A new 4-amino-1,8-naphthalimide hydrazine fluorophore (Nap-NH2) has been synthesized in quantitative yield via a one-pot imidation reaction between 4-amino-1,8-naphthalic anhydride and hydrazine hydrate (N2H4·H2O) and successfully employed as a fluorescent “turn-on” chemosensor for metal cations. The sensor Nap-NH2 displayed a positive solvatochromism in different solvents with varying polarities. The fluorescence titration studies of Nap-NH2 with various metal cations disclosed the high selectivity and reversible binding affinity of Nap-NH2 towards Zn(II) ions with nanomolar (10 nm) sensitivity. The fluorescence emission intensity of Nap-NH2 was drastically enhanced upon binding with Zn(II) ion and the Stern-Volmer binding constant is KSV = 1.13 × 104 M−1. Interestingly, the presence of commonly coexisting different metal cations {Fe(II), Cu(II), Mg(II), Cd(II), Ni(II), Co(II), Mn(II), Ba(II), Al(III), Ce(III), Sn(II), Pb(II), Cr(III) and Ca(II)} showed negligible changes in the emission intensity and thus weak binding interactions with Nap-NH2. These studies demonstrate that Nap-NH2 is a potential fluorescence “turn-on” chemosensor for selective, sensitive detection and quantification of biologically relevant metal cations. © 2022 Elsevier B.V.