In Situ Imaging and Computational Modeling Reveal That Thiophene Complexation with Co(II)porphyrin/Graphite Is Highly Cooperative
In Situ Imaging and Computational Modeling Reveal That Thiophene Complexation with Co(II)porphyrin/Graphite Is Highly Cooperative
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DOI：
10.1021/acs.jpcc.2c06212
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发表时间：
2022-11
期刊：
影响因子：
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通讯作者：
K. N. Johnson;Shammi Rana;Bhaskar Chilukuri;K. W. Hipps;U. Mazur
中科院分区：
文献类型：
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作者：
K. N. Johnson;Shammi Rana;Bhaskar Chilukuri;K. W. Hipps;U. Mazur
用扫描隧道显微镜(STM)定量研究了高有序热解石墨(HOPG)负载的Co(II)八乙基卟啉(CoOEP)与3-苯基噻吩基(Phth)的原位结合。据我们所知，这是第一次在单分子水平上研究金属卟啉和硫碱在溶液/固体界面上的络合反应，也是噻吩类化合物与d7过渡金属配位的少数例子之一。实时成像实验表明，PHTH在室温下可与HOPG负载的CoOEP可逆结合。配位过程随邻苯二甲酸根浓度的增加而增加。STM图像的近邻分析表明，络合反应是协同的。由于PHTH在溶液中不与CoOEP结合，STM结果强烈表明HOPG的存在对于观察该体系中的配体结合和协同作用至关重要。周期平面波密度泛函理论计算证实了Phth在溶液中与CoOEP的结合亲和力较低，但预测配体可以通过与S原子配位或通过与卟啉发色团的非共价π-π键相互作用而吸附到CoOEP/HOPG上。考虑了三种可能的结构，并用密度泛函理论计算了结合能和自由能。在溶液中，π-π组态和η-1(S)组态具有相似的计算能量。η-1(S)结构在从蒸气到吸附的过程中表现出最大的稳定性。我们还发现最近邻的统计分析对协同结合比Temkin或Langmuir等温线更敏感。这意味着，仅有等温线拟合不足以识别表面上的协同结合。
Scanning tunneling microscopy (STM) was employed to quantitively investigate in situ binding of 3-phenyl thiophene (PhTh) to Co(II)octaethyl porphyrin (CoOEP) supported on highly ordered pyrolytic graphite (HOPG) in fluid solution. To our knowledge, this is the first single-molecule level study of a complexation reaction between a metalloporphyrin and a sulfur base at the solution/solid interface and one of the few examples of thiophene coordination with a d7transition metal. Real-time imaging experiments revealed that PhTh binds reversibly to HOPG-supported CoOEP at room temperature. The coordination process increases with increasing PhTh concentration. The nearest-neighbor analysis of STM images indicates that the complexation reaction is cooperative. Because PhTh does not bind to CoOEP in solution, the STM results strongly suggest that the presence of HOPG is crucial to observe ligand binding and cooperativity in this system. Periodic plane-wave density functional theory (DFT) computations corroborate that PhTh has low binding affinity toward CoOEP in solution but predict that the ligand can adsorb to CoOEP/HOPG through coordination with S atoms or interact through noncovalent π–π bonding with the porphyrin chromophore. Three possible structures were considered, and DFT theory was used to calculate binding energies and free energies. In solution and on the HOPG surface both a π–π configuration and a η1(S) configuration have similar computed energies. The η1(S) structure shows the largest stabilization in going from the vapor to adsorbed on HOPG. We also show that statistical analysis of nearest neighbors is more sensitive to cooperative binding than is fitting with the Temkin or Langmuir isotherm. The implication is that isotherm fitting alone is insufficient for identifying cooperative binding on surfaces.