Synthesis of a photosensitive thiocyanate-functionalized trialkoxysilane and its application in patterned surface modifications

A bifunctional molecule, trimethoxy[4-(thiocyanatomethyl)phenyl]silane (Si-SCN), bearing both a photoreactive unit, the benzyl thiocyanate group, and an anchoring unit, the trimethoxysilyl group, was synthesized. Upon irradiation with UV light of 254 nm under inert atmosphere, the benzyl thiocyanate group undergoes an isomerization reaction to the benzyl isothiocyanate. Kinetic investigations of liquid films of Si-SCN by Fourier transform infrared (FTIR) spectroscopy show that the thiocyanate is almost quantitatively consumed during illumination, but only 25-30% of isothiocyanate is formed. From the subsequent reaction with propylamine from the vapor phase, the isothiocyanate groups react to the corresponding thiourea compound. Thin layers of Si-SCN were applied to modify oxidized silicon surfaces. X-ray reflectivity measurements revealed a layer thickness of 6 nm. The above-described photochemistry also proceeds in these very thin layers as determined by FTIR spectroscopy and X-ray photoelectron spectroscopy. Photopatterned surfaces were produced using a contact mask during illumination followed by postmodification with propylamine. The structures of the used photomask were clearly reproduced on the Surface as revealed by friction force microscopy. Because of the versatility of this photochemistry, the new photosensitive silane Si-SCN is a promising molecule for applications in modern immobilization techniques and for the (structured) modification of inorganic surfaces.