Enhancement of Photochemical Grafting of Terminal Alkenes at Surfaces via Molecular Mediators:  The Role of Surface-Bound Electron Acceptors

Abstract

The use of ultraviolet light to functionalize the surface of carbon-based materials with terminal alkenes has emerged as a way to overcome the high chemical stability of these surfaces to create functional interfaces. It was previously shown that surface-bound trifluoroacetic acid protected 10-aminodec-1-ene (TFAAD) can be used to promote the grafting of unreactive alkenes using 254 nm light, but the mechanism by which this enhancement occurs was not understood. Here, we present a detailed study of how surface-bound TFAAD enhances the grafting of organic molecules to the surface of hydrogen-terminated amorphous carbon. Infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy experiments show that pregrafting TFAAD onto carbon surfaces greatly enhances the subsequent grafting of 1-dodecene, dodecane and dodecane-d 26 by locally facilitating photoemission of electrons. Using a photopatterned TFAAD “seed” layer, we demonstrate that subsequent grafting of these hydrocarbons is enhanced in regions immediately adjacent to the seed and proceeds almost exclusively parallel to the carbon surface. The roles of liquid-phase radical species, valence band holes, and the photochemical fragmentation of surface species in controlling the overall reaction mechanism are discussed.

Surface functionalization of thin-film diamond for highly stable and selective biological interfaces

“…1C. The grafting reaction is initiated by UV-induced photoemission of electrons, which is facilitated by the presence of electron-acceptor groups in the reactant liquid or pregrafted onto the surface (37). The photoemission process creates positively charged, carbocationlike surface sites (24).…”

Fabrication and Characterization of DNA Arrays Prepared on Carbon-on-Metal Substrates

“…Here, 9-decen-1-ol was attached to the surface through an ultraviolet (UV) light-assisted reaction. The UV light is thought to promote a photo-mediated electron ejection from the surface, which in turn generates a surface-bound radical that reacts with the alkene functional group 31,32. Alkene-containing molecules have also been attached to amorphous carbon substrates via a thermally-mediated reaction 33.…”

Copper‐Catalyzed Selective Semihydrogenation of Terminal Alkynes with Hypophosphorous Acid

“…Terminal alkenes are important building blocks of organic synthesis1 and have wide applications in the chemical industry,2 pharmaceuticals,3 agrochemicals4 and material science 5. Transition metal‐catalyzed semihydrogenation of alkynes is one of the most straightforward methods for synthesis of such alkenes.…”