CdS-Oleic Acid Quantum Dots as Long-Wavelength Photoinitiators in Organic Solvent and Preparation of Luminescent, Colloidal CdS/Polymer Nanocomposites

Photoexcitation of luminescent semiconductor quantum dots (QDs) generates an electron-hole pair, which can be utilized for photoinitiation of radical polymerization reactions. Here, oleic acid coated CdS QDs (CdS-OA) are demonstrated as successful photoinitiators in the absence of a protic solvent or a hole scavenger for the first time. This provides photopolymerization of hydrophobic methyl methacrylate in toluene, providing colloidal and strongly luminescent CdS/poly(methacrylic acid) (PMMA) hybrid structures with improved stability of the CdS. Besides, successful photopolymerization of poly(ethylene glycol)diacrylate at different excitation windows (320-480 and 400-500 nm) is demonstrated. This indicates that CdS-OA can act as a long-wavelength initiator. Electron spin resonance (ESR) studies and control experiments suggest decarboxylation of the oleic acid as the initial source of the free radical. This method represents a unique and very simple way to create luminescent, small, stable, and colloidal QD/polymer hybrids.