Multi-ion detection and molecular switching behaviour of reversible dual fluorescent sensor

Glucosamine Schiff bases as fluorescent sensors for recognition of Al+3 and Zn+2 ions

Glucosamine salicylidene (GAS) and Glucosamine-4-nitrosalicylidene (GANS) were synthesized using microwave and investigated as water-soluble chemosensors for aluminum and zinc ions. UV-vis, fluorescence titration, binding constant, and jobs plot experiments showed high selectivity and sensitivity towards aluminum and zinc ions. The limit of detection for Al(III) and Zn(II) ions was 0.19 μM and 0.25 μM, respectively. The sensor demonstrated practical applications in solid-state surface and fluorescence intracellular imaging of ions in the HEK-293 cell lines.

TD-DFT investigation on anion recognition mechanism of anthraldehyde-based fluorescent thiosemicarbazone derivatives

The mechanism of host-guest interaction of receptors towards fluoride ion has been investigated using computational methods. To distinguish the effect of aromaticity in host-guest interaction, we investigated unsubstituted (ATSC) and phenyl-substituted (APTSC) anthracene thiosemicarbazones towards different ions. In the ground state of receptor-fluoride complex, the added fluoride ion made hydrogen bond through N - H^…F^…H - N, whereas the intramolecular hydrogen bonding was through F - H^…N in the excited state of receptor-fluoride complex. Experimental absorption and emission spectra were well reproduced by the calculated vertical excitation energies. The transition state (TS) calculations were performed to understand the thermodynamic features and mechanism of host-guest interaction. The natural bond orbital analyses show that the second perturbation energy for donor-acceptor interaction of F^- with hydrogen is more than 300 kcal/mol^-1 at the excited state of receptor-fluoride complex, which indicates the strong single bond between fluoride and hydrogen atom. The PES scan confirms that deprotonation took place at the excited state of receptor-fluoride complex. The results indicate the excited-state proton transfer (ESPT) process from N-H group nearby the anthracene moiety. The APTSC is a better chemosensor than ATSC. This infers that the aromaticity will increase the efficiency of fluorescence receptor towards fluoride ion. A schematic representation of sensing mode of anthracene-based thiosemicarbazones toward fluoride ion. The fluoride ion first makes a hydrogen bond with NH proton nearby anthracene moiety. The excited state proton transfer mechanism was confirmed by PES and NBO studies.

Reusable colorimetric and fluorescent chemosensors based on 1,8-naphthalimide derivatives for fluoride ion detection

Two 1, 8-naphthalimide derivatives, 2-(2-ethylhexyl)-6-(2-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzylidene)hydrazinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (named as NAOZ) and 2-(2-ethylhexyl)-6-(2-(4-(5-phenyl-1,3,4-thiadiazol-2-yl)benzylidene)hydrazinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (named as NATZ), containing hydrazone and thiadiazole/oxadiazole, were successfully synthesized. Compounds NAOZ and NATZ were further served as efficient reversible colorimetric and fluorescent chemosensors for fluoride ion over a wide range of other anions (Cl^-, Br^-, I^-, NO₃^-, ClO₄^-, HSO₄^-, BF₄^-, and PF₆^- as their (C₄H₉)₄N⁺ salts) because fluoride ion can deprotonate the hydrazone moiety, leading to the observed long-wavelength color change. Interestingly, CO₂ can recover the charge transfer (CT) absorption and photoluminescence intensities of compound NAOZ/NATZ + F^-, because CO₂ can react with a small amount of water to form acids, which can provide protons.