NUCLEOPHILIC DISPLACEMENTS IN MIXED SELF-ASSEMBLED MONOLAYERS

Synthetic elaboration of self-assembled monolayers (SAMs) provides a p owerful method for the preparation of smooth, ordered surfaces with ca refully controlled functionality. Chemically rugged siloxane-based SAM s have been employed as a foundation for the preparation of a variety of functionalized surfaces. Nucleophilic displacements are described b etween halide-terminated SAMs and anionic nucleophiles (e.g. azide, th iocyanate, thiolate). Problems were encountered due to the steric cong estion surrounding the terminal bromomethylene carbon. The concept of trajectory control is applied to these displacement reactions. In addi tion, reactions between ester-terminated SAMs and neutral nucleophiles (e.g. amines, hydrazine, hydroxylamine) are described. Evidence is pr esented suggesting that a modest amount of cross-linking (i.e. imide f ormation) takes place in the amidation reactions, while reaction stoic hiometry indicates that cross-linking is virtually complete for the bi functional nucleophiles. These synthetic elaborations were also carrie d out on mixed monolayers to create functionalized SAMs with systemati cally varied loading densities. Linear correlation (or lack thereof) o f elemental composition to predicted functional composition is used to provide an estimation of reaction efficiency.