Electrostatic and covalent interactions in CdTe nanocrystalline assemblies

This paper focuses on the interactions between cysteamine-stabilized CdTe nanocrystals [CdTe(CA) NCs] and thioglycolic-acid-stabilized CdTe nanocrystals [CdTe(TGA) NCs]. These interactions were examined by the absorption, continuous, and time-resolved photoluminescence (PL) spectra of the electrostatically mixed and the covalently linked NCs assemblies comprised of the oppositely surface charged CdTe(CA) and CdTe(TGA) NCs and by a comparison with those of the corresponding pristine NCs. The CdTe(CA)-CdTe(TGA) coupling is dictated by the surfactant spacer, ranging between 0.93 and 1.14 nm and by electrostatic and covalent interactions, enabling a Forster resonance energy transfer (FRET) process among the NCs. The results revealed an excellent spectral overlap between the emission of the CdTe(TGA) NCs and the absorption of the CdTe(CA) NCs as well as a PL spectral red shift on the formation of electrostatic and covalent interactions. Furthermore, the measurements showed a lifetime ranging between 1.2 and 3 ns for the electrostatically mixed and the covalently linked assemblies, shorter than those of the pristine CdTe(CA) NCs and CdTe(TGA) NCs, both of which measured as similar to 5.5 ns. When CdTe(TGA) NCs performed as the most efficient donors, FRET rates of 10(10)-10(11) s(-1) were calculated for the electrostatically mixed NCs or covalently linked NCs.