Colloidal stable quantum dots modified by dual functional group polymers for inkjet printing

Abstract

Quantum dots (QDs) with unique fluorescence properties have been applied in a variety of applications. Here, we report an effective method to prepare water-dispersible QDs that have remarkable colloidal stability and can be used in inkjet printing. A new dual functional group polymer, mercaptopropionic polyethylenimine (MPPEI), as a ligand combines the thiol of 3-mercaptopropionic acid (MPA) with the amine of polyethylenimine (PEI) for the surface functionalization of CdSe/CdS/ZnS quantum dots (QDs). These ligands reduce issues of thiol oxidation and the weak binding affinity of the amino group. Ligation with these polymers provides fluorescent QDs with excellent acid resistance, base resistance, photostability and thermostability, since the branched structure of MPPEI can provide QDs with very effective protection. We use these stable QDs as security inks and obtain a fluorescent pattern that is invisible under ambient light.