A chemosensor for the Al3+ ion, 1-[(3-hydroxypyridin -2-ylamino) methylene naphthalen-2(1H)-one (H2L), based on inhibited excited-state intramolecular proton transfer was synthesized. The experimental and theoretical calculations at B3LYP+PCM/6-31G(d) revealed that Al3+ and H2L, form a 1:1 complex, [AlL(OH)(H2O)](2), in dimethyl sulfoxide that exhibits two remarkably enhanced fluorescent emissions at 523 and 553 nm. It is confirmed that H2L could be used to detect Al3+ ions in cells by bioimaging.