Synthesis of a fluorescent, single-benzene-based molecule for rapid detection of HCl gas

A deprotonated 2,5-dihydroxyterephthalic acid (DHT) was synthesized to obtain a water-soluble, fluorescent molecule (DHT-K). The deprotonated DHT-K was converted to DHT upon exposure to acidic gas, changing fluorescence color from yellow to blue. DHT-K was incorporated to poly(vinyl alcohol) to form a film, and the film showed the same fluorescence change when exposed to HCl gas. The blue fluorescence of HCl-exposed DHT-K film was returned to yellow emission by simple treatment with NH3 gas, showing effective regeneration. Using detectable fluorescence changes by the naked eye, DHT-K can be a potential candidate for a fluorescent indicator toward HCl gas.