Influence of the Central Metal Ion on the Desorption Kinetics of a Porphyrin from the Solution/HOPG Interface
Influence of the Central Metal Ion on the Desorption Kinetics of a Porphyrin from the Solution/HOPG Interface
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DOI：
10.1021/acs.jpcc.6b05964
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发表时间：
2016-08-18
影响因子：
3.7
通讯作者：
Hipps, K. W.
中科院分区：
文献类型：
--
作者：
Bhattarai, Ashish;Marchbanks-Owens, Kevin;Hipps, K. W.
用扫描隧道显微镜（STM）研究了金属离子引入卟啉环后脱附动力学的变化。在20-110 ℃温度范围内进行了钴（II）八乙基卟啉（CoOEP）和游离碱八乙基卟啉（H2OEP）在1-苯基辛烷/HOPG界面处的解吸研究。CoOEP和H2OEP的混合物的这些研究表明，所得单层组合物在20 ℃下稳定超过一年，并且通过动力学控制到100 ℃以上。在90 ℃、100 ℃和110 ℃下对CoOEP和H2OEP进行定量温度和时间依赖性表面覆盖研究。两种卟啉的脱附活化能均为（1.25 +/- 0.05）× 10（2）kJ/mol。CoOEP的解吸速率和吸附速率与H2OEP的相应速率相似，表明用钴离子取代中心质子对吸附只有很小的影响。因此，吸附强度由卟啉环和HOPG之间的相互作用决定。这些结果与先前发表的工作NiOEP/CoOEP系统的比较表明，在解吸过程中存在弱的协同性。我们还发现，将样品电位相对于地球设置为+/-1.5 V，持续一小时左右，对50 ℃下的解吸速率没有影响。另一方面，尖端和样品之间的大电位差确实产生了解吸速率的显着变化。
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 degrees 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 degrees C, and are controlled by kinetics to above 100 degrees C. Quantitative temperature and time dependent surface coverage studies were performed on both CoOEP and H2OEP at 90, 100, and 110 degrees C. The desorption activation energies for both porphyrins were found to be (1.25 +/- 0.05) x 10(2) 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 degrees C. On the other hand, a large potential difference between the tip and sample did produce a significant change in desorption rate.