Structural switching of sumanene mechanically induced by AFM

抄録

Mechanical stimuli, such as a compression, tensile, or shear stress, applied on solid sometimes induces chemical reaction and changes the physical or chemical properties. Such mechanically induced reaction is known as the mechanochemistry and attract large interest. Recent decade, thanks to the high spatial resolution of the scanning tunneling microscope (STM) and atomic force microscope (AFM), many chemical reactions have been studied in the single molecule/atom scale. On the other hand, in general, the mechanochemistry has been performed in macroscopic scale. So far, only a few experiments reported the chemical reactions of single molecule induced by the mechanical stimuli from tip of scanning probe microscope[1, 2].

In this study, we demonstrate the structural change of single molecule induced by the mechanical stimuli from AFM tip. We used sumanene molecule. As shown in fig. (a), sumanene is a molecule with bowl-shape. Inversion of a bowl is expected by simply applying the force by AFM tip. Experiments were carried out by qPlus type AFM/STM system operated in ultra high vacuum at 77 or 5 K. Sumanene molecule was thermally deposited on clean Au(111) substrate. Figure (b) shows high resolution AFM image of sumanene layer on Au(111) substrate. According to AFM image, this layer consist of bowl-up and -down sumanene and form 6 x 6 periodicity. This structure is different from the previously reported sumanene layer on Au(111)[3] but rather similar to that on Ag(111)[4]. This is because we successfully prepared sumanene layer with a monolayer thickness. We applied repulsive force on one of the sumanene molecule in the bowl-down state by bringing AFM tip close to the molecule. As a result, structural inversion from down to up was successfully observed. Almost no tunneling current flowed during this switching process, therefore, this is purely force induced reaction.

References

[1] J. N. Ladentjin et al., Nat. Chem., 8, 935 (2016).

[2] A. Ishi et al., Chem. Sci., 12, 13301 (2021).

[3] S. Fujii et al., J. Am. Chem. Soc., 138, 12142 (2016).

[4] R. Jaafar et al., J. Am. Chem. Soc., 136, 13666 (2014).