We synthesized an original reversible colorimetric chemosensor PDJ ((E)-9-((2-(6-chloropyridazin-3-yl)hydrazono)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol) for the detection of F−. PDJ displayed a selective colorimetric detection to F− with a variation of color from colorless to yellow. Limit of detection of PDJ for F− was calculated as 12.1 µM. The binding mode of PDJ and F− turned out to be a 1:1 ratio using Job plot. Sensing process of F− by PDJ was demonstrated by 1H NMR titration and DFT calculation studies that suggested hydrogen bond interactions followed by deprotonation. Moreover, the practicality of PDJ was demonstrated via a reversible test with TFA (trifluoroacetic acid).