Impact of the metal core on the electrochemiluminescence of a pair of atomically precise Au(20) nanocluster isomers

Although the electrochemiluminescence (ECL) of metal nanoclusters has been reported, revealing the correlation between structure and ECL at an atomic level is highly challenging. Here, we reported the impact of the metal core of Au(20)(SAdm)(12)(CHT)(4) (Au(20)-AC for short; SAdm = 1-adamantanethiolate; CHT= cyclohexanethiol) and its isomer Au(20)(TBBT)(16) (TBBT = 4-tert-butylthiophenol) on their solution-state and solid-state electrochemiluminescence. In self-annihilation ECL experiments, Au(20)-AC showed a strong cathodic ECL but a weak anodic ECL, while the ECL signal of Au(20)(TBBT)(16) was weak and barely detectable. Density functional theory (DFT) calculations showed that the Au(7) kernel of [Au(20)-AC](-) is metastable, weakening its anodic ECL. Au(20)-AC in solution-state displayed an intense co-reactant ECL in the near-infrared region, which is 7 times higher than that of standard Ru(bpy)(3)(2+). The strongest solid-state ECL emissions of Au(20)-AC and Au(20)(TBBT)(16) were at 860 and 770 nm, respectively — 15 nm red-shifted for Au(20)-AC and 20 nm blue-shifted for Au(20)(TBBT)(16), compared to their corresponding solid-state photoluminescence (PL) emissions. This work shows that ECL is significantly affected by the subtle differences of the metal core, and offers a potential basis for sensing and immunoassay platforms based on atomically precise emissive metal nanoclusters.