Development of fluorochromic polymer doped materials as platforms for temperature sensing using three dansyl derivatives bearing a sulfur bridge

Abstract

Three novel bis-dansyl derivatives bearing a sulfur bridge have been synthesized, fully characterized, and their photophysical characterization studied in solution, as well as, in the solid state. All compounds exhibit fluorescence emission with quantum yields up to 60%, which vary significantly depending on the solvent used, and the inherent molecular structure. Moreover, these compounds demonstrate positive solvatofluorochromic behaviour emitting from bluish-green to yellow. Kamlet-Taft studies were performed to better understand the solute–solvent interactions. Due to the intrinsic characteristics of the compounds, efforts were made to understand their potential usefulness for environmental remediation and thus metal ion sensing studies were investigated. Compounds L1 and L2 showed high sensitivity to Cu2+ and Hg2+ ions and were found to modulate their emission extensively, with L2 capable of detecting and quantifying up to 4 µM of Hg2+. Considering the solid-state emission of these compounds, the application towards temperature sensing was put forth. L3 was found to quench its emission in a linear relation with temperature up to 170 °C. Several doped polymer thin films were fabricated, which served as a platform to establish a linear relation with temperature beyond their melting point. Polymethylmetacrylate (PMMA) films emitted up to temperatures of 218 °C, which could be fully restored at room temperature. These results suggest the potential application of these bis-chromophoric compounds as molecular thermometers.