A subtle change in substituent enabled multi-ways fluorine anion signals including paper-strip colorimetric detection using urea-functionalized push–pull chromophore receptor

•Multi-ways responses for fluorine anion was achieved by the judicious choice of charge-transfer by apt substitution.•1H-NMR and other data unveil that the sensing mechanism involves H-bonding and deprotonation at the NH (urea) moiety.•Colorimetric strip-detection reported with minimum detection limit upto 1 and 3 ppm in DMSO and H2O/DMSO 1:1, respectively.•It is a low-cost method, as it does not require any instruments including UV lamp and no chemical treated paper.•High selectivity was achieved including common interfering anions such as acetate and phosphate.