Reaction intermediates in the synthesis of colloidal nanocrystals

Over the past 40 years, scientists have developed routes to synthesize colloidal nanocrystals of different compositions and with tunable size and shape. These features dictate the properties of these nanomaterials and, thus, their control aids the discovery of different physical chemical phenomena, many of which have contributed to technological advances; for example, the use of semiconductor nanocrystals as active components in displays with excellent colour purity. Yet, the synthesis of colloidal nanocrystals still proceeds by trial and error. The search for the reaction conditions to obtain nanocrystals with the desired compositions, sizes and shapes is time consuming and can fail to deliver the target product. In this Perspective, we discuss the importance of identifying reaction intermediates during the formation of colloidal nanocrystals for the development of a retrosynthetic approach to these nanomaterials. We select molecular complexes and clusters, coordination polymers and mesophases, and inorganic nanoparticles as some of the most common intermediates. The discovered pathways pinpoint the steps that enable a more predictive synthesis of colloidal nanocrystals. This Perspective encourages more mechanistic studies to eventually implement the concept of retrosynthesis for these nanomaterials.