Highly fluorescent lipophilic 2,1,3-benzothiadiazole fluorophores as optical sensors for tagging material and gasoline adulteration with ethanol

Abstract

Lipophilic 2,1,3-benzothiadiazoles were obtained in a short synthesis with excellent yields by a Sonogashira coupling reaction followed by a 1,3-dipolar cycloaddition reaction with alkyl azides. The obtained compounds presented high solubility in a wide range of solvents with different polarities. The benzothiadiazoles present absorption in the violet region due to fully spin- and symmetry-allowed π-π* electronic tansitions and an emission located in the blue-green region with a large Stokes shift. The high solubility in apolar media, along with their photophysical properties allowed their use as tagging materials up to a detection limit of 0.005 ppm. Moreover, their application as chemosensors for the detection of fuel adulteration in commercial gasoline in the range of 5–50 % ethanol/gasoline (v/v) was also sucesfully presented and discussed.