Dissecting the Triplet-State Properties and Intersystem Crossing Mechanism of the Ligand-Protected Au 13 Superatom.

Icosahedral Au 13 nanoclusters are among the most typical superatoms and are of great interest as promising building blocks for nanocluster-assembled materials. Herein, the key parameters involved in the intersystem crossing (ISC) process of [Au 13 (dppe) 5 Cl 2 ] 3+ ( Au 13 ; dppe = 1,2-bis(diphenylphosphino)ethane) were characterized. Quenching experiments using aromatic compounds revealed that the T 1 energy of Au 13 is 1.63 eV. An integrative interpretation of our experimental results and the relevant literature uncovered important facts concerning the Au 13 superatom: the ISC quantum yield is unity due to the ultrafast ISC (∼10 12 s -1 ), the lowest absorption band includes contributions of direct singlet-triplet transitions, and there exists a large S 1 -T 1 gap of 0.73 eV. To explain the efficient ISC, the El-Sayed rule was applied to the superatomic orbitals corresponding to the excited-state hole/electron distributions obtained from theoretical calculations. The strong spin-orbit coupling between the S 1 and T 2 -T 4 states offers a reasonable explanation for the ultrafast ISC.