Self-Assembly of Organic Monolayers onto Hydrogen-Terminated Silicon: 1-Alkynes Are Better Than 1-Alkenes

Abstract

Recently, a new method for the preparation of high-quality organic monolayers with 1-alkynes at room temperature in the dark (i.e., without any external activation) was reported. To pinpoint the precise origin of this self-assembly process and to compare the reactivity of 1-alkenes and 1-alkynes toward hydrogen-terminated Si(111) [H-Si(111)], we followed the gradual formation of both monolayers at room temperature by static water contact angle measurements. Subsequently, attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) were used to obtain detailed information about the structure and quality of the resulting monolayers. Our data clearly demonstrate that 1-alkynes are considerably more reactive toward H-Si(111) than 1-alkenes. 1-Alkynes are able to self-assemble into densely packed hydrophobic monolayers without any external activation (i.e., at room temperature under ambient light and even in the dark) whereas for 1-alkenes under the same conditions hardly any reactivity toward H-Si(111) was observed. The self-assembly of 1-alkynes on H-Si(111) at room temperature is explained by three factors: the higher nucleophilicity of 1-alkynes, which results in a facile attack at the electron-hole pairs at the H-Si surface and easy Si-C bond formation, the stabilization of the beta radical by delocalization over the double bond, and the lower-energy barrier encountered for H abstractions.

Organic Monolayers from 1-Alkynes Covalently Attached to Chromium Nitride: Alkyl and Fluoroalkyl Termination

“…We note that similar data with carbonyl-related peaks were observed for the attachment of 1-alkynes to alumina surfaces, 29 whereas this contrasts strongly with the formation of the signals obtained for Si−CHCH-bound monolayers obtained from 1-alkynes on H-terminated Si(111) surfaces. 3,61 Stimulated by earlier work in our group on the oxidative binding of C16YNE on porous anodic alumina, 29 we also used 2-hydroxyhexadecanoic acid (2HHDA) as a reference. Ter Maat et al observed a remarkable resemblance between the XPS and IR spectra obtained from C16YNE-modified and 2HHDA-modified porous anodic alumina surfaces.…”

A Mechanistic Study of the Oxidative Reaction of Hydrogen-Terminated Si(111) Surfaces with Liquid Methanol

“…4 Moreover, hydrosilylation reactions of molecular silanes typically require ultraviolet illumination, whereas H-Si(111) surfaces react with unsaturated hydrocarbons under visible-light illumination 51 as well as under certain circumstances in the dark at room temperature. 50,78 The mechanisms for the reactions of Grignard reagents, alkenes, and alkynes at H-Si(111) surfaces involve electron transfer kinetics that closely parallel the reaction of CH 3 OH with HSi(111) surfaces. These reactions are known to be sensitive to the bulk electronic structure of the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 34 which nucleophiles, including alcohols, alkenes, alkynes, and Grignards, can undergo reaction with H-Si(111) surfaces in the presence or absence of an oxidant and/or an illumination source.…”

Silicon Surface Modification and Characterization for Emergent Photovoltaic Applications Based on Energy Transfer

“…181 The increased reactivity of alkynes allows the hydrosilylation reaction to occur under very mild conditions (room temperature) in the dark, 182 while producing higher-quality surfaces than obtained with alkenes. 183 Concerns that elevated temperatures may activate functional groups and enable side reactions with the Si−H surface have limited the widespread use of thermally activated hydrosilylation. However, it has been found that this method allows for the fabrication of high-quality SAMs, which can be transformed into reactive functional groups such as carboxylic acids.…”