A pentadentate Schiff-based ligand incorporating a pyridine binding moiety has been synthesized and characterized. This ligand is of potential interest in the development of a fluorescent chemosensor for the biologically relevant Zn2+. This mixed oxo and aza donor ligand shows highly selective fluorescent response to Zn2+ compared to alkali, alkaline, transition metal, and lanthanide ions, exhibiting a quantum yield of 1.60% when bound to Zn2+. The system exhibits a limit of detection of 7.2 µM. Examination of twelve other metal ions in competition with the ZnL complex found a unique augmentation in fluorescence upon addition of K, Ca, Mg, and Cd ions, an effect not previously observed in similar chemosensor systems. Cooperative binding of ligand, Zn, and K resulted in the largest increase in quantum yield to 2.71%.