Structural Diversity of a Monodendron Molecule Self-Assembly in Different Solvents Investigated by Scanning Tunneling Microscopy: From Dispersant to Counterpart

A monodendron molecule, 5-(benzyloxy)isophthalic acid derivative (BIC, C47H76O7), has been employed to fabricate self-assembly on graphite surface. The molecules were dissolved in different solvents of 1-phenyloctane, 1,2,4-trichlorobenzene (TCB), and 1-octanoic acid. The effects of these solvents on BIC self-assemblies were investigated by scanning tunneling microscopy (STM) at the liquid/graphite interface. It is found that 1-phenyloctane exerts as a dispersant without coadsorption in the self-assembly, although a structural transformation of BIC adlayer from lamella to hexamer can be seen with concentration decrease. TCB solvent coadsorbs with BIC molecules and affects the structure and stability of the BIC adlayer. In contrast, a stable BIC linear adlayer is formed with the coadsorption of 1-octanoic acid. The intermolecular hydrogen bonds between solvent molecule I-octanoic acid and the BIC molecule are responsible for the formation of the linear structure. Furthermore, the effect of mixed solvents on BIC adlayer was also investigated. The results demonstrate that the solvent plays the important role of not only a simple dispersant but also a counterpart in forming the two-dimensional (2D) monodendron molecular self-assembly and provides an efficient approach to fabricating and controlling monodendron molecular nanostructure by changing solvent and molecular concentration.