K W Hipps - Influence of the Central Metal Ion on the Desorption Kinetics of a Porphyrin from the Solution/HOPG Interface

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      Publication Details (including relevant citation   information):

      Bhattarai, Ashish, Marchbanks-Owens, Kevin, Mazur, Ursula, Hipps,   K. W. The Journal of Physical Chemistry C  2016 120 (32) 18140-18150

      Abstract: The changes in desorption kinetics   that result from incorporating a metal ion into a porphyrin ring   are studied by scanning tunneling microscopy (STM). Desorption   studies of cobalt(II) octaethylporphyrin (CoOEP) and free base   octaethylporphyrin (H2OEP) at the 1-phenyloctane/HOPG interface   were performed in the 20–110 °C temperature range. These studies   of mixtures of CoOEP and H2OEP have shown that the resulting   monolayer compositions are stable for more than one year at 20   °C, and are controlled by kinetics to above 100 °C. Quantitative   temperature and time dependent surface coverage studies were   performed on both CoOEP and H2OEP at 90, 100, and 110 °C. The   desorption activation energies for both porphyrins were found to   be (1.25 ± 0.05) × 102 kJ/mol. The rate of desorption and the   rate of adsorption for CoOEP are similar to the corresponding   rates for H2OEP, indicating that replacing the central protons   with a cobalt ion has only a minor influence on adsorption. Thus,   the adsorption strength is dominated by the interactions between   the porphyrin ring and HOPG. Comparison of these results with   previously published work for the NiOEP/CoOEP system suggests the   presence of weak cooperativity in the desorption process. We also   found that setting the sample potential to ±1.5 V relative to the   earth for periods of the order of an hour had no effect on   desorption rates at 50 °C. On the other hand, a large potential   difference between the tip and sample did produce a significant   change in desorption rate.

      Address (URL): http://dx.doi.org/10.1021/acs.jpcc.6b05964