A pyrene derivative (KB-3) was synthesized and demonstrated as a colorimetric and ratiometric chemosensor for selective detection of fluoride ion with the detection limit of 391 nM. The mechanism of fluoride ion detection is due to the complete deprotonation of NH proton in KB-3 as revealed by H-1 NMR studies. Further, the deprotonated KB-3 is demonstrated for perceptive detection of CO2 gas down to 0.1 ml. Moreover, detection of fluoride using KB-3 is explored to develop INHIBIT type logic gate at molecular level.