High photoluminescent TPA and the ratiometric sensor for free chlorine

A facile and high yield method is introduced to synthesize 3,5-dihydro-5-oxo-2H-thiazolo[3,2-a]pyridine-3,7-dicarboxylic acid (TPA) through the one-step condensation reaction of citric acid and L-cysteine. For the first time, the produced TPA molecules are purified by the simple crystallization, and the photoluminescence (PL) properties of the TPA are investigated. The obtained purified TPA shows bright blue PL, with a PL quantum yield as high as 90.5%. The sulfur atom of TPA molecule can be selectively oxidized by free chlorine into sulfoxide, which is a strong electron withdrawing group. As a result, the conjugation is decreased, leading to a great PL quenching. On the basis, a sensitive and selective PL sensor is developed for the detection of free chlorine. Furthermore, tris(2,2-bipyridine)ruthenium(II) chloride hexahydrate, whose red PL signal is inert to the free chlorine, can be used to provide a background PL signal. Thus, a visual PL ratiometric sensor is developed, which is convenient for the on-site and on-line detection of free chlorine. (C) 2017 Elsevier B.V. All rights reserved.