calculations inwhich the absolute enthalpy (H) and Gibbs free energy (G) of the resultant complexes and the fluorophores (L¹ and L2²) at different temperatures were determined. Enhanced fluorescence of the Zn²⁺ bound probes wasdue to the inhibition of excited-state intramolecular proton transfer (ESIPT). Effect of solvents, pH, and temperature on the fluorometric detection of Zn²⁺ was also probed in the present work. The results were translated into the visual detection of Zn²⁺ on paper-based fluorescence probe and later we demonstrated thesensing of mobile Zn²⁺ ions by the probes in living HeLa cells as the proof of concept of our present investigations