Anisotropic 2D Cu_2- Se Nanocrystals from Dodecaneselenol and Their Conversion to CdSe and CuInSe₂ Nanoparticles

We present the synthesis of colloidal anisotropic Cu_2- Se nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu_2- Se NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe₂ quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu_2- Se NCs into hexagonal wurtzite CdSe and CuInSe₂, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu_2- Se NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe₂, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals.