Defect-Mediated Charge Carrier Recombination of Zinc–Silver–Indium Sulfide QDs in the Presence of Naphthoquinone Derivatives: An Insight into the Interfacial Surface Dynamics

Although quantum dots (QDs) are perceived to be similar to fluorescent organic dyes, the underlying mechanism behind their photophysical response in the presence of analytes may not necessarily follow the path usually taken by molecular dyes. With the aim to understand how the exciton dynamics of QDs proceeds in the presence of chemical analytes, a thorough spectroscopic investigation of less-toxic zinc-silver-indium sulfide (ZAIS) QDs in the presence of selected naphthoquinone derivatives (analytes) has been undertaken in an aqueous medium. Specifically, the charge carrier recombination dynamics of ZAIS has been probed in the presence of chosen analytes by systematically varying the chemical functionalities attached to these analytes. The absorbance, fluorescence, and transient absorption measurements infer that fluorescence quenching of ZAIS in the presence of analytes proceeds through a very different pathway from that usually observed for molecular dye analyte systems. This observation has been rationalized by considering the presence of active surface of QDs and subsequent changes in their surface dynamics in the presence of analytes.