羟基苯基卟啉温度诱导去质子化和底物介导氢转移的光电子能谱学研究
Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin
摘要：
用光电子能谱学研究了5，10，15，20-四对羟基苯基卟啉的温度依赖性分步去质子化反应。在Ag（110）表面上，随着退火温度的升高，-NH-与-N=的比例逐渐减小，而在Au（111）表面上，随着退火温度的升高，-NH-与-N=的比例逐渐减小。羟基的部分解离和随后的氢扩散和重新键合到中心氮原子上，导致两性离子分子，观察此外，部分C-H键断裂和与相邻分子或表面形成新的共价键开始于300°C的相对高的退火温度。该反应被确定为发生在吡咯环的碳原子处，这也导致N 1 s信号的移位和分子的价带的变化。我们的研究结果表明，退火可以显着改变的分子沉积取决于最高温度和特定衬底的催化性能。如果通过脱附从多层膜制备分子单层膜，或者如果应用退火来增强分子结构的自组装，则应考虑热稳定性。
英文摘要：
The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of -NH- to -N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C-H bond cleavage and the formation of new covalent bonds with adjacent molecules or the surface starts at a relatively high annealing temperature of 300°C. This reaction is identified to occur at the carbon atoms of the pyrrole rings, which leads also to a shift in the N 1s signal and changes in the valence band of the molecules. Our results show that annealing can significantly alter the molecules which were deposited depending on the maximum temperature and the catalytic properties of the specific substrate. The thermal stability should be considered if a molecular monolayer is prepared from a multilayer by desorption, or if annealing is applied to enhance the self-assembly of molecular structures.
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