A silver-alkynyl cluster encapsulating a fluorescent polyoxometalate core: enhanced emission and fluorescence modulation

A new silver(I)-alkynyl cluster with a [Eu(W5O18)(2)](9-) polyoxoanionic core of [Ag-42{Eu(W5O18)(2)}-((BuC)-Bu-t C)(28)Cl-4] [OH]center dot H2O (1) has been designed and synthesized. The [Eu(W5O18)(2)](9-) polyoxoanion acts as a template to induce the formation of the surrounding 42-core Ag(I) cage. Due to the hydrophobic silver(I)-alkynyl shell, 1 features an unusual fluorescence enhancement as compared to the precursor of the [Eu(W5O18)(2)](9-) polyoxoanionic core. Interestingly, the silver ions in the shell silver(I)-alkynyl cage can only be reduced to silver atoms by irradiation with high energy UV light (2 kW). Upon high UV irradiation, fluorescence quenching of 1 has been observed. Moreover, the solution fluorescence of 1 can be modulated by addition of S2- ions into the system, which also leads to the fluorescence quenching phenomenon. The successful synthesis of 1 demonstrates a new route to the detection of high energy UV irradiation or S2- ions by elaborate design of fluorescence quenching of silver(I)-alkynyl clusters.