Exciton-Mediated Hydrosilylation on Photoluminescent\nNanocrystalline Silicon

Abstract

A novel white light-promoted reaction using photoluminescent nanocrystalline silicon enables the\nhydrosilylation of alkenes and alkynes, providing stabilization of the porous silicon without significant loss of\nthe photoemissive qualities of the material. Photopatterning and lithographic fabrication of isolated porous\nsilicon structures are made possible. Experiments and observations are presented which indicate that the light\npromoted hydrosilylation reaction is unique to photoluminescent silicon, and does not function on nonemissive\nmaterial. Hydrosilylation using a reactive center generated from a surface-localized exciton is proposed based\nupon experimental evidence, explaining the photoluminescence requirement. Indirect excitons formed by light\nabsorption mediate the formation of localized electrophilic surface states which are attacked by incoming\nalkene or alkyne nucleophiles. Supra-band gap charge carriers have sufficient energy to react with nucleophilic\nalkenes and alkynes, thereupon causing Si−C bond formation, an irreversible event. The light-promoted\nhydrosilylation reaction is quenched by reagents that quench the light emission from porous silicon, via both\ncharge transfer and energy transfer pathways.