Fabrication of Multilayer Assemblies Based on a Boronate-Terminated Self-Assembled Monolayer

A new methodology for the fabrication of covalently bound multilayers has been developed on the basis of a self-assembled monolayer (SAM) prepared from 5-(2-methyl-1,3,2-dioxaborinan-5-yl)pentyltrichlorosilane (<BO>1</BO>). The SAM was prepared by immersion of an aluminized silicon wafer into a toluene solution of <BO>1</BO>; its thickness was determined by ellipsometry to be 1.5 ± 0.3 nm, a value very similar to the molecular size of <BO>1</BO>. The fabrication of a two-layer film was successfully achieved by hydrolysis of the boronate protecting group of the SAM with water/ethanol to the diol-terminated group followed by treatment of the hydrolyzed monolayer with a toluene solution of <BO>1</BO>; the thickness (2.9 ± 0.3 nm) was nearly twice that of the starting monolayer. Similar treatment of the two-layer film with water/ethanol effected the selective hydrolysis of the boronate end group without significant loss of the second-layer unit, and subsequent reactions of the hydrolyzed two-layer film with <BO>1</BO> or octadecyltrichlorosilane smoothly occurred to give the corresponding three-layer assembly with thickness of 4.2 ± 0.4 or 5.4 ± 0.5 nm each.