Ag(I) induced emission with azines having donor-acceptor-donor chromophore

Two azine molecules, [3-{4-(dimethylamino) phenyl} prop-2-en-1-ylidene] hydrazone (HL) and [4-(dimethylamino) benzylidene] hydrazone (LL) synthesized via Schiff base condensation, show an absorption band due to intra-ligand charge transfer (ILCT). Both ligands show weak emission in the absence of a metal ion as input. When Ag+ ions are added to either compound in THF, the metal ion gets bonded to the azine moiety resulting in a high intensity emission (similar to 400 fold). While Cu+ shows a slight enhancement of emission, other first-row transition, alkali or alkaline-earth metal ions do not show any emission allowing Ag+ ions to be detected in the presence of these metal ions. Both the Ag+ complexes were characterised by X-ray crystallography and show solid-state spectra similar to their solution spectra. Time-resolved fluorescence measurements done on the complexes show two excited-state lifetimes.