Photo-Induced Cluster-to-Cluster Transformation of [Au37-xAgx(PPh3)13Cl10]3+ into [Au25-yAgy(PPh3)10Cl8]+: Fragmentation of a Trimer of 8-Electron Superatoms by Light.

We present the photoinduced size/structure transformation of [Au37-xAgx(PPh3)13Cl10]3+ (M37) into [Au25-yAgy(PPh3)10Cl8]+ (M25) cluster. Single-crystal X-ray diffraction revealed that M37 has a tri-icosahedron M36 metal core assembled via the fusion of three Au7Ag6 icosahedrons in a cyclic fashion and that the M36 core is further protected by phosphine and chloride ligands. The M37 cluster is found to be highly sensitive toward ambient light, and the M37 → M25 transition is observed with 530 nm irradiation, monitored by time-dependent UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and femtosecond transient absorption spectroscopy. Linear-response time-dependent DFT calculations indicated that the strong absorption of the M37 cluster close to 500 nm induces an antibonding-type configuration in the induced electron density within the plane of the three 8-electron systems, possibly promoting dissociation of one of the 8-electron superatoms. This theoretical result supports the experimental observation of the sensitivity of the M37 → M25 transition to 530 nm irradiation.