Paper SS1-ThA1
Stability Reversal and Superstructure Formation of Photochromic Diarylethene on Noble Metals

Thursday, October 31, 2013, 2:00 pm, Room 201 A

We have studied using scanning tunneling microscopy (STM) and density functional theory calculations one of the diarylethene molecules [1] adsorbed on Au(111) and Cu(111). Two isomers of this molecule, open-form and closed-from, are known to be thermally stable, and its isomerization reactions are induced by irradiation of UV and visible light for the cyclization and cycloreversion reaction, respectively, in solution and single crystalline. Based on STM measurements after deposition of either form of the isomer as well as with and without annealing process, we found that the closed-form was more stable than the open-form on both Au(111) and Cu(111), which is opposite to gas phase. We expect that the stability reversal upon adsorption could arise from the partial ionization of the molecule due to the charge transfer between the molecule and the substrate metal, which stabilizes the closed-form isomer more than the open-from. It is also revealed that while small clusters are formed on clean metallic surfaces, a largely extended 2D superstructure can be fabricated when NaCl is co-deposited on Cu(111). Similar to earlier studies of other organic molecules [2,3], x-ray photoelectron spectroscopy data can be reasonably explained by assuming Na ion incorporation into the superstructure and Cl diffusion into the bulk. We propose a superstructure model where a Na ion binds fluorine and sulfur atoms of the adjacent molecules.

[1] M. Irie, S. Kobatake and M. Horichi, Science 291, 1769 (2001).

[2] Ch. Wackerlin et al., Chem. Commun. 47, 9146 (2011).

[3] D. Skomski et al., J. Am. Chem. Soc. 134, 14165 (2012).