Comparison and stability of CdSe nanocrystals covered with amphiphilic poly(amidoamine) dendrimers

This paper describes the surface modification of CdSe nanoparticles (NPs) with amphiphilic and flexible poly(amidoamine) (PAMAM) dendrimers carrying different numbers of hydrophobic aliphatic chains. Although hydrophilic full generation dendrimers with primary amine termini caused aggregation of the CdSe particles, the amphiphilic dendrimers proved to be useful caps for the CdSe nanocrystals and solubilized them in chloroform. Complete exchange of the original TOPO/TOP caps was achieved through a CdSe/pyridine intermediate. It Was found that both amine groups (which interact with the nanoparticle surface) and hydrophobic chains (which provide the particles with solubility in the solvent) were necessary to stabilize the CdSe NPs. The PAMAM covered CdSe nanocrystals were characterized using NMR, UV-visible absorption, photoluminescence (PL), and TEM. UV-vis absorption and PL of such CdSe/PAMAM systems were studied during a two month period, and it was found that PAMAM derivatives with only secondary and tertiary amines provided a better protection for the nanocrystals than those with primary amines.