A new fluorescent chemosensor based on 8-aminoquinoline L1 bearing a benzimidazole moiety was synthesized, which exists as two predominant tautomers L1A and L1B in diluted DMSO-d₆ solution. Among various metal ions, L1 showed a highly selective and sensitive turn-on fluorescence response to the presence of Zn²⁺ ions in methanol. The detection limit for Zn²⁺ by L1 was calculated to be 1.76 × 10⁻⁷ M. The 1 : 1 complexation ratio of the L1–Zn complex was confirmed through Job plot measurements. Complexation studies were performed by FT-IR, NMR and HR-ESI MS measurements and DFT calculations. With the gained insight, it was possible to successfully apply L1 in water sample analysis.