The monohydrazone of quinoxaline aldehyde (HOQA) is found to be a ratiometric and colorimetric probe for Ni²⁺. HOQA shows a remarkable color change from colorless to yellow upon specific and selective binding to nickel that can be identified even by the naked eye. The cation recognition property of the receptor is monitored by UV-vis and ¹H-NMR titrations and also by DFT (Density Functional Theory) and TD-DFT (Time Dependent Density Functional Theory) calculations.