The fluorescent and stable aqueous solution of 3-Cyano-4,6-dimethyl-2-pyridone (CDPy) has been used as a probe for selective detection of Hg+2 ions in natural river water. The fluorescence intensity of the probe was reduced on adding Hg+2 ions. The DFT and TD-DFT confirmed that the reduction in fluorescence intensity occurred due to excited state charge transfer between the CDPy molecule and Hg+2 ions. This procedure can be used to detect Hg+2 ions up to a detection limit similar to 0.41 mu M. It is reproducible with excellent stability (similar to 10 weeks) and applicable in a wide linear range (3-231 mu M). (C) 2017 Published by Elsevier B.V.