AgAuSe quantum dots with absolute photoluminescence quantum yield of 87.2%: The effect of capping ligand chain length

Surface ligands of colloidal quantum dots (QDs) have a profound influence on their surface states, which has been verified in the studies of the effect of ligand head groups on the photoluminescence (PL) properties of QDs. However, the investigation of the ligand chain length is limited. Here, we systematically explored the effect of chain length on the Ag₂Se QDs by selecting three ligands, 1-octanethiol (OTT), 1-dodecanethiol (DDT), and 1-hexadecanethiol (HDT), with diverse chain lengths. We found that the PL intensity of Ag₂Se QDs increased with the decrease of the ligand chain length due to the enhanced passivation of surface defects emerging from the robust QD-ligand interface binding affinity and the weaker hydrophobic chain–chain interaction. Subsequently, AgAuSe QDs terminated with OTT were obtained by alloying parent OTT-Ag₂Se QDs with Au precursor with a record absolute PL quantum yield (PLQY) of 87.2% at 970 nm, facilitating ultrasensitive in vivo angiography imaging in a nude mouse model. We expect that our finding of the important role of the ligand chain length on the optical properties of QDs will be suggestive to the design and synthesis of high-quality QDs, and also look forward to the clinical applications of the ultra-bright AgAuSe QDs.