Facile Exchange of Tightly Bonded L-Type Oleylamine and Diphenylphosphine Ligands on Copper Indium Diselenide Nanocrystals Mediated by Molecular Iodine

Copper indium diselenide (CuInSe2) nanocrystals are a prototypical I–III–VI semiconductor quantum dot material, typically synthesized in oleylamine (OLAm) as a solvent and capping ligand, often with the addition of diphenylphosphine (DPP) to improve the reaction yield. Using 1H nuclear magnetic resonance spectroscopy, we study the association of OLAm and DPP on CuInSe2 nanocrystals and find that they both behave as tightly bonded L-type ligands. There is no observable desorption of OLAm or DPP when a toluene-d8 dispersion is heated to 100 °C, and no ligand exchange occurs when the nanocrystals are exposed to other L-type species like trioctylphosphine (TOP) or octadecanethiol (ODT), which can bind as either X-type or L-type. Molecular iodine (I2), however, is found to readily displace both OLAm and DPP from the nanocrystal surface and facilitate efficient and complete ligand exchange with either TOP or ODT and appears to behave as a Lewis acid Z-type ligand. We also find that the X-type ligand, stearic acid, does not bond to the CuInSe2 nanocrystals under any circumstances.