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

Abstract

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 (Φ_F = 3.2, 3.4) in comparison to their metal–carbene counterparts (Φ_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.