A Schiff base based on triphenylamine and thiophene moieties as a fluorescent sensor for Cr (III) ions: Synthesis, characterization and fluorescent applications

A Schiff base fluorescent sensor was designed for selective detection of Cr3+ ions in aqueous solution. The procedure for the study was fulfilled in three steps which comprised the synthesis of 4-nitro-triphenylamine (TPA-NO2), 4-amino-triphenylamine (TPA-NH2) and Schiff base (TPA-Th) using 2,2′-bithiophene-5-carboxaldehyde, respectively. Structural characterization of the purely synthesized compounds was acquired by using UV–Vis, FT-IR, 1H NMR and 13C NMR analyses. Their electrochemical, thermal, and the optical sensor properties for metal ions were enlightened by cyclic voltammetry (CV), thermal-TG-DTA and photoluminescence (PL) techniques, respectively. Non-fluorescent TPA-Th displayed a fluorescence enhancement after chelation with Cr3+ ions with high selectivity and overall emission change of 59-fold at an excitation wavelength of 320 nm. The limit of detection (LOD) value was as low as 1.5 × 10−6 M for Cr3+ ions, accompanied by an association constant (Ka) of 2.8 × 104 M−1. TPA-Th was beneficial for the design and development of metal-complexed fluorescent sensor and light emitting devices.