Phase transition of two-dimensional chiral supramolecular nanostructure tuned by electrochemical potential.

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 < or = 0.65 V, region II), the stripe patterns gradually dissolved, and two types of new chiral network structures (3 square root(7) x 4 square root(7)) and (3 square root(7) x 3 square root(7)) 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 adsorption-induced chiral p-CPAEt species together with lateral hydrogen-bonding interaction (C-H...N[triple bond]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.