Synthesis of red fluorescent dye with acid gas sensitive optical properties and fabrication of a washable and wearable textile sensor

Two halochromic red fluorescent dyes, whose chromophores are the same as Nile red, were synthesized by introducing dibutyl- and dihexyl-substituents for improving their affinity toward chemically resistant and hydrophobic fibers made of high molecular weight polyethylene. The optical properties of the two synthesized dyes (Dibutyl NR, Dihexyl NR) compared with Ethyl NR (Nile red), such as the maximum absorption, Stokes shift, molar absorption coefficient, and quantum yield, were almost the same. However, the most hydrophobic Dihexyl NR exhibited the best washability of the three dyes. It was shown that the change of both the color and the fluorescence emission properties can be achieved not only in a hydrochloric acid solution but also inside the polyethylenic fiber on exposure to the gaseous phase of hydrogen chloride even at very low concentrations. The sensing performance was maintained even after several repeats. The highly sensitive and visible fluorescent acid gas sensing textile sensor having washability and reusability was fabricated.