Here we demonstrate a new approach to fluorogenic labelling, where a cationic hemicyanine (CHyC) exhibits disaggregation-induced emission (DIE) upon undergoing an azide-alkyne "click" reaction. CHyC self-associates and is self-quenched in aqueous buffer over a low micromolar concentration range. When an azido nucleoside (AmdU) or azide-containing cellular DNA is added to CHyC in the presence of Cu(I), a copper-catalysed azide-alkyne cycloaddition drives dye disaggregation, significantly increasing the fluorescence intensity of the probe upon its covalent attachment to modified biomolecules.