Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu2+, Hg2+ and Pb2+ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg2+ and Pb2+ ions in CH3CN and CH3CN–H2O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu2+ ion in CH3CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN− ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction.