Three Methods for Stabilization and Functionalization of Porous Silicon Surfaces via Hydrosilylation and Electrografting Reactions

Abstract

Three reactions are discussed which accomplish a high degree of substitution of the silicon hydride bonds on the porous silicon (pSi) surface with silicon–carbon bonds. Lewis acid mediated (LAM) and white light-promoted (LP) hydrosilylation of alkynes and alkenes gives surfaces with alkenyl and alkyl residues, respectively. Evidence for the silicon–carbon bonds is given by solid-state NMR spectroscopy of free-standing pSi material. The extent of the substitution of the surface bonds is termed reaction efficiency (E) which is measured by the change in the integrated area of the silicon hydride stretch region in FTIR spectra (2000–2200 cm—1). The LAM hydrosilylation gives a higher E value than the LP reaction. The E value of the LAM reaction is believed to be limited by the efficiency of the catalyst diffusion throughout the porous structure. In the case of the LP reaction, it is limited by the relative quantity of visible light-exposed material in comparison to the entire amount of IR-apparent silicon hydride bonds. The cathodic electrografting (CEG) reaction gives directly attached alkynyl residues via reduction of a silicon hydride bond to generate alkynyl carbanions, which then react with silicon–silicon bonds.