Size-Dependent Photoluminescence from Thiolate-Protected Water-Soluble Cobalt Nanoclusters

Abstract

The luminescence property of highly oxidative transition metal nanostructures using Co, Ni and Cu are being challenging. Due to their high susceptibility for oxidation and non‐existence of appropriate synthesis methodologies and lack of efficient mechanism to confirm their luminescence properties. To overcome these shortcomings, herein we report a new synthesis strategy to develop a novel tripeptide thiolate ligand i. e., glutathione (GS) protected ultrasmall water‐soluble cobalt nanoclusters, Con(GS)m. As achieved Con(GS)m clusters were isolated from the crude CoGS using polyacrylamide gel electrophoresis (PAGE) technique. The PAGE separation for the crude CoGS sample resulted in three bands of varying sizes i. e., 2–5 nm (band 1), 6–18 nm (band 2) and 13–28 nm (band 3), which exhibits size‐dependent luminescence with quantum yields of 10 %, 7.5 % and 5.8 % respectively. Among them, the maximum quantum yield for the ultrasmall Con(GS)m nanoclusters from the band 1 exhibits a blue emission which could be as result of synergetic behaviour from the aggregation induced emission (AIE) and ligand‐metal‐metal charge transfer (LMMCT) relaxations offered by the triplet state of Con(GS)m nanoclusters. This significant results for the water‐soluble, highly robust and luminescent Con(GS)m nanoclusters confirm their potential ability to act as an alternative to expensive metal nanoparticles and conventional fluorescent materials for the technological and bioimaging applications.