An effective fluorescent optical sensor: Thiazolo-thiazole based dye exhibiting anion/cation sensitivities and acidochromism

Abstract

Fluorescent 2,5-bis(4-hydroxyphenyl)thiazolo[5,4-d]thiazole (HPhTT) sensor molecule consisting of thiazolo-thiazole (TTz) binding central unit and phenolic signalling side groups was synthesized with a symmetric structure. The selectivity, sensitivity and reversibility properties of optical sensor towards cations and anions were investigated. TTz unit of the sensor was responsible from cation and proton interactions resulting with fluorescent quenching, while phenolic–OH groups were sensitive to anions with a deprotonation mechanism. The fluorescence quenching in the presence of Au3+ with high selectivity, sensitivity and fast response, making it clear that the sensor was very effective in detecting Au3+. Fluorescent sensor (HPhTT) was also found to be able to recognize AcO-, F- and CN– anions accompanied by obvious UV–vis absorption change and fluorescence switch-on response, and exhibited enhanced intramolecular charge transfer (ICT) strongly depending on the forming conjugated acid after addition of anions. Ratiometric detection and reversible usage of the sensor for AcO-, F- and CN– anions were also possible. The sensor showed remarkable detection ability in a pH > 9 media and it has also been demonstrated that it can be used successfully as a pH sensor in an aqueous media. A colour calculator study using F- anion to estimate colour change, colour purity and colour coordinates under UV light excitation with I550/I444 ratio indicated that HPhTT dye had a promising potential for fluorescent sensor studies.