We report the ability of a pyrazino[2,3-g]quinoxaline derivative substituted with eight peripheral flexible n-octyloxy chains, to sense the volatile trifluoroacetic acid in trace amounts (in parts per billion levels). The reversible detection of acid sensing behavior was visually perceivable in both solution as well as in the drop-casted film on a TLC paper based strip. Density functional theory studies were carried out to elucidate the mechanism of the sensing behavior.