A new triphenylamine-based tetraimidazolium salt L was developed for silver(I)−carbene bond-directed synthesis of tetranuclear silver(I) octacarbene ([Ag 4 (L) 2 ](PF 6 ) 4 ) metallacage 1. Interestingly, after assembly formation, metallacage 1 showed a nine-fold emission enhancement in dilute solution while ligand L 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 1 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 1. For metallacage 1, 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.
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