Linkage induced enhancement of fluorescence in metal-carbene bond directed metallacycles and metallacages

Two new 1,4-dihydropyrrolo[3,2-b]pyrrole based aggregation induced emission (AIE)-inactive di- and tetra-imidazolium salts were employed with Ag(i) for the synthesis of a Ag-carbene bond directed metallacycle (1) and metallacage (2), respectively. Transmetalation of these complexes allowed their facile conversion to their respective Au(i)-metallacycle (3) and metallacage (4). The final assemblies exhibit linkage induced enhancement of fluorescence (LIEF). The free ligands are almost non-fluorescent (phi(F) = 3.2, 3.4) in comparison to their metal-carbene counterparts (phi(F) up to 32.0). Thus, without using any AIEgen, obtaining high emission efficiencies in complexes Ag-I-C-NHC (1, 2) via linkage is a nice approach towards turn-on fluorescence.