A new thiosemicarbazide-naphthalene-based fluorescent chemosensor FNC ((2-(furan-2-carbonyl)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide)) for Zn2+ was synthesized and identified. FNC was applied to selectively detect Zn2+ with fluorescent turn-on response. The detection limit was determined to be 1.93 µM, which is much below the WHO standard (76.5 µM). The detecting mechanism of FNC to Zn2+ was revealed to bind FNC to Zn2+ in the proportion of 1: 1 by Job plot, ESI-mass and 1H NMR titrations. DFT and TD-DFT calculations were performed for FNC and FNC-Zn2+, which provide insight into structural, electronic and photophysical properties.