Fluorescent Schiff Bases with Phenothiazine and Coumarin Moieties: Synthesis, Characterization, Photophysical, Electrochemical, Computational and Biological Studies.

We present the design and synthesis of four new schiff bases viz., two each of phenothiazine and coumarin derivatives. The structures were proposed based on FT-IR, 1H NMR, 13C NMR and mass spectral data. The photophysical, solvatochromic and electrochemical studies of all the compounds were carried out. Furthermore, theoretical studies such as density functional theory (DFT) were carried out to gain a better understanding of the compounds' intramolecular charge transfer properties and electronic structures. Good agreement was noticed between the HOMO-LUMO energy gap obtained from DFT studies and that calculated from absorption threshold wavelengths. All the compounds showed Stokes shifts in the range of 6345-11,405 cm-1. These findings showed that the new schiff bases could be considered as attractive candidates for use in the development of OLEDs, organic electrical devices and optoelectronic devices. Newly synthesized compounds were tested for biological activities. When compared to conventional standards, gallic acid and indomethacin, the schiff bases showed better antioxidant and antiinflammatory activities, respectively.

Spectroscopic Investigation of Coumarin Based Novel Fluorescent TURN OFF Sensor for the Selective Detection of Fe3+: In-vitro Live Cell Imaging Application.

The novel TURN-OFF fluorescent sensors 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) and 4-(6-Bromo-benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BBHC) are designed and synthesized for the spectrofluorometric detection of the biologically important Fe3+ ions, which has sensitive and selective fluorescence quenching over other competitive metal ions. The effectiveness of the sensors and rapid response are validated through UV-Visible, and fluorescence spectral changes. These spectral changes could be due to the formation of coordination bond between ligand and metal ion. The binding stoichiometry of both sensors with Fe3+ ions is studied with the help of Job's plot, which gives a 1:2 coordination ratio; this is further confirmed through DFT, IR and NMR studies. The association constants of 4BHC and 4BBHC are calculated through Benesie-Hildebrand plots, and they are found to be 6 × 104 M-1 and 11.2 × 104 M-1 respectively. Following, LOD is calculated to define the range of sensitivity of the proposed sensors and is found to be 3.43 µM and 2.14 µM respectively. The chemical hardness parameter suggested that both sensors are soft molecules. In addition, low cytotoxicity levels of 4BHC and 4BBHC led to the demonstration of their efficacy in In-Vitro imaging of Fe3+ ions inside living cells, which ensures that these sensors are promising candidates for bioimaging.