Steric matching and the concentration induced self-assembled structural variety of 2,7-bis(n-alkoxy)-9-fluorenone at the aliphatic solvent/graphite interface.
Controlling and unraveling structural polymorphism has received special attention in 2D self-assembled monolayers. In this work, we investigated the steric matching and solution concentration controlled structural variety in the self-assembly of 2,7-bis(n-alkoxy)-9-fluorenone (F-OCn) at the n-tetradecane and n-tridecane/graphite interface under different concentrations, respectively. Scanning tunneling microscopy (STM) revealed that the coadsorbed adlayers of F-OCn and solvents (n = 12 to 16) were formed and exhibited concentration dependent 2D phases due to the steric matching. The self-assembled monolayer of F-OCn (n = 12 to 16) evolved from a low-density coadsorbed linear lamellar packing, which was formed at low concentrations, to higher-density patterns at relatively high concentrations. F-OC14 exhibited a complex structural variety, in which a systematic trend of decrease in the molecular density per unit cell with decreasing concentration was obtained. Except for F-OCn (n = 13, 15, 17), the zigzag structure showing the linear lamella with dimers was observed. Systematic experiments revealed that the self-assembly of F-OCn was chain-length dependent. The results provide insight into the structural variety exhibited by a series of organic molecules and furnish important guidelines to control the morphology by changing the solution concentration.
College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China. msxrmiao@scut.edu.cn wldeng@scut.edu.cn.
Xinrui
X
Miao
Li
L
Xu
Lihua
L
Cui
Wenli
W
Deng