Photochromism of diarylethene single molecules on metals and insulating films

利用扫描隧道显微镜和非接触原子力显微镜，我们在单分子水平上研究了二芳基乙烯的吸附结构、电子态、热稳定性和光反应性。在Cu和Au衬底上，热稳定性丧失，封闭形式的异构体变得比开放形式更稳定，这与溶液和单晶相相反。这是因为分子和金属之间的电荷转移，导致分子电离。我们还发现该分子与NaCl绝缘膜反应，通过Na离子与分子偶极相互作用形成自组织超结构。没有发生光反应，这表明例如尖端增强效应的必要性。最后，我们成功地在高分辨率原子力显微镜成像的分子的内部结构。

Using scanning tunneling and non-contact atomic force microscopies, we have investigated adsorption structure, electronic states, thermal stability and photo-reactivity of diarylethene at the single molecular level. On Cu and Au substrates, thermal stability is lost and closed-form isomer becomes more stable than the open-form, which is opposite to solution and single crystalline phases. This is because of the charge transfer between the molecule and metal, resulting in the ionization of the molecule. We also found that the molecule reacted with NaCl insulating film, and formed self-organized superstructure by the interaction between Na ion and molecular dipole. Photo-reaction did not occur, which suggests the necessity of, for example, tip-enhanced effect. Finally we succeeded in high-resolution AFM to image internal structure of the molecule.