物理化学学报 >> 2020, Vol. 36 >> Issue (1): 1907043.doi: 10.3866/PKU.WHXB201907043

所属专题: 庆祝唐有祺院士百岁华诞特刊

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Au(111)表面Verdazyl自由基的构象转换

黄智超,戴亚中,温晓杰,刘丹,林宇轩,徐珍,裴坚*(),吴凯*()   

  • 收稿日期:2019-07-15 录用日期:2019-08-22 发布日期:2019-08-30
  • 通讯作者: 裴坚,吴凯 E-mail:jianpei@pku.edu.cn;kaiwu@pku.edu.cn
  • 基金资助:
    国家自然科学基金(21821004);中华人民共和国科学技术部(2017YFA0204702)

Conformational Switching of Verdazyl Radicals on Au(111)

Zhichao Huang,Yazhong Dai,Xiaojie Wen,Dan Liu,Yuxuan Lin,Zhen Xu,Jian Pei*(),Kai Wu*()   

  • Received:2019-07-15 Accepted:2019-08-22 Published:2019-08-30
  • Contact: Jian Pei,Kai Wu E-mail:jianpei@pku.edu.cn;kaiwu@pku.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21821004);the Ministry of Science and Technology of China(2017YFA0204702)

摘要:

本文使用扫描隧道显微镜(STM)与密度泛函理论(DFT)技术,研究了1, 5-二异丙基-3-(苯并[b]苯并[4,5]噻吩并[2, 3-d]噻吩-2-基)-6-oxoverdazyl分子(简称B2P分子)与1, 5-二异丙基-3-(苯并[b]苯并[4,5]噻吩并[2, 3-d]噻吩-4-基)-6-oxoverdazyl分子(简称B4P分子)在Au(111)表面的吸附与构象转换行为。B2P分子在Au(111)表面可形成单体、二聚体、三聚体与四聚体结构,无法形成有序组装结构,且在STM图像上可观测到“P”构象与“T”构象两种构象。而对于B4P分子,当覆盖度较低时在Au(111)表面形成二聚体结构,覆盖度较高时则形成有序的组装结构,同样的,B4P分子在STM图像上也可以观测到“P”构象与“T”构象。在+2.0 V的偏压下,B2P与B4P都可以通过针尖诱导发生构象转换。结合STM图像与DFT模拟结果,确认了两种构象的差异源于分子的verdazyl自由基与Au(111)表面的夹角不同。

关键词: verdazyl自由基, 扫描隧道显微镜, 密度泛函理论, 电子自旋

Abstract:

Pure organic radical molecules on metal surfaces are of great significance in exploration of the electron spin behavior. However, only a few of them are investigated in surface studies due to their poor thermal stability. The adsorption and conformational switching of two verdazyl radical molecules, namely, 1, 5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2, 3-d]thiophen-2-yl)-6-oxoverdazyl (B2P) and 1, 5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2, 3-d]thiophen-4-yl)-6-oxoverdazyl (B4P), are studied by scanning tunneling microscopy (STM) and density functional theory (DFT). The adsorbed B2P molecules on Au(111) form dimers, trimers and tetramers without any ordered assembly structure in which two distinct appearances of B2P in STM images are observed and assigned to be its "P" and "T" conformations. The "P" conformation molecules appear in the STM image with a large elliptical protrusion and two small ones of equal size, while the "T" ones appear with a large protrusion and two small ones of different size. Likewise, the B4P molecules on Au(111) form dimers at low coverage, strip structure at medium coverage and assembled structure at high coverage which also consists of above-mentioned two conformations. Both B2P molecules and B4P molecules are held together by weak intermolecular interaction rather than chemical bond. STM tip induced conformational switching of both verdayzl radicals is observed at the bias voltage of +2.0 V. The "T" conformation of B2P can be switched to the "P" while the "P" conformation of B4P can be switched to the "T" one. For both molecules, such a conformational switching is irreversible. The DFT calculations with Perdew-Burke-Ernzerhof version exchange-correlation functional are used to optimize the model structure and simulate the STM images. STM images of several possible molecular conformations with different isopropyl orientation and different tilt angle between verdazyl radical and Au(111) surface are simulated. For conformations with different isopropyl orientation, the STM simulated images are similar, while different tilt angles of verdazyl radical lead to significantly different STM simulated images. Combined STM experiments and DFT simulations reveal that the conformational switching originates from the change of tilting angle between the verdazyl radical and Au(111) surface. The tilt angles in "P" and "T" conformations are 0° and 50°, respectively. In this study, two different adsorption conformations of verdazyl radicals on the Au(111) surface are presented and their exact adsorption structures are identified. This study provides a possible way to study the relationship between the electron spin and configuration conversion of pure organic radical molecules and a reference for designing more conformational switchable radical molecules that can be employed as interesting molecular switches.

Key words: Verdazyl radical, Scanning tunneling microscopy, Density functional theory, Electron spin

MSC2000: 

  • O647