(733e) Si Nanocrystal Surface Chemistry: Room Temperature Hydrosilylation and Thermally-Induced Thiolation

Silicon (Si) nanocrystals are heavy-metal free, light-emitting nanomaterials that could be used in applications such as biomedical imaging and light emitting devices.  They exhibit stable, bright, size-tunable photo- and electroluminescence. To prevent surface corrosion and degradation, Si nanocrystals are typically passivated with covalently bound ligand monolayers to eliminate surface dangling bonds and provide dispersibility in solvents.  One common approach to ligand passivation is via hydrosilylation between surface Si-H species and terminal alkenes. Hydrosilylation requires either high temperature or photon irradiation, which can cause unwanted side reactions in certain cases, such as derivatization with bio-active molecules or other temperature/light sensitive ligands. We have discovered a path to room temperature hydrosilylation of Si nanocrystals that does not require light irradiation or added catalyst.  The hydrosilylation reaction is promoted by polar ester or carboxylic acid groups, which facilitate direct nucleophilic attack of the highly curved Si surface with unsaturated C-C bonds, leading to covalent Si-C linkages to the hydrocarbon capping ligands.  As a proof of concept, the mild hydrosilylation conditions were utilized for styrene passivation of Si nanocrystals without thermally-induced self-polymerization of styrene as a side reaction.  Besides Si-C bonds, we have found that Si-S bonds can also be formed to passivate Si nanocrystals, through thermally-induced thiolation. In contrast to a Si-C passivated Si nanocrystals, which are stable in water for several months, Si-S passivated Si nanocrystals are extremely sensitive to moisture.