Near-Infrared Dual Emission from the Au(SR) Nanocluster and Tailoring of Intersystem Crossing.

This work presents the synthesis and intriguing photoluminescence of the Au(PET) (PET = 2-phenylethanethiolate) nanocluster (NC). The Au(PET) NC exhibits dual emission at 875 and 1040 nm, which are revealed to be fluorescence and phosphorescence, respectively. The emission quantum yield (QY) of Au(PET) in dichloromethane is 11.9% at room temperature in air, which is quite rare for thiolate-protected Au NCs. When Au(PET) NCs are embedded in polystyrene films (solid state), the fluorescence was dramatically suppressed while the phosphorescence was significantly enhanced. This divergent behavior is explained by dipolar interaction-induced enhancement of intersystem crossing from singlet to triplet excited state.