Silver(I)–Carbene Bond-Directed Rigidification-Induced Emissive Metallacage for Picric Acid Detection

Abstract

A new triphenylamine-based tetraimidazolium salt <b>L</b> was developed for silver(I)-carbene bond-directed synthesis of tetranuclear silver(I) octacarbene ([Ag₄(L)₂](PF₆)₄) metallacage <b>1</b>. Interestingly, after assembly formation, metallacage <b>1</b> showed a nine-fold emission enhancement in dilute solution while ligand <b>L</b> was weakly fluorescent. This is attributed to the rigidity induced to the system by metal-carbene bond formation where the metal center acts as a rigidification unit. The enhanced emission intensity in dilute solution and the presence of the triphenylamine core made <b>1</b> a potential candidate for recognition of picric acid (PA). This recognition can be ascribed to the dual effect of ground-state charge-transfer complex formation and resonance energy transfer between the picrate and metallacage <b>1</b>. For metallacage <b>1</b>, a considerable detection limit toward PA was observed. The use of such metal-carbene bond-directed rigidification-induced enhanced emission for PA sensing is noteworthy.