Abstract Covalently with a fluorescence support linked nitroarylester groups quench the fluorescence. The substitution of the fragment with the quenching group by an other functional group initiates fluorescence. If this substitution reaction is chemoselective, a reagent for the selective detection of a special functional group is available. The non fluorescent compounds 1a and 1b are OH-(resp. F(-)) selective; the compounds 5 and 7 are NH-selective and the compounds 8 and 9 are SH-selective. Dansyl-nitroimidazolide 7a discriminates between neutral and basic α-amino acids.