Surface Of Two-dimensional Supramolecular Self-assembly Structure And Nature Study

The construction and tuning of the surface supramolecular nanostructure are the prerequisite for the realization of molecular devices. The self-assembly technique is an important approach to construct supramolecular nanostructure. Due to the imaging at the stomic level, scanning tunneling microscopy (STM) has a great advantage in the research of nanostructures.Taking STM as the main research means, combing scanning tunneling spectrum (STS), some new two dimensional (2D) supramolecular nanostructures were fabricated, and the assembling structures could be controlled eaxctly by designing the molecular structure and changing the assembling conditions. The main conclusions are follows:(1) The chemical engineering of the constituting molecules is a feasible approach to the construction and adjustment of a wide range of supramolecular architectures absorbed on surfaces. A series of star-shaped oligofluorenes end-capped with carboxylic acid groups (S-COOHn, n = 1, 2, 3) were synthesized, and their adsorption and self-assembling behaviors on highly oriented pyrolytic graphite (HOPG) were studied by scanning tunneling microscopy (STM) under ambient conditions. It is found that star-shaped oligofluorenes end-capped with different numbers of carboxylic acid groups could form different supramolecular nanostructures. Therefor, the COOH…COOH hydrogen bonding between intermolecular interactions plays important roles in forming different supramolecular nanostructure.(2) Similarly, the supramolecular nanostructure was controlled by chemical engineering of two-component systems. With 1,14-tetradecanedioic acid as bridge, a new uniform two-dimensional arrays of 1,14-tetradecanedioic acid/DQP nanostructure was successfully fabricated. The result illustrates that the COOH…N hydrogen bonding possess crucial influences on new supramolecular nanostructure。(3) Further more, the solvent effect on supramolecular nanostructure of S-COOH3 was studied. In four representative solvents, the same S-COOH3 molecule forms different supramolecular nanostructures. The result indicates the solvent is very important for this system because the solvent takes part in molecular self-assembly.(4) The bias effect on assembling behaviors of D-A-D system, which have different adsorption conformations, were investigated by scanning tunneling microscopy and spectroscopy (STM/STS). The result demonstrates the electronic properties of the supramolecular molecules were affected by eletronic field, which result from different electronic coupling interaction between molecules and substrate.(5) The controlled assemblying of 2D supramolecular nanostructure was also studied. Taking TMA and coronene as hosts, and S-COOH3 as guest, the muli-component system could form well-ordered patters on surface. meantime, the eaxct tuning of supramolecular nanostructures could be realized by changing molar ratio of different components. The result indicates that the new supramolecular nanostructure could be fabricated by interactions between muli-components.