Improved photoreaction yields for soft ultraviolet photolithography in organothiol self-assembled monolayers

Patterned surfaces can be obtained by soft UV (365 nm) irradiation of thiol-on-gold SAMs (self-assembled monolayers) terminated with ortho-nitrobenzyl-protected carboxylic acid groupings. However, direct irradiation in air leads to incomplete photolysis (<50%). Here we demonstrate that the photolysis yield can be greatly improved (∼96%) by acid catalysis. However, if HCl/methanol is used as the catalyst, esterification is observed. This methyl ester formation can be prevented by using a sterically hindered alcohol, such as isopropanol, thereby leading to high yield photolysis. Finally, we demonstrate that such photopatterned SAMs can be used to create functionalized surfaces by covalent attachment of amine-modified microspheres.