Lewis Acid Mediated Hydrosilylation on Porous Silicon Surfaces

Abstract

Lewis acid mediated hydrosilylation of alkynes and alkenes on non-oxidized hydride-terminated porous silicon derivatizes the surface with alkenyl and alkyl functionalities, respectively. A very broad range of chemical groups may be incorporated, allowing for tailoring of the interfacial characteristics of the material. The reaction is shown to protect and stabilize porous silicon surfaces from atmospheric or direct chemical attack without compromising its valuable material properties such as high porosity, surface area and visible room-temperature photoluminescence. The reaction is shown to act on alkenes and alkynes of all possible regiochemistries (terminal and internal alkynes; mono-, cis- and trans-, di-, tri-, and tetrasubstituted alkenes). FTIR as well as liquid- and solid-state NMR spectroscopies show anti-Markovnikov addition and cis stereochemistry in the case of hydrosilylated terminal alkynes. Material hydrosilylated with long-chain hydrophobic alkynes and alkenes shows a substantially slower surface oxidation and hydrolysis rate in air as monitored by long-term FTIR monitoring and chemography. BJH and BET measurements reveal that the surface area and average pore size of the material are reduced only slightly after hydrosilylation, indicating that the porous silicon skeleton remains intact. Elemental analysis and SIMS depth profiling show a consistent level of carbon incorporation throughout the porous silicon which demonstrates that the reaction occurs uniformly throughout the depth of the film. The effects of functionalization on photoluminescence were investigated and are shown to depend on the organic substituents.

Wet chemical routes to the assembly of organic monolayers on silicon surfaces via the formation of Si–C bonds: surface preparation, passivation and functionalization

“…A well-established functionalization approach for the derivatization of hydride-terminated porous silicon (PSi) 186,187 is the Lewis acid-mediated (e.g. AlEtCl 2 ) attachment of olefins and acetylenes.…”

Optical Characterization of Ultrasmall Si Nanoparticles Prepared through Electrochemical Dispersion of Bulk Si

“…They also have the advantage of direct compatibility with organic materials via the strong and stable Si-C bond, providing a larger degree of freedom and flexibility in possible surface passivations and functionalities. [3][4][5][6][7][40][41][42][43] For example, it was recently demonstrated that H-passivated Si-np can be directly functionalized through a Si-C linkage terminating with a carboxylic acid group toward the solvent. This modification preserves the strong PL of the Si core, adds a hydrophilic interface for stability in aqueous media, and is easily reacted with primary amines to label biomolecules, all while adding only a small amount to the overall size.…”

“…The analysis has generally focused on the source of PL and the debate between the quantum confinement (delocalized) and surface state (localized) mechanisms. Researchers studying porous Si structures, [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] for example, have attributed the PL to various sources ranging from quantum-confined nanorods and nanodots [44][45][46] to surface state silanone and siloxane groups. [47][48][49][50][51][52][53][54][55][56] For Si and Ge nanoparticles prepared through various routes such as solution-phase synthesis, [1][2][3][4][8][9] electrochemical etching, 10-13 laser ablation, 14,15 and using supercritical fluids, [16][17][18] the suggested PL sources have ranged from delocalized quantum confinement states 15 to localized SiSi surface dimer states.…”

Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

“…Alkylpassivation is thought to have negligible effects on the photophysical properties of the Si domains, similar to hydride-passivation. 76 To this end, experimental evidence suggests that the Si NP surface can undergo alkyl-passivation as a means to preserve interband PL. 9 Consequently, numerous methods have been developed to form stable, Si-C passivated surfaces.…”

“…76,79,80 For example, reaction of hydride-passivated porous silicon surfaces with terminal alkenes and alkynes in the presence of catalytic amounts of EtAlCl 2 was shown to form stable Si-C bonding at room temperature. 80 In that study, the authors reported a maximum reaction efficiency of 28 % when hydrosilylation was conducted with terminal alkenes, which was determined by calculating the percent decrease in the integrated intensity of the Si-H bond at 2100 cm -1 , as monitored by infrared (IR) spectroscopy.…”