Directed, selective insertion of single molecules into patterned self-assembled monolayers of alkanethiols with different chain lengths

Abstract

Pd(II) pincer adsorbate molecules (1) were inserted into self-assembled monolayers (SAMs) of alkanethiols with different chain lengths (C₈ to C₁₈) on annealed gold substrates. Their presence was brought to expression by reaction of 1 with Au nanoclusters bearing phosphine moieties (2). The surface-confined Au nanoclusters were observed only on the shorter chain SAMs (C₈SH to C₁₆SH) and not on C₁₈SH SAMs. This is attributed to the longer chain length of C₁₈SH preventing the insertion of pincer molecules. Microcontact printing (μCP) with C₁₈SH on unannealed gold substrates and the subsequent immersion of the substrates into C₈SH, C₁₀SH, C₁₂SH, or C₁₆SH solutions, yielded a series of patterned SAMs that have areas of thiols of different chain lengths. Insertion of 1 followed by expression using 2, or insertion of 3 showed inserted molecules only in the shorter chain SAM areas. The absolute particle densities in the former case were higher than on the corresponding homogeneous SAMs on annealed substrates, probably due to larger numbers of defects in the SAMs on unannealed substrates.