Ligand-Solvent Compatibility: The Unsung Hero in the Digestive Ripening Story

Digestive ripening (DR) is a process where a polydisperse nanocrystal (NC) system is converted into a monodisperse one with the aid of thermal heating of NCs in the presence of an excess surface-active organic ligand called digestive ripening agent (DRA) and a solvent. Here, we demonstrate that the solvent-DRA compatibility influences the final size and size distribution of the NCs in a significant manner. Accordingly, in this study, using the DR of gold NCs as the test case with alkanethiol (decanethiol/C10HT) and fluorinated thiol (1 H,1 H,2 H,2 H-perfluorodecanethiol/C10FT) as DRA's and toluene and α,α,α-trifluoro-toluene (TFT) and their combination as solvents, we clearly establish that alkanethiols result in best-quality NCs after DR in toluene while the fluorinated thiols provide reasonably monodispersed NCs in TFT. Our results also ascertain that even when DR is carried out in a mixture of solvents, as long as the compatible solvent is the major component, the DR process results in reasonably monodisperse NCs. As soon as the amount of uncompatible solvent exceeds a threshold limit, there is perceptible increase in the polydispersity of the NCs. We conclude that the polarity of the solvent, which affects the buildup of ligated atoms/clusters, plays a key role in controlling the size distributions of the NCs.