An allyloxynitrophenylimio-propylhydroxyl appended rhodamine (RD-3) specifically recognises Cr3+ in aqueous buffer medium at pH 7.4. The visible light excitable reagent (λex 505 nm) on selective binding to Cr3+ exhibited a strong fluorescence turn-on response with powerful emission at 557 nm and the tail of this luminescence band is extended to ∼650 nm. Interference studies confirm that other metal ions (27 ions) do not hamper the detection process of Cr3+. The sensing mechanism is studied by absorption, fluorescence, Job's plot, and 1H NMR titration studies. The detection limit is as low as 33 nM. The practical applicability of RD-3 is examined for imaging Cr(iii) ions in HCT116 (human colorectal carcinoma) cells.