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Single-Molecule Investigations of Conformation Adaptation of Porphyrins on Surfaces

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posted on 01.03.2017, 00:00 by Qiushi Zhang, Xiaoyan Zheng, Guowen Kuang, Weihua Wang, Lizhe Zhu, Rui Pang, Xingqiang Shi, Xuesong Shang, Xuhui Huang, Pei Nian Liu, Nian Lin
The porphyrin macrocyclic core features dynamic conformational transformations in free space because of its structural flexibility. Once attached to a substrate, the molecule–substrate interaction often restricts this flexibility and stabilizes the porphyrin in a specific conformation. Here using molecular dynamic and density-functional theory simulations and scanning tunneling microscopy and spectroscopy, we investigated the conformation relaxation and stabilization processes of two porphyrin derivatives (5,15-dibromophenyl-10,20-diphenylporphyrin, Br2TPP, and 5,15-diphenylporphyrin, DPP) adsorbed on Au(111) and Pb(111) surfaces. We found that Br2TPP adopts either dome or saddle conformations on Au(111) but only the saddle conformation on Pb(111), whereas DPP deforms to a ruffled conformation on Au(111). We also resolved the structural transformation pathway of Br2TPP from the free-space conformations to the surface-anchored conformations. These findings provide unprecedented insights revealing the conformation adaptation process. We anticipate that our results may be useful for controlling the conformation of surface-anchored porphyrin molecules.