Phase Transition of Two-Dimensional Chiral Supramolecular Nanostructure Tuned by Electrochemical Potential

摘要

Molecular chiralty and phase transition of p-phenylenedi(alpha-cyanoacrylicacid) di-n-ethyl ester (p-CPAEt) assembled on Au(111) have been studied in the electric double layer region in 0.1 M HClO_(4) by electrochemical scanning tunneling microscopy (ECSTM) technique. Three types of chiral supramolecular nanostructures were resolved at differently charged interfaces. Within a potential range (0.65 V < E < 0.8 V, region I), a close-packed physisorbed adlayer of chiral stripe pattern, with the (3 X 6) structure, has been observed. At more negative potential (0.2 V < E <= 0.65 V, region II), the stripe patterns gradually dissolved, and two types of new chiral network structures (3 7~(1/2) X 4 7~(1/2)) and (3 7~(1/2) X 3 7~(1/2)) evolved on reconstructed and unreconstructed surfaces, respectively. On the basis of the high-resolution STM images, it was tentatively proposed that three types of chiral supramolecular nanostructures were formed by two-dimensional adorption-induced chiral p-CPAEt species together with lateral hydrogen-bonding interaction (C-H...N(ident to)C). Intriguingly, ECSTM images allow in situ monitoring of the phase transition process of these chiral adlayers driven by the electrochemical potential. The detailed dynamic results showed that the chiral two-dimensional adlayers could be reversibly tuned purely by the applied electrode potential.