Molecular geometry influencing thermal-based nucleophilic reactions on silicon (111) hydride surfaces

Abstract In order to gain insights on how molecular geometry and steric effects can influence surface reactions, we described the reaction outcome between aliphatic 3-Butyn-1-ol (BTL) and sterically hindered 2-methylbut-3-yn-2-ol (MBL) on silicon (111) hydride surface at high temperatures (~150 °C). X-ray photoelectron spectroscopy, atomic force microscopy and water angle goniometry were performed to determine the physicochemical nature of the surface linkage. In the absence of sterically hindering methyl groups, thermal grafting of BTL to silicon hydride (Si-H) surfaces was observed to have extensively roughened the silicon surface via Si-O-C linkages and extensive back-bond breakage was observed. On the other hand, the extent of surface roughening for sterically hindered MBL grafting was substantially lower and concentration dependent. DFT optimized molecular geometry of both molecules had shown merging of the negative domains for MBL between the OH group and the alkyne and this enabled for the formation of both Si-C and Si-O-C bonds on the surfaces while BTL reacted to the surface predominantly via the Si-O-C linkage. This study represents one of few reports that had experimentally discussed the role of steric hindrance as well as molecular geometry affecting nucleophilic grafting towards silicon hydride surfaces.