Enhanced photochemical stability of CdSe/CdS quantum dots capped by imidazolium-based ionic liquids

The novel thiol-functionalized ionic liquids (ILs), 1-(10-mercaptodecyl)-3-methylimidazolium chloride ([HS-C10mim]Cl) and 1-(4-mercaptobutyl)-3-methylimidazolium chloride ([HS-C4mim]Cl), were synthesized by introducing thiol groups onto the alkyl chains in imidazolium-based ILs. The ILs exhibit strong affinity toward CdSe/CdS quantum dots (QDs), and can readily transfer the QDs from organic phases to aqueous phase. The IL-capped CdSe/CdS QDs are extremely soluble in water, and their photochemical stability was measured by absorption spectra. It is shown that the [HS-C10mim]Cl-capped QDs in water present much better anti-photooxidation than [HS-C4mim]Cl-capped those. The measurements of Zeta potential and hydrodynamic diameter reveal that the enhanced mechanism of [HS-C10mim]Cl depends mainly on the specific physico-chemical properties of the ILs. In particular, CdSe/CdS QDs with high surface potential, small hydrodynamic diameter, and optimal photochemical stability can be harvested by the solubilization of free [HS-C10mim]Cl in ligand shells of the QDs.