Increasing\nPrecursor Reactivity Enables Continuous\nTunability of Copper Nanocrystals from Single-Crystalline to Twinned\nand Stacking Fault-Lined

Colloidal\nnanocrystals (NCs) are active materials in different\napplications, wherein their shape dictates their properties, such\nas optical or catalytic properties, and, thus, their performance.\nHence, learning to tune the NC shape is an important goal in chemistry,\nwith implications in other fields of research. A knowledge gap exists\nin the chemistry of non-noble metals, wherein design rules for shape\ncontrol of NCs are still poorly defined compared to those of other\nclasses of materials. Herein, we demonstrate that tuning the precursor\nreactivity is crucial to obtaining a continuous shape modulation from\nsingle-crystalline to twinned and stacking fault-lined Cu NCs. This\ntunability is unprecedented for non-noble metal NCs. We achieve this\nresult by using diphenylphosphine in place of the most commonly used\ntrioctylphosphine. Using in situ X-ray absorption spectroscopy, we\nshow that the temperature modifies the reaction kinetics of an in\nsitu-forming copper(I)bromide–diphenylphosphine complex during\nthe synthesis of Cu NCs. We propose the presence of a P–H functionality\nin the phosphine to explain the higher reactivity of this precursor\ncomplex formed with diphenylphosphine compared to that formed with\ntrioctylphosphine. This work inspires future studies on the role of\nphosphine ligands during the synthesis of Cu NCs to rationally target\nnew morphologies, such as high-index faceted Cu NCs, and can be conceptually\ntranslated to other transition-metal NCs.