Structural Changes in Self-Catalyzed Adsorption of
Carbon Monoxide on 1,4-Phenylene Diisocyanide Modified Au(111)
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Abstract
The
self-accelerated adsorption of CO on 1,4-phenylene diisocyanide
(PDI)-derived oligomers on Au(111) is explored by reflection–absorption
infrared spectroscopy and scanning tunneling microscopy. PDI incorporates
gold adatoms from the Au(111) surface to form one-dimensional −(Au–PDI)<sub><i>n</i></sub>– chains that can also connect between
gold nanoparticles on mica to form a conductive pathway between them.
CO adsorption occurs in two stages; it first adsorbs adjacent to the
oligomers that move to optimize CO adsorption. Further CO exposure
induces PDI decoordination to form Au–PDI adatom complexes
thereby causing the conductivity of a PDI-linked gold nanoparticle
array on mica to decrease to act as a chemically drive molecular switch.
This simple system enables the adsorption process to be explored in
detail. DFT calculations reveal that both the −(Au–PDI)<sub><i>n</i></sub>– oligomer chain and the Au–PDI
adatom complex are stabilized by coadsorbed CO. A kinetic “foot-in-the-door”
model is proposed in which fluctuations in PDI coordination allow
CO to diffuse into the gap between gold adatoms to prevent the PDI
from reattaching, thereby allowing additional CO to adsorb, to provide
kinetic model for allosteric CO adsorption on PDI-covered gold