Controlled Polymerization of Substituted Diacetylene Self-Organized Monolayers Confined in Molecule Corrals

Abstract

We have shown that STM-tip-induced chain polymerization of 10,12-tricosadiynoic acid (TCDA) in a self-organized monolayer at the liquid−solid interface of TCDA on highly oriented pyrolytic graphite is possible. The oligomers thus produced started at the point where a voltage pulse was applied between the STM tip and the sample during a short period when the feedback condition was momentarily suspended (as it is for scanning tunneling spectroscopy). Polymerization probabilities depended upon the length of the applied voltage pulse and were generally higher for longer pulse widths in the 10-ms to 100-μs time scales, approaching unit probability for the former and decreasing quickly to a few tens of percent for the latter. The polymerization could be confined to certain nanometer-sized areas by using “molecule corrals,” and polymerization appeared to be governed by topochemical constraints. Polymerization across domain boundaries, or over molecule corral edges, was never observed in over 150 observations. Due to the constant supply of nonpolymerized molecules from the covering solution, a dynamic exchange between molecules on the surface and in the solution was possible. This exchange occurred on a time scale that was comparable to the image acquisition time (101 s), and appeared to depend weakly upon the length of the desorbing oligomer. The desorption process was probably also influenced by interactions with the STM tip.