Metallophilic Bond‐Induced Quenching of Delayed Fluorescence in Au 25 @BSA Nanoclusters

The metallophilic bond is a weak interaction between closed‐shell ions and has been widely used a probe for various sensing of toxic chemicals for environmental safety concerns. Here, the interaction between Au nanoclusters (NCs) and metallic ions (mercury (Hg 2+ ) and copper (Cu 2+ ) ions) is explored using steady‐state and time‐resolved luminescence and transient absorption measurements. For Hg 2+ ions, the delayed fluorescence (DF) of bovine serum albumin (BSA) protected Au 25 (Au 25 @BSA) NCs is quenched via an effective triplet state electron transfer through the metallophilic bond. However, the Cu 2+ ions do not alter the DF in Au 25 @BSA NCs because of the absence of the metallophilic interaction. Furthermore, for Au 8 @BSA and Au 10 @histidine, in which there are no Au + ions on the surface, the fluorescence is not quenched by Hg 2+ ions. Such a novel triplet electron transfer process through metallophilic bonds are observed and reported for the first time. The reduction of the reverse intersystem crossing is the crucial for Hg 2+ ion sensing in the fluorescent Au 25 @BSA NCs.