Quantum Clusters of Gold Exhibiting FRET

Fluorescence resonance energy transfer between the metal core and the ligand in Au<sub>25</sub>SG<sub>18</sub> (SG-glutathione thiolate) is demonstrated using dansyl chromophores attached to the cluster core through glutathione linkers. The dansyl chromophore functionalization of the cluster has been carried out by two different routes. Efficient energy transfer from the dansyl donor to the Au<sub>25</sub> core is manifested by way of the reduced lifetime of the excited state of the former and drastic quenching of its fluorescence. The donor−acceptor separation observed in the two synthetic routes reflects the asymmetry in the ligand binding on the cluster core, which is in agreement with the recent theoretical and experimental results on the structure of Au<sub>25</sub>.