FORMATION AND NAPHTHOYL DERIVATIZATION OF AROMATIC AMINOSILANE SELF-ASSEMBLED MONOLAYERS - CHARACTERIZATION BY ATOMIC-FORCE MICROSCOPY AND ULTRAVIOLET SPECTROSCOPY

Self-assembled monolayers (SAMs) prepared from short chain aminoalkyl- and aromatic aminoalkysilanes have recently proven valuable in controlling the adhesive properties of silica substrates for chemical, biological, and microelectronic applications. To gain insight to the structure and amine reactivity of these films, we have studied the formation of SAMs formed on silica surfaces from ((((aminoethyl) amino)methyl) phenethyl) trimethoxysilane (PEDA), and their modification with 2-naphthoyl chloride (NAP-C1). Atomic force microscopy was used to demonstrate that PEDA and PEDA-NAP SAMs do not pack in a periodic or regular array on the surface but in fact are highly disordered relative to surface-deposited Langmuir-Blodgett (LB) phospholipid films, organothiol SAMs on gold, and at least one perfluorinated alkyl monochlorosilane SAM. In contrast to chromophores in well-ordered monolayers, the UV absorbance lineshapes and ratio of peaks corresponding to the (1)A-B-1(b) and (1)A-(1)L(a) transitions of the NAP chromophore remain relatively unchanged after immobilization. A simple first-order model, used to estimate molecular densities and reaction stoichiometries, suggests that in reaction-site-limited PEDA SAMs, the amine reactivity is limited by the maximum packing density of the NAP chromophore.