Novel, low-molecular-weight fluorescent sensors based on a pyridine–pyridone core structure, which functions as both the chelating part moiety for Zn²⁺ and as the fluorophore, were investigated. The length of the methylene spacer between the phenyl ring and the 3-position of the pyridone ring greatly influenced the emission wavelength and intensity upon Zn²⁺ binding. 5-Benzyl-4-(methylsulfanyl)-[2,2′-bipyridin]-6(1H)-one (2) (MW = 308) with a methylene spacer of n = 1 showed good water solubility, a 30 nm bathochromic shift in its emission wavelength and an 18-fold fluorescence enhancement in response to Zn²⁺. In addition, fluorescence microscopy imaging showed that 2 could be used to detect Zn²⁺ in living cells.