Schiff bases and oligomers derived from trifluoromethylaniline-based monomers: Thermal, optical, electrochemical properties and applications as fluorescent probes for Sn2+

Within the scope of the study, three different Schiff bases were synthesized from 3,5-bis(trifluoromethyl)aniline, a halogen-containing aniline derivative, with three different aldehydes, 3-hydroxy-4-methoxy-benzaldehyde, salicylaldehyde and 2-hydroxy-1-naphthaldehyde. These three synthesized Schiff bases were evaluated as monomers and oxidatively polymerized in the presence of sodium hypochlorite, a strong oxidant. The structural properties of these three monomers and three polymers were elucidated with the help of UV-Vis, FT-IR, 1 H NMR, 13C NMR spectra. Their molecular weights were determined by gel permeation chromatography (GPC) and it was determined that the macromolecules obtained as a result of the oxidation reaction were in the oligomer order. In order to investigate their electrochemical properties, cyclic voltammetry (CV) was used to find their oxidationreduction potentials. The HOMO-LUMO potentials and electrochemical band gap values of the synthesized Schiff bases and oligomers were calculated. Thermal stabilities of the monomers and oligomers were determined by thermogravimetric-differantial thermal analysis (TG-DTA). It was determined that the thermal stabilities of the obtained oligomers were higher than those of the Schiff bases. The glass transition temperature (Tg) and surface morphologies of oligomers were determined from DSC and SEM measurements, respectively. Their optical properties were examined by UV-Vis and fluorescence spectra. It was found that 1-(((3,5-bis(trifluoromethyl) phenyl)imino)methyl) naphthalene-2-ol (TFMHN), one of the Schiff bases, has a turn-on fluorescence sensor property with increasing fluorescence emission intensity in the presence of Sn2+ among a series of metal ions and can be used as a selective and sensitive fluorescence probe for Sn2+ with a limit of dedection (LOD) value of 7.14 x 10- 8 M.