Self-assembled Nanostructure And Formation Mechanism Of Liquid Crystal And Photoelectric Functional Molecules Induced By Weak Bond At The Solid/Liquid Interface

The construction of two-dimensional polymorphic self-assembled structures has received extensive attention in various fields.For special functional materials,the arrangement and interaction of molecules have an important influence on the properties of the materials.It is of great significance to improve the properties of the materials by adjusting the two-dimensional self-assembly structure of the molecules at the solid/liquid interface.In this dissertation,we designed and synthesized a series of fluorenone and thienophenanthrene derivatives,combined with scanning tunneling microscopy(STM)and theoretical calculations,systematically studied the effect of molecular conformation,tail groups,side chains,concentration and solvent on the formation and transformation of the two-dimensional self-assembled structure at the solidliquid interface.The main works and innovative results in this dissertation are summarized as follows:(1)Systematically explored the self-assembly behavior of liquid crystal molecules FTQ at different concentrations.The DFT calculation revealed the formation mechanism of selfassembled structures.With the decrease of solution concentration,three nanostructures(parallelogram,wave-like,and double-S patterns)are formed at the 1-phenyloctane/HOPG interface.More importantly,the molecular cis-trans isomerization is observed,resulting from different packing fashions of the side chains.The dimers are the basic building units due to the similar C-H···O=C hydrogen bonds formed between the hydrogen atom in the thiophene group and the oxygen atom in the carbonyl group.DFT results show that the isomerized structure constructing by the S-shaped conformation is more stable.We speculate that the double-S structure might be in accordance with the molecular conformation in liquid crystalline phase.(2)Systematically explored the regulatory effect of tail groups on the self-assembly structure of FE and FEC molecules.For FE molecules,we observed two structures: Linear and Dimer.Although the benzene ring at the tail is bent to different degrees,it does not affect the general conformation and arrangement of the molecule.Intermolecular hydrogen bonding is the main driving force for the formation of Dimer structure.In contrast,the adsorption conformation of FEC molecules is significantly different,and the STM images shows that the molecules are in a semicircular conformation,and accompanied by solvent co-adsorption.The molecules arranged into dimers,the hydrogen bonds cannot formed between the molecules,because of larger bending of the molecular tail groups.Therefore,the hydrogen bond between molecules and solvent molecules is the main driving force for structural stability.(3)Explore the self-assembly of thienophenanthrene derivatives with different side chain lengths at the solid/liquid interface.We have observed that both TENTD-14 and TENTD-16 can form zigzag structure with poor regularity and dendritic structure with better regularity.The difference is that both the Sawtooth-I and Branch-I structures form hydrogen bonds.In the Sawtooth-I structure,there are three types of hydrogen bonds I,II and III,of which type III hydrogen bonds dominate.Sawtooth-? structure only has type ? and type ? hydrogen bonds,type ? hydrogen bonds dominate,and there is no hydrogen bond in Branch-? structure.The calculation results and STM images show that although the type I hydrogen bond interaction is stronger,the molecular packing density is reduced,so the molecules are arranged mainly by type II and III hydrogen bonds.In addition,TENTD-16 was also observed to form a new Flower-like structure.