Copper Nanoclusters Exhibiting Aggregation-Induced Delayed Fluorescence for the Fluorescent Detection of Hg²⁺ and ClO^– Ions

Aggregation-induced fluorescence exhibits huge potential in modifying the luminescent properties of metal nanoclusters, as aggregation enhances both prompt and delayed fluorescence (DF). The aggregation-induced delayed fluorescence (AIDF) widens the chemical sensing abilities due to extended luminescence lifetimes. Here, we demonstrate an unprecedented aggregation effect on the photoluminescence mode of copper nanoclusters (CuNCs) from prompt to delayed fluorescence upon addition of metal salts. The aggregation behavior and the corresponding AIDF depend on the nature of metal ions and the corresponding counteranions (SO 4 2–, CH 3 COO –, and NO 3 – ). Zn 2+ ions effectively promoted the AIDF compared to other metal ions. Surprisingly, the Zn 2+ -induced AIDF was augmented only in the presence of the acetate (CH 3 COO − ) anion, which resulted in a narrow size distribution due to its strong ability to stabilize the primary nanoclusters. On the other hand, NO 3 – could not stabilize the nanoclusters, which resulted in a broad distribution, forming less organized self-assembly. Moreover, AIDF harnessed from Zn-CuNCs was successfully employed to detect hypochlorite (ClO – ) and mercuric (Hg 2+ ) ions in aqueous medium, which was further compared with normal fluorescence sensing. The limits of detection (LODs) of ClO – and Hg 2+ for DF were 1.05 and 6.63 nM, whereas the LODs obtained by fluorescence sensing were 4.14 and 8.16 nM, respectively. Thus, AIDF improves the sensing property of Zn-CuNCs compared to normal fluorescence.