An Unsymmetrical Squaraine-Dye-Based Chemical Platform for Multiple Analyte Recognition

The design of fluorescent molecular platforms capable of responding to multiple analytes is a topic of great interest. Herein, the use of a Zn²⁺ -complexed unsymmetrical squaraine dye, Sq-Zn²⁺ , as a chemical platform for recognizing structurally distinct analytes is reported. The squaraine ring is substituted on one side with a dipicolylamine unit, which acts as the metal ion receptor, whereas the other part of the molecule carries a dibutylaniline moiety, which is an electron donor. The molecular system is unique because it can respond specifically to different types of analytes, namely, atmospheric carbon dioxide, cyclic phosphates, and picric acid. Moreover, the interaction of these analytes can be monitored colorimetrically and fluorimetrically, which favors both qualitative and quantitative analyses. The distinct response towards cyclic and linear phosphates, as well as the selective response towards picric acid, among the various nitroaromatic compounds was achieved with sensitivity at the ppm level. The flexible coordination offered by Zn²⁺ plays a significant role in the discrimination of these analytes with high specificity. Dye Sq-Zn²⁺ introduced herein is a single-molecule construct that can be used for the selective and sensitive response towards analytes of environmental and biological relevance.