A new class of capping ligands for CdSe nanocrystal synthesis

A new method is described for the synthesis of high-quality CdSe nanocrystals (NCs) that eliminates the need for tri-octylphosphine oxide (TOPO). This new method is an adaptation of previously reported methods that use Cd salts as precursors for the CdSe NCs. High-boiling esters and ketones such as hexadecyl hexadecanoate (HH) and benzophenone (BP) appear to be excellent replacements for TOPO in this reaction. Compared with TOPO, HH offers a significant synthetic advantage as it slows the initial growth of the NC nuclei formed after injection of the Se precursor. This allows for superior control over particle size in the initial stages of the reaction, and thus permits facile production of high-quality CdSe NCs with very small diameters (<4 nm). Based upon the results presented here, a possible role is identified for TOPO in the CdSe NC synthesis. Understanding of the role of TOPO and other reaction components is crucial for continued progress in the synthesis of high-quality NCs.